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src/hotspot/share/runtime/synchronizer.cpp

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rev 57586 : imported patch 8235931.patch.cr0
rev 57587 : imported patch 8236035.patch.cr0
rev 57588 : dholmes CR - rename simply_set_owner_from() -> set_owner_from() and simply_set_owner_from_BasicLock() -> set_owner_from_BasicLock(); rename release_clear_owner_with_barrier() -> release_clear_owner() and refactor barrier code back into the call sites.
rev 57591 : imported patch 8235795.patch.cr0.merged
rev 57592 : dholmes CR - refactor common code, refactor atomic load of LVars.population in monitors_used_above_threshold, simplify list walking in ObjectSynchronizer::om_release() so we lock fewer ObjectMonitors, remove unnecessary locking from ObjectSynchronizer::deflate_monitor_list(), add NoSafepointVerifier helpers to main list management functions, remove unnecessary storestore(), remove unnecessary comments, clarify/fix comments.
rev 57593 : coleenp CR part1: add ObjectMonitor::next_om(), set_next_om(), and try_set_next_om(); ObjectMonitor::_next_om field is now private; rename ListGlobals -> ObjectMonitorListGlobals, rename LVars -> om_list_globals, and prefix each ObjectMonitorListGlobals field with '_'; delete static set_next() function; clarify comments; coleenp CR part2: delete stale comments about mux*().
rev 57595 : v2.09a with 8235795, 8235931 and 8236035 extracted; rebased to jdk-14+28; merge with 8236035.patch.cr1; merge with 8235795.patch.cr1; merge with 8236035.patch.cr2; merge with 8235795.patch.cr2; merge with 8235795.patch.cr3.


  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/vmSymbols.hpp"
  27 #include "logging/log.hpp"
  28 #include "logging/logStream.hpp"
  29 #include "jfr/jfrEvents.hpp"
  30 #include "memory/allocation.inline.hpp"
  31 #include "memory/metaspaceShared.hpp"
  32 #include "memory/padded.hpp"
  33 #include "memory/resourceArea.hpp"
  34 #include "memory/universe.hpp"
  35 #include "oops/markWord.hpp"
  36 #include "oops/oop.inline.hpp"
  37 #include "runtime/atomic.hpp"
  38 #include "runtime/biasedLocking.hpp"
  39 #include "runtime/handles.inline.hpp"

  40 #include "runtime/interfaceSupport.inline.hpp"
  41 #include "runtime/mutexLocker.hpp"
  42 #include "runtime/objectMonitor.hpp"
  43 #include "runtime/objectMonitor.inline.hpp"
  44 #include "runtime/osThread.hpp"

  45 #include "runtime/safepointVerifiers.hpp"
  46 #include "runtime/sharedRuntime.hpp"
  47 #include "runtime/stubRoutines.hpp"
  48 #include "runtime/synchronizer.hpp"
  49 #include "runtime/thread.inline.hpp"
  50 #include "runtime/timer.hpp"
  51 #include "runtime/vframe.hpp"
  52 #include "runtime/vmThread.hpp"
  53 #include "utilities/align.hpp"
  54 #include "utilities/dtrace.hpp"
  55 #include "utilities/events.hpp"
  56 #include "utilities/preserveException.hpp"
  57 
  58 // The "core" versions of monitor enter and exit reside in this file.
  59 // The interpreter and compilers contain specialized transliterated
  60 // variants of the enter-exit fast-path operations.  See i486.ad fast_lock(),
  61 // for instance.  If you make changes here, make sure to modify the
  62 // interpreter, and both C1 and C2 fast-path inline locking code emission.
  63 //
  64 // -----------------------------------------------------------------------------


 101   }
 102 
 103 #else //  ndef DTRACE_ENABLED
 104 
 105 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 106 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 107 
 108 #endif // ndef DTRACE_ENABLED
 109 
 110 // This exists only as a workaround of dtrace bug 6254741
 111 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
 112   DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
 113   return 0;
 114 }
 115 
 116 #define NINFLATIONLOCKS 256
 117 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
 118 
 119 // global list of blocks of monitors
 120 PaddedObjectMonitor* ObjectSynchronizer::g_block_list = NULL;



 121 
 122 struct ObjectMonitorListGlobals {
 123   char         _pad_prefix[OM_CACHE_LINE_SIZE];
 124   // These are highly shared list related variables.
 125   // To avoid false-sharing they need to be the sole occupants of a cache line.
 126 
 127   // Global ObjectMonitor free list. Newly allocated and deflated
 128   // ObjectMonitors are prepended here.
 129   ObjectMonitor* _free_list;
 130   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
 131 
 132   // Global ObjectMonitor in-use list. When a JavaThread is exiting,
 133   // ObjectMonitors on its per-thread in-use list are prepended here.
 134   ObjectMonitor* _in_use_list;
 135   DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
 136 








 137   int _free_count;    // # on free_list
 138   DEFINE_PAD_MINUS_SIZE(3, OM_CACHE_LINE_SIZE, sizeof(int));
 139 
 140   int _in_use_count;  // # on in_use_list
 141   DEFINE_PAD_MINUS_SIZE(4, OM_CACHE_LINE_SIZE, sizeof(int));
 142 
 143   int _population;    // # Extant -- in circulation
 144   DEFINE_PAD_MINUS_SIZE(5, OM_CACHE_LINE_SIZE, sizeof(int));



 145 };
 146 static ObjectMonitorListGlobals om_list_globals;
 147 
 148 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
 149 
 150 
 151 // =====================> Spin-lock functions
 152 
 153 // ObjectMonitors are not lockable outside of this file. We use spin-locks
 154 // implemented using a bit in the _next_om field instead of the heavier
 155 // weight locking mechanisms for faster list management.
 156 
 157 #define OM_LOCK_BIT 0x1
 158 
 159 // Return true if the ObjectMonitor is locked.
 160 // Otherwise returns false.
 161 static bool is_locked(ObjectMonitor* om) {
 162   return ((intptr_t)om->next_om() & OM_LOCK_BIT) == OM_LOCK_BIT;
 163 }
 164 


 282       Atomic::add(&om_list_globals._population, _BLOCKSIZE - 1);
 283       break;
 284     }
 285     // Implied else: try it all again
 286   }
 287 
 288   // Second we handle om_list_globals._free_list:
 289   prepend_list_to_common(new_blk + 1, &new_blk[_BLOCKSIZE - 1], _BLOCKSIZE - 1,
 290                          &om_list_globals._free_list, &om_list_globals._free_count);
 291 }
 292 
 293 // Prepend a list of ObjectMonitors to om_list_globals._free_list.
 294 // 'tail' is the last ObjectMonitor in the list and there are 'count'
 295 // on the list. Also updates om_list_globals._free_count.
 296 static void prepend_list_to_global_free_list(ObjectMonitor* list,
 297                                              ObjectMonitor* tail, int count) {
 298   prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
 299                          &om_list_globals._free_count);
 300 }
 301 










 302 // Prepend a list of ObjectMonitors to om_list_globals._in_use_list.
 303 // 'tail' is the last ObjectMonitor in the list and there are 'count'
 304 // on the list. Also updates om_list_globals._in_use_list.
 305 static void prepend_list_to_global_in_use_list(ObjectMonitor* list,
 306                                                ObjectMonitor* tail, int count) {
 307   prepend_list_to_common(list, tail, count, &om_list_globals._in_use_list,
 308                          &om_list_globals._in_use_count);
 309 }
 310 
 311 // Prepend an ObjectMonitor to the specified list. Also updates
 312 // the specified counter.
 313 static void prepend_to_common(ObjectMonitor* m, ObjectMonitor** list_p,
 314                               int* count_p) {
 315   while (true) {
 316     om_lock(m);  // Lock m so we can safely update its next field.
 317     ObjectMonitor* cur = NULL;
 318     // Lock the list head to guard against races with a list walker
 319     // thread:
 320     if ((cur = get_list_head_locked(list_p)) != NULL) {
 321       // List head is now locked so we can safely switch it.
 322       m->set_next_om(cur);  // m now points to cur (and unlocks m)
 323       Atomic::store(list_p, m);  // Switch list head to unlocked m.
 324       om_unlock(cur);
 325       break;
 326     }
 327     // The list is empty so try to set the list head.
 328     assert(cur == NULL, "cur must be NULL: cur=" INTPTR_FORMAT, p2i(cur));
 329     m->set_next_om(cur);  // m now points to NULL (and unlocks m)
 330     if (Atomic::cmpxchg(list_p, cur, m) == cur) {
 331       // List head is now unlocked m.
 332       break;
 333     }
 334     // Implied else: try it all again
 335   }
 336   Atomic::inc(count_p);
 337 }
 338 
 339 // Prepend an ObjectMonitor to a per-thread om_free_list.
 340 // Also updates the per-thread om_free_count.
 341 static void prepend_to_om_free_list(Thread* self, ObjectMonitor* m) {
 342   prepend_to_common(m, &self->om_free_list, &self->om_free_count);
 343 }
 344 
 345 // Prepend an ObjectMonitor to a per-thread om_in_use_list.
 346 // Also updates the per-thread om_in_use_count.
 347 static void prepend_to_om_in_use_list(Thread* self, ObjectMonitor* m) {
 348   prepend_to_common(m, &self->om_in_use_list, &self->om_in_use_count);
 349 }
 350 
 351 // Take an ObjectMonitor from the start of the specified list. Also
 352 // decrements the specified counter. Returns NULL if none are available.
 353 static ObjectMonitor* take_from_start_of_common(ObjectMonitor** list_p,
 354                                                 int* count_p) {
 355   ObjectMonitor* take = NULL;
 356   // Lock the list head to guard against races with a list walker
 357   // thread:
 358   if ((take = get_list_head_locked(list_p)) == NULL) {
 359     return NULL;  // None are available.
 360   }
 361   ObjectMonitor* next = unmarked_next(take);
 362   // Switch locked list head to next (which unlocks the list head, but
 363   // leaves take locked):
 364   Atomic::store(list_p, next);
 365   Atomic::dec(count_p);
 366   // Unlock take, but leave the next value for any lagging list
 367   // walkers. It will get cleaned up when take is prepended to
 368   // the in-use list:
 369   om_unlock(take);
 370   return take;
 371 }
 372 
 373 // Take an ObjectMonitor from the start of the om_list_globals._free_list.
 374 // Also updates om_list_globals._free_count. Returns NULL if none are
 375 // available.
 376 static ObjectMonitor* take_from_start_of_global_free_list() {
 377   return take_from_start_of_common(&om_list_globals._free_list,


 446   }
 447 
 448   // biased locking and any other IMS exception states take the slow-path
 449   return false;
 450 }
 451 
 452 
 453 // The LockNode emitted directly at the synchronization site would have
 454 // been too big if it were to have included support for the cases of inflated
 455 // recursive enter and exit, so they go here instead.
 456 // Note that we can't safely call AsyncPrintJavaStack() from within
 457 // quick_enter() as our thread state remains _in_Java.
 458 
 459 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
 460                                      BasicLock * lock) {
 461   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 462   assert(self->is_Java_thread(), "invariant");
 463   assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
 464   NoSafepointVerifier nsv;
 465   if (obj == NULL) return false;       // Need to throw NPE


 466   const markWord mark = obj->mark();
 467 
 468   if (mark.has_monitor()) {
 469     ObjectMonitor* const m = mark.monitor();






 470     assert(m->object() == obj, "invariant");
 471     Thread* const owner = (Thread *) m->_owner;
 472 
 473     // Lock contention and Transactional Lock Elision (TLE) diagnostics
 474     // and observability
 475     // Case: light contention possibly amenable to TLE
 476     // Case: TLE inimical operations such as nested/recursive synchronization
 477 
 478     if (owner == self) {
 479       m->_recursions++;
 480       return true;
 481     }
 482 
 483     // This Java Monitor is inflated so obj's header will never be
 484     // displaced to this thread's BasicLock. Make the displaced header
 485     // non-NULL so this BasicLock is not seen as recursive nor as
 486     // being locked. We do this unconditionally so that this thread's
 487     // BasicLock cannot be mis-interpreted by any stack walkers. For
 488     // performance reasons, stack walkers generally first check for
 489     // Biased Locking in the object's header, the second check is for
 490     // stack-locking in the object's header, the third check is for
 491     // recursive stack-locking in the displaced header in the BasicLock,
 492     // and last are the inflated Java Monitor (ObjectMonitor) checks.
 493     lock->set_displaced_header(markWord::unused_mark());
 494 
 495     if (owner == NULL && m->try_set_owner_from(NULL, self) == NULL) {
 496       assert(m->_recursions == 0, "invariant");
 497       return true;
 498     }












 499   }
 500 
 501   // Note that we could inflate in quick_enter.
 502   // This is likely a useful optimization
 503   // Critically, in quick_enter() we must not:
 504   // -- perform bias revocation, or
 505   // -- block indefinitely, or
 506   // -- reach a safepoint
 507 
 508   return false;        // revert to slow-path
 509 }
 510 
 511 // -----------------------------------------------------------------------------
 512 // Monitor Enter/Exit
 513 // The interpreter and compiler assembly code tries to lock using the fast path
 514 // of this algorithm. Make sure to update that code if the following function is
 515 // changed. The implementation is extremely sensitive to race condition. Be careful.
 516 
 517 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, TRAPS) {
 518   if (UseBiasedLocking) {


 530     // Anticipate successful CAS -- the ST of the displaced mark must
 531     // be visible <= the ST performed by the CAS.
 532     lock->set_displaced_header(mark);
 533     if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
 534       return;
 535     }
 536     // Fall through to inflate() ...
 537   } else if (mark.has_locker() &&
 538              THREAD->is_lock_owned((address)mark.locker())) {
 539     assert(lock != mark.locker(), "must not re-lock the same lock");
 540     assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
 541     lock->set_displaced_header(markWord::from_pointer(NULL));
 542     return;
 543   }
 544 
 545   // The object header will never be displaced to this lock,
 546   // so it does not matter what the value is, except that it
 547   // must be non-zero to avoid looking like a re-entrant lock,
 548   // and must not look locked either.
 549   lock->set_displaced_header(markWord::unused_mark());
 550   inflate(THREAD, obj(), inflate_cause_monitor_enter)->enter(THREAD);


 551 }
 552 
 553 void ObjectSynchronizer::exit(oop object, BasicLock* lock, TRAPS) {
 554   markWord mark = object->mark();
 555   // We cannot check for Biased Locking if we are racing an inflation.
 556   assert(mark == markWord::INFLATING() ||
 557          !mark.has_bias_pattern(), "should not see bias pattern here");
 558 
 559   markWord dhw = lock->displaced_header();
 560   if (dhw.value() == 0) {
 561     // If the displaced header is NULL, then this exit matches up with
 562     // a recursive enter. No real work to do here except for diagnostics.
 563 #ifndef PRODUCT
 564     if (mark != markWord::INFLATING()) {
 565       // Only do diagnostics if we are not racing an inflation. Simply
 566       // exiting a recursive enter of a Java Monitor that is being
 567       // inflated is safe; see the has_monitor() comment below.
 568       assert(!mark.is_neutral(), "invariant");
 569       assert(!mark.has_locker() ||
 570              THREAD->is_lock_owned((address)mark.locker()), "invariant");


 579         // does not own the Java Monitor.
 580         ObjectMonitor* m = mark.monitor();
 581         assert(((oop)(m->object()))->mark() == mark, "invariant");
 582         assert(m->is_entered(THREAD), "invariant");
 583       }
 584     }
 585 #endif
 586     return;
 587   }
 588 
 589   if (mark == markWord::from_pointer(lock)) {
 590     // If the object is stack-locked by the current thread, try to
 591     // swing the displaced header from the BasicLock back to the mark.
 592     assert(dhw.is_neutral(), "invariant");
 593     if (object->cas_set_mark(dhw, mark) == mark) {
 594       return;
 595     }
 596   }
 597 
 598   // We have to take the slow-path of possible inflation and then exit.
 599   inflate(THREAD, object, inflate_cause_vm_internal)->exit(true, THREAD);


 600 }
 601 
 602 // -----------------------------------------------------------------------------
 603 // Class Loader  support to workaround deadlocks on the class loader lock objects
 604 // Also used by GC
 605 // complete_exit()/reenter() are used to wait on a nested lock
 606 // i.e. to give up an outer lock completely and then re-enter
 607 // Used when holding nested locks - lock acquisition order: lock1 then lock2
 608 //  1) complete_exit lock1 - saving recursion count
 609 //  2) wait on lock2
 610 //  3) when notified on lock2, unlock lock2
 611 //  4) reenter lock1 with original recursion count
 612 //  5) lock lock2
 613 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 614 intx ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
 615   if (UseBiasedLocking) {
 616     BiasedLocking::revoke(obj, THREAD);
 617     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 618   }
 619 
 620   ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
 621 
 622   return monitor->complete_exit(THREAD);

 623 }
 624 
 625 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 626 void ObjectSynchronizer::reenter(Handle obj, intx recursions, TRAPS) {
 627   if (UseBiasedLocking) {
 628     BiasedLocking::revoke(obj, THREAD);
 629     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 630   }
 631 
 632   ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
 633 
 634   monitor->reenter(recursions, THREAD);
 635 }
 636 // -----------------------------------------------------------------------------
 637 // JNI locks on java objects
 638 // NOTE: must use heavy weight monitor to handle jni monitor enter
 639 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
 640   // the current locking is from JNI instead of Java code
 641   if (UseBiasedLocking) {
 642     BiasedLocking::revoke(obj, THREAD);
 643     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 644   }
 645   THREAD->set_current_pending_monitor_is_from_java(false);
 646   inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);


 647   THREAD->set_current_pending_monitor_is_from_java(true);
 648 }
 649 
 650 // NOTE: must use heavy weight monitor to handle jni monitor exit
 651 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
 652   if (UseBiasedLocking) {
 653     Handle h_obj(THREAD, obj);
 654     BiasedLocking::revoke(h_obj, THREAD);
 655     obj = h_obj();
 656   }
 657   assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 658 
 659   ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);


 660   // If this thread has locked the object, exit the monitor. We
 661   // intentionally do not use CHECK here because we must exit the
 662   // monitor even if an exception is pending.
 663   if (monitor->check_owner(THREAD)) {
 664     monitor->exit(true, THREAD);
 665   }
 666 }
 667 
 668 // -----------------------------------------------------------------------------
 669 // Internal VM locks on java objects
 670 // standard constructor, allows locking failures
 671 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) {
 672   _dolock = do_lock;
 673   _thread = thread;
 674   _thread->check_for_valid_safepoint_state();
 675   _obj = obj;
 676 
 677   if (_dolock) {
 678     ObjectSynchronizer::enter(_obj, &_lock, _thread);
 679   }
 680 }
 681 
 682 ObjectLocker::~ObjectLocker() {
 683   if (_dolock) {
 684     ObjectSynchronizer::exit(_obj(), &_lock, _thread);
 685   }
 686 }
 687 
 688 
 689 // -----------------------------------------------------------------------------
 690 //  Wait/Notify/NotifyAll
 691 // NOTE: must use heavy weight monitor to handle wait()
 692 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 693   if (UseBiasedLocking) {
 694     BiasedLocking::revoke(obj, THREAD);
 695     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 696   }
 697   if (millis < 0) {
 698     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 699   }
 700   ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);


 701 
 702   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
 703   monitor->wait(millis, true, THREAD);
 704 
 705   // This dummy call is in place to get around dtrace bug 6254741.  Once
 706   // that's fixed we can uncomment the following line, remove the call
 707   // and change this function back into a "void" func.
 708   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 709   return dtrace_waited_probe(monitor, obj, THREAD);

 710 }
 711 
 712 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
 713   if (UseBiasedLocking) {
 714     BiasedLocking::revoke(obj, THREAD);
 715     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 716   }
 717   if (millis < 0) {
 718     THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 719   }
 720   inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD);


 721 }
 722 
 723 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 724   if (UseBiasedLocking) {
 725     BiasedLocking::revoke(obj, THREAD);
 726     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 727   }
 728 
 729   markWord mark = obj->mark();
 730   if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
 731     return;
 732   }
 733   inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD);


 734 }
 735 
 736 // NOTE: see comment of notify()
 737 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 738   if (UseBiasedLocking) {
 739     BiasedLocking::revoke(obj, THREAD);
 740     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 741   }
 742 
 743   markWord mark = obj->mark();
 744   if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
 745     return;
 746   }
 747   inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD);


 748 }
 749 
 750 // -----------------------------------------------------------------------------
 751 // Hash Code handling
 752 //
 753 // Performance concern:
 754 // OrderAccess::storestore() calls release() which at one time stored 0
 755 // into the global volatile OrderAccess::dummy variable. This store was
 756 // unnecessary for correctness. Many threads storing into a common location
 757 // causes considerable cache migration or "sloshing" on large SMP systems.
 758 // As such, I avoided using OrderAccess::storestore(). In some cases
 759 // OrderAccess::fence() -- which incurs local latency on the executing
 760 // processor -- is a better choice as it scales on SMP systems.
 761 //
 762 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
 763 // a discussion of coherency costs. Note that all our current reference
 764 // platforms provide strong ST-ST order, so the issue is moot on IA32,
 765 // x64, and SPARC.
 766 //
 767 // As a general policy we use "volatile" to control compiler-based reordering


 920       Handle hobj(self, obj);
 921       // Relaxing assertion for bug 6320749.
 922       assert(Universe::verify_in_progress() ||
 923              !SafepointSynchronize::is_at_safepoint(),
 924              "biases should not be seen by VM thread here");
 925       BiasedLocking::revoke(hobj, JavaThread::current());
 926       obj = hobj();
 927       assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 928     }
 929   }
 930 
 931   // hashCode() is a heap mutator ...
 932   // Relaxing assertion for bug 6320749.
 933   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 934          !SafepointSynchronize::is_at_safepoint(), "invariant");
 935   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 936          self->is_Java_thread() , "invariant");
 937   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 938          ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
 939 

 940   ObjectMonitor* monitor = NULL;
 941   markWord temp, test;
 942   intptr_t hash;
 943   markWord mark = read_stable_mark(obj);
 944 
 945   // object should remain ineligible for biased locking
 946   assert(!mark.has_bias_pattern(), "invariant");
 947 
 948   if (mark.is_neutral()) {            // if this is a normal header
 949     hash = mark.hash();
 950     if (hash != 0) {                  // if it has a hash, just return it
 951       return hash;
 952     }
 953     hash = get_next_hash(self, obj);  // get a new hash
 954     temp = mark.copy_set_hash(hash);  // merge the hash into header
 955                                       // try to install the hash
 956     test = obj->cas_set_mark(temp, mark);
 957     if (test == mark) {               // if the hash was installed, return it
 958       return hash;
 959     }
 960     // Failed to install the hash. It could be that another thread
 961     // installed the hash just before our attempt or inflation has
 962     // occurred or... so we fall thru to inflate the monitor for
 963     // stability and then install the hash.
 964   } else if (mark.has_monitor()) {
 965     monitor = mark.monitor();






 966     temp = monitor->header();
 967     assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());



 968     hash = temp.hash();
 969     if (hash != 0) {                  // if it has a hash, just return it
 970       return hash;
 971     }
 972     // Fall thru so we only have one place that installs the hash in
 973     // the ObjectMonitor.
 974   } else if (self->is_lock_owned((address)mark.locker())) {
 975     // This is a stack lock owned by the calling thread so fetch the
 976     // displaced markWord from the BasicLock on the stack.
 977     temp = mark.displaced_mark_helper();
 978     assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 979     hash = temp.hash();
 980     if (hash != 0) {                  // if it has a hash, just return it
 981       return hash;
 982     }
 983     // WARNING:
 984     // The displaced header in the BasicLock on a thread's stack
 985     // is strictly immutable. It CANNOT be changed in ANY cases.
 986     // So we have to inflate the stack lock into an ObjectMonitor
 987     // even if the current thread owns the lock. The BasicLock on
 988     // a thread's stack can be asynchronously read by other threads
 989     // during an inflate() call so any change to that stack memory
 990     // may not propagate to other threads correctly.
 991   }
 992 
 993   // Inflate the monitor to set the hash.
 994   monitor = inflate(self, obj, inflate_cause_hash_code);


 995   // Load ObjectMonitor's header/dmw field and see if it has a hash.
 996   mark = monitor->header();
 997   assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());



 998   hash = mark.hash();
 999   if (hash == 0) {                    // if it does not have a hash
1000     hash = get_next_hash(self, obj);  // get a new hash
1001     temp = mark.copy_set_hash(hash);  // merge the hash into header






1002     assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1003     uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1004     test = markWord(v);
1005     if (test != mark) {
1006       // The attempt to update the ObjectMonitor's header/dmw field
1007       // did not work. This can happen if another thread managed to
1008       // merge in the hash just before our cmpxchg().


1009       // If we add any new usages of the header/dmw field, this code
1010       // will need to be updated.





1011       hash = test.hash();
1012       assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1013       assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1014     }
1015   }
1016   // We finally get the hash.
1017   return hash;

1018 }
1019 
1020 // Deprecated -- use FastHashCode() instead.
1021 
1022 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1023   return FastHashCode(Thread::current(), obj());
1024 }
1025 
1026 
1027 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
1028                                                    Handle h_obj) {
1029   if (UseBiasedLocking) {
1030     BiasedLocking::revoke(h_obj, thread);
1031     assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1032   }
1033 
1034   assert(thread == JavaThread::current(), "Can only be called on current thread");
1035   oop obj = h_obj();
1036 

1037   markWord mark = read_stable_mark(obj);
1038 
1039   // Uncontended case, header points to stack
1040   if (mark.has_locker()) {
1041     return thread->is_lock_owned((address)mark.locker());
1042   }
1043   // Contended case, header points to ObjectMonitor (tagged pointer)
1044   if (mark.has_monitor()) {
1045     ObjectMonitor* monitor = mark.monitor();
1046     return monitor->is_entered(thread) != 0;






1047   }
1048   // Unlocked case, header in place
1049   assert(mark.is_neutral(), "sanity check");
1050   return false;

1051 }
1052 
1053 // Be aware of this method could revoke bias of the lock object.
1054 // This method queries the ownership of the lock handle specified by 'h_obj'.
1055 // If the current thread owns the lock, it returns owner_self. If no
1056 // thread owns the lock, it returns owner_none. Otherwise, it will return
1057 // owner_other.
1058 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
1059 (JavaThread *self, Handle h_obj) {
1060   // The caller must beware this method can revoke bias, and
1061   // revocation can result in a safepoint.
1062   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
1063   assert(self->thread_state() != _thread_blocked, "invariant");
1064 
1065   // Possible mark states: neutral, biased, stack-locked, inflated
1066 
1067   if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
1068     // CASE: biased
1069     BiasedLocking::revoke(h_obj, self);
1070     assert(!h_obj->mark().has_bias_pattern(),
1071            "biases should be revoked by now");
1072   }
1073 
1074   assert(self == JavaThread::current(), "Can only be called on current thread");
1075   oop obj = h_obj();


1076   markWord mark = read_stable_mark(obj);
1077 
1078   // CASE: stack-locked.  Mark points to a BasicLock on the owner's stack.
1079   if (mark.has_locker()) {
1080     return self->is_lock_owned((address)mark.locker()) ?
1081       owner_self : owner_other;
1082   }
1083 
1084   // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
1085   // The Object:ObjectMonitor relationship is stable as long as we're
1086   // not at a safepoint.
1087   if (mark.has_monitor()) {
1088     void* owner = mark.monitor()->_owner;







1089     if (owner == NULL) return owner_none;
1090     return (owner == self ||
1091             self->is_lock_owned((address)owner)) ? owner_self : owner_other;
1092   }
1093 
1094   // CASE: neutral
1095   assert(mark.is_neutral(), "sanity check");
1096   return owner_none;           // it's unlocked

1097 }
1098 
1099 // FIXME: jvmti should call this
1100 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1101   if (UseBiasedLocking) {
1102     if (SafepointSynchronize::is_at_safepoint()) {
1103       BiasedLocking::revoke_at_safepoint(h_obj);
1104     } else {
1105       BiasedLocking::revoke(h_obj, JavaThread::current());
1106     }
1107     assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1108   }
1109 
1110   oop obj = h_obj();
1111   address owner = NULL;
1112 


1113   markWord mark = read_stable_mark(obj);
1114 
1115   // Uncontended case, header points to stack
1116   if (mark.has_locker()) {
1117     owner = (address) mark.locker();
1118   }
1119 
1120   // Contended case, header points to ObjectMonitor (tagged pointer)
1121   else if (mark.has_monitor()) {
1122     ObjectMonitor* monitor = mark.monitor();






1123     assert(monitor != NULL, "monitor should be non-null");
1124     owner = (address) monitor->owner();
1125   }
1126 
1127   if (owner != NULL) {
1128     // owning_thread_from_monitor_owner() may also return NULL here
1129     return Threads::owning_thread_from_monitor_owner(t_list, owner);
1130   }
1131 
1132   // Unlocked case, header in place
1133   // Cannot have assertion since this object may have been
1134   // locked by another thread when reaching here.
1135   // assert(mark.is_neutral(), "sanity check");
1136 
1137   return NULL;

1138 }
1139 
1140 // Visitors ...
1141 
1142 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
1143   PaddedObjectMonitor* block = Atomic::load(&g_block_list);
1144   while (block != NULL) {
1145     assert(block->object() == CHAINMARKER, "must be a block header");
1146     for (int i = _BLOCKSIZE - 1; i > 0; i--) {
1147       ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1148       oop object = (oop)mid->object();
1149       if (object != NULL) {


1150         // Only process with closure if the object is set.


1151         closure->do_monitor(mid);
1152       }
1153     }
1154     // unmarked_next() is not needed with g_block_list (no locking
1155     // used with block linkage _next_om fields).
1156     block = (PaddedObjectMonitor*)block->next_om();
1157   }
1158 }
1159 
1160 static bool monitors_used_above_threshold() {
1161   int population = Atomic::load(&om_list_globals._population);
1162   if (population == 0) {
1163     return false;
1164   }
1165   if (MonitorUsedDeflationThreshold > 0) {
1166     int monitors_used = population - Atomic::load(&om_list_globals._free_count);



1167     int monitor_usage = (monitors_used * 100LL) / population;
1168     return monitor_usage > MonitorUsedDeflationThreshold;
1169   }
1170   return false;
1171 }
1172 
1173 // Returns true if MonitorBound is set (> 0) and if the specified
1174 // cnt is > MonitorBound. Otherwise returns false.
1175 static bool is_MonitorBound_exceeded(const int cnt) {
1176   const int mx = MonitorBound;
1177   return mx > 0 && cnt > mx;
1178 }
1179 
1180 bool ObjectSynchronizer::is_cleanup_needed() {
1181   if (monitors_used_above_threshold()) {
1182     // Too many monitors in use.



1183     return true;
1184   }
1185   return needs_monitor_scavenge();



















1186 }
1187 
1188 bool ObjectSynchronizer::needs_monitor_scavenge() {
1189   if (Atomic::load(&_forceMonitorScavenge) == 1) {
1190     log_info(monitorinflation)("Monitor scavenge needed, triggering safepoint cleanup.");
1191     return true;
1192   }
1193   return false;
1194 }
1195 




















1196 void ObjectSynchronizer::oops_do(OopClosure* f) {
1197   // We only scan the global used list here (for moribund threads), and
1198   // the thread-local monitors in Thread::oops_do().
1199   global_used_oops_do(f);
1200 }
1201 
1202 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1203   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1204   list_oops_do(Atomic::load(&om_list_globals._in_use_list), f);
1205 }
1206 
1207 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1208   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1209   list_oops_do(thread->om_in_use_list, f);
1210 }
1211 
1212 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1213   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1214   // The oops_do() phase does not overlap with monitor deflation
1215   // so no need to lock ObjectMonitors for the list traversal.


1216   for (ObjectMonitor* mid = list; mid != NULL; mid = unmarked_next(mid)) {
1217     if (mid->object() != NULL) {
1218       f->do_oop((oop*)mid->object_addr());
1219     }
1220   }
1221 }
1222 
1223 
1224 // -----------------------------------------------------------------------------
1225 // ObjectMonitor Lifecycle
1226 // -----------------------
1227 // Inflation unlinks monitors from om_list_globals._free_list or a per-thread
1228 // free list and associates them with objects. Deflation -- which occurs at
1229 // STW-time -- disassociates idle monitors from objects.
1230 // Such scavenged monitors are returned to the om_list_globals._free_list.
1231 //
1232 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1233 //
1234 // Lifecycle:
1235 // --   unassigned and on the om_list_globals._free_list
1236 // --   unassigned and on a per-thread free list
1237 // --   assigned to an object.  The object is inflated and the mark refers
1238 //      to the ObjectMonitor.
1239 
1240 
1241 // Constraining monitor pool growth via MonitorBound ...
1242 //
1243 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled.
1244 //

1245 // The monitor pool is grow-only.  We scavenge at STW safepoint-time, but the
1246 // the rate of scavenging is driven primarily by GC.  As such,  we can find
1247 // an inordinate number of monitors in circulation.
1248 // To avoid that scenario we can artificially induce a STW safepoint
1249 // if the pool appears to be growing past some reasonable bound.
1250 // Generally we favor time in space-time tradeoffs, but as there's no
1251 // natural back-pressure on the # of extant monitors we need to impose some
1252 // type of limit.  Beware that if MonitorBound is set to too low a value
1253 // we could just loop. In addition, if MonitorBound is set to a low value
1254 // we'll incur more safepoints, which are harmful to performance.
1255 // See also: GuaranteedSafepointInterval
1256 //
1257 // If MonitorBound is set, the boundry applies to

1258 //     (om_list_globals._population - om_list_globals._free_count)
1259 // i.e., if there are not enough ObjectMonitors on the global free list,
1260 // then a safepoint deflation is induced. Picking a good MonitorBound value
1261 // is non-trivial.










1262 
1263 static void InduceScavenge(Thread* self, const char * Whence) {


1264   // Induce STW safepoint to trim monitors
1265   // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1266   // More precisely, trigger a cleanup safepoint as the number
1267   // of active monitors passes the specified threshold.
1268   // TODO: assert thread state is reasonable
1269 
1270   if (Atomic::xchg(&_forceMonitorScavenge, 1) == 0) {
1271     VMThread::check_for_forced_cleanup();
1272   }
1273 }
1274 
1275 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1276   // A large MAXPRIVATE value reduces both list lock contention
1277   // and list coherency traffic, but also tends to increase the
1278   // number of ObjectMonitors in circulation as well as the STW
1279   // scavenge costs.  As usual, we lean toward time in space-time
1280   // tradeoffs.
1281   const int MAXPRIVATE = 1024;
1282   NoSafepointVerifier nsv;
1283 
1284   stringStream ss;
1285   for (;;) {
1286     ObjectMonitor* m;
1287 
1288     // 1: try to allocate from the thread's local om_free_list.
1289     // Threads will attempt to allocate first from their local list, then
1290     // from the global list, and only after those attempts fail will the
1291     // thread attempt to instantiate new monitors. Thread-local free lists
1292     // improve allocation latency, as well as reducing coherency traffic
1293     // on the shared global list.
1294     m = take_from_start_of_om_free_list(self);
1295     if (m != NULL) {
1296       guarantee(m->object() == NULL, "invariant");

1297       prepend_to_om_in_use_list(self, m);
1298       return m;
1299     }
1300 
1301     // 2: try to allocate from the global om_list_globals._free_list
1302     // If we're using thread-local free lists then try
1303     // to reprovision the caller's free list.
1304     if (Atomic::load(&om_list_globals._free_list) != NULL) {
1305       // Reprovision the thread's om_free_list.
1306       // Use bulk transfers to reduce the allocation rate and heat
1307       // on various locks.
1308       for (int i = self->om_free_provision; --i >= 0;) {
1309         ObjectMonitor* take = take_from_start_of_global_free_list();
1310         if (take == NULL) {
1311           break;  // No more are available.
1312         }
1313         guarantee(take->object() == NULL, "invariant");



















1314         take->Recycle();




1315         om_release(self, take, false);
1316       }
1317       self->om_free_provision += 1 + (self->om_free_provision / 2);
1318       if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1319 
1320       if (is_MonitorBound_exceeded(Atomic::load(&om_list_globals._population) -

1321                                    Atomic::load(&om_list_globals._free_count))) {
1322         // Not enough ObjectMonitors on the global free list.
1323         // We can't safely induce a STW safepoint from om_alloc() as our thread
1324         // state may not be appropriate for such activities and callers may hold
1325         // naked oops, so instead we defer the action.
1326         InduceScavenge(self, "om_alloc");
1327       }
1328       continue;
1329     }
1330 
1331     // 3: allocate a block of new ObjectMonitors
1332     // Both the local and global free lists are empty -- resort to malloc().
1333     // In the current implementation ObjectMonitors are TSM - immortal.
1334     // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1335     // each ObjectMonitor to start at the beginning of a cache line,
1336     // so we use align_up().
1337     // A better solution would be to use C++ placement-new.
1338     // BEWARE: As it stands currently, we don't run the ctors!
1339     assert(_BLOCKSIZE > 1, "invariant");
1340     size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1341     PaddedObjectMonitor* temp;
1342     size_t aligned_size = neededsize + (OM_CACHE_LINE_SIZE - 1);
1343     void* real_malloc_addr = NEW_C_HEAP_ARRAY(char, aligned_size, mtInternal);
1344     temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, OM_CACHE_LINE_SIZE);
1345     (void)memset((void *) temp, 0, neededsize);
1346 
1347     // Format the block.
1348     // initialize the linked list, each monitor points to its next
1349     // forming the single linked free list, the very first monitor
1350     // will points to next block, which forms the block list.
1351     // The trick of using the 1st element in the block as g_block_list
1352     // linkage should be reconsidered.  A better implementation would
1353     // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1354 
1355     for (int i = 1; i < _BLOCKSIZE; i++) {
1356       temp[i].set_next_om((ObjectMonitor*)&temp[i + 1]);

1357     }
1358 
1359     // terminate the last monitor as the end of list
1360     temp[_BLOCKSIZE - 1].set_next_om((ObjectMonitor*)NULL);
1361 
1362     // Element [0] is reserved for global list linkage
1363     temp[0].set_object(CHAINMARKER);
1364 
1365     // Consider carving out this thread's current request from the
1366     // block in hand.  This avoids some lock traffic and redundant
1367     // list activity.
1368 
1369     prepend_block_to_lists(temp);
1370   }
1371 }
1372 
1373 // Place "m" on the caller's private per-thread om_free_list.
1374 // In practice there's no need to clamp or limit the number of
1375 // monitors on a thread's om_free_list as the only non-allocation time
1376 // we'll call om_release() is to return a monitor to the free list after
1377 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1378 // accumulate on a thread's free list.
1379 //
1380 // Key constraint: all ObjectMonitors on a thread's free list and the global
1381 // free list must have their object field set to null. This prevents the
1382 // scavenger -- deflate_monitor_list() -- from reclaiming them while we
1383 // are trying to release them.
1384 
1385 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1386                                     bool from_per_thread_alloc) {
1387   guarantee(m->header().value() == 0, "invariant");
1388   guarantee(m->object() == NULL, "invariant");
1389   NoSafepointVerifier nsv;
1390 
1391   stringStream ss;
1392   guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1393             "%s, recursions=" INTX_FORMAT, m->is_busy_to_string(&ss),
1394             m->_recursions);

1395   // _next_om is used for both per-thread in-use and free lists so
1396   // we have to remove 'm' from the in-use list first (as needed).
1397   if (from_per_thread_alloc) {
1398     // Need to remove 'm' from om_in_use_list.
1399     ObjectMonitor* mid = NULL;
1400     ObjectMonitor* next = NULL;
1401 
1402     // This list walk can only race with another list walker since
1403     // deflation can only happen at a safepoint so we don't have to
1404     // worry about an ObjectMonitor being removed from this list
1405     // while we are walking it.
1406 
1407     // Lock the list head to avoid racing with another list walker.

1408     if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) {
1409       fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self));
1410     }
1411     next = unmarked_next(mid);
1412     if (m == mid) {
1413       // First special case:
1414       // 'm' matches mid, is the list head and is locked. Switch the list
1415       // head to next which unlocks the list head, but leaves the extracted
1416       // mid locked:
1417       Atomic::store(&self->om_in_use_list, next);
1418     } else if (m == next) {
1419       // Second special case:
1420       // 'm' matches next after the list head and we already have the list
1421       // head locked so set mid to what we are extracting:
1422       mid = next;
1423       // Lock mid to prevent races with a list walker:


1424       om_lock(mid);
1425       // Update next to what follows mid (if anything):
1426       next = unmarked_next(mid);
1427       // Switch next after the list head to new next which unlocks the
1428       // list head, but leaves the extracted mid locked:
1429       self->om_in_use_list->set_next_om(next);
1430     } else {
1431       // We have to search the list to find 'm'.
1432       om_unlock(mid);  // unlock the list head
1433       guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT
1434                 " is too short.", p2i(self), p2i(self->om_in_use_list));
1435       // Our starting anchor is next after the list head which is the
1436       // last ObjectMonitor we checked:
1437       ObjectMonitor* anchor = next;





1438       while ((mid = unmarked_next(anchor)) != NULL) {
1439         if (m == mid) {
1440           // We found 'm' on the per-thread in-use list so extract it.
1441           om_lock(anchor);  // Lock the anchor so we can safely modify it.
1442           // Update next to what follows mid (if anything):
1443           next = unmarked_next(mid);
1444           // Switch next after the anchor to new next which unlocks the
1445           // anchor, but leaves the extracted mid locked:
1446           anchor->set_next_om(next);
1447           break;
1448         } else {
1449           anchor = mid;






1450         }
1451       }
1452     }
1453 
1454     if (mid == NULL) {
1455       // Reached end of the list and didn't find 'm' so:
1456       fatal("thread=" INTPTR_FORMAT " must find m=" INTPTR_FORMAT "on om_in_use_list="
1457             INTPTR_FORMAT, p2i(self), p2i(m), p2i(self->om_in_use_list));
1458     }
1459 
1460     // At this point mid is disconnected from the in-use list so
1461     // its lock no longer has any effects on the in-use list.
1462     Atomic::dec(&self->om_in_use_count);
1463     // Unlock mid, but leave the next value for any lagging list
1464     // walkers. It will get cleaned up when mid is prepended to
1465     // the thread's free list:
1466     om_unlock(mid);
1467   }
1468 
1469   prepend_to_om_free_list(self, m);

1470 }
1471 
1472 // Return ObjectMonitors on a moribund thread's free and in-use
1473 // lists to the appropriate global lists. The ObjectMonitors on the
1474 // per-thread in-use list may still be in use by other threads.
1475 //
1476 // We currently call om_flush() from Threads::remove() before the
1477 // thread has been excised from the thread list and is no longer a
1478 // mutator. This means that om_flush() cannot run concurrently with
1479 // a safepoint and interleave with deflate_idle_monitors(). In
1480 // particular, this ensures that the thread's in-use monitors are
1481 // scanned by a GC safepoint, either via Thread::oops_do() (before
1482 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1483 // om_flush() is called).





1484 
1485 void ObjectSynchronizer::om_flush(Thread* self) {
1486   // Process the per-thread in-use list first to be consistent.
1487   int in_use_count = 0;
1488   ObjectMonitor* in_use_list = NULL;
1489   ObjectMonitor* in_use_tail = NULL;
1490   NoSafepointVerifier nsv;
1491 
1492   // This function can race with a list walker thread so we lock the
1493   // list head to prevent confusion.



1494   if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) {
1495     // At this point, we have locked the in-use list head so a racing
1496     // thread cannot come in after us. However, a racing thread could
1497     // be ahead of us; we'll detect that and delay to let it finish.
1498     //
1499     // The thread is going away, however the ObjectMonitors on the
1500     // om_in_use_list may still be in-use by other threads. Link
1501     // them to in_use_tail, which will be linked into the global
1502     // in-use list (om_list_globals._in_use_list) below.
1503     //
1504     // Account for the in-use list head before the loop since it is
1505     // already locked (by this thread):
1506     in_use_tail = in_use_list;
1507     in_use_count++;
1508     for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL; cur_om = unmarked_next(cur_om)) {
1509       if (is_locked(cur_om)) {
1510         // cur_om is locked so there must be a racing walker thread ahead
1511         // of us so we'll give it a chance to finish.
1512         while (is_locked(cur_om)) {
1513           os::naked_short_sleep(1);
1514         }











1515       }
1516       in_use_tail = cur_om;
1517       in_use_count++;

1518     }
1519     guarantee(in_use_tail != NULL, "invariant");
1520     int l_om_in_use_count = Atomic::load(&self->om_in_use_count);
1521     assert(l_om_in_use_count == in_use_count, "in-use counts don't match: "
1522           "l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count);
1523     Atomic::store(&self->om_in_use_count, 0);
1524     // Clear the in-use list head (which also unlocks it):
1525     Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL);
1526     om_unlock(in_use_list);
1527   }
1528 
1529   int free_count = 0;
1530   ObjectMonitor* free_list = NULL;
1531   ObjectMonitor* free_tail = NULL;
1532   // This function can race with a list walker thread so we lock the
1533   // list head to prevent confusion.
1534   if ((free_list = get_list_head_locked(&self->om_free_list)) != NULL) {
1535     // At this point, we have locked the free list head so a racing
1536     // thread cannot come in after us. However, a racing thread could
1537     // be ahead of us; we'll detect that and delay to let it finish.
1538     //
1539     // The thread is going away. Set 'free_tail' to the last per-thread free
1540     // monitor which will be linked to om_list_globals._free_list below.
1541     //
1542     // Account for the free list head before the loop since it is
1543     // already locked (by this thread):
1544     free_tail = free_list;
1545     free_count++;
1546     for (ObjectMonitor* s = unmarked_next(free_list); s != NULL; s = unmarked_next(s)) {
1547       if (is_locked(s)) {
1548         // s is locked so there must be a racing walker thread ahead
1549         // of us so we'll give it a chance to finish.
1550         while (is_locked(s)) {
1551           os::naked_short_sleep(1);
1552         }
1553       }
1554       free_tail = s;
1555       free_count++;
1556       guarantee(s->object() == NULL, "invariant");
1557       stringStream ss;
1558       guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1559     }
1560     guarantee(free_tail != NULL, "invariant");
1561     int l_om_free_count = Atomic::load(&self->om_free_count);
1562     assert(l_om_free_count == free_count, "free counts don't match: "
1563            "l_om_free_count=%d, free_count=%d", l_om_free_count, free_count);
1564     Atomic::store(&self->om_free_count, 0);
1565     Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL);
1566     om_unlock(free_list);
1567   }
1568 
1569   if (free_tail != NULL) {
1570     prepend_list_to_global_free_list(free_list, free_tail, free_count);
1571   }
1572 
1573   if (in_use_tail != NULL) {
1574     prepend_list_to_global_in_use_list(in_use_list, in_use_tail, in_use_count);
1575   }
1576 
1577   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1578   LogStreamHandle(Info, monitorinflation) lsh_info;
1579   LogStream* ls = NULL;
1580   if (log_is_enabled(Debug, monitorinflation)) {
1581     ls = &lsh_debug;
1582   } else if ((free_count != 0 || in_use_count != 0) &&


1585   }
1586   if (ls != NULL) {
1587     ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1588                  ", in_use_count=%d" ", om_free_provision=%d",
1589                  p2i(self), free_count, in_use_count, self->om_free_provision);
1590   }
1591 }
1592 
1593 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1594                                        const oop obj,
1595                                        ObjectSynchronizer::InflateCause cause) {
1596   assert(event != NULL, "invariant");
1597   assert(event->should_commit(), "invariant");
1598   event->set_monitorClass(obj->klass());
1599   event->set_address((uintptr_t)(void*)obj);
1600   event->set_cause((u1)cause);
1601   event->commit();
1602 }
1603 
1604 // Fast path code shared by multiple functions
1605 void ObjectSynchronizer::inflate_helper(oop obj) {

1606   markWord mark = obj->mark();
1607   if (mark.has_monitor()) {
1608     assert(ObjectSynchronizer::verify_objmon_isinpool(mark.monitor()), "monitor is invalid");
1609     assert(mark.monitor()->header().is_neutral(), "monitor must record a good object header");










1610     return;
1611   }
1612   inflate(Thread::current(), obj, inflate_cause_vm_internal);
1613 }
1614 
1615 ObjectMonitor* ObjectSynchronizer::inflate(Thread* self,
1616                                            oop object, const InflateCause cause) {
1617   // Inflate mutates the heap ...
1618   // Relaxing assertion for bug 6320749.
1619   assert(Universe::verify_in_progress() ||
1620          !SafepointSynchronize::is_at_safepoint(), "invariant");
1621 
1622   EventJavaMonitorInflate event;
1623 
1624   for (;;) {
1625     const markWord mark = object->mark();
1626     assert(!mark.has_bias_pattern(), "invariant");
1627 
1628     // The mark can be in one of the following states:
1629     // *  Inflated     - just return
1630     // *  Stack-locked - coerce it to inflated
1631     // *  INFLATING    - busy wait for conversion to complete
1632     // *  Neutral      - aggressively inflate the object.
1633     // *  BIASED       - Illegal.  We should never see this
1634 
1635     // CASE: inflated
1636     if (mark.has_monitor()) {
1637       ObjectMonitor* inf = mark.monitor();





1638       markWord dmw = inf->header();
1639       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1640       assert(inf->object() == object, "invariant");
1641       assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1642       return inf;
1643     }
1644 
1645     // CASE: inflation in progress - inflating over a stack-lock.
1646     // Some other thread is converting from stack-locked to inflated.
1647     // Only that thread can complete inflation -- other threads must wait.
1648     // The INFLATING value is transient.
1649     // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1650     // We could always eliminate polling by parking the thread on some auxiliary list.
1651     if (mark == markWord::INFLATING()) {
1652       read_stable_mark(object);
1653       continue;
1654     }
1655 
1656     // CASE: stack-locked
1657     // Could be stack-locked either by this thread or by some other thread.
1658     //
1659     // Note that we allocate the objectmonitor speculatively, _before_ attempting
1660     // to install INFLATING into the mark word.  We originally installed INFLATING,
1661     // allocated the objectmonitor, and then finally STed the address of the
1662     // objectmonitor into the mark.  This was correct, but artificially lengthened


1668     // critical INFLATING...ST interval.  A thread can transfer
1669     // multiple objectmonitors en-mass from the global free list to its local free list.
1670     // This reduces coherency traffic and lock contention on the global free list.
1671     // Using such local free lists, it doesn't matter if the om_alloc() call appears
1672     // before or after the CAS(INFLATING) operation.
1673     // See the comments in om_alloc().
1674 
1675     LogStreamHandle(Trace, monitorinflation) lsh;
1676 
1677     if (mark.has_locker()) {
1678       ObjectMonitor* m = om_alloc(self);
1679       // Optimistically prepare the objectmonitor - anticipate successful CAS
1680       // We do this before the CAS in order to minimize the length of time
1681       // in which INFLATING appears in the mark.
1682       m->Recycle();
1683       m->_Responsible  = NULL;
1684       m->_SpinDuration = ObjectMonitor::Knob_SpinLimit;   // Consider: maintain by type/class
1685 
1686       markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1687       if (cmp != mark) {

1688         om_release(self, m, true);
1689         continue;       // Interference -- just retry
1690       }
1691 
1692       // We've successfully installed INFLATING (0) into the mark-word.
1693       // This is the only case where 0 will appear in a mark-word.
1694       // Only the singular thread that successfully swings the mark-word
1695       // to 0 can perform (or more precisely, complete) inflation.
1696       //
1697       // Why do we CAS a 0 into the mark-word instead of just CASing the
1698       // mark-word from the stack-locked value directly to the new inflated state?
1699       // Consider what happens when a thread unlocks a stack-locked object.
1700       // It attempts to use CAS to swing the displaced header value from the
1701       // on-stack BasicLock back into the object header.  Recall also that the
1702       // header value (hash code, etc) can reside in (a) the object header, or
1703       // (b) a displaced header associated with the stack-lock, or (c) a displaced
1704       // header in an ObjectMonitor.  The inflate() routine must copy the header
1705       // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1706       // the while preserving the hashCode stability invariants.  If the owner
1707       // decides to release the lock while the value is 0, the unlock will fail
1708       // and control will eventually pass from slow_exit() to inflate.  The owner
1709       // will then spin, waiting for the 0 value to disappear.   Put another way,
1710       // the 0 causes the owner to stall if the owner happens to try to
1711       // drop the lock (restoring the header from the BasicLock to the object)
1712       // while inflation is in-progress.  This protocol avoids races that might
1713       // would otherwise permit hashCode values to change or "flicker" for an object.
1714       // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1715       // 0 serves as a "BUSY" inflate-in-progress indicator.
1716 
1717 
1718       // fetch the displaced mark from the owner's stack.
1719       // The owner can't die or unwind past the lock while our INFLATING
1720       // object is in the mark.  Furthermore the owner can't complete
1721       // an unlock on the object, either.
1722       markWord dmw = mark.displaced_mark_helper();
1723       // Catch if the object's header is not neutral (not locked and
1724       // not marked is what we care about here).
1725       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1726 
1727       // Setup monitor fields to proper values -- prepare the monitor
1728       m->set_header(dmw);
1729 
1730       // Optimization: if the mark.locker stack address is associated
1731       // with this thread we could simply set m->_owner = self.
1732       // Note that a thread can inflate an object
1733       // that it has stack-locked -- as might happen in wait() -- directly
1734       // with CAS.  That is, we can avoid the xchg-NULL .... ST idiom.



1735       m->set_owner_from(NULL, mark.locker());

1736       m->set_object(object);
1737       // TODO-FIXME: assert BasicLock->dhw != 0.
1738 


1739       // Must preserve store ordering. The monitor state must
1740       // be stable at the time of publishing the monitor address.
1741       guarantee(object->mark() == markWord::INFLATING(), "invariant");
1742       object->release_set_mark(markWord::encode(m));
1743 





1744       // Hopefully the performance counters are allocated on distinct cache lines
1745       // to avoid false sharing on MP systems ...
1746       OM_PERFDATA_OP(Inflations, inc());
1747       if (log_is_enabled(Trace, monitorinflation)) {
1748         ResourceMark rm(self);
1749         lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1750                      INTPTR_FORMAT ", type='%s'", p2i(object),
1751                      object->mark().value(), object->klass()->external_name());
1752       }
1753       if (event.should_commit()) {
1754         post_monitor_inflate_event(&event, object, cause);
1755       }
1756       return m;

1757     }
1758 
1759     // CASE: neutral
1760     // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1761     // If we know we're inflating for entry it's better to inflate by swinging a
1762     // pre-locked ObjectMonitor pointer into the object header.   A successful
1763     // CAS inflates the object *and* confers ownership to the inflating thread.
1764     // In the current implementation we use a 2-step mechanism where we CAS()
1765     // to inflate and then CAS() again to try to swing _owner from NULL to self.
1766     // An inflateTry() method that we could call from enter() would be useful.
1767 
1768     // Catch if the object's header is not neutral (not locked and
1769     // not marked is what we care about here).
1770     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1771     ObjectMonitor* m = om_alloc(self);
1772     // prepare m for installation - set monitor to initial state
1773     m->Recycle();
1774     m->set_header(mark);



1775     m->set_object(object);
1776     m->_Responsible  = NULL;
1777     m->_SpinDuration = ObjectMonitor::Knob_SpinLimit;       // consider: keep metastats by type/class
1778 


1779     if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1780       m->set_header(markWord::zero());
1781       m->set_object(NULL);
1782       m->Recycle();


1783       om_release(self, m, true);
1784       m = NULL;
1785       continue;
1786       // interference - the markword changed - just retry.
1787       // The state-transitions are one-way, so there's no chance of
1788       // live-lock -- "Inflated" is an absorbing state.
1789     }
1790 





1791     // Hopefully the performance counters are allocated on distinct
1792     // cache lines to avoid false sharing on MP systems ...
1793     OM_PERFDATA_OP(Inflations, inc());
1794     if (log_is_enabled(Trace, monitorinflation)) {
1795       ResourceMark rm(self);
1796       lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1797                    INTPTR_FORMAT ", type='%s'", p2i(object),
1798                    object->mark().value(), object->klass()->external_name());
1799     }
1800     if (event.should_commit()) {
1801       post_monitor_inflate_event(&event, object, cause);
1802     }
1803     return m;

1804   }
1805 }
1806 
1807 
1808 // We maintain a list of in-use monitors for each thread.
1809 //

1810 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1811 // deflate_idle_monitors() scans only a global list of in-use monitors which
1812 // is populated only as a thread dies (see om_flush()).
1813 //
1814 // These operations are called at all safepoints, immediately after mutators
1815 // are stopped, but before any objects have moved. Collectively they traverse
1816 // the population of in-use monitors, deflating where possible. The scavenged
1817 // monitors are returned to the global monitor free list.
1818 //
1819 // Beware that we scavenge at *every* stop-the-world point. Having a large
1820 // number of monitors in-use could negatively impact performance. We also want
1821 // to minimize the total # of monitors in circulation, as they incur a small
1822 // footprint penalty.
1823 //
1824 // Perversely, the heap size -- and thus the STW safepoint rate --
1825 // typically drives the scavenge rate.  Large heaps can mean infrequent GC,
1826 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1827 // This is an unfortunate aspect of this design.


































1828 
1829 // Deflate a single monitor if not in-use
1830 // Return true if deflated, false if in-use
1831 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1832                                          ObjectMonitor** free_head_p,
1833                                          ObjectMonitor** free_tail_p) {
1834   bool deflated;
1835   // Normal case ... The monitor is associated with obj.
1836   const markWord mark = obj->mark();
1837   guarantee(mark == markWord::encode(mid), "should match: mark="
1838             INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
1839             markWord::encode(mid).value());
1840   // Make sure that mark.monitor() and markWord::encode() agree:
1841   guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1842             ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
1843   const markWord dmw = mid->header();
1844   guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1845 
1846   if (mid->is_busy()) {
1847     // Easy checks are first - the ObjectMonitor is busy so no deflation.

1848     deflated = false;
1849   } else {
1850     // Deflate the monitor if it is no longer being used
1851     // It's idle - scavenge and return to the global free list
1852     // plain old deflation ...
1853     if (log_is_enabled(Trace, monitorinflation)) {
1854       ResourceMark rm;
1855       log_trace(monitorinflation)("deflate_monitor: "
1856                                   "object=" INTPTR_FORMAT ", mark="
1857                                   INTPTR_FORMAT ", type='%s'", p2i(obj),
1858                                   mark.value(), obj->klass()->external_name());
1859     }
1860 
1861     // Restore the header back to obj
1862     obj->release_set_mark(dmw);







1863     mid->clear();
1864 
1865     assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1866            p2i(mid->object()));

1867 
1868     // Move the deflated ObjectMonitor to the working free list
1869     // defined by free_head_p and free_tail_p.
1870     if (*free_head_p == NULL) *free_head_p = mid;
1871     if (*free_tail_p != NULL) {
1872       // We append to the list so the caller can use mid->_next_om
1873       // to fix the linkages in its context.
1874       ObjectMonitor* prevtail = *free_tail_p;
1875       // Should have been cleaned up by the caller:
1876       // Note: Should not have to lock prevtail here since we're at a
1877       // safepoint and ObjectMonitors on the local free list should
1878       // not be accessed in parallel.
1879 #ifdef ASSERT
1880       ObjectMonitor* l_next_om = prevtail->next_om();
1881 #endif
1882       assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
1883       prevtail->set_next_om(mid);
1884     }
1885     *free_tail_p = mid;
1886     // At this point, mid->_next_om still refers to its current
1887     // value and another ObjectMonitor's _next_om field still
1888     // refers to this ObjectMonitor. Those linkages have to be
1889     // cleaned up by the caller who has the complete context.
1890     deflated = true;
1891   }
1892   return deflated;
1893 }
1894 



















































































































































1895 // Walk a given monitor list, and deflate idle monitors.
1896 // The given list could be a per-thread list or a global list.
1897 //
1898 // In the case of parallel processing of thread local monitor lists,
1899 // work is done by Threads::parallel_threads_do() which ensures that
1900 // each Java thread is processed by exactly one worker thread, and
1901 // thus avoid conflicts that would arise when worker threads would
1902 // process the same monitor lists concurrently.
1903 //
1904 // See also ParallelSPCleanupTask and
1905 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1906 // Threads::parallel_java_threads_do() in thread.cpp.
1907 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
1908                                              int* count_p,
1909                                              ObjectMonitor** free_head_p,
1910                                              ObjectMonitor** free_tail_p) {
1911   ObjectMonitor* cur_mid_in_use = NULL;
1912   ObjectMonitor* mid = NULL;
1913   ObjectMonitor* next = NULL;
1914   int deflated_count = 0;


1925       // by unlinking mid from the global or per-thread in-use list.
1926       if (cur_mid_in_use == NULL) {
1927         // mid is the list head so switch the list head to next:
1928         Atomic::store(list_p, next);
1929       } else {
1930         // Switch cur_mid_in_use's next field to next:
1931         cur_mid_in_use->set_next_om(next);
1932       }
1933       // At this point mid is disconnected from the in-use list.
1934       deflated_count++;
1935       Atomic::dec(count_p);
1936       // mid is current tail in the free_head_p list so NULL terminate it:
1937       mid->set_next_om(NULL);
1938     } else {
1939       cur_mid_in_use = mid;
1940     }
1941   }
1942   return deflated_count;
1943 }
1944 













































































































































1945 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1946   counters->n_in_use = 0;              // currently associated with objects
1947   counters->n_in_circulation = 0;      // extant
1948   counters->n_scavenged = 0;           // reclaimed (global and per-thread)
1949   counters->per_thread_scavenged = 0;  // per-thread scavenge total
1950   counters->per_thread_times = 0.0;    // per-thread scavenge times
1951 }
1952 
1953 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1954   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");









1955   bool deflated = false;
1956 
1957   ObjectMonitor* free_head_p = NULL;  // Local SLL of scavenged monitors
1958   ObjectMonitor* free_tail_p = NULL;
1959   elapsedTimer timer;
1960 
1961   if (log_is_enabled(Info, monitorinflation)) {
1962     timer.start();
1963   }
1964 
1965   // Note: the thread-local monitors lists get deflated in
1966   // a separate pass. See deflate_thread_local_monitors().
1967 
1968   // For moribund threads, scan om_list_globals._in_use_list
1969   int deflated_count = 0;
1970   if (Atomic::load(&om_list_globals._in_use_list) != NULL) {
1971     // Update n_in_circulation before om_list_globals._in_use_count is
1972     // updated by deflation.
1973     Atomic::add(&counters->n_in_circulation,
1974                 Atomic::load(&om_list_globals._in_use_count));


1987 #endif
1988     assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
1989     prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
1990     Atomic::add(&counters->n_scavenged, deflated_count);
1991   }
1992   timer.stop();
1993 
1994   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1995   LogStreamHandle(Info, monitorinflation) lsh_info;
1996   LogStream* ls = NULL;
1997   if (log_is_enabled(Debug, monitorinflation)) {
1998     ls = &lsh_debug;
1999   } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2000     ls = &lsh_info;
2001   }
2002   if (ls != NULL) {
2003     ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2004   }
2005 }
2006 






























































































































































































2007 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2008   // Report the cumulative time for deflating each thread's idle
2009   // monitors. Note: if the work is split among more than one
2010   // worker thread, then the reported time will likely be more
2011   // than a beginning to end measurement of the phase.
2012   log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
2013 







2014   if (log_is_enabled(Debug, monitorinflation)) {
2015     // exit_globals()'s call to audit_and_print_stats() is done
2016     // at the Info level and not at a safepoint.



2017     ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2018   } else if (log_is_enabled(Info, monitorinflation)) {
2019     log_info(monitorinflation)("global_population=%d, global_in_use_count=%d, "
2020                                "global_free_count=%d",
2021                                Atomic::load(&om_list_globals._population),
2022                                Atomic::load(&om_list_globals._in_use_count),
2023                                Atomic::load(&om_list_globals._free_count));

2024   }
2025 
2026   Atomic::store(&_forceMonitorScavenge, 0);    // Reset
2027 
2028   OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
2029   OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
2030 
2031   GVars.stw_random = os::random();
2032   GVars.stw_cycle++;




2033 }
2034 
2035 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2036   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2037 





2038   ObjectMonitor* free_head_p = NULL;  // Local SLL of scavenged monitors
2039   ObjectMonitor* free_tail_p = NULL;
2040   elapsedTimer timer;
2041 
2042   if (log_is_enabled(Info, safepoint, cleanup) ||
2043       log_is_enabled(Info, monitorinflation)) {
2044     timer.start();
2045   }
2046 
2047   // Update n_in_circulation before om_in_use_count is updated by deflation.
2048   Atomic::add(&counters->n_in_circulation, Atomic::load(&thread->om_in_use_count));
2049 
2050   int deflated_count = deflate_monitor_list(&thread->om_in_use_list, &thread->om_in_use_count, &free_head_p, &free_tail_p);
2051   Atomic::add(&counters->n_in_use, Atomic::load(&thread->om_in_use_count));
2052 
2053   if (free_head_p != NULL) {
2054     // Move the deflated ObjectMonitors back to the global free list.
2055     guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2056 #ifdef ASSERT
2057     ObjectMonitor* l_next_om = free_tail_p->next_om();


2189   if (Atomic::load(&om_list_globals._population) == chk_om_population) {
2190     ls->print_cr("global_population=%d equals chk_om_population=%d",
2191                  Atomic::load(&om_list_globals._population), chk_om_population);
2192   } else {
2193     // With fine grained locks on the monitor lists, it is possible for
2194     // log_monitor_list_counts() to return a value that doesn't match
2195     // om_list_globals._population. So far a higher value has been
2196     // seen in testing so something is being double counted by
2197     // log_monitor_list_counts().
2198     ls->print_cr("WARNING: global_population=%d is not equal to "
2199                  "chk_om_population=%d",
2200                  Atomic::load(&om_list_globals._population), chk_om_population);
2201   }
2202 
2203   // Check om_list_globals._in_use_list and om_list_globals._in_use_count:
2204   chk_global_in_use_list_and_count(ls, &error_cnt);
2205 
2206   // Check om_list_globals._free_list and om_list_globals._free_count:
2207   chk_global_free_list_and_count(ls, &error_cnt);
2208 





2209   ls->print_cr("Checking per-thread lists:");
2210 
2211   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2212     // Check om_in_use_list and om_in_use_count:
2213     chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2214 
2215     // Check om_free_list and om_free_count:
2216     chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2217   }
2218 
2219   if (error_cnt == 0) {
2220     ls->print_cr("No errors found in monitor list checks.");
2221   } else {
2222     log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2223   }
2224 
2225   if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2226       (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2227     // When exiting this log output is at the Info level. When called
2228     // at a safepoint, this log output is at the Trace level since


2239 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
2240                                         outputStream * out, int *error_cnt_p) {
2241   stringStream ss;
2242   if (n->is_busy()) {
2243     if (jt != NULL) {
2244       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2245                     ": free per-thread monitor must not be busy: %s", p2i(jt),
2246                     p2i(n), n->is_busy_to_string(&ss));
2247     } else {
2248       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2249                     "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
2250     }
2251     *error_cnt_p = *error_cnt_p + 1;
2252   }
2253   if (n->header().value() != 0) {
2254     if (jt != NULL) {
2255       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2256                     ": free per-thread monitor must have NULL _header "
2257                     "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2258                     n->header().value());
2259     } else {

2260       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2261                     "must have NULL _header field: _header=" INTPTR_FORMAT,
2262                     p2i(n), n->header().value());
2263     }
2264     *error_cnt_p = *error_cnt_p + 1;
2265   }

2266   if (n->object() != NULL) {
2267     if (jt != NULL) {
2268       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2269                     ": free per-thread monitor must have NULL _object "
2270                     "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
2271                     p2i(n->object()));
2272     } else {
2273       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2274                     "must have NULL _object field: _object=" INTPTR_FORMAT,
2275                     p2i(n), p2i(n->object()));
2276     }
2277     *error_cnt_p = *error_cnt_p + 1;
2278   }
2279 }
2280 
2281 // Lock the next ObjectMonitor for traversal and unlock the current
2282 // ObjectMonitor. Returns the next ObjectMonitor if there is one.
2283 // Otherwise returns NULL (after unlocking the current ObjectMonitor).
2284 // This function is used by the various list walker functions to
2285 // safely walk a list without allowing an ObjectMonitor to be moved


2311       if (cur == NULL) {
2312         break;
2313       }
2314     }
2315   }
2316   int l_free_count = Atomic::load(&om_list_globals._free_count);
2317   if (l_free_count == chk_om_free_count) {
2318     out->print_cr("global_free_count=%d equals chk_om_free_count=%d",
2319                   l_free_count, chk_om_free_count);
2320   } else {
2321     // With fine grained locks on om_list_globals._free_list, it
2322     // is possible for an ObjectMonitor to be prepended to
2323     // om_list_globals._free_list after we started calculating
2324     // chk_om_free_count so om_list_globals._free_count may not
2325     // match anymore.
2326     out->print_cr("WARNING: global_free_count=%d is not equal to "
2327                   "chk_om_free_count=%d", l_free_count, chk_om_free_count);
2328   }
2329 }
2330 






























2331 // Check the global in-use list and count; log the results of the checks.
2332 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
2333                                                           int *error_cnt_p) {
2334   int chk_om_in_use_count = 0;
2335   ObjectMonitor* cur = NULL;
2336   if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
2337     // Marked the global in-use list head so process the list.
2338     while (true) {
2339       chk_in_use_entry(NULL /* jt */, cur, out, error_cnt_p);
2340       chk_om_in_use_count++;
2341 
2342       cur = lock_next_for_traversal(cur);
2343       if (cur == NULL) {
2344         break;
2345       }
2346     }
2347   }
2348   int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
2349   if (l_in_use_count == chk_om_in_use_count) {
2350     out->print_cr("global_in_use_count=%d equals chk_om_in_use_count=%d",


2469   if (l_om_in_use_count == chk_om_in_use_count) {
2470     out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
2471                   "chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
2472                   chk_om_in_use_count);
2473   } else {
2474     out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
2475                   "equal to chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
2476                   chk_om_in_use_count);
2477     *error_cnt_p = *error_cnt_p + 1;
2478   }
2479 }
2480 
2481 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2482 // flags indicate why the entry is in-use, 'object' and 'object type'
2483 // indicate the associated object and its type.
2484 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out) {
2485   stringStream ss;
2486   if (Atomic::load(&om_list_globals._in_use_count) > 0) {
2487     out->print_cr("In-use global monitor info:");
2488     out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2489     out->print_cr("%18s  %s  %18s  %18s",
2490                   "monitor", "BHL", "object", "object type");
2491     out->print_cr("==================  ===  ==================  ==================");
2492     ObjectMonitor* cur = NULL;
2493     if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
2494       // Marked the global in-use list head so process the list.
2495       while (true) {
2496         const oop obj = (oop) cur->object();
2497         const markWord mark = cur->header();
2498         ResourceMark rm;
2499         out->print(INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT "  %s", p2i(cur),
2500                    cur->is_busy() != 0, mark.hash() != 0, cur->owner() != NULL,
2501                    p2i(obj), obj->klass()->external_name());
2502         if (cur->is_busy() != 0) {
2503           out->print(" (%s)", cur->is_busy_to_string(&ss));
2504           ss.reset();
2505         }
2506         out->cr();
2507 
2508         cur = lock_next_for_traversal(cur);
2509         if (cur == NULL) {
2510           break;
2511         }
2512       }
2513     }
2514   }
2515 
2516   out->print_cr("In-use per-thread monitor info:");
2517   out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2518   out->print_cr("%18s  %18s  %s  %18s  %18s",
2519                 "jt", "monitor", "BHL", "object", "object type");
2520   out->print_cr("==================  ==================  ===  ==================  ==================");
2521   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2522     ObjectMonitor* cur = NULL;
2523     if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
2524       // Marked the global in-use list head so process the list.
2525       while (true) {
2526         const oop obj = (oop) cur->object();
2527         const markWord mark = cur->header();
2528         ResourceMark rm;
2529         out->print(INTPTR_FORMAT "  " INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT
2530                    "  %s", p2i(jt), p2i(cur), cur->is_busy() != 0,
2531                    mark.hash() != 0, cur->owner() != NULL, p2i(obj),
2532                    obj->klass()->external_name());
2533         if (cur->is_busy() != 0) {
2534           out->print(" (%s)", cur->is_busy_to_string(&ss));
2535           ss.reset();
2536         }
2537         out->cr();
2538 
2539         cur = lock_next_for_traversal(cur);
2540         if (cur == NULL) {
2541           break;
2542         }
2543       }
2544     }
2545   }
2546 
2547   out->flush();
2548 }
2549 
2550 // Log counts for the global and per-thread monitor lists and return
2551 // the population count.
2552 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2553   int pop_count = 0;
2554   out->print_cr("%18s  %10s  %10s  %10s",
2555                 "Global Lists:", "InUse", "Free", "Total");
2556   out->print_cr("==================  ==========  ==========  ==========");
2557   int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
2558   int l_free_count = Atomic::load(&om_list_globals._free_count);
2559   out->print_cr("%18s  %10d  %10d  %10d", "", l_in_use_count,
2560                 l_free_count, Atomic::load(&om_list_globals._population));


2561   pop_count += l_in_use_count + l_free_count;



2562 
2563   out->print_cr("%18s  %10s  %10s  %10s",
2564                 "Per-Thread Lists:", "InUse", "Free", "Provision");
2565   out->print_cr("==================  ==========  ==========  ==========");
2566 
2567   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2568     int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
2569     int l_om_free_count = Atomic::load(&jt->om_free_count);
2570     out->print_cr(INTPTR_FORMAT "  %10d  %10d  %10d", p2i(jt),
2571                   l_om_in_use_count, l_om_free_count, jt->om_free_provision);
2572     pop_count += l_om_in_use_count + l_om_free_count;
2573   }
2574   return pop_count;
2575 }
2576 
2577 #ifndef PRODUCT
2578 
2579 // Check if monitor belongs to the monitor cache
2580 // The list is grow-only so it's *relatively* safe to traverse
2581 // the list of extant blocks without taking a lock.


  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/vmSymbols.hpp"
  27 #include "logging/log.hpp"
  28 #include "logging/logStream.hpp"
  29 #include "jfr/jfrEvents.hpp"
  30 #include "memory/allocation.inline.hpp"
  31 #include "memory/metaspaceShared.hpp"
  32 #include "memory/padded.hpp"
  33 #include "memory/resourceArea.hpp"
  34 #include "memory/universe.hpp"
  35 #include "oops/markWord.hpp"
  36 #include "oops/oop.inline.hpp"
  37 #include "runtime/atomic.hpp"
  38 #include "runtime/biasedLocking.hpp"
  39 #include "runtime/handles.inline.hpp"
  40 #include "runtime/handshake.hpp"
  41 #include "runtime/interfaceSupport.inline.hpp"
  42 #include "runtime/mutexLocker.hpp"
  43 #include "runtime/objectMonitor.hpp"
  44 #include "runtime/objectMonitor.inline.hpp"
  45 #include "runtime/osThread.hpp"
  46 #include "runtime/safepointMechanism.inline.hpp"
  47 #include "runtime/safepointVerifiers.hpp"
  48 #include "runtime/sharedRuntime.hpp"
  49 #include "runtime/stubRoutines.hpp"
  50 #include "runtime/synchronizer.hpp"
  51 #include "runtime/thread.inline.hpp"
  52 #include "runtime/timer.hpp"
  53 #include "runtime/vframe.hpp"
  54 #include "runtime/vmThread.hpp"
  55 #include "utilities/align.hpp"
  56 #include "utilities/dtrace.hpp"
  57 #include "utilities/events.hpp"
  58 #include "utilities/preserveException.hpp"
  59 
  60 // The "core" versions of monitor enter and exit reside in this file.
  61 // The interpreter and compilers contain specialized transliterated
  62 // variants of the enter-exit fast-path operations.  See i486.ad fast_lock(),
  63 // for instance.  If you make changes here, make sure to modify the
  64 // interpreter, and both C1 and C2 fast-path inline locking code emission.
  65 //
  66 // -----------------------------------------------------------------------------


 103   }
 104 
 105 #else //  ndef DTRACE_ENABLED
 106 
 107 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 108 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 109 
 110 #endif // ndef DTRACE_ENABLED
 111 
 112 // This exists only as a workaround of dtrace bug 6254741
 113 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
 114   DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
 115   return 0;
 116 }
 117 
 118 #define NINFLATIONLOCKS 256
 119 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
 120 
 121 // global list of blocks of monitors
 122 PaddedObjectMonitor* ObjectSynchronizer::g_block_list = NULL;
 123 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
 124 bool volatile ObjectSynchronizer::_is_special_deflation_requested = false;
 125 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
 126 
 127 struct ObjectMonitorListGlobals {
 128   char         _pad_prefix[OM_CACHE_LINE_SIZE];
 129   // These are highly shared list related variables.
 130   // To avoid false-sharing they need to be the sole occupants of a cache line.
 131 
 132   // Global ObjectMonitor free list. Newly allocated and deflated
 133   // ObjectMonitors are prepended here.
 134   ObjectMonitor* _free_list;
 135   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
 136 
 137   // Global ObjectMonitor in-use list. When a JavaThread is exiting,
 138   // ObjectMonitors on its per-thread in-use list are prepended here.
 139   ObjectMonitor* _in_use_list;
 140   DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
 141 
 142   // Global ObjectMonitor wait list. If HandshakeAfterDeflateIdleMonitors
 143   // is true, deflated ObjectMonitors wait on this list until after a
 144   // handshake or a safepoint for platforms that don't support handshakes.
 145   // After the handshake or safepoint, the deflated ObjectMonitors are
 146   // prepended to free_list.
 147   ObjectMonitor* _wait_list;
 148   DEFINE_PAD_MINUS_SIZE(3, OM_CACHE_LINE_SIZE, sizeof(ObjectMonitor*));
 149 
 150   int _free_count;    // # on free_list
 151   DEFINE_PAD_MINUS_SIZE(4, OM_CACHE_LINE_SIZE, sizeof(int));
 152 
 153   int _in_use_count;  // # on in_use_list
 154   DEFINE_PAD_MINUS_SIZE(5, OM_CACHE_LINE_SIZE, sizeof(int));
 155 
 156   int _population;    // # Extant -- in circulation
 157   DEFINE_PAD_MINUS_SIZE(6, OM_CACHE_LINE_SIZE, sizeof(int));
 158 
 159   int _wait_count;    // # on wait_list
 160   DEFINE_PAD_MINUS_SIZE(7, OM_CACHE_LINE_SIZE, sizeof(int));
 161 };
 162 static ObjectMonitorListGlobals om_list_globals;
 163 
 164 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
 165 
 166 
 167 // =====================> Spin-lock functions
 168 
 169 // ObjectMonitors are not lockable outside of this file. We use spin-locks
 170 // implemented using a bit in the _next_om field instead of the heavier
 171 // weight locking mechanisms for faster list management.
 172 
 173 #define OM_LOCK_BIT 0x1
 174 
 175 // Return true if the ObjectMonitor is locked.
 176 // Otherwise returns false.
 177 static bool is_locked(ObjectMonitor* om) {
 178   return ((intptr_t)om->next_om() & OM_LOCK_BIT) == OM_LOCK_BIT;
 179 }
 180 


 298       Atomic::add(&om_list_globals._population, _BLOCKSIZE - 1);
 299       break;
 300     }
 301     // Implied else: try it all again
 302   }
 303 
 304   // Second we handle om_list_globals._free_list:
 305   prepend_list_to_common(new_blk + 1, &new_blk[_BLOCKSIZE - 1], _BLOCKSIZE - 1,
 306                          &om_list_globals._free_list, &om_list_globals._free_count);
 307 }
 308 
 309 // Prepend a list of ObjectMonitors to om_list_globals._free_list.
 310 // 'tail' is the last ObjectMonitor in the list and there are 'count'
 311 // on the list. Also updates om_list_globals._free_count.
 312 static void prepend_list_to_global_free_list(ObjectMonitor* list,
 313                                              ObjectMonitor* tail, int count) {
 314   prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
 315                          &om_list_globals._free_count);
 316 }
 317 
 318 // Prepend a list of ObjectMonitors to om_list_globals._wait_list.
 319 // 'tail' is the last ObjectMonitor in the list and there are 'count'
 320 // on the list. Also updates om_list_globals._wait_count.
 321 static void prepend_list_to_global_wait_list(ObjectMonitor* list,
 322                                              ObjectMonitor* tail, int count) {
 323   assert(HandshakeAfterDeflateIdleMonitors, "sanity check");
 324   prepend_list_to_common(list, tail, count, &om_list_globals._wait_list,
 325                          &om_list_globals._wait_count);
 326 }
 327 
 328 // Prepend a list of ObjectMonitors to om_list_globals._in_use_list.
 329 // 'tail' is the last ObjectMonitor in the list and there are 'count'
 330 // on the list. Also updates om_list_globals._in_use_list.
 331 static void prepend_list_to_global_in_use_list(ObjectMonitor* list,
 332                                                ObjectMonitor* tail, int count) {
 333   prepend_list_to_common(list, tail, count, &om_list_globals._in_use_list,
 334                          &om_list_globals._in_use_count);
 335 }
 336 
 337 // Prepend an ObjectMonitor to the specified list. Also updates
 338 // the specified counter.
 339 static void prepend_to_common(ObjectMonitor* m, ObjectMonitor** list_p,
 340                               int* count_p) {
 341   while (true) {
 342     om_lock(m);  // Lock m so we can safely update its next field.
 343     ObjectMonitor* cur = NULL;
 344     // Lock the list head to guard against races with a list walker
 345     // or async deflater thread (which only races in om_in_use_list):
 346     if ((cur = get_list_head_locked(list_p)) != NULL) {
 347       // List head is now locked so we can safely switch it.
 348       m->set_next_om(cur);  // m now points to cur (and unlocks m)
 349       Atomic::store(list_p, m);  // Switch list head to unlocked m.
 350       om_unlock(cur);
 351       break;
 352     }
 353     // The list is empty so try to set the list head.
 354     assert(cur == NULL, "cur must be NULL: cur=" INTPTR_FORMAT, p2i(cur));
 355     m->set_next_om(cur);  // m now points to NULL (and unlocks m)
 356     if (Atomic::cmpxchg(list_p, cur, m) == cur) {
 357       // List head is now unlocked m.
 358       break;
 359     }
 360     // Implied else: try it all again
 361   }
 362   Atomic::inc(count_p);
 363 }
 364 
 365 // Prepend an ObjectMonitor to a per-thread om_free_list.
 366 // Also updates the per-thread om_free_count.
 367 static void prepend_to_om_free_list(Thread* self, ObjectMonitor* m) {
 368   prepend_to_common(m, &self->om_free_list, &self->om_free_count);
 369 }
 370 
 371 // Prepend an ObjectMonitor to a per-thread om_in_use_list.
 372 // Also updates the per-thread om_in_use_count.
 373 static void prepend_to_om_in_use_list(Thread* self, ObjectMonitor* m) {
 374   prepend_to_common(m, &self->om_in_use_list, &self->om_in_use_count);
 375 }
 376 
 377 // Take an ObjectMonitor from the start of the specified list. Also
 378 // decrements the specified counter. Returns NULL if none are available.
 379 static ObjectMonitor* take_from_start_of_common(ObjectMonitor** list_p,
 380                                                 int* count_p) {
 381   ObjectMonitor* take = NULL;
 382   // Lock the list head to guard against races with a list walker
 383   // or async deflater thread (which only races in om_list_globals._free_list):
 384   if ((take = get_list_head_locked(list_p)) == NULL) {
 385     return NULL;  // None are available.
 386   }
 387   ObjectMonitor* next = unmarked_next(take);
 388   // Switch locked list head to next (which unlocks the list head, but
 389   // leaves take locked):
 390   Atomic::store(list_p, next);
 391   Atomic::dec(count_p);
 392   // Unlock take, but leave the next value for any lagging list
 393   // walkers. It will get cleaned up when take is prepended to
 394   // the in-use list:
 395   om_unlock(take);
 396   return take;
 397 }
 398 
 399 // Take an ObjectMonitor from the start of the om_list_globals._free_list.
 400 // Also updates om_list_globals._free_count. Returns NULL if none are
 401 // available.
 402 static ObjectMonitor* take_from_start_of_global_free_list() {
 403   return take_from_start_of_common(&om_list_globals._free_list,


 472   }
 473 
 474   // biased locking and any other IMS exception states take the slow-path
 475   return false;
 476 }
 477 
 478 
 479 // The LockNode emitted directly at the synchronization site would have
 480 // been too big if it were to have included support for the cases of inflated
 481 // recursive enter and exit, so they go here instead.
 482 // Note that we can't safely call AsyncPrintJavaStack() from within
 483 // quick_enter() as our thread state remains _in_Java.
 484 
 485 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
 486                                      BasicLock * lock) {
 487   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 488   assert(self->is_Java_thread(), "invariant");
 489   assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
 490   NoSafepointVerifier nsv;
 491   if (obj == NULL) return false;       // Need to throw NPE
 492 
 493   while (true) {
 494     const markWord mark = obj->mark();
 495 
 496     if (mark.has_monitor()) {
 497       ObjectMonitorHandle omh;
 498       if (!omh.save_om_ptr(obj, mark)) {
 499         // Lost a race with async deflation so try again.
 500         assert(AsyncDeflateIdleMonitors, "sanity check");
 501         continue;
 502       }
 503       ObjectMonitor* const m = omh.om_ptr();
 504       assert(m->object() == obj, "invariant");
 505       Thread* const owner = (Thread *) m->_owner;
 506 
 507       // Lock contention and Transactional Lock Elision (TLE) diagnostics
 508       // and observability
 509       // Case: light contention possibly amenable to TLE
 510       // Case: TLE inimical operations such as nested/recursive synchronization
 511 
 512       if (owner == self) {
 513         m->_recursions++;
 514         return true;
 515       }
 516 
 517       // This Java Monitor is inflated so obj's header will never be
 518       // displaced to this thread's BasicLock. Make the displaced header
 519       // non-NULL so this BasicLock is not seen as recursive nor as
 520       // being locked. We do this unconditionally so that this thread's
 521       // BasicLock cannot be mis-interpreted by any stack walkers. For
 522       // performance reasons, stack walkers generally first check for
 523       // Biased Locking in the object's header, the second check is for
 524       // stack-locking in the object's header, the third check is for
 525       // recursive stack-locking in the displaced header in the BasicLock,
 526       // and last are the inflated Java Monitor (ObjectMonitor) checks.
 527       lock->set_displaced_header(markWord::unused_mark());
 528 
 529       if (owner == NULL && m->try_set_owner_from(NULL, self) == NULL) {
 530         assert(m->_recursions == 0, "invariant");
 531         return true;
 532       }
 533 
 534       if (AsyncDeflateIdleMonitors &&
 535           m->try_set_owner_from(DEFLATER_MARKER, self) == DEFLATER_MARKER) {
 536         // The deflation protocol finished the first part (setting owner),
 537         // but it failed the second part (making ref_count negative) and
 538         // bailed. Or the ObjectMonitor was async deflated and reused.
 539         // Acquired the monitor.
 540         assert(m->_recursions == 0, "invariant");
 541         return true;
 542       }
 543     }
 544     break;
 545   }
 546 
 547   // Note that we could inflate in quick_enter.
 548   // This is likely a useful optimization
 549   // Critically, in quick_enter() we must not:
 550   // -- perform bias revocation, or
 551   // -- block indefinitely, or
 552   // -- reach a safepoint
 553 
 554   return false;        // revert to slow-path
 555 }
 556 
 557 // -----------------------------------------------------------------------------
 558 // Monitor Enter/Exit
 559 // The interpreter and compiler assembly code tries to lock using the fast path
 560 // of this algorithm. Make sure to update that code if the following function is
 561 // changed. The implementation is extremely sensitive to race condition. Be careful.
 562 
 563 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, TRAPS) {
 564   if (UseBiasedLocking) {


 576     // Anticipate successful CAS -- the ST of the displaced mark must
 577     // be visible <= the ST performed by the CAS.
 578     lock->set_displaced_header(mark);
 579     if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
 580       return;
 581     }
 582     // Fall through to inflate() ...
 583   } else if (mark.has_locker() &&
 584              THREAD->is_lock_owned((address)mark.locker())) {
 585     assert(lock != mark.locker(), "must not re-lock the same lock");
 586     assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
 587     lock->set_displaced_header(markWord::from_pointer(NULL));
 588     return;
 589   }
 590 
 591   // The object header will never be displaced to this lock,
 592   // so it does not matter what the value is, except that it
 593   // must be non-zero to avoid looking like a re-entrant lock,
 594   // and must not look locked either.
 595   lock->set_displaced_header(markWord::unused_mark());
 596   ObjectMonitorHandle omh;
 597   inflate(&omh, THREAD, obj(), inflate_cause_monitor_enter);
 598   omh.om_ptr()->enter(THREAD);
 599 }
 600 
 601 void ObjectSynchronizer::exit(oop object, BasicLock* lock, TRAPS) {
 602   markWord mark = object->mark();
 603   // We cannot check for Biased Locking if we are racing an inflation.
 604   assert(mark == markWord::INFLATING() ||
 605          !mark.has_bias_pattern(), "should not see bias pattern here");
 606 
 607   markWord dhw = lock->displaced_header();
 608   if (dhw.value() == 0) {
 609     // If the displaced header is NULL, then this exit matches up with
 610     // a recursive enter. No real work to do here except for diagnostics.
 611 #ifndef PRODUCT
 612     if (mark != markWord::INFLATING()) {
 613       // Only do diagnostics if we are not racing an inflation. Simply
 614       // exiting a recursive enter of a Java Monitor that is being
 615       // inflated is safe; see the has_monitor() comment below.
 616       assert(!mark.is_neutral(), "invariant");
 617       assert(!mark.has_locker() ||
 618              THREAD->is_lock_owned((address)mark.locker()), "invariant");


 627         // does not own the Java Monitor.
 628         ObjectMonitor* m = mark.monitor();
 629         assert(((oop)(m->object()))->mark() == mark, "invariant");
 630         assert(m->is_entered(THREAD), "invariant");
 631       }
 632     }
 633 #endif
 634     return;
 635   }
 636 
 637   if (mark == markWord::from_pointer(lock)) {
 638     // If the object is stack-locked by the current thread, try to
 639     // swing the displaced header from the BasicLock back to the mark.
 640     assert(dhw.is_neutral(), "invariant");
 641     if (object->cas_set_mark(dhw, mark) == mark) {
 642       return;
 643     }
 644   }
 645 
 646   // We have to take the slow-path of possible inflation and then exit.
 647   ObjectMonitorHandle omh;
 648   inflate(&omh, THREAD, object, inflate_cause_vm_internal);
 649   omh.om_ptr()->exit(true, THREAD);
 650 }
 651 
 652 // -----------------------------------------------------------------------------
 653 // Class Loader  support to workaround deadlocks on the class loader lock objects
 654 // Also used by GC
 655 // complete_exit()/reenter() are used to wait on a nested lock
 656 // i.e. to give up an outer lock completely and then re-enter
 657 // Used when holding nested locks - lock acquisition order: lock1 then lock2
 658 //  1) complete_exit lock1 - saving recursion count
 659 //  2) wait on lock2
 660 //  3) when notified on lock2, unlock lock2
 661 //  4) reenter lock1 with original recursion count
 662 //  5) lock lock2
 663 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 664 intx ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
 665   if (UseBiasedLocking) {
 666     BiasedLocking::revoke(obj, THREAD);
 667     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 668   }
 669 
 670   ObjectMonitorHandle omh;
 671   inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
 672   intptr_t ret_code = omh.om_ptr()->complete_exit(THREAD);
 673   return ret_code;
 674 }
 675 
 676 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 677 void ObjectSynchronizer::reenter(Handle obj, intx recursions, TRAPS) {
 678   if (UseBiasedLocking) {
 679     BiasedLocking::revoke(obj, THREAD);
 680     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 681   }
 682 
 683   ObjectMonitorHandle omh;
 684   inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
 685   omh.om_ptr()->reenter(recursions, THREAD);
 686 }
 687 // -----------------------------------------------------------------------------
 688 // JNI locks on java objects
 689 // NOTE: must use heavy weight monitor to handle jni monitor enter
 690 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
 691   // the current locking is from JNI instead of Java code
 692   if (UseBiasedLocking) {
 693     BiasedLocking::revoke(obj, THREAD);
 694     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 695   }
 696   THREAD->set_current_pending_monitor_is_from_java(false);
 697   ObjectMonitorHandle omh;
 698   inflate(&omh, THREAD, obj(), inflate_cause_jni_enter);
 699   omh.om_ptr()->enter(THREAD);
 700   THREAD->set_current_pending_monitor_is_from_java(true);
 701 }
 702 
 703 // NOTE: must use heavy weight monitor to handle jni monitor exit
 704 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
 705   if (UseBiasedLocking) {
 706     Handle h_obj(THREAD, obj);
 707     BiasedLocking::revoke(h_obj, THREAD);
 708     obj = h_obj();
 709   }
 710   assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 711 
 712   ObjectMonitorHandle omh;
 713   inflate(&omh, THREAD, obj, inflate_cause_jni_exit);
 714   ObjectMonitor* monitor = omh.om_ptr();
 715   // If this thread has locked the object, exit the monitor. We
 716   // intentionally do not use CHECK here because we must exit the
 717   // monitor even if an exception is pending.
 718   if (monitor->check_owner(THREAD)) {
 719     monitor->exit(true, THREAD);
 720   }
 721 }
 722 
 723 // -----------------------------------------------------------------------------
 724 // Internal VM locks on java objects
 725 // standard constructor, allows locking failures
 726 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) {
 727   _dolock = do_lock;
 728   _thread = thread;
 729   _thread->check_for_valid_safepoint_state();
 730   _obj = obj;
 731 
 732   if (_dolock) {
 733     ObjectSynchronizer::enter(_obj, &_lock, _thread);
 734   }
 735 }
 736 
 737 ObjectLocker::~ObjectLocker() {
 738   if (_dolock) {
 739     ObjectSynchronizer::exit(_obj(), &_lock, _thread);
 740   }
 741 }
 742 
 743 
 744 // -----------------------------------------------------------------------------
 745 //  Wait/Notify/NotifyAll
 746 // NOTE: must use heavy weight monitor to handle wait()
 747 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 748   if (UseBiasedLocking) {
 749     BiasedLocking::revoke(obj, THREAD);
 750     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 751   }
 752   if (millis < 0) {
 753     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 754   }
 755   ObjectMonitorHandle omh;
 756   inflate(&omh, THREAD, obj(), inflate_cause_wait);
 757   ObjectMonitor* monitor = omh.om_ptr();
 758 
 759   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
 760   monitor->wait(millis, true, THREAD);
 761 
 762   // This dummy call is in place to get around dtrace bug 6254741.  Once
 763   // that's fixed we can uncomment the following line, remove the call
 764   // and change this function back into a "void" func.
 765   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 766   int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
 767   return ret_code;
 768 }
 769 
 770 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
 771   if (UseBiasedLocking) {
 772     BiasedLocking::revoke(obj, THREAD);
 773     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 774   }
 775   if (millis < 0) {
 776     THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 777   }
 778   ObjectMonitorHandle omh;
 779   inflate(&omh, THREAD, obj(), inflate_cause_wait);
 780   omh.om_ptr()->wait(millis, false, THREAD);
 781 }
 782 
 783 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 784   if (UseBiasedLocking) {
 785     BiasedLocking::revoke(obj, THREAD);
 786     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 787   }
 788 
 789   markWord mark = obj->mark();
 790   if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
 791     return;
 792   }
 793   ObjectMonitorHandle omh;
 794   inflate(&omh, THREAD, obj(), inflate_cause_notify);
 795   omh.om_ptr()->notify(THREAD);
 796 }
 797 
 798 // NOTE: see comment of notify()
 799 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 800   if (UseBiasedLocking) {
 801     BiasedLocking::revoke(obj, THREAD);
 802     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 803   }
 804 
 805   markWord mark = obj->mark();
 806   if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
 807     return;
 808   }
 809   ObjectMonitorHandle omh;
 810   inflate(&omh, THREAD, obj(), inflate_cause_notify);
 811   omh.om_ptr()->notifyAll(THREAD);
 812 }
 813 
 814 // -----------------------------------------------------------------------------
 815 // Hash Code handling
 816 //
 817 // Performance concern:
 818 // OrderAccess::storestore() calls release() which at one time stored 0
 819 // into the global volatile OrderAccess::dummy variable. This store was
 820 // unnecessary for correctness. Many threads storing into a common location
 821 // causes considerable cache migration or "sloshing" on large SMP systems.
 822 // As such, I avoided using OrderAccess::storestore(). In some cases
 823 // OrderAccess::fence() -- which incurs local latency on the executing
 824 // processor -- is a better choice as it scales on SMP systems.
 825 //
 826 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
 827 // a discussion of coherency costs. Note that all our current reference
 828 // platforms provide strong ST-ST order, so the issue is moot on IA32,
 829 // x64, and SPARC.
 830 //
 831 // As a general policy we use "volatile" to control compiler-based reordering


 984       Handle hobj(self, obj);
 985       // Relaxing assertion for bug 6320749.
 986       assert(Universe::verify_in_progress() ||
 987              !SafepointSynchronize::is_at_safepoint(),
 988              "biases should not be seen by VM thread here");
 989       BiasedLocking::revoke(hobj, JavaThread::current());
 990       obj = hobj();
 991       assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 992     }
 993   }
 994 
 995   // hashCode() is a heap mutator ...
 996   // Relaxing assertion for bug 6320749.
 997   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 998          !SafepointSynchronize::is_at_safepoint(), "invariant");
 999   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1000          self->is_Java_thread() , "invariant");
1001   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
1002          ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
1003 
1004   while (true) {
1005     ObjectMonitor* monitor = NULL;
1006     markWord temp, test;
1007     intptr_t hash;
1008     markWord mark = read_stable_mark(obj);
1009 
1010     // object should remain ineligible for biased locking
1011     assert(!mark.has_bias_pattern(), "invariant");
1012 
1013     if (mark.is_neutral()) {            // if this is a normal header
1014       hash = mark.hash();
1015       if (hash != 0) {                  // if it has a hash, just return it
1016         return hash;
1017       }
1018       hash = get_next_hash(self, obj);  // get a new hash
1019       temp = mark.copy_set_hash(hash);  // merge the hash into header
1020                                         // try to install the hash
1021       test = obj->cas_set_mark(temp, mark);
1022       if (test == mark) {               // if the hash was installed, return it
1023         return hash;
1024       }
1025       // Failed to install the hash. It could be that another thread
1026       // installed the hash just before our attempt or inflation has
1027       // occurred or... so we fall thru to inflate the monitor for
1028       // stability and then install the hash.
1029     } else if (mark.has_monitor()) {
1030       ObjectMonitorHandle omh;
1031       if (!omh.save_om_ptr(obj, mark)) {
1032         // Lost a race with async deflation so try again.
1033         assert(AsyncDeflateIdleMonitors, "sanity check");
1034         continue;
1035       }
1036       monitor = omh.om_ptr();
1037       temp = monitor->header();
1038       // Allow for a lagging install_displaced_markword_in_object() to
1039       // have marked the ObjectMonitor's header/dmw field.
1040       assert(temp.is_neutral() || (AsyncDeflateIdleMonitors && temp.is_marked()),
1041              "invariant: header=" INTPTR_FORMAT, temp.value());
1042       hash = temp.hash();
1043       if (hash != 0) {                  // if it has a hash, just return it
1044         return hash;
1045       }
1046       // Fall thru so we only have one place that installs the hash in
1047       // the ObjectMonitor.
1048     } else if (self->is_lock_owned((address)mark.locker())) {
1049       // This is a stack lock owned by the calling thread so fetch the
1050       // displaced markWord from the BasicLock on the stack.
1051       temp = mark.displaced_mark_helper();
1052       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1053       hash = temp.hash();
1054       if (hash != 0) {                  // if it has a hash, just return it
1055         return hash;
1056       }
1057       // WARNING:
1058       // The displaced header in the BasicLock on a thread's stack
1059       // is strictly immutable. It CANNOT be changed in ANY cases.
1060       // So we have to inflate the stack lock into an ObjectMonitor
1061       // even if the current thread owns the lock. The BasicLock on
1062       // a thread's stack can be asynchronously read by other threads
1063       // during an inflate() call so any change to that stack memory
1064       // may not propagate to other threads correctly.
1065     }
1066 
1067     // Inflate the monitor to set the hash.
1068     ObjectMonitorHandle omh;
1069     inflate(&omh, self, obj, inflate_cause_hash_code);
1070     monitor = omh.om_ptr();
1071     // Load ObjectMonitor's header/dmw field and see if it has a hash.
1072     mark = monitor->header();
1073     // Allow for a lagging install_displaced_markword_in_object() to
1074     // have marked the ObjectMonitor's header/dmw field.
1075     assert(mark.is_neutral() || (AsyncDeflateIdleMonitors && mark.is_marked()),
1076            "invariant: header=" INTPTR_FORMAT, mark.value());
1077     hash = mark.hash();
1078     if (hash == 0) {                    // if it does not have a hash
1079       hash = get_next_hash(self, obj);  // get a new hash
1080       temp = mark.copy_set_hash(hash);  // merge the hash into header
1081       if (AsyncDeflateIdleMonitors && temp.is_marked()) {
1082         // A lagging install_displaced_markword_in_object() has marked
1083         // the ObjectMonitor's header/dmw field. We clear it to avoid
1084         // any confusion if we are able to set the hash.
1085         temp.set_unmarked();
1086       }
1087       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1088       uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1089       test = markWord(v);
1090       if (test != mark) {
1091         // The attempt to update the ObjectMonitor's header/dmw field
1092         // did not work. This can happen if another thread managed to
1093         // merge in the hash just before our cmpxchg(). With async
1094         // deflation, a lagging install_displaced_markword_in_object()
1095         // could have just marked or just unmarked the header/dmw field.
1096         // If we add any new usages of the header/dmw field, this code
1097         // will need to be updated.
1098         if (AsyncDeflateIdleMonitors) {
1099           // Since async deflation gives us two possible reasons for
1100           // the cmwxchg() to fail, it is easier to simply retry.
1101           continue;
1102         }
1103         hash = test.hash();
1104         assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1105         assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1106       }
1107     }
1108     // We finally get the hash.
1109     return hash;
1110   }
1111 }
1112 
1113 // Deprecated -- use FastHashCode() instead.
1114 
1115 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1116   return FastHashCode(Thread::current(), obj());
1117 }
1118 
1119 
1120 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
1121                                                    Handle h_obj) {
1122   if (UseBiasedLocking) {
1123     BiasedLocking::revoke(h_obj, thread);
1124     assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1125   }
1126 
1127   assert(thread == JavaThread::current(), "Can only be called on current thread");
1128   oop obj = h_obj();
1129 
1130   while (true) {
1131     markWord mark = read_stable_mark(obj);
1132 
1133     // Uncontended case, header points to stack
1134     if (mark.has_locker()) {
1135       return thread->is_lock_owned((address)mark.locker());
1136     }
1137     // Contended case, header points to ObjectMonitor (tagged pointer)
1138     if (mark.has_monitor()) {
1139       ObjectMonitorHandle omh;
1140       if (!omh.save_om_ptr(obj, mark)) {
1141         // Lost a race with async deflation so try again.
1142         assert(AsyncDeflateIdleMonitors, "sanity check");
1143         continue;
1144       }
1145       bool ret_code = omh.om_ptr()->is_entered(thread) != 0;
1146       return ret_code;
1147     }
1148     // Unlocked case, header in place
1149     assert(mark.is_neutral(), "sanity check");
1150     return false;
1151   }
1152 }
1153 
1154 // Be aware of this method could revoke bias of the lock object.
1155 // This method queries the ownership of the lock handle specified by 'h_obj'.
1156 // If the current thread owns the lock, it returns owner_self. If no
1157 // thread owns the lock, it returns owner_none. Otherwise, it will return
1158 // owner_other.
1159 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
1160 (JavaThread *self, Handle h_obj) {
1161   // The caller must beware this method can revoke bias, and
1162   // revocation can result in a safepoint.
1163   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
1164   assert(self->thread_state() != _thread_blocked, "invariant");
1165 
1166   // Possible mark states: neutral, biased, stack-locked, inflated
1167 
1168   if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
1169     // CASE: biased
1170     BiasedLocking::revoke(h_obj, self);
1171     assert(!h_obj->mark().has_bias_pattern(),
1172            "biases should be revoked by now");
1173   }
1174 
1175   assert(self == JavaThread::current(), "Can only be called on current thread");
1176   oop obj = h_obj();
1177 
1178   while (true) {
1179     markWord mark = read_stable_mark(obj);
1180 
1181     // CASE: stack-locked.  Mark points to a BasicLock on the owner's stack.
1182     if (mark.has_locker()) {
1183       return self->is_lock_owned((address)mark.locker()) ?
1184         owner_self : owner_other;
1185     }
1186 
1187     // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
1188     // The Object:ObjectMonitor relationship is stable as long as we're
1189     // not at a safepoint and AsyncDeflateIdleMonitors is false.
1190     if (mark.has_monitor()) {
1191       ObjectMonitorHandle omh;
1192       if (!omh.save_om_ptr(obj, mark)) {
1193         // Lost a race with async deflation so try again.
1194         assert(AsyncDeflateIdleMonitors, "sanity check");
1195         continue;
1196       }
1197       ObjectMonitor* monitor = omh.om_ptr();
1198       void* owner = monitor->_owner;
1199       if (owner == NULL) return owner_none;
1200       return (owner == self ||
1201               self->is_lock_owned((address)owner)) ? owner_self : owner_other;
1202     }
1203 
1204     // CASE: neutral
1205     assert(mark.is_neutral(), "sanity check");
1206     return owner_none;           // it's unlocked
1207   }
1208 }
1209 
1210 // FIXME: jvmti should call this
1211 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1212   if (UseBiasedLocking) {
1213     if (SafepointSynchronize::is_at_safepoint()) {
1214       BiasedLocking::revoke_at_safepoint(h_obj);
1215     } else {
1216       BiasedLocking::revoke(h_obj, JavaThread::current());
1217     }
1218     assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1219   }
1220 
1221   oop obj = h_obj();

1222 
1223   while (true) {
1224     address owner = NULL;
1225     markWord mark = read_stable_mark(obj);
1226 
1227     // Uncontended case, header points to stack
1228     if (mark.has_locker()) {
1229       owner = (address) mark.locker();
1230     }
1231 
1232     // Contended case, header points to ObjectMonitor (tagged pointer)
1233     else if (mark.has_monitor()) {
1234       ObjectMonitorHandle omh;
1235       if (!omh.save_om_ptr(obj, mark)) {
1236         // Lost a race with async deflation so try again.
1237         assert(AsyncDeflateIdleMonitors, "sanity check");
1238         continue;
1239       }
1240       ObjectMonitor* monitor = omh.om_ptr();
1241       assert(monitor != NULL, "monitor should be non-null");
1242       owner = (address) monitor->owner();
1243     }
1244 
1245     if (owner != NULL) {
1246       // owning_thread_from_monitor_owner() may also return NULL here
1247       return Threads::owning_thread_from_monitor_owner(t_list, owner);
1248     }
1249 
1250     // Unlocked case, header in place
1251     // Cannot have assertion since this object may have been
1252     // locked by another thread when reaching here.
1253     // assert(mark.is_neutral(), "sanity check");
1254 
1255     return NULL;
1256   }
1257 }
1258 
1259 // Visitors ...
1260 
1261 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
1262   PaddedObjectMonitor* block = Atomic::load(&g_block_list);
1263   while (block != NULL) {
1264     assert(block->object() == CHAINMARKER, "must be a block header");
1265     for (int i = _BLOCKSIZE - 1; i > 0; i--) {
1266       ObjectMonitor* mid = (ObjectMonitor *)(block + i);
1267       ObjectMonitorHandle omh;
1268       if (!mid->is_free() && omh.set_om_ptr_if_safe(mid)) {
1269         // The ObjectMonitor* is not free and it has been made safe.
1270         if (mid->object() == NULL) {
1271           // Only process with closure if the object is set.
1272           continue;
1273         }
1274         closure->do_monitor(mid);
1275       }
1276     }
1277     // unmarked_next() is not needed with g_block_list (no locking
1278     // used with block linkage _next_om fields).
1279     block = (PaddedObjectMonitor*)block->next_om();
1280   }
1281 }
1282 
1283 static bool monitors_used_above_threshold() {
1284   int population = Atomic::load(&om_list_globals._population);
1285   if (population == 0) {
1286     return false;
1287   }
1288   if (MonitorUsedDeflationThreshold > 0) {
1289     int monitors_used = population - Atomic::load(&om_list_globals._free_count);
1290     if (HandshakeAfterDeflateIdleMonitors) {
1291       monitors_used -= Atomic::load(&om_list_globals._wait_count);
1292     }
1293     int monitor_usage = (monitors_used * 100LL) / population;
1294     return monitor_usage > MonitorUsedDeflationThreshold;
1295   }
1296   return false;
1297 }
1298 
1299 // Returns true if MonitorBound is set (> 0) and if the specified
1300 // cnt is > MonitorBound. Otherwise returns false.
1301 static bool is_MonitorBound_exceeded(const int cnt) {
1302   const int mx = MonitorBound;
1303   return mx > 0 && cnt > mx;
1304 }
1305 
1306 bool ObjectSynchronizer::is_async_deflation_needed() {
1307   if (!AsyncDeflateIdleMonitors) {
1308     return false;
1309   }
1310   if (is_async_deflation_requested()) {
1311     // Async deflation request.
1312     return true;
1313   }
1314   if (AsyncDeflationInterval > 0 &&
1315       time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1316       monitors_used_above_threshold()) {
1317     // It's been longer than our specified deflate interval and there
1318     // are too many monitors in use. We don't deflate more frequently
1319     // than AsyncDeflationInterval (unless is_async_deflation_requested)
1320     // in order to not swamp the ServiceThread.
1321     _last_async_deflation_time_ns = os::javaTimeNanos();
1322     return true;
1323   }
1324   int monitors_used = Atomic::load(&om_list_globals._population) -
1325                       Atomic::load(&om_list_globals._free_count);
1326   if (HandshakeAfterDeflateIdleMonitors) {
1327     monitors_used -= Atomic::load(&om_list_globals._wait_count);
1328   }
1329   if (is_MonitorBound_exceeded(monitors_used)) {
1330     // Not enough ObjectMonitors on the global free list.
1331     return true;
1332   }
1333   return false;
1334 }
1335 
1336 bool ObjectSynchronizer::needs_monitor_scavenge() {
1337   if (Atomic::load(&_forceMonitorScavenge) == 1) {
1338     log_info(monitorinflation)("Monitor scavenge needed, triggering safepoint cleanup.");
1339     return true;
1340   }
1341   return false;
1342 }
1343 
1344 bool ObjectSynchronizer::is_safepoint_deflation_needed() {
1345   if (!AsyncDeflateIdleMonitors) {
1346     if (monitors_used_above_threshold()) {
1347       // Too many monitors in use.
1348       return true;
1349     }
1350      return needs_monitor_scavenge();
1351   }
1352   if (is_special_deflation_requested()) {
1353     // For AsyncDeflateIdleMonitors only do a safepoint deflation
1354     // if there is a special deflation request.
1355     return true;
1356   }
1357   return false;
1358 }
1359 
1360 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1361   return (os::javaTimeNanos() - _last_async_deflation_time_ns) / (NANOUNITS / MILLIUNITS);
1362 }
1363 
1364 void ObjectSynchronizer::oops_do(OopClosure* f) {
1365   // We only scan the global used list here (for moribund threads), and
1366   // the thread-local monitors in Thread::oops_do().
1367   global_used_oops_do(f);
1368 }
1369 
1370 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1371   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1372   list_oops_do(Atomic::load(&om_list_globals._in_use_list), f);
1373 }
1374 
1375 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1376   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1377   list_oops_do(thread->om_in_use_list, f);
1378 }
1379 
1380 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1381   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1382   // The oops_do() phase does not overlap with monitor deflation
1383   // so no need to lock ObjectMonitors for the list traversal and
1384   // no need to update the ObjectMonitor's ref_count for this
1385   // ObjectMonitor* use.
1386   for (ObjectMonitor* mid = list; mid != NULL; mid = unmarked_next(mid)) {
1387     if (mid->object() != NULL) {
1388       f->do_oop((oop*)mid->object_addr());
1389     }
1390   }
1391 }
1392 
1393 
1394 // -----------------------------------------------------------------------------
1395 // ObjectMonitor Lifecycle
1396 // -----------------------
1397 // Inflation unlinks monitors from om_list_globals._free_list or a per-thread
1398 // free list and associates them with objects. Deflation -- which occurs at
1399 // STW-time or asynchronously -- disassociates idle monitors from objects.
1400 // Such scavenged monitors are returned to the om_list_globals._free_list.
1401 //
1402 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1403 //
1404 // Lifecycle:
1405 // --   unassigned and on the om_list_globals._free_list
1406 // --   unassigned and on a per-thread free list
1407 // --   assigned to an object.  The object is inflated and the mark refers
1408 //      to the ObjectMonitor.
1409 
1410 
1411 // Constraining monitor pool growth via MonitorBound ...
1412 //
1413 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled.
1414 //
1415 // When safepoint deflation is being used (!AsyncDeflateIdleMonitors):
1416 // The monitor pool is grow-only.  We scavenge at STW safepoint-time, but the
1417 // the rate of scavenging is driven primarily by GC.  As such,  we can find
1418 // an inordinate number of monitors in circulation.
1419 // To avoid that scenario we can artificially induce a STW safepoint
1420 // if the pool appears to be growing past some reasonable bound.
1421 // Generally we favor time in space-time tradeoffs, but as there's no
1422 // natural back-pressure on the # of extant monitors we need to impose some
1423 // type of limit.  Beware that if MonitorBound is set to too low a value
1424 // we could just loop. In addition, if MonitorBound is set to a low value
1425 // we'll incur more safepoints, which are harmful to performance.
1426 // See also: GuaranteedSafepointInterval
1427 //
1428 // When safepoint deflation is being used and MonitorBound is set, the
1429 // boundry applies to
1430 //     (om_list_globals._population - om_list_globals._free_count)
1431 // i.e., if there are not enough ObjectMonitors on the global free list,
1432 // then a safepoint deflation is induced. Picking a good MonitorBound value
1433 // is non-trivial.
1434 //
1435 // When async deflation is being used:
1436 // The monitor pool is still grow-only. Async deflation is requested
1437 // by a safepoint's cleanup phase or by the ServiceThread at periodic
1438 // intervals when is_async_deflation_needed() returns true. In
1439 // addition to other policies that are checked, if there are not
1440 // enough ObjectMonitors on the global free list, then
1441 // is_async_deflation_needed() will return true. The ServiceThread
1442 // calls deflate_global_idle_monitors_using_JT() and also calls
1443 // deflate_per_thread_idle_monitors_using_JT() as needed.
1444 
1445 static void InduceScavenge(Thread* self, const char * Whence) {
1446   assert(!AsyncDeflateIdleMonitors, "is not used by async deflation");
1447 
1448   // Induce STW safepoint to trim monitors
1449   // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1450   // More precisely, trigger a cleanup safepoint as the number
1451   // of active monitors passes the specified threshold.
1452   // TODO: assert thread state is reasonable
1453 
1454   if (Atomic::xchg(&_forceMonitorScavenge, 1) == 0) {
1455     VMThread::check_for_forced_cleanup();
1456   }
1457 }
1458 
1459 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self) {
1460   // A large MAXPRIVATE value reduces both list lock contention
1461   // and list coherency traffic, but also tends to increase the
1462   // number of ObjectMonitors in circulation as well as the STW
1463   // scavenge costs.  As usual, we lean toward time in space-time
1464   // tradeoffs.
1465   const int MAXPRIVATE = 1024;
1466   NoSafepointVerifier nsv;
1467 
1468   stringStream ss;
1469   for (;;) {
1470     ObjectMonitor* m;
1471 
1472     // 1: try to allocate from the thread's local om_free_list.
1473     // Threads will attempt to allocate first from their local list, then
1474     // from the global list, and only after those attempts fail will the
1475     // thread attempt to instantiate new monitors. Thread-local free lists
1476     // improve allocation latency, as well as reducing coherency traffic
1477     // on the shared global list.
1478     m = take_from_start_of_om_free_list(self);
1479     if (m != NULL) {
1480       guarantee(m->object() == NULL, "invariant");
1481       m->set_allocation_state(ObjectMonitor::New);
1482       prepend_to_om_in_use_list(self, m);
1483       return m;
1484     }
1485 
1486     // 2: try to allocate from the global om_list_globals._free_list
1487     // If we're using thread-local free lists then try
1488     // to reprovision the caller's free list.
1489     if (Atomic::load(&om_list_globals._free_list) != NULL) {
1490       // Reprovision the thread's om_free_list.
1491       // Use bulk transfers to reduce the allocation rate and heat
1492       // on various locks.
1493       for (int i = self->om_free_provision; --i >= 0;) {
1494         ObjectMonitor* take = take_from_start_of_global_free_list();
1495         if (take == NULL) {
1496           break;  // No more are available.
1497         }
1498         guarantee(take->object() == NULL, "invariant");
1499         if (AsyncDeflateIdleMonitors) {
1500           // We allowed 3 field values to linger during async deflation.
1501           // We clear header and restore ref_count here, but we leave
1502           // owner == DEFLATER_MARKER so the simple C2 ObjectMonitor
1503           // enter optimization can no longer race with async deflation
1504           // and reuse.
1505           take->set_header(markWord::zero());
1506           if (take->ref_count() < 0) {
1507             // Add back max_jint to restore the ref_count field to its
1508             // proper value.
1509             Atomic::add(&take->_ref_count, max_jint);
1510 
1511 #ifdef ASSERT
1512             jint l_ref_count = take->ref_count();
1513 #endif
1514             assert(l_ref_count >= 0, "must not be negative: l_ref_count=%d, ref_count=%d",
1515                    l_ref_count, take->ref_count());
1516           }
1517         }
1518         take->Recycle();
1519         // Since we're taking from the global free-list, take must be Free.
1520         // om_release() also sets the allocation state to Free because it
1521         // is called from other code paths.
1522         assert(take->is_free(), "invariant");
1523         om_release(self, take, false);
1524       }
1525       self->om_free_provision += 1 + (self->om_free_provision / 2);
1526       if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1527 
1528       if (!AsyncDeflateIdleMonitors &&
1529           is_MonitorBound_exceeded(Atomic::load(&om_list_globals._population) -
1530                                    Atomic::load(&om_list_globals._free_count))) {
1531         // Not enough ObjectMonitors on the global free list.
1532         // We can't safely induce a STW safepoint from om_alloc() as our thread
1533         // state may not be appropriate for such activities and callers may hold
1534         // naked oops, so instead we defer the action.
1535         InduceScavenge(self, "om_alloc");
1536       }
1537       continue;
1538     }
1539 
1540     // 3: allocate a block of new ObjectMonitors
1541     // Both the local and global free lists are empty -- resort to malloc().
1542     // In the current implementation ObjectMonitors are TSM - immortal.
1543     // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1544     // each ObjectMonitor to start at the beginning of a cache line,
1545     // so we use align_up().
1546     // A better solution would be to use C++ placement-new.
1547     // BEWARE: As it stands currently, we don't run the ctors!
1548     assert(_BLOCKSIZE > 1, "invariant");
1549     size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1550     PaddedObjectMonitor* temp;
1551     size_t aligned_size = neededsize + (OM_CACHE_LINE_SIZE - 1);
1552     void* real_malloc_addr = NEW_C_HEAP_ARRAY(char, aligned_size, mtInternal);
1553     temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, OM_CACHE_LINE_SIZE);
1554     (void)memset((void *) temp, 0, neededsize);
1555 
1556     // Format the block.
1557     // initialize the linked list, each monitor points to its next
1558     // forming the single linked free list, the very first monitor
1559     // will points to next block, which forms the block list.
1560     // The trick of using the 1st element in the block as g_block_list
1561     // linkage should be reconsidered.  A better implementation would
1562     // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1563 
1564     for (int i = 1; i < _BLOCKSIZE; i++) {
1565       temp[i].set_next_om((ObjectMonitor*)&temp[i + 1]);
1566       assert(temp[i].is_free(), "invariant");
1567     }
1568 
1569     // terminate the last monitor as the end of list
1570     temp[_BLOCKSIZE - 1].set_next_om((ObjectMonitor*)NULL);
1571 
1572     // Element [0] is reserved for global list linkage
1573     temp[0].set_object(CHAINMARKER);
1574 
1575     // Consider carving out this thread's current request from the
1576     // block in hand.  This avoids some lock traffic and redundant
1577     // list activity.
1578 
1579     prepend_block_to_lists(temp);
1580   }
1581 }
1582 
1583 // Place "m" on the caller's private per-thread om_free_list.
1584 // In practice there's no need to clamp or limit the number of
1585 // monitors on a thread's om_free_list as the only non-allocation time
1586 // we'll call om_release() is to return a monitor to the free list after
1587 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1588 // accumulate on a thread's free list.
1589 //
1590 // Key constraint: all ObjectMonitors on a thread's free list and the global
1591 // free list must have their object field set to null. This prevents the
1592 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1593 // -- from reclaiming them while we are trying to release them.
1594 
1595 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1596                                     bool from_per_thread_alloc) {
1597   guarantee(m->header().value() == 0, "invariant");
1598   guarantee(m->object() == NULL, "invariant");
1599   NoSafepointVerifier nsv;
1600 
1601   stringStream ss;
1602   guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1603             "%s, recursions=" INTX_FORMAT, m->is_busy_to_string(&ss),
1604             m->_recursions);
1605   m->set_allocation_state(ObjectMonitor::Free);
1606   // _next_om is used for both per-thread in-use and free lists so
1607   // we have to remove 'm' from the in-use list first (as needed).
1608   if (from_per_thread_alloc) {
1609     // Need to remove 'm' from om_in_use_list.
1610     ObjectMonitor* mid = NULL;
1611     ObjectMonitor* next = NULL;
1612 
1613     // This list walk can race with another list walker or with async
1614     // deflation so we have to worry about an ObjectMonitor being
1615     // removed from this list while we are walking it.

1616 
1617     // Lock the list head to avoid racing with another list walker
1618     // or with async deflation.
1619     if ((mid = get_list_head_locked(&self->om_in_use_list)) == NULL) {
1620       fatal("thread=" INTPTR_FORMAT " in-use list must not be empty.", p2i(self));
1621     }
1622     next = unmarked_next(mid);
1623     if (m == mid) {
1624       // First special case:
1625       // 'm' matches mid, is the list head and is locked. Switch the list
1626       // head to next which unlocks the list head, but leaves the extracted
1627       // mid locked:
1628       Atomic::store(&self->om_in_use_list, next);
1629     } else if (m == next) {
1630       // Second special case:
1631       // 'm' matches next after the list head and we already have the list
1632       // head locked so set mid to what we are extracting:
1633       mid = next;
1634       // Lock mid to prevent races with a list walker or an async
1635       // deflater thread that's ahead of us. The locked list head
1636       // prevents races from behind us.
1637       om_lock(mid);
1638       // Update next to what follows mid (if anything):
1639       next = unmarked_next(mid);
1640       // Switch next after the list head to new next which unlocks the
1641       // list head, but leaves the extracted mid locked:
1642       self->om_in_use_list->set_next_om(next);
1643     } else {
1644       // We have to search the list to find 'm'.

1645       guarantee(next != NULL, "thread=" INTPTR_FORMAT ": om_in_use_list=" INTPTR_FORMAT
1646                 " is too short.", p2i(self), p2i(self->om_in_use_list));
1647       // Our starting anchor is next after the list head which is the
1648       // last ObjectMonitor we checked:
1649       ObjectMonitor* anchor = next;
1650       // Lock anchor to prevent races with a list walker or an async
1651       // deflater thread that's ahead of us. The locked list head
1652       // prevents races from behind us.
1653       om_lock(anchor);
1654       om_unlock(mid);  // Unlock the list head now that anchor is locked.
1655       while ((mid = unmarked_next(anchor)) != NULL) {
1656         if (m == mid) {
1657           // We found 'm' on the per-thread in-use list so extract it.

1658           // Update next to what follows mid (if anything):
1659           next = unmarked_next(mid);
1660           // Switch next after the anchor to new next which unlocks the
1661           // anchor, but leaves the extracted mid locked:
1662           anchor->set_next_om(next);
1663           break;
1664         } else {
1665           // Lock the next anchor to prevent races with a list walker
1666           // or an async deflater thread that's ahead of us. The locked
1667           // current anchor prevents races from behind us.
1668           om_lock(mid);
1669           // Unlock current anchor now that next anchor is locked:
1670           om_unlock(anchor);
1671           anchor = mid;  // Advance to new anchor and try again.
1672         }
1673       }
1674     }
1675 
1676     if (mid == NULL) {
1677       // Reached end of the list and didn't find 'm' so:
1678       fatal("thread=" INTPTR_FORMAT " must find m=" INTPTR_FORMAT "on om_in_use_list="
1679             INTPTR_FORMAT, p2i(self), p2i(m), p2i(self->om_in_use_list));
1680     }
1681 
1682     // At this point mid is disconnected from the in-use list so
1683     // its lock no longer has any effects on the in-use list.
1684     Atomic::dec(&self->om_in_use_count);
1685     // Unlock mid, but leave the next value for any lagging list
1686     // walkers. It will get cleaned up when mid is prepended to
1687     // the thread's free list:
1688     om_unlock(mid);
1689   }
1690 
1691   prepend_to_om_free_list(self, m);
1692   guarantee(m->is_free(), "invariant");
1693 }
1694 
1695 // Return ObjectMonitors on a moribund thread's free and in-use
1696 // lists to the appropriate global lists. The ObjectMonitors on the
1697 // per-thread in-use list may still be in use by other threads.
1698 //
1699 // We currently call om_flush() from Threads::remove() before the
1700 // thread has been excised from the thread list and is no longer a
1701 // mutator. This means that om_flush() cannot run concurrently with
1702 // a safepoint and interleave with deflate_idle_monitors(). In
1703 // particular, this ensures that the thread's in-use monitors are
1704 // scanned by a GC safepoint, either via Thread::oops_do() (before
1705 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1706 // om_flush() is called).
1707 //
1708 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1709 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1710 // run at the same time as om_flush() so we have to follow a careful
1711 // protocol to prevent list corruption.
1712 
1713 void ObjectSynchronizer::om_flush(Thread* self) {
1714   // Process the per-thread in-use list first to be consistent.
1715   int in_use_count = 0;
1716   ObjectMonitor* in_use_list = NULL;
1717   ObjectMonitor* in_use_tail = NULL;
1718   NoSafepointVerifier nsv;
1719 
1720   // This function can race with a list walker or with an async
1721   // deflater thread so we lock the list head to prevent confusion.
1722   // An async deflater thread checks to see if the target thread
1723   // is exiting, but if it has made it past that check before we
1724   // started exiting, then it is racing to get to the in-use list.
1725   if ((in_use_list = get_list_head_locked(&self->om_in_use_list)) != NULL) {
1726     // At this point, we have locked the in-use list head so a racing
1727     // thread cannot come in after us. However, a racing thread could
1728     // be ahead of us; we'll detect that and delay to let it finish.
1729     //
1730     // The thread is going away, however the ObjectMonitors on the
1731     // om_in_use_list may still be in-use by other threads. Link
1732     // them to in_use_tail, which will be linked into the global
1733     // in-use list (om_list_globals._in_use_list) below.
1734     //
1735     // Account for the in-use list head before the loop since it is
1736     // already locked (by this thread):
1737     in_use_tail = in_use_list;
1738     in_use_count++;
1739     for (ObjectMonitor* cur_om = unmarked_next(in_use_list); cur_om != NULL;) {
1740       if (is_locked(cur_om)) {
1741         // cur_om is locked so there must be a racing walker or async
1742         // deflater thread ahead of us so we'll give it a chance to finish.
1743         while (is_locked(cur_om)) {
1744           os::naked_short_sleep(1);
1745         }
1746         // Refetch the possibly changed next field and try again.
1747         cur_om = unmarked_next(in_use_tail);
1748         continue;
1749       }
1750       if (cur_om->is_free()) {
1751         // cur_om was deflated and the allocation state was changed
1752         // to Free while it was locked. We happened to see it just
1753         // after it was unlocked (and added to the free list).
1754         // Refetch the possibly changed next field and try again.
1755         cur_om = unmarked_next(in_use_tail);
1756         continue;
1757       }
1758       in_use_tail = cur_om;
1759       in_use_count++;
1760       cur_om = unmarked_next(cur_om);
1761     }
1762     guarantee(in_use_tail != NULL, "invariant");
1763     int l_om_in_use_count = Atomic::load(&self->om_in_use_count);
1764     ADIM_guarantee(l_om_in_use_count == in_use_count, "in-use counts don't match: "
1765                    "l_om_in_use_count=%d, in_use_count=%d", l_om_in_use_count, in_use_count);
1766     Atomic::store(&self->om_in_use_count, 0);
1767     // Clear the in-use list head (which also unlocks it):
1768     Atomic::store(&self->om_in_use_list, (ObjectMonitor*)NULL);
1769     om_unlock(in_use_list);
1770   }
1771 
1772   int free_count = 0;
1773   ObjectMonitor* free_list = NULL;
1774   ObjectMonitor* free_tail = NULL;
1775   // This function can race with a list walker thread so we lock the
1776   // list head to prevent confusion.
1777   if ((free_list = get_list_head_locked(&self->om_free_list)) != NULL) {
1778     // At this point, we have locked the free list head so a racing
1779     // thread cannot come in after us. However, a racing thread could
1780     // be ahead of us; we'll detect that and delay to let it finish.
1781     //
1782     // The thread is going away. Set 'free_tail' to the last per-thread free
1783     // monitor which will be linked to om_list_globals._free_list below.
1784     //
1785     // Account for the free list head before the loop since it is
1786     // already locked (by this thread):
1787     free_tail = free_list;
1788     free_count++;
1789     for (ObjectMonitor* s = unmarked_next(free_list); s != NULL; s = unmarked_next(s)) {
1790       if (is_locked(s)) {
1791         // s is locked so there must be a racing walker thread ahead
1792         // of us so we'll give it a chance to finish.
1793         while (is_locked(s)) {
1794           os::naked_short_sleep(1);
1795         }
1796       }
1797       free_tail = s;
1798       free_count++;
1799       guarantee(s->object() == NULL, "invariant");
1800       stringStream ss;
1801       guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1802     }
1803     guarantee(free_tail != NULL, "invariant");
1804     int l_om_free_count = Atomic::load(&self->om_free_count);
1805     ADIM_guarantee(l_om_free_count == free_count, "free counts don't match: "
1806                    "l_om_free_count=%d, free_count=%d", l_om_free_count, free_count);
1807     Atomic::store(&self->om_free_count, 0);
1808     Atomic::store(&self->om_free_list, (ObjectMonitor*)NULL);
1809     om_unlock(free_list);
1810   }
1811 
1812   if (free_tail != NULL) {
1813     prepend_list_to_global_free_list(free_list, free_tail, free_count);
1814   }
1815 
1816   if (in_use_tail != NULL) {
1817     prepend_list_to_global_in_use_list(in_use_list, in_use_tail, in_use_count);
1818   }
1819 
1820   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1821   LogStreamHandle(Info, monitorinflation) lsh_info;
1822   LogStream* ls = NULL;
1823   if (log_is_enabled(Debug, monitorinflation)) {
1824     ls = &lsh_debug;
1825   } else if ((free_count != 0 || in_use_count != 0) &&


1828   }
1829   if (ls != NULL) {
1830     ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1831                  ", in_use_count=%d" ", om_free_provision=%d",
1832                  p2i(self), free_count, in_use_count, self->om_free_provision);
1833   }
1834 }
1835 
1836 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1837                                        const oop obj,
1838                                        ObjectSynchronizer::InflateCause cause) {
1839   assert(event != NULL, "invariant");
1840   assert(event->should_commit(), "invariant");
1841   event->set_monitorClass(obj->klass());
1842   event->set_address((uintptr_t)(void*)obj);
1843   event->set_cause((u1)cause);
1844   event->commit();
1845 }
1846 
1847 // Fast path code shared by multiple functions
1848 void ObjectSynchronizer::inflate_helper(ObjectMonitorHandle* omh_p, oop obj) {
1849   while (true) {
1850     markWord mark = obj->mark();
1851     if (mark.has_monitor()) {
1852       if (!omh_p->save_om_ptr(obj, mark)) {
1853         // Lost a race with async deflation so try again.
1854         assert(AsyncDeflateIdleMonitors, "sanity check");
1855         continue;
1856       }
1857       ObjectMonitor* monitor = omh_p->om_ptr();
1858       assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor is invalid");
1859       markWord dmw = monitor->header();
1860       assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1861       return;
1862     }
1863     inflate(omh_p, Thread::current(), obj, inflate_cause_vm_internal);
1864     return;
1865   }

1866 }
1867 
1868 void ObjectSynchronizer::inflate(ObjectMonitorHandle* omh_p, Thread* self,
1869                                  oop object, const InflateCause cause) {
1870   // Inflate mutates the heap ...
1871   // Relaxing assertion for bug 6320749.
1872   assert(Universe::verify_in_progress() ||
1873          !SafepointSynchronize::is_at_safepoint(), "invariant");
1874 
1875   EventJavaMonitorInflate event;
1876 
1877   for (;;) {
1878     const markWord mark = object->mark();
1879     assert(!mark.has_bias_pattern(), "invariant");
1880 
1881     // The mark can be in one of the following states:
1882     // *  Inflated     - just return
1883     // *  Stack-locked - coerce it to inflated
1884     // *  INFLATING    - busy wait for conversion to complete
1885     // *  Neutral      - aggressively inflate the object.
1886     // *  BIASED       - Illegal.  We should never see this
1887 
1888     // CASE: inflated
1889     if (mark.has_monitor()) {
1890       if (!omh_p->save_om_ptr(object, mark)) {
1891         // Lost a race with async deflation so try again.
1892         assert(AsyncDeflateIdleMonitors, "sanity check");
1893         continue;
1894       }
1895       ObjectMonitor* inf = omh_p->om_ptr();
1896       markWord dmw = inf->header();
1897       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1898       assert(inf->object() == object, "invariant");
1899       assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1900       return;
1901     }
1902 
1903     // CASE: inflation in progress - inflating over a stack-lock.
1904     // Some other thread is converting from stack-locked to inflated.
1905     // Only that thread can complete inflation -- other threads must wait.
1906     // The INFLATING value is transient.
1907     // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1908     // We could always eliminate polling by parking the thread on some auxiliary list.
1909     if (mark == markWord::INFLATING()) {
1910       read_stable_mark(object);
1911       continue;
1912     }
1913 
1914     // CASE: stack-locked
1915     // Could be stack-locked either by this thread or by some other thread.
1916     //
1917     // Note that we allocate the objectmonitor speculatively, _before_ attempting
1918     // to install INFLATING into the mark word.  We originally installed INFLATING,
1919     // allocated the objectmonitor, and then finally STed the address of the
1920     // objectmonitor into the mark.  This was correct, but artificially lengthened


1926     // critical INFLATING...ST interval.  A thread can transfer
1927     // multiple objectmonitors en-mass from the global free list to its local free list.
1928     // This reduces coherency traffic and lock contention on the global free list.
1929     // Using such local free lists, it doesn't matter if the om_alloc() call appears
1930     // before or after the CAS(INFLATING) operation.
1931     // See the comments in om_alloc().
1932 
1933     LogStreamHandle(Trace, monitorinflation) lsh;
1934 
1935     if (mark.has_locker()) {
1936       ObjectMonitor* m = om_alloc(self);
1937       // Optimistically prepare the objectmonitor - anticipate successful CAS
1938       // We do this before the CAS in order to minimize the length of time
1939       // in which INFLATING appears in the mark.
1940       m->Recycle();
1941       m->_Responsible  = NULL;
1942       m->_SpinDuration = ObjectMonitor::Knob_SpinLimit;   // Consider: maintain by type/class
1943 
1944       markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1945       if (cmp != mark) {
1946         // om_release() will reset the allocation state from New to Free.
1947         om_release(self, m, true);
1948         continue;       // Interference -- just retry
1949       }
1950 
1951       // We've successfully installed INFLATING (0) into the mark-word.
1952       // This is the only case where 0 will appear in a mark-word.
1953       // Only the singular thread that successfully swings the mark-word
1954       // to 0 can perform (or more precisely, complete) inflation.
1955       //
1956       // Why do we CAS a 0 into the mark-word instead of just CASing the
1957       // mark-word from the stack-locked value directly to the new inflated state?
1958       // Consider what happens when a thread unlocks a stack-locked object.
1959       // It attempts to use CAS to swing the displaced header value from the
1960       // on-stack BasicLock back into the object header.  Recall also that the
1961       // header value (hash code, etc) can reside in (a) the object header, or
1962       // (b) a displaced header associated with the stack-lock, or (c) a displaced
1963       // header in an ObjectMonitor.  The inflate() routine must copy the header
1964       // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1965       // the while preserving the hashCode stability invariants.  If the owner
1966       // decides to release the lock while the value is 0, the unlock will fail
1967       // and control will eventually pass from slow_exit() to inflate.  The owner
1968       // will then spin, waiting for the 0 value to disappear.   Put another way,
1969       // the 0 causes the owner to stall if the owner happens to try to
1970       // drop the lock (restoring the header from the BasicLock to the object)
1971       // while inflation is in-progress.  This protocol avoids races that might
1972       // would otherwise permit hashCode values to change or "flicker" for an object.
1973       // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1974       // 0 serves as a "BUSY" inflate-in-progress indicator.
1975 
1976 
1977       // fetch the displaced mark from the owner's stack.
1978       // The owner can't die or unwind past the lock while our INFLATING
1979       // object is in the mark.  Furthermore the owner can't complete
1980       // an unlock on the object, either.
1981       markWord dmw = mark.displaced_mark_helper();
1982       // Catch if the object's header is not neutral (not locked and
1983       // not marked is what we care about here).
1984       ADIM_guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1985 
1986       // Setup monitor fields to proper values -- prepare the monitor
1987       m->set_header(dmw);
1988 
1989       // Optimization: if the mark.locker stack address is associated
1990       // with this thread we could simply set m->_owner = self.
1991       // Note that a thread can inflate an object
1992       // that it has stack-locked -- as might happen in wait() -- directly
1993       // with CAS.  That is, we can avoid the xchg-NULL .... ST idiom.
1994       if (AsyncDeflateIdleMonitors) {
1995         m->set_owner_from(NULL, DEFLATER_MARKER, mark.locker());
1996       } else {
1997         m->set_owner_from(NULL, mark.locker());
1998       }
1999       m->set_object(object);
2000       // TODO-FIXME: assert BasicLock->dhw != 0.
2001 
2002       omh_p->set_om_ptr(m);
2003 
2004       // Must preserve store ordering. The monitor state must
2005       // be stable at the time of publishing the monitor address.
2006       guarantee(object->mark() == markWord::INFLATING(), "invariant");
2007       object->release_set_mark(markWord::encode(m));
2008 
2009       // Once ObjectMonitor is configured and the object is associated
2010       // with the ObjectMonitor, it is safe to allow async deflation:
2011       assert(m->is_new(), "freshly allocated monitor must be new");
2012       m->set_allocation_state(ObjectMonitor::Old);
2013 
2014       // Hopefully the performance counters are allocated on distinct cache lines
2015       // to avoid false sharing on MP systems ...
2016       OM_PERFDATA_OP(Inflations, inc());
2017       if (log_is_enabled(Trace, monitorinflation)) {
2018         ResourceMark rm(self);
2019         lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
2020                      INTPTR_FORMAT ", type='%s'", p2i(object),
2021                      object->mark().value(), object->klass()->external_name());
2022       }
2023       if (event.should_commit()) {
2024         post_monitor_inflate_event(&event, object, cause);
2025       }
2026       ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
2027       return;
2028     }
2029 
2030     // CASE: neutral
2031     // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
2032     // If we know we're inflating for entry it's better to inflate by swinging a
2033     // pre-locked ObjectMonitor pointer into the object header.   A successful
2034     // CAS inflates the object *and* confers ownership to the inflating thread.
2035     // In the current implementation we use a 2-step mechanism where we CAS()
2036     // to inflate and then CAS() again to try to swing _owner from NULL to self.
2037     // An inflateTry() method that we could call from enter() would be useful.
2038 
2039     // Catch if the object's header is not neutral (not locked and
2040     // not marked is what we care about here).
2041     ADIM_guarantee(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
2042     ObjectMonitor* m = om_alloc(self);
2043     // prepare m for installation - set monitor to initial state
2044     m->Recycle();
2045     m->set_header(mark);
2046     // If we leave _owner == DEFLATER_MARKER here, then the simple C2
2047     // ObjectMonitor enter optimization can no longer race with async
2048     // deflation and reuse.
2049     m->set_object(object);
2050     m->_Responsible  = NULL;
2051     m->_SpinDuration = ObjectMonitor::Knob_SpinLimit;       // consider: keep metastats by type/class
2052 
2053     omh_p->set_om_ptr(m);
2054 
2055     if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
2056       m->set_header(markWord::zero());
2057       m->set_object(NULL);
2058       m->Recycle();
2059       omh_p->set_om_ptr(NULL);
2060       // om_release() will reset the allocation state from New to Free.
2061       om_release(self, m, true);
2062       m = NULL;
2063       continue;
2064       // interference - the markword changed - just retry.
2065       // The state-transitions are one-way, so there's no chance of
2066       // live-lock -- "Inflated" is an absorbing state.
2067     }
2068 
2069     // Once the ObjectMonitor is configured and object is associated
2070     // with the ObjectMonitor, it is safe to allow async deflation:
2071     assert(m->is_new(), "freshly allocated monitor must be new");
2072     m->set_allocation_state(ObjectMonitor::Old);
2073 
2074     // Hopefully the performance counters are allocated on distinct
2075     // cache lines to avoid false sharing on MP systems ...
2076     OM_PERFDATA_OP(Inflations, inc());
2077     if (log_is_enabled(Trace, monitorinflation)) {
2078       ResourceMark rm(self);
2079       lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
2080                    INTPTR_FORMAT ", type='%s'", p2i(object),
2081                    object->mark().value(), object->klass()->external_name());
2082     }
2083     if (event.should_commit()) {
2084       post_monitor_inflate_event(&event, object, cause);
2085     }
2086     ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
2087     return;
2088   }
2089 }
2090 
2091 
2092 // We maintain a list of in-use monitors for each thread.
2093 //
2094 // For safepoint based deflation:
2095 // deflate_thread_local_monitors() scans a single thread's in-use list, while
2096 // deflate_idle_monitors() scans only a global list of in-use monitors which
2097 // is populated only as a thread dies (see om_flush()).
2098 //
2099 // These operations are called at all safepoints, immediately after mutators
2100 // are stopped, but before any objects have moved. Collectively they traverse
2101 // the population of in-use monitors, deflating where possible. The scavenged
2102 // monitors are returned to the global monitor free list.
2103 //
2104 // Beware that we scavenge at *every* stop-the-world point. Having a large
2105 // number of monitors in-use could negatively impact performance. We also want
2106 // to minimize the total # of monitors in circulation, as they incur a small
2107 // footprint penalty.
2108 //
2109 // Perversely, the heap size -- and thus the STW safepoint rate --
2110 // typically drives the scavenge rate.  Large heaps can mean infrequent GC,
2111 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
2112 // This is an unfortunate aspect of this design.
2113 //
2114 // For async deflation:
2115 // If a special deflation request is made, then the safepoint based
2116 // deflation mechanism is used. Otherwise, an async deflation request
2117 // is registered with the ServiceThread and it is notified.
2118 
2119 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* counters) {
2120   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2121 
2122   // The per-thread in-use lists are handled in
2123   // ParallelSPCleanupThreadClosure::do_thread().
2124 
2125   if (!AsyncDeflateIdleMonitors || is_special_deflation_requested()) {
2126     // Use the older mechanism for the global in-use list or if a
2127     // special deflation has been requested before the safepoint.
2128     ObjectSynchronizer::deflate_idle_monitors(counters);
2129     return;
2130   }
2131 
2132   log_debug(monitorinflation)("requesting async deflation of idle monitors.");
2133   // Request deflation of idle monitors by the ServiceThread:
2134   set_is_async_deflation_requested(true);
2135   MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
2136   ml.notify_all();
2137 
2138   if (log_is_enabled(Debug, monitorinflation)) {
2139     // exit_globals()'s call to audit_and_print_stats() is done
2140     // at the Info level and not at a safepoint.
2141     // For safepoint based deflation, audit_and_print_stats() is called
2142     // in ObjectSynchronizer::finish_deflate_idle_monitors() at the
2143     // Debug level at a safepoint.
2144     ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2145   }
2146 }
2147 
2148 // Deflate a single monitor if not in-use
2149 // Return true if deflated, false if in-use
2150 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
2151                                          ObjectMonitor** free_head_p,
2152                                          ObjectMonitor** free_tail_p) {
2153   bool deflated;
2154   // Normal case ... The monitor is associated with obj.
2155   const markWord mark = obj->mark();
2156   guarantee(mark == markWord::encode(mid), "should match: mark="
2157             INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
2158             markWord::encode(mid).value());
2159   // Make sure that mark.monitor() and markWord::encode() agree:
2160   guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
2161             ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
2162   const markWord dmw = mid->header();
2163   guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
2164 
2165   if (mid->is_busy() || mid->ref_count() != 0) {
2166     // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor*
2167     // is in use so no deflation.
2168     deflated = false;
2169   } else {
2170     // Deflate the monitor if it is no longer being used
2171     // It's idle - scavenge and return to the global free list
2172     // plain old deflation ...
2173     if (log_is_enabled(Trace, monitorinflation)) {
2174       ResourceMark rm;
2175       log_trace(monitorinflation)("deflate_monitor: "
2176                                   "object=" INTPTR_FORMAT ", mark="
2177                                   INTPTR_FORMAT ", type='%s'", p2i(obj),
2178                                   mark.value(), obj->klass()->external_name());
2179     }
2180 
2181     // Restore the header back to obj
2182     obj->release_set_mark(dmw);
2183     if (AsyncDeflateIdleMonitors) {
2184       // clear() expects the owner field to be NULL and we won't race
2185       // with the simple C2 ObjectMonitor enter optimization since
2186       // we're at a safepoint. DEFLATER_MARKER is the only non-NULL
2187       // value we should see here.
2188       mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2189     }
2190     mid->clear();
2191 
2192     assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
2193            p2i(mid->object()));
2194     assert(mid->is_free(), "invariant");
2195 
2196     // Move the deflated ObjectMonitor to the working free list
2197     // defined by free_head_p and free_tail_p.
2198     if (*free_head_p == NULL) *free_head_p = mid;
2199     if (*free_tail_p != NULL) {
2200       // We append to the list so the caller can use mid->_next_om
2201       // to fix the linkages in its context.
2202       ObjectMonitor* prevtail = *free_tail_p;
2203       // Should have been cleaned up by the caller:
2204       // Note: Should not have to lock prevtail here since we're at a
2205       // safepoint and ObjectMonitors on the local free list should
2206       // not be accessed in parallel.
2207 #ifdef ASSERT
2208       ObjectMonitor* l_next_om = prevtail->next_om();
2209 #endif
2210       assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2211       prevtail->set_next_om(mid);
2212     }
2213     *free_tail_p = mid;
2214     // At this point, mid->_next_om still refers to its current
2215     // value and another ObjectMonitor's _next_om field still
2216     // refers to this ObjectMonitor. Those linkages have to be
2217     // cleaned up by the caller who has the complete context.
2218     deflated = true;
2219   }
2220   return deflated;
2221 }
2222 
2223 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
2224 // Returns true if it was deflated and false otherwise.
2225 //
2226 // The async deflation protocol sets owner to DEFLATER_MARKER and
2227 // makes ref_count negative as signals to contending threads that
2228 // an async deflation is in progress. There are a number of checks
2229 // as part of the protocol to make sure that the calling thread has
2230 // not lost the race to a contending thread or to a thread that just
2231 // wants to use the ObjectMonitor*.
2232 //
2233 // The ObjectMonitor has been successfully async deflated when:
2234 // (owner == DEFLATER_MARKER && ref_count < 0)
2235 // Contending threads or ObjectMonitor* using threads that see those
2236 // values know to retry their operation.
2237 //
2238 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
2239                                                   ObjectMonitor** free_head_p,
2240                                                   ObjectMonitor** free_tail_p) {
2241   assert(AsyncDeflateIdleMonitors, "sanity check");
2242   assert(Thread::current()->is_Java_thread(), "precondition");
2243   // A newly allocated ObjectMonitor should not be seen here so we
2244   // avoid an endless inflate/deflate cycle.
2245   assert(mid->is_old(), "must be old: allocation_state=%d",
2246          (int) mid->allocation_state());
2247 
2248   if (mid->is_busy() || mid->ref_count() != 0) {
2249     // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor*
2250     // is in use so no deflation.
2251     return false;
2252   }
2253 
2254   if (mid->try_set_owner_from(NULL, DEFLATER_MARKER) == NULL) {
2255     // ObjectMonitor is not owned by another thread. Our setting
2256     // owner to DEFLATER_MARKER forces any contending thread through
2257     // the slow path. This is just the first part of the async
2258     // deflation dance.
2259 
2260     if (mid->_contentions != 0 || mid->_waiters != 0) {
2261       // Another thread has raced to enter the ObjectMonitor after
2262       // mid->is_busy() above or has already entered and waited on
2263       // it which makes it busy so no deflation. Restore owner to
2264       // NULL if it is still DEFLATER_MARKER.
2265       mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2266       return false;
2267     }
2268 
2269     if (Atomic::cmpxchg(&mid->_ref_count, (jint)0, -max_jint) == 0) {
2270       // Make ref_count negative to force any contending threads or
2271       // ObjectMonitor* using threads to retry. This is the second
2272       // part of the async deflation dance.
2273 
2274       if (mid->owner_is_DEFLATER_MARKER()) {
2275         // If owner is still DEFLATER_MARKER, then we have successfully
2276         // signaled any contending threads to retry. If it is not, then we
2277         // have lost the race to an entering thread and the ObjectMonitor
2278         // is now busy. This is the third and final part of the async
2279         // deflation dance.
2280         // Note: This owner check solves the ABA problem with ref_count
2281         // where another thread acquired the ObjectMonitor, finished
2282         // using it and restored the ref_count to zero.
2283 
2284         // Sanity checks for the races:
2285         guarantee(mid->_contentions == 0, "must be 0: contentions=%d",
2286                   mid->_contentions);
2287         guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
2288         guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
2289                   INTPTR_FORMAT, p2i(mid->_cxq));
2290         guarantee(mid->_EntryList == NULL,
2291                   "must be no entering threads: EntryList=" INTPTR_FORMAT,
2292                   p2i(mid->_EntryList));
2293 
2294         const oop obj = (oop) mid->object();
2295         if (log_is_enabled(Trace, monitorinflation)) {
2296           ResourceMark rm;
2297           log_trace(monitorinflation)("deflate_monitor_using_JT: "
2298                                       "object=" INTPTR_FORMAT ", mark="
2299                                       INTPTR_FORMAT ", type='%s'",
2300                                       p2i(obj), obj->mark().value(),
2301                                       obj->klass()->external_name());
2302         }
2303 
2304         // Install the old mark word if nobody else has already done it.
2305         mid->install_displaced_markword_in_object(obj);
2306         mid->clear_using_JT();
2307 
2308         assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
2309                p2i(mid->object()));
2310         assert(mid->is_free(), "must be free: allocation_state=%d",
2311                (int) mid->allocation_state());
2312 
2313         // Move the deflated ObjectMonitor to the working free list
2314         // defined by free_head_p and free_tail_p. No races on this list
2315         // so no need for load_acquire() or store_release().
2316         if (*free_head_p == NULL) {
2317           // First one on the list.
2318           *free_head_p = mid;
2319         }
2320         if (*free_tail_p != NULL) {
2321           // We append to the list so the caller can use mid->_next_om
2322           // to fix the linkages in its context.
2323           ObjectMonitor* prevtail = *free_tail_p;
2324           // Should have been cleaned up by the caller:
2325           om_lock(prevtail);
2326 #ifdef ASSERT
2327           ObjectMonitor* l_next_om = unmarked_next(prevtail);
2328 #endif
2329           assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2330           prevtail->set_next_om(mid);  // prevtail now points to mid (and is unlocked)
2331         }
2332         *free_tail_p = mid;
2333 
2334         // At this point, mid->_next_om still refers to its current
2335         // value and another ObjectMonitor's _next_om field still
2336         // refers to this ObjectMonitor. Those linkages have to be
2337         // cleaned up by the caller who has the complete context.
2338 
2339         // We leave owner == DEFLATER_MARKER and ref_count < 0
2340         // to force any racing threads to retry.
2341         return true;  // Success, ObjectMonitor has been deflated.
2342       }
2343 
2344       // The owner was changed from DEFLATER_MARKER so we lost the
2345       // race since the ObjectMonitor is now busy.
2346 
2347       // Add back max_jint to restore the ref_count field to its
2348       // proper value (which may not be what we saw above):
2349       Atomic::add(&mid->_ref_count, max_jint);
2350 
2351 #ifdef ASSERT
2352       jint l_ref_count = mid->ref_count();
2353 #endif
2354       assert(l_ref_count >= 0, "must not be negative: l_ref_count=%d, ref_count=%d",
2355              l_ref_count, mid->ref_count());
2356       return false;
2357     }
2358 
2359     // The ref_count was no longer 0 so we lost the race since the
2360     // ObjectMonitor is now busy or the ObjectMonitor* is now is use.
2361     // Restore owner to NULL if it is still DEFLATER_MARKER:
2362     mid->try_set_owner_from(DEFLATER_MARKER, NULL);
2363   }
2364 
2365   // The owner field is no longer NULL so we lost the race since the
2366   // ObjectMonitor is now busy.
2367   return false;
2368 }
2369 
2370 // Walk a given monitor list, and deflate idle monitors.
2371 // The given list could be a per-thread list or a global list.
2372 //
2373 // In the case of parallel processing of thread local monitor lists,
2374 // work is done by Threads::parallel_threads_do() which ensures that
2375 // each Java thread is processed by exactly one worker thread, and
2376 // thus avoid conflicts that would arise when worker threads would
2377 // process the same monitor lists concurrently.
2378 //
2379 // See also ParallelSPCleanupTask and
2380 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
2381 // Threads::parallel_java_threads_do() in thread.cpp.
2382 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
2383                                              int* count_p,
2384                                              ObjectMonitor** free_head_p,
2385                                              ObjectMonitor** free_tail_p) {
2386   ObjectMonitor* cur_mid_in_use = NULL;
2387   ObjectMonitor* mid = NULL;
2388   ObjectMonitor* next = NULL;
2389   int deflated_count = 0;


2400       // by unlinking mid from the global or per-thread in-use list.
2401       if (cur_mid_in_use == NULL) {
2402         // mid is the list head so switch the list head to next:
2403         Atomic::store(list_p, next);
2404       } else {
2405         // Switch cur_mid_in_use's next field to next:
2406         cur_mid_in_use->set_next_om(next);
2407       }
2408       // At this point mid is disconnected from the in-use list.
2409       deflated_count++;
2410       Atomic::dec(count_p);
2411       // mid is current tail in the free_head_p list so NULL terminate it:
2412       mid->set_next_om(NULL);
2413     } else {
2414       cur_mid_in_use = mid;
2415     }
2416   }
2417   return deflated_count;
2418 }
2419 
2420 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
2421 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
2422 // list could be a per-thread in-use list or the global in-use list.
2423 // If a safepoint has started, then we save state via saved_mid_in_use_p
2424 // and return to the caller to honor the safepoint.
2425 //
2426 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p,
2427                                                       int* count_p,
2428                                                       ObjectMonitor** free_head_p,
2429                                                       ObjectMonitor** free_tail_p,
2430                                                       ObjectMonitor** saved_mid_in_use_p) {
2431   assert(AsyncDeflateIdleMonitors, "sanity check");
2432   JavaThread* self = JavaThread::current();
2433 
2434   ObjectMonitor* cur_mid_in_use = NULL;
2435   ObjectMonitor* mid = NULL;
2436   ObjectMonitor* next = NULL;
2437   ObjectMonitor* next_next = NULL;
2438   int deflated_count = 0;
2439   NoSafepointVerifier nsv;
2440 
2441   // We use the more complicated lock-cur_mid_in_use-and-mid-as-we-go
2442   // protocol because om_release() can do list deletions in parallel;
2443   // this also prevents races with a list walker thread. We also
2444   // lock-next-next-as-we-go to prevent an om_flush() that is behind
2445   // this thread from passing us.
2446   if (*saved_mid_in_use_p == NULL) {
2447     // No saved state so start at the beginning.
2448     // Lock the list head so we can possibly deflate it:
2449     if ((mid = get_list_head_locked(list_p)) == NULL) {
2450       return 0;  // The list is empty so nothing to deflate.
2451     }
2452     next = unmarked_next(mid);
2453   } else {
2454     // We're restarting after a safepoint so restore the necessary state
2455     // before we resume.
2456     cur_mid_in_use = *saved_mid_in_use_p;
2457     // Lock cur_mid_in_use so we can possibly update its
2458     // next field to extract a deflated ObjectMonitor.
2459     om_lock(cur_mid_in_use);
2460     mid = unmarked_next(cur_mid_in_use);
2461     if (mid == NULL) {
2462       om_unlock(cur_mid_in_use);
2463       *saved_mid_in_use_p = NULL;
2464       return 0;  // The remainder is empty so nothing more to deflate.
2465     }
2466     // Lock mid so we can possibly deflate it:
2467     om_lock(mid);
2468     next = unmarked_next(mid);
2469   }
2470 
2471   while (true) {
2472     // The current mid's next field is marked at this point. If we have
2473     // a cur_mid_in_use, then its next field is also marked at this point.
2474 
2475     if (next != NULL) {
2476       // We lock next so that an om_flush() thread that is behind us
2477       // cannot pass us when we unlock the current mid.
2478       om_lock(next);
2479       next_next = unmarked_next(next);
2480     }
2481 
2482     // Only try to deflate if there is an associated Java object and if
2483     // mid is old (is not newly allocated and is not newly freed).
2484     if (mid->object() != NULL && mid->is_old() &&
2485         deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) {
2486       // Deflation succeeded and already updated free_head_p and
2487       // free_tail_p as needed. Finish the move to the local free list
2488       // by unlinking mid from the global or per-thread in-use list.
2489       if (cur_mid_in_use == NULL) {
2490         // mid is the list head and it is locked. Switch the list head
2491         // to next which is also locked (if not NULL) and also leave
2492         // mid locked:
2493         Atomic::store(list_p, next);
2494       } else {
2495         ObjectMonitor* locked_next = mark_om_ptr(next);
2496         // mid and cur_mid_in_use are locked. Switch cur_mid_in_use's
2497         // next field to locked_next and also leave mid locked:
2498         cur_mid_in_use->set_next_om(locked_next);
2499       }
2500       // At this point mid is disconnected from the in-use list so
2501       // its lock longer has any effects on in-use list.
2502       deflated_count++;
2503       Atomic::dec(count_p);
2504       // mid is current tail in the free_head_p list so NULL terminate it
2505       // (which also unlocks it):
2506       mid->set_next_om(NULL);
2507 
2508       // All the list management is done so move on to the next one:
2509       mid = next;  // mid keeps non-NULL next's locked state
2510       next = next_next;
2511     } else {
2512       // mid is considered in-use if it does not have an associated
2513       // Java object or mid is not old or deflation did not succeed.
2514       // A mid->is_new() node can be seen here when it is freshly
2515       // returned by om_alloc() (and skips the deflation code path).
2516       // A mid->is_old() node can be seen here when deflation failed.
2517       // A mid->is_free() node can be seen here when a fresh node from
2518       // om_alloc() is released by om_release() due to losing the race
2519       // in inflate().
2520 
2521       // All the list management is done so move on to the next one:
2522       if (cur_mid_in_use != NULL) {
2523         om_unlock(cur_mid_in_use);
2524       }
2525       // The next cur_mid_in_use keeps mid's lock state so
2526       // that it is stable for a possible next field change. It
2527       // cannot be modified by om_release() while it is locked.
2528       cur_mid_in_use = mid;
2529       mid = next;  // mid keeps non-NULL next's locked state
2530       next = next_next;
2531 
2532       if (SafepointMechanism::should_block(self) &&
2533           cur_mid_in_use != Atomic::load(list_p) && cur_mid_in_use->is_old()) {
2534         // If a safepoint has started and cur_mid_in_use is not the list
2535         // head and is old, then it is safe to use as saved state. Return
2536         // to the caller before blocking.
2537         *saved_mid_in_use_p = cur_mid_in_use;
2538         om_unlock(cur_mid_in_use);
2539         if (mid != NULL) {
2540           om_unlock(mid);
2541         }
2542         return deflated_count;
2543       }
2544     }
2545     if (mid == NULL) {
2546       if (cur_mid_in_use != NULL) {
2547         om_unlock(cur_mid_in_use);
2548       }
2549       break;  // Reached end of the list so nothing more to deflate.
2550     }
2551 
2552     // The current mid's next field is locked at this point. If we have
2553     // a cur_mid_in_use, then it is also locked at this point.
2554   }
2555   // We finished the list without a safepoint starting so there's
2556   // no need to save state.
2557   *saved_mid_in_use_p = NULL;
2558   return deflated_count;
2559 }
2560 
2561 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2562   counters->n_in_use = 0;              // currently associated with objects
2563   counters->n_in_circulation = 0;      // extant
2564   counters->n_scavenged = 0;           // reclaimed (global and per-thread)
2565   counters->per_thread_scavenged = 0;  // per-thread scavenge total
2566   counters->per_thread_times = 0.0;    // per-thread scavenge times
2567 }
2568 
2569 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2570   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2571 
2572   if (AsyncDeflateIdleMonitors) {
2573     // Nothing to do when global idle ObjectMonitors are deflated using
2574     // a JavaThread unless a special deflation has been requested.
2575     if (!is_special_deflation_requested()) {
2576       return;
2577     }
2578   }
2579 
2580   bool deflated = false;
2581 
2582   ObjectMonitor* free_head_p = NULL;  // Local SLL of scavenged monitors
2583   ObjectMonitor* free_tail_p = NULL;
2584   elapsedTimer timer;
2585 
2586   if (log_is_enabled(Info, monitorinflation)) {
2587     timer.start();
2588   }
2589 
2590   // Note: the thread-local monitors lists get deflated in
2591   // a separate pass. See deflate_thread_local_monitors().
2592 
2593   // For moribund threads, scan om_list_globals._in_use_list
2594   int deflated_count = 0;
2595   if (Atomic::load(&om_list_globals._in_use_list) != NULL) {
2596     // Update n_in_circulation before om_list_globals._in_use_count is
2597     // updated by deflation.
2598     Atomic::add(&counters->n_in_circulation,
2599                 Atomic::load(&om_list_globals._in_use_count));


2612 #endif
2613     assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2614     prepend_list_to_global_free_list(free_head_p, free_tail_p, deflated_count);
2615     Atomic::add(&counters->n_scavenged, deflated_count);
2616   }
2617   timer.stop();
2618 
2619   LogStreamHandle(Debug, monitorinflation) lsh_debug;
2620   LogStreamHandle(Info, monitorinflation) lsh_info;
2621   LogStream* ls = NULL;
2622   if (log_is_enabled(Debug, monitorinflation)) {
2623     ls = &lsh_debug;
2624   } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2625     ls = &lsh_info;
2626   }
2627   if (ls != NULL) {
2628     ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2629   }
2630 }
2631 
2632 class HandshakeForDeflation : public HandshakeClosure {
2633  public:
2634   HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
2635 
2636   void do_thread(Thread* thread) {
2637     log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
2638                                 INTPTR_FORMAT, p2i(thread));
2639   }
2640 };
2641 
2642 void ObjectSynchronizer::deflate_idle_monitors_using_JT() {
2643   assert(AsyncDeflateIdleMonitors, "sanity check");
2644 
2645   // Deflate any global idle monitors.
2646   deflate_global_idle_monitors_using_JT();
2647 
2648   int count = 0;
2649   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2650     if (Atomic::load(&jt->om_in_use_count) > 0 && !jt->is_exiting()) {
2651       // This JavaThread is using ObjectMonitors so deflate any that
2652       // are idle unless this JavaThread is exiting; do not race with
2653       // ObjectSynchronizer::om_flush().
2654       deflate_per_thread_idle_monitors_using_JT(jt);
2655       count++;
2656     }
2657   }
2658   if (count > 0) {
2659     log_debug(monitorinflation)("did async deflation of idle monitors for %d thread(s).", count);
2660   }
2661 
2662   log_info(monitorinflation)("async global_population=%d, global_in_use_count=%d, "
2663                              "global_free_count=%d, global_wait_count=%d",
2664                              Atomic::load(&om_list_globals._population),
2665                              Atomic::load(&om_list_globals._in_use_count),
2666                              Atomic::load(&om_list_globals._free_count),
2667                              Atomic::load(&om_list_globals._wait_count));
2668 
2669   // The ServiceThread's async deflation request has been processed.
2670   set_is_async_deflation_requested(false);
2671 
2672   if (HandshakeAfterDeflateIdleMonitors &&
2673       Atomic::load(&om_list_globals._wait_count) > 0) {
2674     // There are deflated ObjectMonitors waiting for a handshake
2675     // (or a safepoint) for safety.
2676 
2677     ObjectMonitor* list = Atomic::load(&om_list_globals._wait_list);
2678     ADIM_guarantee(list != NULL, "om_list_globals._wait_list must not be NULL");
2679     int count = Atomic::load(&om_list_globals._wait_count);
2680     Atomic::store(&om_list_globals._wait_count, 0);
2681     Atomic::store(&om_list_globals._wait_list, (ObjectMonitor*)NULL);
2682 
2683     // Find the tail for prepend_list_to_common(). No need to mark
2684     // ObjectMonitors for this list walk since only the deflater
2685     // thread manages the wait list.
2686     int l_count = 0;
2687     ObjectMonitor* tail = NULL;
2688     for (ObjectMonitor* n = list; n != NULL; n = unmarked_next(n)) {
2689       tail = n;
2690       l_count++;
2691     }
2692     ADIM_guarantee(count == l_count, "count=%d != l_count=%d", count, l_count);
2693 
2694     // Will execute a safepoint if !ThreadLocalHandshakes:
2695     HandshakeForDeflation hfd_hc;
2696     Handshake::execute(&hfd_hc);
2697 
2698     prepend_list_to_common(list, tail, count, &om_list_globals._free_list,
2699                            &om_list_globals._free_count);
2700 
2701     log_info(monitorinflation)("moved %d idle monitors from global waiting list to global free list", count);
2702   }
2703 }
2704 
2705 // Deflate global idle ObjectMonitors using a JavaThread.
2706 //
2707 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2708   assert(AsyncDeflateIdleMonitors, "sanity check");
2709   assert(Thread::current()->is_Java_thread(), "precondition");
2710   JavaThread* self = JavaThread::current();
2711 
2712   deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2713 }
2714 
2715 // Deflate the specified JavaThread's idle ObjectMonitors using a JavaThread.
2716 //
2717 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT(JavaThread* target) {
2718   assert(AsyncDeflateIdleMonitors, "sanity check");
2719   assert(Thread::current()->is_Java_thread(), "precondition");
2720 
2721   deflate_common_idle_monitors_using_JT(false /* !is_global */, target);
2722 }
2723 
2724 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2725 //
2726 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* target) {
2727   JavaThread* self = JavaThread::current();
2728 
2729   int deflated_count = 0;
2730   ObjectMonitor* free_head_p = NULL;  // Local SLL of scavenged ObjectMonitors
2731   ObjectMonitor* free_tail_p = NULL;
2732   ObjectMonitor* saved_mid_in_use_p = NULL;
2733   elapsedTimer timer;
2734 
2735   if (log_is_enabled(Info, monitorinflation)) {
2736     timer.start();
2737   }
2738 
2739   if (is_global) {
2740     OM_PERFDATA_OP(MonExtant, set_value(Atomic::load(&om_list_globals._in_use_count)));
2741   } else {
2742     OM_PERFDATA_OP(MonExtant, inc(Atomic::load(&target->om_in_use_count)));
2743   }
2744 
2745   do {
2746     int local_deflated_count;
2747     if (is_global) {
2748       local_deflated_count =
2749           deflate_monitor_list_using_JT(&om_list_globals._in_use_list,
2750                                         &om_list_globals._in_use_count,
2751                                         &free_head_p, &free_tail_p,
2752                                         &saved_mid_in_use_p);
2753     } else {
2754       local_deflated_count = deflate_monitor_list_using_JT(&target->om_in_use_list, &target->om_in_use_count, &free_head_p, &free_tail_p, &saved_mid_in_use_p);
2755     }
2756     deflated_count += local_deflated_count;
2757 
2758     if (free_head_p != NULL) {
2759       // Move the deflated ObjectMonitors to the global free list.
2760       guarantee(free_tail_p != NULL && local_deflated_count > 0, "free_tail_p=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(free_tail_p), local_deflated_count);
2761       // Note: The target thread can be doing an om_alloc() that
2762       // is trying to prepend an ObjectMonitor on its in-use list
2763       // at the same time that we have deflated the current in-use
2764       // list head and put it on the local free list. prepend_to_common()
2765       // will detect the race and retry which avoids list corruption,
2766       // but the next field in free_tail_p can flicker to marked
2767       // and then unmarked while prepend_to_common() is sorting it
2768       // all out.
2769 #ifdef ASSERT
2770       ObjectMonitor* l_next_om = unmarked_next(free_tail_p);
2771 #endif
2772       assert(l_next_om == NULL, "must be NULL: _next_om=" INTPTR_FORMAT, p2i(l_next_om));
2773 
2774       if (HandshakeAfterDeflateIdleMonitors) {
2775         prepend_list_to_global_wait_list(free_head_p, free_tail_p, local_deflated_count);
2776       } else {
2777         prepend_list_to_global_free_list(free_head_p, free_tail_p, local_deflated_count);
2778       }
2779 
2780       OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2781     }
2782 
2783     if (saved_mid_in_use_p != NULL) {
2784       // deflate_monitor_list_using_JT() detected a safepoint starting.
2785       timer.stop();
2786       {
2787         if (is_global) {
2788           log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2789         } else {
2790           log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(target));
2791         }
2792         assert(SafepointMechanism::should_block(self), "sanity check");
2793         ThreadBlockInVM blocker(self);
2794       }
2795       // Prepare for another loop after the safepoint.
2796       free_head_p = NULL;
2797       free_tail_p = NULL;
2798       if (log_is_enabled(Info, monitorinflation)) {
2799         timer.start();
2800       }
2801     }
2802   } while (saved_mid_in_use_p != NULL);
2803   timer.stop();
2804 
2805   LogStreamHandle(Debug, monitorinflation) lsh_debug;
2806   LogStreamHandle(Info, monitorinflation) lsh_info;
2807   LogStream* ls = NULL;
2808   if (log_is_enabled(Debug, monitorinflation)) {
2809     ls = &lsh_debug;
2810   } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2811     ls = &lsh_info;
2812   }
2813   if (ls != NULL) {
2814     if (is_global) {
2815       ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2816     } else {
2817       ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(target), timer.seconds(), deflated_count);
2818     }
2819   }
2820 }
2821 
2822 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2823   // Report the cumulative time for deflating each thread's idle
2824   // monitors. Note: if the work is split among more than one
2825   // worker thread, then the reported time will likely be more
2826   // than a beginning to end measurement of the phase.
2827   log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
2828 
2829   bool needs_special_deflation = is_special_deflation_requested();
2830   if (AsyncDeflateIdleMonitors && !needs_special_deflation) {
2831     // Nothing to do when idle ObjectMonitors are deflated using
2832     // a JavaThread unless a special deflation has been requested.
2833     return;
2834   }
2835 
2836   if (log_is_enabled(Debug, monitorinflation)) {
2837     // exit_globals()'s call to audit_and_print_stats() is done
2838     // at the Info level and not at a safepoint.
2839     // For async deflation, audit_and_print_stats() is called in
2840     // ObjectSynchronizer::do_safepoint_work() at the Debug level
2841     // at a safepoint.
2842     ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2843   } else if (log_is_enabled(Info, monitorinflation)) {
2844     log_info(monitorinflation)("global_population=%d, global_in_use_count=%d, "
2845                                "global_free_count=%d, global_wait_count=%d",
2846                                Atomic::load(&om_list_globals._population),
2847                                Atomic::load(&om_list_globals._in_use_count),
2848                                Atomic::load(&om_list_globals._free_count),
2849                                Atomic::load(&om_list_globals._wait_count));
2850   }
2851 
2852   Atomic::store(&_forceMonitorScavenge, 0);    // Reset
2853 
2854   OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
2855   OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
2856 
2857   GVars.stw_random = os::random();
2858   GVars.stw_cycle++;
2859 
2860   if (needs_special_deflation) {
2861     set_is_special_deflation_requested(false);  // special deflation is done
2862   }
2863 }
2864 
2865 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2866   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2867 
2868   if (AsyncDeflateIdleMonitors && !is_special_deflation_requested()) {
2869     // Nothing to do if a special deflation has NOT been requested.
2870     return;
2871   }
2872 
2873   ObjectMonitor* free_head_p = NULL;  // Local SLL of scavenged monitors
2874   ObjectMonitor* free_tail_p = NULL;
2875   elapsedTimer timer;
2876 
2877   if (log_is_enabled(Info, safepoint, cleanup) ||
2878       log_is_enabled(Info, monitorinflation)) {
2879     timer.start();
2880   }
2881 
2882   // Update n_in_circulation before om_in_use_count is updated by deflation.
2883   Atomic::add(&counters->n_in_circulation, Atomic::load(&thread->om_in_use_count));
2884 
2885   int deflated_count = deflate_monitor_list(&thread->om_in_use_list, &thread->om_in_use_count, &free_head_p, &free_tail_p);
2886   Atomic::add(&counters->n_in_use, Atomic::load(&thread->om_in_use_count));
2887 
2888   if (free_head_p != NULL) {
2889     // Move the deflated ObjectMonitors back to the global free list.
2890     guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2891 #ifdef ASSERT
2892     ObjectMonitor* l_next_om = free_tail_p->next_om();


3024   if (Atomic::load(&om_list_globals._population) == chk_om_population) {
3025     ls->print_cr("global_population=%d equals chk_om_population=%d",
3026                  Atomic::load(&om_list_globals._population), chk_om_population);
3027   } else {
3028     // With fine grained locks on the monitor lists, it is possible for
3029     // log_monitor_list_counts() to return a value that doesn't match
3030     // om_list_globals._population. So far a higher value has been
3031     // seen in testing so something is being double counted by
3032     // log_monitor_list_counts().
3033     ls->print_cr("WARNING: global_population=%d is not equal to "
3034                  "chk_om_population=%d",
3035                  Atomic::load(&om_list_globals._population), chk_om_population);
3036   }
3037 
3038   // Check om_list_globals._in_use_list and om_list_globals._in_use_count:
3039   chk_global_in_use_list_and_count(ls, &error_cnt);
3040 
3041   // Check om_list_globals._free_list and om_list_globals._free_count:
3042   chk_global_free_list_and_count(ls, &error_cnt);
3043 
3044   if (HandshakeAfterDeflateIdleMonitors) {
3045     // Check om_list_globals._wait_list and om_list_globals._wait_count:
3046     chk_global_wait_list_and_count(ls, &error_cnt);
3047   }
3048 
3049   ls->print_cr("Checking per-thread lists:");
3050 
3051   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3052     // Check om_in_use_list and om_in_use_count:
3053     chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
3054 
3055     // Check om_free_list and om_free_count:
3056     chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
3057   }
3058 
3059   if (error_cnt == 0) {
3060     ls->print_cr("No errors found in monitor list checks.");
3061   } else {
3062     log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
3063   }
3064 
3065   if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
3066       (!on_exit && log_is_enabled(Trace, monitorinflation))) {
3067     // When exiting this log output is at the Info level. When called
3068     // at a safepoint, this log output is at the Trace level since


3079 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
3080                                         outputStream * out, int *error_cnt_p) {
3081   stringStream ss;
3082   if (n->is_busy()) {
3083     if (jt != NULL) {
3084       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3085                     ": free per-thread monitor must not be busy: %s", p2i(jt),
3086                     p2i(n), n->is_busy_to_string(&ss));
3087     } else {
3088       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
3089                     "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
3090     }
3091     *error_cnt_p = *error_cnt_p + 1;
3092   }
3093   if (n->header().value() != 0) {
3094     if (jt != NULL) {
3095       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3096                     ": free per-thread monitor must have NULL _header "
3097                     "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
3098                     n->header().value());
3099       *error_cnt_p = *error_cnt_p + 1;
3100     } else if (!AsyncDeflateIdleMonitors) {
3101       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
3102                     "must have NULL _header field: _header=" INTPTR_FORMAT,
3103                     p2i(n), n->header().value());

3104       *error_cnt_p = *error_cnt_p + 1;
3105     }
3106   }
3107   if (n->object() != NULL) {
3108     if (jt != NULL) {
3109       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
3110                     ": free per-thread monitor must have NULL _object "
3111                     "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
3112                     p2i(n->object()));
3113     } else {
3114       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
3115                     "must have NULL _object field: _object=" INTPTR_FORMAT,
3116                     p2i(n), p2i(n->object()));
3117     }
3118     *error_cnt_p = *error_cnt_p + 1;
3119   }
3120 }
3121 
3122 // Lock the next ObjectMonitor for traversal and unlock the current
3123 // ObjectMonitor. Returns the next ObjectMonitor if there is one.
3124 // Otherwise returns NULL (after unlocking the current ObjectMonitor).
3125 // This function is used by the various list walker functions to
3126 // safely walk a list without allowing an ObjectMonitor to be moved


3152       if (cur == NULL) {
3153         break;
3154       }
3155     }
3156   }
3157   int l_free_count = Atomic::load(&om_list_globals._free_count);
3158   if (l_free_count == chk_om_free_count) {
3159     out->print_cr("global_free_count=%d equals chk_om_free_count=%d",
3160                   l_free_count, chk_om_free_count);
3161   } else {
3162     // With fine grained locks on om_list_globals._free_list, it
3163     // is possible for an ObjectMonitor to be prepended to
3164     // om_list_globals._free_list after we started calculating
3165     // chk_om_free_count so om_list_globals._free_count may not
3166     // match anymore.
3167     out->print_cr("WARNING: global_free_count=%d is not equal to "
3168                   "chk_om_free_count=%d", l_free_count, chk_om_free_count);
3169   }
3170 }
3171 
3172 // Check the global wait list and count; log the results of the checks.
3173 void ObjectSynchronizer::chk_global_wait_list_and_count(outputStream * out,
3174                                                         int *error_cnt_p) {
3175   int chk_om_wait_count = 0;
3176   ObjectMonitor* cur = NULL;
3177   if ((cur = get_list_head_locked(&om_list_globals._wait_list)) != NULL) {
3178     // Marked the global wait list head so process the list.
3179     while (true) {
3180       // Rules for om_list_globals._wait_list are the same as for
3181       // om_list_globals._free_list:
3182       chk_free_entry(NULL /* jt */, cur, out, error_cnt_p);
3183       chk_om_wait_count++;
3184 
3185       cur = lock_next_for_traversal(cur);
3186       if (cur == NULL) {
3187         break;
3188       }
3189     }
3190   }
3191   if (Atomic::load(&om_list_globals._wait_count) == chk_om_wait_count) {
3192     out->print_cr("global_wait_count=%d equals chk_om_wait_count=%d",
3193                   Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
3194   } else {
3195     out->print_cr("ERROR: global_wait_count=%d is not equal to "
3196                   "chk_om_wait_count=%d",
3197                   Atomic::load(&om_list_globals._wait_count), chk_om_wait_count);
3198     *error_cnt_p = *error_cnt_p + 1;
3199   }
3200 }
3201 
3202 // Check the global in-use list and count; log the results of the checks.
3203 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
3204                                                           int *error_cnt_p) {
3205   int chk_om_in_use_count = 0;
3206   ObjectMonitor* cur = NULL;
3207   if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
3208     // Marked the global in-use list head so process the list.
3209     while (true) {
3210       chk_in_use_entry(NULL /* jt */, cur, out, error_cnt_p);
3211       chk_om_in_use_count++;
3212 
3213       cur = lock_next_for_traversal(cur);
3214       if (cur == NULL) {
3215         break;
3216       }
3217     }
3218   }
3219   int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
3220   if (l_in_use_count == chk_om_in_use_count) {
3221     out->print_cr("global_in_use_count=%d equals chk_om_in_use_count=%d",


3340   if (l_om_in_use_count == chk_om_in_use_count) {
3341     out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
3342                   "chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
3343                   chk_om_in_use_count);
3344   } else {
3345     out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
3346                   "equal to chk_om_in_use_count=%d", p2i(jt), l_om_in_use_count,
3347                   chk_om_in_use_count);
3348     *error_cnt_p = *error_cnt_p + 1;
3349   }
3350 }
3351 
3352 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
3353 // flags indicate why the entry is in-use, 'object' and 'object type'
3354 // indicate the associated object and its type.
3355 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out) {
3356   stringStream ss;
3357   if (Atomic::load(&om_list_globals._in_use_count) > 0) {
3358     out->print_cr("In-use global monitor info:");
3359     out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
3360     out->print_cr("%18s  %s  %7s  %18s  %18s",
3361                   "monitor", "BHL", "ref_cnt", "object", "object type");
3362     out->print_cr("==================  ===  =======  ==================  ==================");
3363     ObjectMonitor* cur = NULL;
3364     if ((cur = get_list_head_locked(&om_list_globals._in_use_list)) != NULL) {
3365       // Marked the global in-use list head so process the list.
3366       while (true) {
3367         const oop obj = (oop) cur->object();
3368         const markWord mark = cur->header();
3369         ResourceMark rm;
3370         out->print(INTPTR_FORMAT "  %d%d%d  %7d  " INTPTR_FORMAT "  %s", p2i(cur),
3371                    cur->is_busy() != 0, mark.hash() != 0, cur->owner() != NULL,
3372                    (int)cur->ref_count(), p2i(obj), obj->klass()->external_name());
3373         if (cur->is_busy() != 0) {
3374           out->print(" (%s)", cur->is_busy_to_string(&ss));
3375           ss.reset();
3376         }
3377         out->cr();
3378 
3379         cur = lock_next_for_traversal(cur);
3380         if (cur == NULL) {
3381           break;
3382         }
3383       }
3384     }
3385   }
3386 
3387   out->print_cr("In-use per-thread monitor info:");
3388   out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
3389   out->print_cr("%18s  %18s  %s  %7s  %18s  %18s",
3390                 "jt", "monitor", "BHL", "ref_cnt", "object", "object type");
3391   out->print_cr("==================  ==================  ===  =======  ==================  ==================");
3392   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3393     ObjectMonitor* cur = NULL;
3394     if ((cur = get_list_head_locked(&jt->om_in_use_list)) != NULL) {
3395       // Marked the global in-use list head so process the list.
3396       while (true) {
3397         const oop obj = (oop) cur->object();
3398         const markWord mark = cur->header();
3399         ResourceMark rm;
3400         out->print(INTPTR_FORMAT "  " INTPTR_FORMAT "  %d%d%d  %7d  " INTPTR_FORMAT
3401                    "  %s", p2i(jt), p2i(cur), cur->is_busy() != 0,
3402                    mark.hash() != 0, cur->owner() != NULL, (int)cur->ref_count(),
3403                    p2i(obj), obj->klass()->external_name());
3404         if (cur->is_busy() != 0) {
3405           out->print(" (%s)", cur->is_busy_to_string(&ss));
3406           ss.reset();
3407         }
3408         out->cr();
3409 
3410         cur = lock_next_for_traversal(cur);
3411         if (cur == NULL) {
3412           break;
3413         }
3414       }
3415     }
3416   }
3417 
3418   out->flush();
3419 }
3420 
3421 // Log counts for the global and per-thread monitor lists and return
3422 // the population count.
3423 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
3424   int pop_count = 0;
3425   out->print_cr("%18s  %10s  %10s  %10s  %10s",
3426                 "Global Lists:", "InUse", "Free", "Wait", "Total");
3427   out->print_cr("==================  ==========  ==========  ==========  ==========");
3428   int l_in_use_count = Atomic::load(&om_list_globals._in_use_count);
3429   int l_free_count = Atomic::load(&om_list_globals._free_count);
3430   int l_wait_count = Atomic::load(&om_list_globals._wait_count);
3431   out->print_cr("%18s  %10d  %10d  %10d  %10d", "", l_in_use_count,
3432                 l_free_count, l_wait_count,
3433                 Atomic::load(&om_list_globals._population));
3434   pop_count += l_in_use_count + l_free_count;
3435   if (HandshakeAfterDeflateIdleMonitors) {
3436     pop_count += l_wait_count;
3437   }
3438 
3439   out->print_cr("%18s  %10s  %10s  %10s",
3440                 "Per-Thread Lists:", "InUse", "Free", "Provision");
3441   out->print_cr("==================  ==========  ==========  ==========");
3442 
3443   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
3444     int l_om_in_use_count = Atomic::load(&jt->om_in_use_count);
3445     int l_om_free_count = Atomic::load(&jt->om_free_count);
3446     out->print_cr(INTPTR_FORMAT "  %10d  %10d  %10d", p2i(jt),
3447                   l_om_in_use_count, l_om_free_count, jt->om_free_provision);
3448     pop_count += l_om_in_use_count + l_om_free_count;
3449   }
3450   return pop_count;
3451 }
3452 
3453 #ifndef PRODUCT
3454 
3455 // Check if monitor belongs to the monitor cache
3456 // The list is grow-only so it's *relatively* safe to traverse
3457 // the list of extant blocks without taking a lock.
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