1 /*
   2  * Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  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 "oops/markOop.hpp"
  35 #include "oops/oop.inline.hpp"
  36 #include "runtime/atomic.hpp"
  37 #include "runtime/biasedLocking.hpp"
  38 #include "runtime/handles.inline.hpp"
  39 #include "runtime/interfaceSupport.inline.hpp"
  40 #include "runtime/mutexLocker.hpp"
  41 #include "runtime/objectMonitor.hpp"
  42 #include "runtime/objectMonitor.inline.hpp"
  43 #include "runtime/osThread.hpp"
  44 #include "runtime/safepointVerifiers.hpp"
  45 #include "runtime/sharedRuntime.hpp"
  46 #include "runtime/stubRoutines.hpp"
  47 #include "runtime/synchronizer.hpp"
  48 #include "runtime/thread.inline.hpp"
  49 #include "runtime/timer.hpp"
  50 #include "runtime/vframe.hpp"
  51 #include "runtime/vmThread.hpp"
  52 #include "utilities/align.hpp"
  53 #include "utilities/dtrace.hpp"
  54 #include "utilities/events.hpp"
  55 #include "utilities/preserveException.hpp"
  56 
  57 // The "core" versions of monitor enter and exit reside in this file.
  58 // The interpreter and compilers contain specialized transliterated
  59 // variants of the enter-exit fast-path operations.  See i486.ad fast_lock(),
  60 // for instance.  If you make changes here, make sure to modify the
  61 // interpreter, and both C1 and C2 fast-path inline locking code emission.
  62 //
  63 // -----------------------------------------------------------------------------
  64 
  65 #ifdef DTRACE_ENABLED
  66 
  67 // Only bother with this argument setup if dtrace is available
  68 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
  69 
  70 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
  71   char* bytes = NULL;                                                      \
  72   int len = 0;                                                             \
  73   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
  74   Symbol* klassname = ((oop)(obj))->klass()->name();                       \
  75   if (klassname != NULL) {                                                 \
  76     bytes = (char*)klassname->bytes();                                     \
  77     len = klassname->utf8_length();                                        \
  78   }
  79 
  80 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
  81   {                                                                        \
  82     if (DTraceMonitorProbes) {                                             \
  83       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
  84       HOTSPOT_MONITOR_WAIT(jtid,                                           \
  85                            (uintptr_t)(monitor), bytes, len, (millis));    \
  86     }                                                                      \
  87   }
  88 
  89 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
  90 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
  91 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
  92 
  93 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
  94   {                                                                        \
  95     if (DTraceMonitorProbes) {                                             \
  96       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
  97       HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */             \
  98                                     (uintptr_t)(monitor), bytes, len);     \
  99     }                                                                      \
 100   }
 101 
 102 #else //  ndef DTRACE_ENABLED
 103 
 104 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 105 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 106 
 107 #endif // ndef DTRACE_ENABLED
 108 
 109 // This exists only as a workaround of dtrace bug 6254741
 110 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
 111   DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
 112   return 0;
 113 }
 114 
 115 #define NINFLATIONLOCKS 256
 116 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
 117 
 118 // global list of blocks of monitors
 119 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL;
 120 // global monitor free list
 121 ObjectMonitor * volatile ObjectSynchronizer::gFreeList  = NULL;
 122 // global monitor in-use list, for moribund threads,
 123 // monitors they inflated need to be scanned for deflation
 124 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList  = NULL;
 125 // count of entries in gOmInUseList
 126 int ObjectSynchronizer::gOmInUseCount = 0;
 127 
 128 static volatile intptr_t gListLock = 0;      // protects global monitor lists
 129 static volatile int gMonitorFreeCount  = 0;  // # on gFreeList
 130 static volatile int gMonitorPopulation = 0;  // # Extant -- in circulation
 131 
 132 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
 133 
 134 
 135 // =====================> Quick functions
 136 
 137 // The quick_* forms are special fast-path variants used to improve
 138 // performance.  In the simplest case, a "quick_*" implementation could
 139 // simply return false, in which case the caller will perform the necessary
 140 // state transitions and call the slow-path form.
 141 // The fast-path is designed to handle frequently arising cases in an efficient
 142 // manner and is just a degenerate "optimistic" variant of the slow-path.
 143 // returns true  -- to indicate the call was satisfied.
 144 // returns false -- to indicate the call needs the services of the slow-path.
 145 // A no-loitering ordinance is in effect for code in the quick_* family
 146 // operators: safepoints or indefinite blocking (blocking that might span a
 147 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
 148 // entry.
 149 //
 150 // Consider: An interesting optimization is to have the JIT recognize the
 151 // following common idiom:
 152 //   synchronized (someobj) { .... ; notify(); }
 153 // That is, we find a notify() or notifyAll() call that immediately precedes
 154 // the monitorexit operation.  In that case the JIT could fuse the operations
 155 // into a single notifyAndExit() runtime primitive.
 156 
 157 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
 158   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 159   assert(self->is_Java_thread(), "invariant");
 160   assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
 161   NoSafepointVerifier nsv;
 162   if (obj == NULL) return false;  // slow-path for invalid obj
 163   const markOop mark = obj->mark();
 164 
 165   if (mark->has_locker() && self->is_lock_owned((address)mark->locker())) {
 166     // Degenerate notify
 167     // stack-locked by caller so by definition the implied waitset is empty.
 168     return true;
 169   }
 170 
 171   if (mark->has_monitor()) {
 172     ObjectMonitor * const mon = mark->monitor();
 173     assert(oopDesc::equals((oop) mon->object(), obj), "invariant");
 174     if (mon->owner() != self) return false;  // slow-path for IMS exception
 175 
 176     if (mon->first_waiter() != NULL) {
 177       // We have one or more waiters. Since this is an inflated monitor
 178       // that we own, we can transfer one or more threads from the waitset
 179       // to the entrylist here and now, avoiding the slow-path.
 180       if (all) {
 181         DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
 182       } else {
 183         DTRACE_MONITOR_PROBE(notify, mon, obj, self);
 184       }
 185       int tally = 0;
 186       do {
 187         mon->INotify(self);
 188         ++tally;
 189       } while (mon->first_waiter() != NULL && all);
 190       OM_PERFDATA_OP(Notifications, inc(tally));
 191     }
 192     return true;
 193   }
 194 
 195   // biased locking and any other IMS exception states take the slow-path
 196   return false;
 197 }
 198 
 199 
 200 // The LockNode emitted directly at the synchronization site would have
 201 // been too big if it were to have included support for the cases of inflated
 202 // recursive enter and exit, so they go here instead.
 203 // Note that we can't safely call AsyncPrintJavaStack() from within
 204 // quick_enter() as our thread state remains _in_Java.
 205 
 206 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
 207                                      BasicLock * lock) {
 208   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 209   assert(Self->is_Java_thread(), "invariant");
 210   assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
 211   NoSafepointVerifier nsv;
 212   if (obj == NULL) return false;       // Need to throw NPE
 213   const markOop mark = obj->mark();
 214 
 215   if (mark->has_monitor()) {
 216     ObjectMonitor * const m = mark->monitor();
 217     assert(oopDesc::equals((oop) m->object(), obj), "invariant");
 218     Thread * const owner = (Thread *) m->_owner;
 219 
 220     // Lock contention and Transactional Lock Elision (TLE) diagnostics
 221     // and observability
 222     // Case: light contention possibly amenable to TLE
 223     // Case: TLE inimical operations such as nested/recursive synchronization
 224 
 225     if (owner == Self) {
 226       m->_recursions++;
 227       return true;
 228     }
 229 
 230     // This Java Monitor is inflated so obj's header will never be
 231     // displaced to this thread's BasicLock. Make the displaced header
 232     // non-NULL so this BasicLock is not seen as recursive nor as
 233     // being locked. We do this unconditionally so that this thread's
 234     // BasicLock cannot be mis-interpreted by any stack walkers. For
 235     // performance reasons, stack walkers generally first check for
 236     // Biased Locking in the object's header, the second check is for
 237     // stack-locking in the object's header, the third check is for
 238     // recursive stack-locking in the displaced header in the BasicLock,
 239     // and last are the inflated Java Monitor (ObjectMonitor) checks.
 240     lock->set_displaced_header(markOopDesc::unused_mark());
 241 
 242     if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
 243       assert(m->_recursions == 0, "invariant");
 244       assert(m->_owner == Self, "invariant");
 245       return true;
 246     }
 247   }
 248 
 249   // Note that we could inflate in quick_enter.
 250   // This is likely a useful optimization
 251   // Critically, in quick_enter() we must not:
 252   // -- perform bias revocation, or
 253   // -- block indefinitely, or
 254   // -- reach a safepoint
 255 
 256   return false;        // revert to slow-path
 257 }
 258 
 259 // -----------------------------------------------------------------------------
 260 //  Fast Monitor Enter/Exit
 261 // This the fast monitor enter. The interpreter and compiler use
 262 // some assembly copies of this code. Make sure update those code
 263 // if the following function is changed. The implementation is
 264 // extremely sensitive to race condition. Be careful.
 265 
 266 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
 267                                     bool attempt_rebias, TRAPS) {
 268   if (UseBiasedLocking) {
 269     if (!SafepointSynchronize::is_at_safepoint()) {
 270       BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
 271       if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
 272         return;
 273       }
 274     } else {
 275       assert(!attempt_rebias, "can not rebias toward VM thread");
 276       BiasedLocking::revoke_at_safepoint(obj);
 277     }
 278     assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 279   }
 280 
 281   slow_enter(obj, lock, THREAD);
 282 }
 283 
 284 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
 285   markOop mark = object->mark();
 286   // We cannot check for Biased Locking if we are racing an inflation.
 287   assert(mark == markOopDesc::INFLATING() ||
 288          !mark->has_bias_pattern(), "should not see bias pattern here");
 289 
 290   markOop dhw = lock->displaced_header();
 291   if (dhw == NULL) {
 292     // If the displaced header is NULL, then this exit matches up with
 293     // a recursive enter. No real work to do here except for diagnostics.
 294 #ifndef PRODUCT
 295     if (mark != markOopDesc::INFLATING()) {
 296       // Only do diagnostics if we are not racing an inflation. Simply
 297       // exiting a recursive enter of a Java Monitor that is being
 298       // inflated is safe; see the has_monitor() comment below.
 299       assert(!mark->is_neutral(), "invariant");
 300       assert(!mark->has_locker() ||
 301              THREAD->is_lock_owned((address)mark->locker()), "invariant");
 302       if (mark->has_monitor()) {
 303         // The BasicLock's displaced_header is marked as a recursive
 304         // enter and we have an inflated Java Monitor (ObjectMonitor).
 305         // This is a special case where the Java Monitor was inflated
 306         // after this thread entered the stack-lock recursively. When a
 307         // Java Monitor is inflated, we cannot safely walk the Java
 308         // Monitor owner's stack and update the BasicLocks because a
 309         // Java Monitor can be asynchronously inflated by a thread that
 310         // does not own the Java Monitor.
 311         ObjectMonitor * m = mark->monitor();
 312         assert(((oop)(m->object()))->mark() == mark, "invariant");
 313         assert(m->is_entered(THREAD), "invariant");
 314       }
 315     }
 316 #endif
 317     return;
 318   }
 319 
 320   if (mark == (markOop) lock) {
 321     // If the object is stack-locked by the current thread, try to
 322     // swing the displaced header from the BasicLock back to the mark.
 323     assert(dhw->is_neutral(), "invariant");
 324     if (object->cas_set_mark(dhw, mark) == mark) {
 325       return;
 326     }
 327   }
 328 
 329   // We have to take the slow-path of possible inflation and then exit.
 330   inflate(THREAD, object, inflate_cause_vm_internal)->exit(true, THREAD);
 331 }
 332 
 333 // -----------------------------------------------------------------------------
 334 // Interpreter/Compiler Slow Case
 335 // This routine is used to handle interpreter/compiler slow case
 336 // We don't need to use fast path here, because it must have been
 337 // failed in the interpreter/compiler code.
 338 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
 339   markOop mark = obj->mark();
 340   assert(!mark->has_bias_pattern(), "should not see bias pattern here");
 341 
 342   if (mark->is_neutral()) {
 343     // Anticipate successful CAS -- the ST of the displaced mark must
 344     // be visible <= the ST performed by the CAS.
 345     lock->set_displaced_header(mark);
 346     if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
 347       return;
 348     }
 349     // Fall through to inflate() ...
 350   } else if (mark->has_locker() &&
 351              THREAD->is_lock_owned((address)mark->locker())) {
 352     assert(lock != mark->locker(), "must not re-lock the same lock");
 353     assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
 354     lock->set_displaced_header(NULL);
 355     return;
 356   }
 357 
 358   // The object header will never be displaced to this lock,
 359   // so it does not matter what the value is, except that it
 360   // must be non-zero to avoid looking like a re-entrant lock,
 361   // and must not look locked either.
 362   lock->set_displaced_header(markOopDesc::unused_mark());
 363   inflate(THREAD, obj(), inflate_cause_monitor_enter)->enter(THREAD);
 364 }
 365 
 366 // This routine is used to handle interpreter/compiler slow case
 367 // We don't need to use fast path here, because it must have
 368 // failed in the interpreter/compiler code. Simply use the heavy
 369 // weight monitor should be ok, unless someone find otherwise.
 370 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
 371   fast_exit(object, lock, THREAD);
 372 }
 373 
 374 // -----------------------------------------------------------------------------
 375 // Class Loader  support to workaround deadlocks on the class loader lock objects
 376 // Also used by GC
 377 // complete_exit()/reenter() are used to wait on a nested lock
 378 // i.e. to give up an outer lock completely and then re-enter
 379 // Used when holding nested locks - lock acquisition order: lock1 then lock2
 380 //  1) complete_exit lock1 - saving recursion count
 381 //  2) wait on lock2
 382 //  3) when notified on lock2, unlock lock2
 383 //  4) reenter lock1 with original recursion count
 384 //  5) lock lock2
 385 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 386 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
 387   if (UseBiasedLocking) {
 388     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 389     assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 390   }
 391 
 392   ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
 393 
 394   return monitor->complete_exit(THREAD);
 395 }
 396 
 397 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 398 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
 399   if (UseBiasedLocking) {
 400     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 401     assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 402   }
 403 
 404   ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
 405 
 406   monitor->reenter(recursion, THREAD);
 407 }
 408 // -----------------------------------------------------------------------------
 409 // JNI locks on java objects
 410 // NOTE: must use heavy weight monitor to handle jni monitor enter
 411 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
 412   // the current locking is from JNI instead of Java code
 413   if (UseBiasedLocking) {
 414     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 415     assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 416   }
 417   THREAD->set_current_pending_monitor_is_from_java(false);
 418   inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
 419   THREAD->set_current_pending_monitor_is_from_java(true);
 420 }
 421 
 422 // NOTE: must use heavy weight monitor to handle jni monitor exit
 423 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
 424   if (UseBiasedLocking) {
 425     Handle h_obj(THREAD, obj);
 426     BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
 427     obj = h_obj();
 428   }
 429   assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 430 
 431   ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
 432   // If this thread has locked the object, exit the monitor.  Note:  can't use
 433   // monitor->check(CHECK); must exit even if an exception is pending.
 434   if (monitor->check(THREAD)) {
 435     monitor->exit(true, THREAD);
 436   }
 437 }
 438 
 439 // -----------------------------------------------------------------------------
 440 // Internal VM locks on java objects
 441 // standard constructor, allows locking failures
 442 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
 443   _dolock = doLock;
 444   _thread = thread;
 445   debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
 446   _obj = obj;
 447 
 448   if (_dolock) {
 449     ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
 450   }
 451 }
 452 
 453 ObjectLocker::~ObjectLocker() {
 454   if (_dolock) {
 455     ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
 456   }
 457 }
 458 
 459 
 460 // -----------------------------------------------------------------------------
 461 //  Wait/Notify/NotifyAll
 462 // NOTE: must use heavy weight monitor to handle wait()
 463 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 464   if (UseBiasedLocking) {
 465     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 466     assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 467   }
 468   if (millis < 0) {
 469     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 470   }
 471   ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
 472 
 473   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
 474   monitor->wait(millis, true, THREAD);
 475 
 476   // This dummy call is in place to get around dtrace bug 6254741.  Once
 477   // that's fixed we can uncomment the following line, remove the call
 478   // and change this function back into a "void" func.
 479   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 480   return dtrace_waited_probe(monitor, obj, THREAD);
 481 }
 482 
 483 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
 484   if (UseBiasedLocking) {
 485     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 486     assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 487   }
 488   if (millis < 0) {
 489     THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 490   }
 491   inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD);
 492 }
 493 
 494 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 495   if (UseBiasedLocking) {
 496     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 497     assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 498   }
 499 
 500   markOop mark = obj->mark();
 501   if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
 502     return;
 503   }
 504   inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD);
 505 }
 506 
 507 // NOTE: see comment of notify()
 508 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 509   if (UseBiasedLocking) {
 510     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 511     assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 512   }
 513 
 514   markOop mark = obj->mark();
 515   if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
 516     return;
 517   }
 518   inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD);
 519 }
 520 
 521 // -----------------------------------------------------------------------------
 522 // Hash Code handling
 523 //
 524 // Performance concern:
 525 // OrderAccess::storestore() calls release() which at one time stored 0
 526 // into the global volatile OrderAccess::dummy variable. This store was
 527 // unnecessary for correctness. Many threads storing into a common location
 528 // causes considerable cache migration or "sloshing" on large SMP systems.
 529 // As such, I avoided using OrderAccess::storestore(). In some cases
 530 // OrderAccess::fence() -- which incurs local latency on the executing
 531 // processor -- is a better choice as it scales on SMP systems.
 532 //
 533 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
 534 // a discussion of coherency costs. Note that all our current reference
 535 // platforms provide strong ST-ST order, so the issue is moot on IA32,
 536 // x64, and SPARC.
 537 //
 538 // As a general policy we use "volatile" to control compiler-based reordering
 539 // and explicit fences (barriers) to control for architectural reordering
 540 // performed by the CPU(s) or platform.
 541 
 542 struct SharedGlobals {
 543   char         _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
 544   // These are highly shared mostly-read variables.
 545   // To avoid false-sharing they need to be the sole occupants of a cache line.
 546   volatile int stwRandom;
 547   volatile int stwCycle;
 548   DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
 549   // Hot RW variable -- Sequester to avoid false-sharing
 550   volatile int hcSequence;
 551   DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
 552 };
 553 
 554 static SharedGlobals GVars;
 555 static int MonitorScavengeThreshold = 1000000;
 556 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
 557 
 558 static markOop ReadStableMark(oop obj) {
 559   markOop mark = obj->mark();
 560   if (!mark->is_being_inflated()) {
 561     return mark;       // normal fast-path return
 562   }
 563 
 564   int its = 0;
 565   for (;;) {
 566     markOop mark = obj->mark();
 567     if (!mark->is_being_inflated()) {
 568       return mark;    // normal fast-path return
 569     }
 570 
 571     // The object is being inflated by some other thread.
 572     // The caller of ReadStableMark() must wait for inflation to complete.
 573     // Avoid live-lock
 574     // TODO: consider calling SafepointSynchronize::do_call_back() while
 575     // spinning to see if there's a safepoint pending.  If so, immediately
 576     // yielding or blocking would be appropriate.  Avoid spinning while
 577     // there is a safepoint pending.
 578     // TODO: add inflation contention performance counters.
 579     // TODO: restrict the aggregate number of spinners.
 580 
 581     ++its;
 582     if (its > 10000 || !os::is_MP()) {
 583       if (its & 1) {
 584         os::naked_yield();
 585       } else {
 586         // Note that the following code attenuates the livelock problem but is not
 587         // a complete remedy.  A more complete solution would require that the inflating
 588         // thread hold the associated inflation lock.  The following code simply restricts
 589         // the number of spinners to at most one.  We'll have N-2 threads blocked
 590         // on the inflationlock, 1 thread holding the inflation lock and using
 591         // a yield/park strategy, and 1 thread in the midst of inflation.
 592         // A more refined approach would be to change the encoding of INFLATING
 593         // to allow encapsulation of a native thread pointer.  Threads waiting for
 594         // inflation to complete would use CAS to push themselves onto a singly linked
 595         // list rooted at the markword.  Once enqueued, they'd loop, checking a per-thread flag
 596         // and calling park().  When inflation was complete the thread that accomplished inflation
 597         // would detach the list and set the markword to inflated with a single CAS and
 598         // then for each thread on the list, set the flag and unpark() the thread.
 599         // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
 600         // wakes at most one thread whereas we need to wake the entire list.
 601         int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
 602         int YieldThenBlock = 0;
 603         assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
 604         assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
 605         Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
 606         while (obj->mark() == markOopDesc::INFLATING()) {
 607           // Beware: NakedYield() is advisory and has almost no effect on some platforms
 608           // so we periodically call Self->_ParkEvent->park(1).
 609           // We use a mixed spin/yield/block mechanism.
 610           if ((YieldThenBlock++) >= 16) {
 611             Thread::current()->_ParkEvent->park(1);
 612           } else {
 613             os::naked_yield();
 614           }
 615         }
 616         Thread::muxRelease(gInflationLocks + ix);
 617       }
 618     } else {
 619       SpinPause();       // SMP-polite spinning
 620     }
 621   }
 622 }
 623 
 624 // hashCode() generation :
 625 //
 626 // Possibilities:
 627 // * MD5Digest of {obj,stwRandom}
 628 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
 629 // * A DES- or AES-style SBox[] mechanism
 630 // * One of the Phi-based schemes, such as:
 631 //   2654435761 = 2^32 * Phi (golden ratio)
 632 //   HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
 633 // * A variation of Marsaglia's shift-xor RNG scheme.
 634 // * (obj ^ stwRandom) is appealing, but can result
 635 //   in undesirable regularity in the hashCode values of adjacent objects
 636 //   (objects allocated back-to-back, in particular).  This could potentially
 637 //   result in hashtable collisions and reduced hashtable efficiency.
 638 //   There are simple ways to "diffuse" the middle address bits over the
 639 //   generated hashCode values:
 640 
 641 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
 642   intptr_t value = 0;
 643   if (hashCode == 0) {
 644     // This form uses global Park-Miller RNG.
 645     // On MP system we'll have lots of RW access to a global, so the
 646     // mechanism induces lots of coherency traffic.
 647     value = os::random();
 648   } else if (hashCode == 1) {
 649     // This variation has the property of being stable (idempotent)
 650     // between STW operations.  This can be useful in some of the 1-0
 651     // synchronization schemes.
 652     intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
 653     value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
 654   } else if (hashCode == 2) {
 655     value = 1;            // for sensitivity testing
 656   } else if (hashCode == 3) {
 657     value = ++GVars.hcSequence;
 658   } else if (hashCode == 4) {
 659     value = cast_from_oop<intptr_t>(obj);
 660   } else {
 661     // Marsaglia's xor-shift scheme with thread-specific state
 662     // This is probably the best overall implementation -- we'll
 663     // likely make this the default in future releases.
 664     unsigned t = Self->_hashStateX;
 665     t ^= (t << 11);
 666     Self->_hashStateX = Self->_hashStateY;
 667     Self->_hashStateY = Self->_hashStateZ;
 668     Self->_hashStateZ = Self->_hashStateW;
 669     unsigned v = Self->_hashStateW;
 670     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
 671     Self->_hashStateW = v;
 672     value = v;
 673   }
 674 
 675   value &= markOopDesc::hash_mask;
 676   if (value == 0) value = 0xBAD;
 677   assert(value != markOopDesc::no_hash, "invariant");
 678   return value;
 679 }
 680 
 681 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
 682   if (UseBiasedLocking) {
 683     // NOTE: many places throughout the JVM do not expect a safepoint
 684     // to be taken here, in particular most operations on perm gen
 685     // objects. However, we only ever bias Java instances and all of
 686     // the call sites of identity_hash that might revoke biases have
 687     // been checked to make sure they can handle a safepoint. The
 688     // added check of the bias pattern is to avoid useless calls to
 689     // thread-local storage.
 690     if (obj->mark()->has_bias_pattern()) {
 691       // Handle for oop obj in case of STW safepoint
 692       Handle hobj(Self, obj);
 693       // Relaxing assertion for bug 6320749.
 694       assert(Universe::verify_in_progress() ||
 695              !SafepointSynchronize::is_at_safepoint(),
 696              "biases should not be seen by VM thread here");
 697       BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
 698       obj = hobj();
 699       assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 700     }
 701   }
 702 
 703   // hashCode() is a heap mutator ...
 704   // Relaxing assertion for bug 6320749.
 705   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 706          !SafepointSynchronize::is_at_safepoint(), "invariant");
 707   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 708          Self->is_Java_thread() , "invariant");
 709   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 710          ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
 711 
 712   ObjectMonitor* monitor = NULL;
 713   markOop temp, test;
 714   intptr_t hash;
 715   markOop mark = ReadStableMark(obj);
 716 
 717   // object should remain ineligible for biased locking
 718   assert(!mark->has_bias_pattern(), "invariant");
 719 
 720   if (mark->is_neutral()) {
 721     hash = mark->hash();              // this is a normal header
 722     if (hash != 0) {                  // if it has hash, just return it
 723       return hash;
 724     }
 725     hash = get_next_hash(Self, obj);  // allocate a new hash code
 726     temp = mark->copy_set_hash(hash); // merge the hash code into header
 727     // use (machine word version) atomic operation to install the hash
 728     test = obj->cas_set_mark(temp, mark);
 729     if (test == mark) {
 730       return hash;
 731     }
 732     // If atomic operation failed, we must inflate the header
 733     // into heavy weight monitor. We could add more code here
 734     // for fast path, but it does not worth the complexity.
 735   } else if (mark->has_monitor()) {
 736     monitor = mark->monitor();
 737     temp = monitor->header();
 738     assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i((address)temp));
 739     hash = temp->hash();
 740     if (hash != 0) {
 741       return hash;
 742     }
 743     // Skip to the following code to reduce code size
 744   } else if (Self->is_lock_owned((address)mark->locker())) {
 745     temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
 746     assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i((address)temp));
 747     hash = temp->hash();              // by current thread, check if the displaced
 748     if (hash != 0) {                  // header contains hash code
 749       return hash;
 750     }
 751     // WARNING:
 752     //   The displaced header is strictly immutable.
 753     // It can NOT be changed in ANY cases. So we have
 754     // to inflate the header into heavyweight monitor
 755     // even the current thread owns the lock. The reason
 756     // is the BasicLock (stack slot) will be asynchronously
 757     // read by other threads during the inflate() function.
 758     // Any change to stack may not propagate to other threads
 759     // correctly.
 760   }
 761 
 762   // Inflate the monitor to set hash code
 763   monitor = inflate(Self, obj, inflate_cause_hash_code);
 764   // Load displaced header and check it has hash code
 765   mark = monitor->header();
 766   assert(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i((address)mark));
 767   hash = mark->hash();
 768   if (hash == 0) {
 769     hash = get_next_hash(Self, obj);
 770     temp = mark->copy_set_hash(hash); // merge hash code into header
 771     assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i((address)temp));
 772     test = Atomic::cmpxchg(temp, monitor->header_addr(), mark);
 773     if (test != mark) {
 774       // The only update to the header in the monitor (outside GC)
 775       // is install the hash code. If someone add new usage of
 776       // displaced header, please update this code
 777       hash = test->hash();
 778       assert(test->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i((address)test));
 779       assert(hash != 0, "Trivial unexpected object/monitor header usage.");
 780     }
 781   }
 782   // We finally get the hash
 783   return hash;
 784 }
 785 
 786 // Deprecated -- use FastHashCode() instead.
 787 
 788 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
 789   return FastHashCode(Thread::current(), obj());
 790 }
 791 
 792 
 793 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
 794                                                    Handle h_obj) {
 795   if (UseBiasedLocking) {
 796     BiasedLocking::revoke_and_rebias(h_obj, false, thread);
 797     assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 798   }
 799 
 800   assert(thread == JavaThread::current(), "Can only be called on current thread");
 801   oop obj = h_obj();
 802 
 803   markOop mark = ReadStableMark(obj);
 804 
 805   // Uncontended case, header points to stack
 806   if (mark->has_locker()) {
 807     return thread->is_lock_owned((address)mark->locker());
 808   }
 809   // Contended case, header points to ObjectMonitor (tagged pointer)
 810   if (mark->has_monitor()) {
 811     ObjectMonitor* monitor = mark->monitor();
 812     return monitor->is_entered(thread) != 0;
 813   }
 814   // Unlocked case, header in place
 815   assert(mark->is_neutral(), "sanity check");
 816   return false;
 817 }
 818 
 819 // Be aware of this method could revoke bias of the lock object.
 820 // This method queries the ownership of the lock handle specified by 'h_obj'.
 821 // If the current thread owns the lock, it returns owner_self. If no
 822 // thread owns the lock, it returns owner_none. Otherwise, it will return
 823 // owner_other.
 824 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
 825 (JavaThread *self, Handle h_obj) {
 826   // The caller must beware this method can revoke bias, and
 827   // revocation can result in a safepoint.
 828   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 829   assert(self->thread_state() != _thread_blocked, "invariant");
 830 
 831   // Possible mark states: neutral, biased, stack-locked, inflated
 832 
 833   if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
 834     // CASE: biased
 835     BiasedLocking::revoke_and_rebias(h_obj, false, self);
 836     assert(!h_obj->mark()->has_bias_pattern(),
 837            "biases should be revoked by now");
 838   }
 839 
 840   assert(self == JavaThread::current(), "Can only be called on current thread");
 841   oop obj = h_obj();
 842   markOop mark = ReadStableMark(obj);
 843 
 844   // CASE: stack-locked.  Mark points to a BasicLock on the owner's stack.
 845   if (mark->has_locker()) {
 846     return self->is_lock_owned((address)mark->locker()) ?
 847       owner_self : owner_other;
 848   }
 849 
 850   // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
 851   // The Object:ObjectMonitor relationship is stable as long as we're
 852   // not at a safepoint.
 853   if (mark->has_monitor()) {
 854     void * owner = mark->monitor()->_owner;
 855     if (owner == NULL) return owner_none;
 856     return (owner == self ||
 857             self->is_lock_owned((address)owner)) ? owner_self : owner_other;
 858   }
 859 
 860   // CASE: neutral
 861   assert(mark->is_neutral(), "sanity check");
 862   return owner_none;           // it's unlocked
 863 }
 864 
 865 // FIXME: jvmti should call this
 866 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
 867   if (UseBiasedLocking) {
 868     if (SafepointSynchronize::is_at_safepoint()) {
 869       BiasedLocking::revoke_at_safepoint(h_obj);
 870     } else {
 871       BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
 872     }
 873     assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
 874   }
 875 
 876   oop obj = h_obj();
 877   address owner = NULL;
 878 
 879   markOop mark = ReadStableMark(obj);
 880 
 881   // Uncontended case, header points to stack
 882   if (mark->has_locker()) {
 883     owner = (address) mark->locker();
 884   }
 885 
 886   // Contended case, header points to ObjectMonitor (tagged pointer)
 887   else if (mark->has_monitor()) {
 888     ObjectMonitor* monitor = mark->monitor();
 889     assert(monitor != NULL, "monitor should be non-null");
 890     owner = (address) monitor->owner();
 891   }
 892 
 893   if (owner != NULL) {
 894     // owning_thread_from_monitor_owner() may also return NULL here
 895     return Threads::owning_thread_from_monitor_owner(t_list, owner);
 896   }
 897 
 898   // Unlocked case, header in place
 899   // Cannot have assertion since this object may have been
 900   // locked by another thread when reaching here.
 901   // assert(mark->is_neutral(), "sanity check");
 902 
 903   return NULL;
 904 }
 905 
 906 // Visitors ...
 907 
 908 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
 909   PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
 910   while (block != NULL) {
 911     assert(block->object() == CHAINMARKER, "must be a block header");
 912     for (int i = _BLOCKSIZE - 1; i > 0; i--) {
 913       ObjectMonitor* mid = (ObjectMonitor *)(block + i);
 914       oop object = (oop)mid->object();
 915       if (object != NULL) {
 916         closure->do_monitor(mid);
 917       }
 918     }
 919     block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
 920   }
 921 }
 922 
 923 // Get the next block in the block list.
 924 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
 925   assert(block->object() == CHAINMARKER, "must be a block header");
 926   block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
 927   assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
 928   return block;
 929 }
 930 
 931 static bool monitors_used_above_threshold() {
 932   if (gMonitorPopulation == 0) {
 933     return false;
 934   }
 935   int monitors_used = gMonitorPopulation - gMonitorFreeCount;
 936   int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
 937   return monitor_usage > MonitorUsedDeflationThreshold;
 938 }
 939 
 940 bool ObjectSynchronizer::is_cleanup_needed() {
 941   if (MonitorUsedDeflationThreshold > 0) {
 942     return monitors_used_above_threshold();
 943   }
 944   return false;
 945 }
 946 
 947 void ObjectSynchronizer::oops_do(OopClosure* f) {
 948   // We only scan the global used list here (for moribund threads), and
 949   // the thread-local monitors in Thread::oops_do().
 950   global_used_oops_do(f);
 951 }
 952 
 953 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
 954   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
 955   list_oops_do(gOmInUseList, f);
 956 }
 957 
 958 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
 959   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
 960   list_oops_do(thread->omInUseList, f);
 961 }
 962 
 963 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
 964   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
 965   ObjectMonitor* mid;
 966   for (mid = list; mid != NULL; mid = mid->FreeNext) {
 967     if (mid->object() != NULL) {
 968       f->do_oop((oop*)mid->object_addr());
 969     }
 970   }
 971 }
 972 
 973 
 974 // -----------------------------------------------------------------------------
 975 // ObjectMonitor Lifecycle
 976 // -----------------------
 977 // Inflation unlinks monitors from the global gFreeList and
 978 // associates them with objects.  Deflation -- which occurs at
 979 // STW-time -- disassociates idle monitors from objects.  Such
 980 // scavenged monitors are returned to the gFreeList.
 981 //
 982 // The global list is protected by gListLock.  All the critical sections
 983 // are short and operate in constant-time.
 984 //
 985 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
 986 //
 987 // Lifecycle:
 988 // --   unassigned and on the global free list
 989 // --   unassigned and on a thread's private omFreeList
 990 // --   assigned to an object.  The object is inflated and the mark refers
 991 //      to the objectmonitor.
 992 
 993 
 994 // Constraining monitor pool growth via MonitorBound ...
 995 //
 996 // The monitor pool is grow-only.  We scavenge at STW safepoint-time, but the
 997 // the rate of scavenging is driven primarily by GC.  As such,  we can find
 998 // an inordinate number of monitors in circulation.
 999 // To avoid that scenario we can artificially induce a STW safepoint
1000 // if the pool appears to be growing past some reasonable bound.
1001 // Generally we favor time in space-time tradeoffs, but as there's no
1002 // natural back-pressure on the # of extant monitors we need to impose some
1003 // type of limit.  Beware that if MonitorBound is set to too low a value
1004 // we could just loop. In addition, if MonitorBound is set to a low value
1005 // we'll incur more safepoints, which are harmful to performance.
1006 // See also: GuaranteedSafepointInterval
1007 //
1008 // The current implementation uses asynchronous VM operations.
1009 
1010 static void InduceScavenge(Thread * Self, const char * Whence) {
1011   // Induce STW safepoint to trim monitors
1012   // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1013   // More precisely, trigger an asynchronous STW safepoint as the number
1014   // of active monitors passes the specified threshold.
1015   // TODO: assert thread state is reasonable
1016 
1017   if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1018     // Induce a 'null' safepoint to scavenge monitors
1019     // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1020     // to the VMthread and have a lifespan longer than that of this activation record.
1021     // The VMThread will delete the op when completed.
1022     VMThread::execute(new VM_ScavengeMonitors());
1023   }
1024 }
1025 
1026 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self) {
1027   // A large MAXPRIVATE value reduces both list lock contention
1028   // and list coherency traffic, but also tends to increase the
1029   // number of objectMonitors in circulation as well as the STW
1030   // scavenge costs.  As usual, we lean toward time in space-time
1031   // tradeoffs.
1032   const int MAXPRIVATE = 1024;
1033   for (;;) {
1034     ObjectMonitor * m;
1035 
1036     // 1: try to allocate from the thread's local omFreeList.
1037     // Threads will attempt to allocate first from their local list, then
1038     // from the global list, and only after those attempts fail will the thread
1039     // attempt to instantiate new monitors.   Thread-local free lists take
1040     // heat off the gListLock and improve allocation latency, as well as reducing
1041     // coherency traffic on the shared global list.
1042     m = Self->omFreeList;
1043     if (m != NULL) {
1044       Self->omFreeList = m->FreeNext;
1045       Self->omFreeCount--;
1046       guarantee(m->object() == NULL, "invariant");
1047       m->FreeNext = Self->omInUseList;
1048       Self->omInUseList = m;
1049       Self->omInUseCount++;
1050       return m;
1051     }
1052 
1053     // 2: try to allocate from the global gFreeList
1054     // CONSIDER: use muxTry() instead of muxAcquire().
1055     // If the muxTry() fails then drop immediately into case 3.
1056     // If we're using thread-local free lists then try
1057     // to reprovision the caller's free list.
1058     if (gFreeList != NULL) {
1059       // Reprovision the thread's omFreeList.
1060       // Use bulk transfers to reduce the allocation rate and heat
1061       // on various locks.
1062       Thread::muxAcquire(&gListLock, "omAlloc(1)");
1063       for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1064         gMonitorFreeCount--;
1065         ObjectMonitor * take = gFreeList;
1066         gFreeList = take->FreeNext;
1067         guarantee(take->object() == NULL, "invariant");
1068         guarantee(!take->is_busy(), "invariant");
1069         take->Recycle();
1070         omRelease(Self, take, false);
1071       }
1072       Thread::muxRelease(&gListLock);
1073       Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1074       if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1075 
1076       const int mx = MonitorBound;
1077       if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1078         // We can't safely induce a STW safepoint from omAlloc() as our thread
1079         // state may not be appropriate for such activities and callers may hold
1080         // naked oops, so instead we defer the action.
1081         InduceScavenge(Self, "omAlloc");
1082       }
1083       continue;
1084     }
1085 
1086     // 3: allocate a block of new ObjectMonitors
1087     // Both the local and global free lists are empty -- resort to malloc().
1088     // In the current implementation objectMonitors are TSM - immortal.
1089     // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1090     // each ObjectMonitor to start at the beginning of a cache line,
1091     // so we use align_up().
1092     // A better solution would be to use C++ placement-new.
1093     // BEWARE: As it stands currently, we don't run the ctors!
1094     assert(_BLOCKSIZE > 1, "invariant");
1095     size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1096     PaddedEnd<ObjectMonitor> * temp;
1097     size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1098     void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1099                                                       mtInternal);
1100     temp = (PaddedEnd<ObjectMonitor> *)
1101              align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1102 
1103     // NOTE: (almost) no way to recover if allocation failed.
1104     // We might be able to induce a STW safepoint and scavenge enough
1105     // objectMonitors to permit progress.
1106     if (temp == NULL) {
1107       vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1108                             "Allocate ObjectMonitors");
1109     }
1110     (void)memset((void *) temp, 0, neededsize);
1111 
1112     // Format the block.
1113     // initialize the linked list, each monitor points to its next
1114     // forming the single linked free list, the very first monitor
1115     // will points to next block, which forms the block list.
1116     // The trick of using the 1st element in the block as gBlockList
1117     // linkage should be reconsidered.  A better implementation would
1118     // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1119 
1120     for (int i = 1; i < _BLOCKSIZE; i++) {
1121       temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1122     }
1123 
1124     // terminate the last monitor as the end of list
1125     temp[_BLOCKSIZE - 1].FreeNext = NULL;
1126 
1127     // Element [0] is reserved for global list linkage
1128     temp[0].set_object(CHAINMARKER);
1129 
1130     // Consider carving out this thread's current request from the
1131     // block in hand.  This avoids some lock traffic and redundant
1132     // list activity.
1133 
1134     // Acquire the gListLock to manipulate gBlockList and gFreeList.
1135     // An Oyama-Taura-Yonezawa scheme might be more efficient.
1136     Thread::muxAcquire(&gListLock, "omAlloc(2)");
1137     gMonitorPopulation += _BLOCKSIZE-1;
1138     gMonitorFreeCount += _BLOCKSIZE-1;
1139 
1140     // Add the new block to the list of extant blocks (gBlockList).
1141     // The very first objectMonitor in a block is reserved and dedicated.
1142     // It serves as blocklist "next" linkage.
1143     temp[0].FreeNext = gBlockList;
1144     // There are lock-free uses of gBlockList so make sure that
1145     // the previous stores happen before we update gBlockList.
1146     OrderAccess::release_store(&gBlockList, temp);
1147 
1148     // Add the new string of objectMonitors to the global free list
1149     temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1150     gFreeList = temp + 1;
1151     Thread::muxRelease(&gListLock);
1152   }
1153 }
1154 
1155 // Place "m" on the caller's private per-thread omFreeList.
1156 // In practice there's no need to clamp or limit the number of
1157 // monitors on a thread's omFreeList as the only time we'll call
1158 // omRelease is to return a monitor to the free list after a CAS
1159 // attempt failed.  This doesn't allow unbounded #s of monitors to
1160 // accumulate on a thread's free list.
1161 //
1162 // Key constraint: all ObjectMonitors on a thread's free list and the global
1163 // free list must have their object field set to null. This prevents the
1164 // scavenger -- deflate_monitor_list() -- from reclaiming them.
1165 
1166 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1167                                    bool fromPerThreadAlloc) {
1168   guarantee(m->header() == NULL, "invariant");
1169   guarantee(m->object() == NULL, "invariant");
1170   guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1171   // Remove from omInUseList
1172   if (fromPerThreadAlloc) {
1173     ObjectMonitor* cur_mid_in_use = NULL;
1174     bool extracted = false;
1175     for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1176       if (m == mid) {
1177         // extract from per-thread in-use list
1178         if (mid == Self->omInUseList) {
1179           Self->omInUseList = mid->FreeNext;
1180         } else if (cur_mid_in_use != NULL) {
1181           cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1182         }
1183         extracted = true;
1184         Self->omInUseCount--;
1185         break;
1186       }
1187     }
1188     assert(extracted, "Should have extracted from in-use list");
1189   }
1190 
1191   // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1192   m->FreeNext = Self->omFreeList;
1193   Self->omFreeList = m;
1194   Self->omFreeCount++;
1195 }
1196 
1197 // Return the monitors of a moribund thread's local free list to
1198 // the global free list.  Typically a thread calls omFlush() when
1199 // it's dying.  We could also consider having the VM thread steal
1200 // monitors from threads that have not run java code over a few
1201 // consecutive STW safepoints.  Relatedly, we might decay
1202 // omFreeProvision at STW safepoints.
1203 //
1204 // Also return the monitors of a moribund thread's omInUseList to
1205 // a global gOmInUseList under the global list lock so these
1206 // will continue to be scanned.
1207 //
1208 // We currently call omFlush() from Threads::remove() _before the thread
1209 // has been excised from the thread list and is no longer a mutator.
1210 // This means that omFlush() cannot run concurrently with a safepoint and
1211 // interleave with the deflate_idle_monitors scavenge operator. In particular,
1212 // this ensures that the thread's monitors are scanned by a GC safepoint,
1213 // either via Thread::oops_do() (if safepoint happens before omFlush()) or via
1214 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1215 // monitors have been transferred to the global in-use list).
1216 
1217 void ObjectSynchronizer::omFlush(Thread * Self) {
1218   ObjectMonitor * list = Self->omFreeList;  // Null-terminated SLL
1219   ObjectMonitor * tail = NULL;
1220   int tally = 0;
1221   if (list != NULL) {
1222     ObjectMonitor * s;
1223     // The thread is going away, the per-thread free monitors
1224     // are freed via set_owner(NULL)
1225     // Link them to tail, which will be linked into the global free list
1226     // gFreeList below, under the gListLock
1227     for (s = list; s != NULL; s = s->FreeNext) {
1228       tally++;
1229       tail = s;
1230       guarantee(s->object() == NULL, "invariant");
1231       guarantee(!s->is_busy(), "invariant");
1232       s->set_owner(NULL);   // redundant but good hygiene
1233     }
1234     guarantee(tail != NULL, "invariant");
1235     assert(Self->omFreeCount == tally, "free-count off");
1236     Self->omFreeList = NULL;
1237     Self->omFreeCount = 0;
1238   }
1239 
1240   ObjectMonitor * inUseList = Self->omInUseList;
1241   ObjectMonitor * inUseTail = NULL;
1242   int inUseTally = 0;
1243   if (inUseList != NULL) {
1244     ObjectMonitor *cur_om;
1245     // The thread is going away, however the omInUseList inflated
1246     // monitors may still be in-use by other threads.
1247     // Link them to inUseTail, which will be linked into the global in-use list
1248     // gOmInUseList below, under the gListLock
1249     for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1250       inUseTail = cur_om;
1251       inUseTally++;
1252     }
1253     guarantee(inUseTail != NULL, "invariant");
1254     assert(Self->omInUseCount == inUseTally, "in-use count off");
1255     Self->omInUseList = NULL;
1256     Self->omInUseCount = 0;
1257   }
1258 
1259   Thread::muxAcquire(&gListLock, "omFlush");
1260   if (tail != NULL) {
1261     tail->FreeNext = gFreeList;
1262     gFreeList = list;
1263     gMonitorFreeCount += tally;
1264   }
1265 
1266   if (inUseTail != NULL) {
1267     inUseTail->FreeNext = gOmInUseList;
1268     gOmInUseList = inUseList;
1269     gOmInUseCount += inUseTally;
1270   }
1271 
1272   Thread::muxRelease(&gListLock);
1273 
1274   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1275   LogStreamHandle(Info, monitorinflation) lsh_info;
1276   LogStream * ls = NULL;
1277   if (log_is_enabled(Debug, monitorinflation)) {
1278     ls = &lsh_debug;
1279   } else if ((tally != 0 || inUseTally != 0) &&
1280              log_is_enabled(Info, monitorinflation)) {
1281     ls = &lsh_info;
1282   }
1283   if (ls != NULL) {
1284     ls->print_cr("omFlush: jt=" INTPTR_FORMAT ", free_monitor_tally=%d"
1285                  ", in_use_monitor_tally=%d" ", omFreeProvision=%d",
1286                  p2i(Self), tally, inUseTally, Self->omFreeProvision);
1287   }
1288 }
1289 
1290 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1291                                        const oop obj,
1292                                        ObjectSynchronizer::InflateCause cause) {
1293   assert(event != NULL, "invariant");
1294   assert(event->should_commit(), "invariant");
1295   event->set_monitorClass(obj->klass());
1296   event->set_address((uintptr_t)(void*)obj);
1297   event->set_cause((u1)cause);
1298   event->commit();
1299 }
1300 
1301 // Fast path code shared by multiple functions
1302 void ObjectSynchronizer::inflate_helper(oop obj) {
1303   markOop mark = obj->mark();
1304   if (mark->has_monitor()) {
1305     assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1306     assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1307     return;
1308   }
1309   inflate(Thread::current(), obj, inflate_cause_vm_internal);
1310 }
1311 
1312 ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self,
1313                                            oop object,
1314                                            const InflateCause cause) {
1315   // Inflate mutates the heap ...
1316   // Relaxing assertion for bug 6320749.
1317   assert(Universe::verify_in_progress() ||
1318          !SafepointSynchronize::is_at_safepoint(), "invariant");
1319 
1320   EventJavaMonitorInflate event;
1321 
1322   for (;;) {
1323     const markOop mark = object->mark();
1324     assert(!mark->has_bias_pattern(), "invariant");
1325 
1326     // The mark can be in one of the following states:
1327     // *  Inflated     - just return
1328     // *  Stack-locked - coerce it to inflated
1329     // *  INFLATING    - busy wait for conversion to complete
1330     // *  Neutral      - aggressively inflate the object.
1331     // *  BIASED       - Illegal.  We should never see this
1332 
1333     // CASE: inflated
1334     if (mark->has_monitor()) {
1335       ObjectMonitor * inf = mark->monitor();
1336       markOop dmw = inf->header();
1337       assert(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i((address)dmw));
1338       assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1339       assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1340       return inf;
1341     }
1342 
1343     // CASE: inflation in progress - inflating over a stack-lock.
1344     // Some other thread is converting from stack-locked to inflated.
1345     // Only that thread can complete inflation -- other threads must wait.
1346     // The INFLATING value is transient.
1347     // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1348     // We could always eliminate polling by parking the thread on some auxiliary list.
1349     if (mark == markOopDesc::INFLATING()) {
1350       ReadStableMark(object);
1351       continue;
1352     }
1353 
1354     // CASE: stack-locked
1355     // Could be stack-locked either by this thread or by some other thread.
1356     //
1357     // Note that we allocate the objectmonitor speculatively, _before_ attempting
1358     // to install INFLATING into the mark word.  We originally installed INFLATING,
1359     // allocated the objectmonitor, and then finally STed the address of the
1360     // objectmonitor into the mark.  This was correct, but artificially lengthened
1361     // the interval in which INFLATED appeared in the mark, thus increasing
1362     // the odds of inflation contention.
1363     //
1364     // We now use per-thread private objectmonitor free lists.
1365     // These list are reprovisioned from the global free list outside the
1366     // critical INFLATING...ST interval.  A thread can transfer
1367     // multiple objectmonitors en-mass from the global free list to its local free list.
1368     // This reduces coherency traffic and lock contention on the global free list.
1369     // Using such local free lists, it doesn't matter if the omAlloc() call appears
1370     // before or after the CAS(INFLATING) operation.
1371     // See the comments in omAlloc().
1372 
1373     LogStreamHandle(Trace, monitorinflation) lsh;
1374 
1375     if (mark->has_locker()) {
1376       ObjectMonitor * m = omAlloc(Self);
1377       // Optimistically prepare the objectmonitor - anticipate successful CAS
1378       // We do this before the CAS in order to minimize the length of time
1379       // in which INFLATING appears in the mark.
1380       m->Recycle();
1381       m->_Responsible  = NULL;
1382       m->_recursions   = 0;
1383       m->_SpinDuration = ObjectMonitor::Knob_SpinLimit;   // Consider: maintain by type/class
1384 
1385       markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1386       if (cmp != mark) {
1387         omRelease(Self, m, true);
1388         continue;       // Interference -- just retry
1389       }
1390 
1391       // We've successfully installed INFLATING (0) into the mark-word.
1392       // This is the only case where 0 will appear in a mark-word.
1393       // Only the singular thread that successfully swings the mark-word
1394       // to 0 can perform (or more precisely, complete) inflation.
1395       //
1396       // Why do we CAS a 0 into the mark-word instead of just CASing the
1397       // mark-word from the stack-locked value directly to the new inflated state?
1398       // Consider what happens when a thread unlocks a stack-locked object.
1399       // It attempts to use CAS to swing the displaced header value from the
1400       // on-stack basiclock back into the object header.  Recall also that the
1401       // header value (hashcode, etc) can reside in (a) the object header, or
1402       // (b) a displaced header associated with the stack-lock, or (c) a displaced
1403       // header in an objectMonitor.  The inflate() routine must copy the header
1404       // value from the basiclock on the owner's stack to the objectMonitor, all
1405       // the while preserving the hashCode stability invariants.  If the owner
1406       // decides to release the lock while the value is 0, the unlock will fail
1407       // and control will eventually pass from slow_exit() to inflate.  The owner
1408       // will then spin, waiting for the 0 value to disappear.   Put another way,
1409       // the 0 causes the owner to stall if the owner happens to try to
1410       // drop the lock (restoring the header from the basiclock to the object)
1411       // while inflation is in-progress.  This protocol avoids races that might
1412       // would otherwise permit hashCode values to change or "flicker" for an object.
1413       // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1414       // 0 serves as a "BUSY" inflate-in-progress indicator.
1415 
1416 
1417       // fetch the displaced mark from the owner's stack.
1418       // The owner can't die or unwind past the lock while our INFLATING
1419       // object is in the mark.  Furthermore the owner can't complete
1420       // an unlock on the object, either.
1421       markOop dmw = mark->displaced_mark_helper();
1422       assert(dmw->is_neutral(), "invariant");
1423 
1424       // Setup monitor fields to proper values -- prepare the monitor
1425       m->set_header(dmw);
1426 
1427       // Optimization: if the mark->locker stack address is associated
1428       // with this thread we could simply set m->_owner = Self.
1429       // Note that a thread can inflate an object
1430       // that it has stack-locked -- as might happen in wait() -- directly
1431       // with CAS.  That is, we can avoid the xchg-NULL .... ST idiom.
1432       m->set_owner(mark->locker());
1433       m->set_object(object);
1434       // TODO-FIXME: assert BasicLock->dhw != 0.
1435 
1436       // Must preserve store ordering. The monitor state must
1437       // be stable at the time of publishing the monitor address.
1438       guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1439       object->release_set_mark(markOopDesc::encode(m));
1440 
1441       // Hopefully the performance counters are allocated on distinct cache lines
1442       // to avoid false sharing on MP systems ...
1443       OM_PERFDATA_OP(Inflations, inc());
1444       if (log_is_enabled(Trace, monitorinflation)) {
1445         ResourceMark rm(Self);
1446         lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1447                      INTPTR_FORMAT ", type='%s'", p2i(object),
1448                      p2i(object->mark()), object->klass()->external_name());
1449       }
1450       if (event.should_commit()) {
1451         post_monitor_inflate_event(&event, object, cause);
1452       }
1453       return m;
1454     }
1455 
1456     // CASE: neutral
1457     // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1458     // If we know we're inflating for entry it's better to inflate by swinging a
1459     // pre-locked objectMonitor pointer into the object header.   A successful
1460     // CAS inflates the object *and* confers ownership to the inflating thread.
1461     // In the current implementation we use a 2-step mechanism where we CAS()
1462     // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1463     // An inflateTry() method that we could call from fast_enter() and slow_enter()
1464     // would be useful.
1465 
1466     assert(mark->is_neutral(), "invariant");
1467     ObjectMonitor * m = omAlloc(Self);
1468     // prepare m for installation - set monitor to initial state
1469     m->Recycle();
1470     m->set_header(mark);
1471     m->set_owner(NULL);
1472     m->set_object(object);
1473     m->_recursions   = 0;
1474     m->_Responsible  = NULL;
1475     m->_SpinDuration = ObjectMonitor::Knob_SpinLimit;       // consider: keep metastats by type/class
1476 
1477     if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1478       m->set_header(NULL);
1479       m->set_object(NULL);
1480       m->Recycle();
1481       omRelease(Self, m, true);
1482       m = NULL;
1483       continue;
1484       // interference - the markword changed - just retry.
1485       // The state-transitions are one-way, so there's no chance of
1486       // live-lock -- "Inflated" is an absorbing state.
1487     }
1488 
1489     // Hopefully the performance counters are allocated on distinct
1490     // cache lines to avoid false sharing on MP systems ...
1491     OM_PERFDATA_OP(Inflations, inc());
1492     if (log_is_enabled(Trace, monitorinflation)) {
1493       ResourceMark rm(Self);
1494       lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1495                    INTPTR_FORMAT ", type='%s'", p2i(object),
1496                    p2i(object->mark()), object->klass()->external_name());
1497     }
1498     if (event.should_commit()) {
1499       post_monitor_inflate_event(&event, object, cause);
1500     }
1501     return m;
1502   }
1503 }
1504 
1505 
1506 // We create a list of in-use monitors for each thread.
1507 //
1508 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1509 // deflate_idle_monitors() scans only a global list of in-use monitors which
1510 // is populated only as a thread dies (see omFlush()).
1511 //
1512 // These operations are called at all safepoints, immediately after mutators
1513 // are stopped, but before any objects have moved. Collectively they traverse
1514 // the population of in-use monitors, deflating where possible. The scavenged
1515 // monitors are returned to the monitor free list.
1516 //
1517 // Beware that we scavenge at *every* stop-the-world point. Having a large
1518 // number of monitors in-use could negatively impact performance. We also want
1519 // to minimize the total # of monitors in circulation, as they incur a small
1520 // footprint penalty.
1521 //
1522 // Perversely, the heap size -- and thus the STW safepoint rate --
1523 // typically drives the scavenge rate.  Large heaps can mean infrequent GC,
1524 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1525 // This is an unfortunate aspect of this design.
1526 
1527 // Deflate a single monitor if not in-use
1528 // Return true if deflated, false if in-use
1529 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1530                                          ObjectMonitor** freeHeadp,
1531                                          ObjectMonitor** freeTailp) {
1532   bool deflated;
1533   // Normal case ... The monitor is associated with obj.
1534   guarantee(obj->mark() == markOopDesc::encode(mid), "invariant");
1535   guarantee(mid == obj->mark()->monitor(), "invariant");
1536   guarantee(mid->header()->is_neutral(), "invariant");
1537 
1538   if (mid->is_busy()) {
1539     deflated = false;
1540   } else {
1541     // Deflate the monitor if it is no longer being used
1542     // It's idle - scavenge and return to the global free list
1543     // plain old deflation ...
1544     if (log_is_enabled(Trace, monitorinflation)) {
1545       ResourceMark rm;
1546       log_trace(monitorinflation)("deflate_monitor: "
1547                                   "object=" INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", type='%s'",
1548                                   p2i(obj), p2i(obj->mark()),
1549                                   obj->klass()->external_name());
1550     }
1551 
1552     // Restore the header back to obj
1553     obj->release_set_mark(mid->header());
1554     mid->clear();
1555 
1556     assert(mid->object() == NULL, "invariant");
1557 
1558     // Move the object to the working free list defined by freeHeadp, freeTailp
1559     if (*freeHeadp == NULL) *freeHeadp = mid;
1560     if (*freeTailp != NULL) {
1561       ObjectMonitor * prevtail = *freeTailp;
1562       assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1563       prevtail->FreeNext = mid;
1564     }
1565     *freeTailp = mid;
1566     deflated = true;
1567   }
1568   return deflated;
1569 }
1570 
1571 // Walk a given monitor list, and deflate idle monitors
1572 // The given list could be a per-thread list or a global list
1573 // Caller acquires gListLock as needed.
1574 //
1575 // In the case of parallel processing of thread local monitor lists,
1576 // work is done by Threads::parallel_threads_do() which ensures that
1577 // each Java thread is processed by exactly one worker thread, and
1578 // thus avoid conflicts that would arise when worker threads would
1579 // process the same monitor lists concurrently.
1580 //
1581 // See also ParallelSPCleanupTask and
1582 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1583 // Threads::parallel_java_threads_do() in thread.cpp.
1584 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1585                                              ObjectMonitor** freeHeadp,
1586                                              ObjectMonitor** freeTailp) {
1587   ObjectMonitor* mid;
1588   ObjectMonitor* next;
1589   ObjectMonitor* cur_mid_in_use = NULL;
1590   int deflated_count = 0;
1591 
1592   for (mid = *listHeadp; mid != NULL;) {
1593     oop obj = (oop) mid->object();
1594     if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1595       // if deflate_monitor succeeded,
1596       // extract from per-thread in-use list
1597       if (mid == *listHeadp) {
1598         *listHeadp = mid->FreeNext;
1599       } else if (cur_mid_in_use != NULL) {
1600         cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1601       }
1602       next = mid->FreeNext;
1603       mid->FreeNext = NULL;  // This mid is current tail in the freeHeadp list
1604       mid = next;
1605       deflated_count++;
1606     } else {
1607       cur_mid_in_use = mid;
1608       mid = mid->FreeNext;
1609     }
1610   }
1611   return deflated_count;
1612 }
1613 
1614 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1615   counters->nInuse = 0;              // currently associated with objects
1616   counters->nInCirculation = 0;      // extant
1617   counters->nScavenged = 0;          // reclaimed (global and per-thread)
1618   counters->perThreadScavenged = 0;  // per-thread scavenge total
1619   counters->perThreadTimes = 0.0;    // per-thread scavenge times
1620 }
1621 
1622 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1623   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1624   bool deflated = false;
1625 
1626   ObjectMonitor * freeHeadp = NULL;  // Local SLL of scavenged monitors
1627   ObjectMonitor * freeTailp = NULL;
1628   elapsedTimer timer;
1629 
1630   if (log_is_enabled(Info, monitorinflation)) {
1631     timer.start();
1632   }
1633 
1634   // Prevent omFlush from changing mids in Thread dtor's during deflation
1635   // And in case the vm thread is acquiring a lock during a safepoint
1636   // See e.g. 6320749
1637   Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
1638 
1639   // Note: the thread-local monitors lists get deflated in
1640   // a separate pass. See deflate_thread_local_monitors().
1641 
1642   // For moribund threads, scan gOmInUseList
1643   int deflated_count = 0;
1644   if (gOmInUseList) {
1645     counters->nInCirculation += gOmInUseCount;
1646     deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1647     gOmInUseCount -= deflated_count;
1648     counters->nScavenged += deflated_count;
1649     counters->nInuse += gOmInUseCount;
1650   }
1651 
1652   // Move the scavenged monitors back to the global free list.
1653   if (freeHeadp != NULL) {
1654     guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant");
1655     assert(freeTailp->FreeNext == NULL, "invariant");
1656     // constant-time list splice - prepend scavenged segment to gFreeList
1657     freeTailp->FreeNext = gFreeList;
1658     gFreeList = freeHeadp;
1659   }
1660   Thread::muxRelease(&gListLock);
1661   timer.stop();
1662 
1663   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1664   LogStreamHandle(Info, monitorinflation) lsh_info;
1665   LogStream * ls = NULL;
1666   if (log_is_enabled(Debug, monitorinflation)) {
1667     ls = &lsh_debug;
1668   } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1669     ls = &lsh_info;
1670   }
1671   if (ls != NULL) {
1672     ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
1673   }
1674 }
1675 
1676 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1677   // Report the cumulative time for deflating each thread's idle
1678   // monitors. Note: if the work is split among more than one
1679   // worker thread, then the reported time will likely be more
1680   // than a beginning to end measurement of the phase.
1681   log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->perThreadTimes, counters->perThreadScavenged);
1682 
1683   gMonitorFreeCount += counters->nScavenged;
1684 
1685   if (log_is_enabled(Debug, monitorinflation)) {
1686     // exit_globals()'s call to audit_and_print_stats() is done
1687     // at the Info level.
1688     ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
1689   } else if (log_is_enabled(Info, monitorinflation)) {
1690     Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
1691     log_info(monitorinflation)("gMonitorPopulation=%d, gOmInUseCount=%d, "
1692                                "gMonitorFreeCount=%d", gMonitorPopulation,
1693                                gOmInUseCount, gMonitorFreeCount);
1694     Thread::muxRelease(&gListLock);
1695   }
1696 
1697   ForceMonitorScavenge = 0;    // Reset
1698 
1699   OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
1700   OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
1701 
1702   GVars.stwRandom = os::random();
1703   GVars.stwCycle++;
1704 }
1705 
1706 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1707   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1708 
1709   ObjectMonitor * freeHeadp = NULL;  // Local SLL of scavenged monitors
1710   ObjectMonitor * freeTailp = NULL;
1711   elapsedTimer timer;
1712 
1713   if (log_is_enabled(Info, safepoint, cleanup) ||
1714       log_is_enabled(Info, monitorinflation)) {
1715     timer.start();
1716   }
1717 
1718   int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
1719 
1720   Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors(1)");
1721 
1722   // Adjust counters
1723   counters->nInCirculation += thread->omInUseCount;
1724   thread->omInUseCount -= deflated_count;
1725   counters->nScavenged += deflated_count;
1726   counters->nInuse += thread->omInUseCount;
1727   counters->perThreadScavenged += deflated_count;
1728 
1729   // Move the scavenged monitors back to the global free list.
1730   if (freeHeadp != NULL) {
1731     guarantee(freeTailp != NULL && deflated_count > 0, "invariant");
1732     assert(freeTailp->FreeNext == NULL, "invariant");
1733 
1734     // constant-time list splice - prepend scavenged segment to gFreeList
1735     freeTailp->FreeNext = gFreeList;
1736     gFreeList = freeHeadp;
1737   }
1738   Thread::muxRelease(&gListLock);
1739 
1740   timer.stop();
1741   if (log_is_enabled(Info, safepoint, cleanup)) {
1742     // Only safepoint logging cares about cumulative perThreadTimes
1743     // and we don't count this muxAcquire() that we have to do in
1744     // order to safely update perThreadTimes.
1745     Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors(2)");
1746     counters->perThreadTimes += timer.seconds();
1747     Thread::muxRelease(&gListLock);
1748   }
1749 
1750   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1751   LogStreamHandle(Info, monitorinflation) lsh_info;
1752   LogStream * ls = NULL;
1753   if (log_is_enabled(Debug, monitorinflation)) {
1754     ls = &lsh_debug;
1755   } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1756     ls = &lsh_info;
1757   }
1758   if (ls != NULL) {
1759     ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
1760   }
1761 }
1762 
1763 // Monitor cleanup on JavaThread::exit
1764 
1765 // Iterate through monitor cache and attempt to release thread's monitors
1766 // Gives up on a particular monitor if an exception occurs, but continues
1767 // the overall iteration, swallowing the exception.
1768 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1769  private:
1770   TRAPS;
1771 
1772  public:
1773   ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1774   void do_monitor(ObjectMonitor* mid) {
1775     if (mid->owner() == THREAD) {
1776       (void)mid->complete_exit(CHECK);
1777     }
1778   }
1779 };
1780 
1781 // Release all inflated monitors owned by THREAD.  Lightweight monitors are
1782 // ignored.  This is meant to be called during JNI thread detach which assumes
1783 // all remaining monitors are heavyweight.  All exceptions are swallowed.
1784 // Scanning the extant monitor list can be time consuming.
1785 // A simple optimization is to add a per-thread flag that indicates a thread
1786 // called jni_monitorenter() during its lifetime.
1787 //
1788 // Instead of No_Savepoint_Verifier it might be cheaper to
1789 // use an idiom of the form:
1790 //   auto int tmp = SafepointSynchronize::_safepoint_counter ;
1791 //   <code that must not run at safepoint>
1792 //   guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1793 // Since the tests are extremely cheap we could leave them enabled
1794 // for normal product builds.
1795 
1796 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1797   assert(THREAD == JavaThread::current(), "must be current Java thread");
1798   NoSafepointVerifier nsv;
1799   ReleaseJavaMonitorsClosure rjmc(THREAD);
1800   Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1801   ObjectSynchronizer::monitors_iterate(&rjmc);
1802   Thread::muxRelease(&gListLock);
1803   THREAD->clear_pending_exception();
1804 }
1805 
1806 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1807   switch (cause) {
1808     case inflate_cause_vm_internal:    return "VM Internal";
1809     case inflate_cause_monitor_enter:  return "Monitor Enter";
1810     case inflate_cause_wait:           return "Monitor Wait";
1811     case inflate_cause_notify:         return "Monitor Notify";
1812     case inflate_cause_hash_code:      return "Monitor Hash Code";
1813     case inflate_cause_jni_enter:      return "JNI Monitor Enter";
1814     case inflate_cause_jni_exit:       return "JNI Monitor Exit";
1815     default:
1816       ShouldNotReachHere();
1817   }
1818   return "Unknown";
1819 }
1820 
1821 //------------------------------------------------------------------------------
1822 // Debugging code
1823 
1824 u_char* ObjectSynchronizer::get_gvars_addr() {
1825   return (u_char*)&GVars;
1826 }
1827 
1828 u_char* ObjectSynchronizer::get_gvars_hcSequence_addr() {
1829   return (u_char*)&GVars.hcSequence;
1830 }
1831 
1832 size_t ObjectSynchronizer::get_gvars_size() {
1833   return sizeof(SharedGlobals);
1834 }
1835 
1836 u_char* ObjectSynchronizer::get_gvars_stwRandom_addr() {
1837   return (u_char*)&GVars.stwRandom;
1838 }
1839 
1840 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1841   assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1842 
1843   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1844   LogStreamHandle(Info, monitorinflation) lsh_info;
1845   LogStreamHandle(Trace, monitorinflation) lsh_trace;
1846   LogStream * ls = NULL;
1847   if (log_is_enabled(Trace, monitorinflation)) {
1848     ls = &lsh_trace;
1849   } else if (log_is_enabled(Debug, monitorinflation)) {
1850     ls = &lsh_debug;
1851   } else if (log_is_enabled(Info, monitorinflation)) {
1852     ls = &lsh_info;
1853   }
1854   assert(ls != NULL, "sanity check");
1855 
1856   if (!on_exit) {
1857     // Not at VM exit so grab the global list lock.
1858     Thread::muxAcquire(&gListLock, "audit_and_print_stats");
1859   }
1860 
1861   // Log counts for the global and per-thread monitor lists:
1862   int chkMonitorPopulation = log_monitor_list_counts(ls);
1863   int error_cnt = 0;
1864 
1865   ls->print_cr("Checking global lists:");
1866 
1867   // Check gMonitorPopulation:
1868   if (gMonitorPopulation == chkMonitorPopulation) {
1869     ls->print_cr("gMonitorPopulation=%d equals chkMonitorPopulation=%d",
1870                  gMonitorPopulation, chkMonitorPopulation);
1871   } else {
1872     ls->print_cr("ERROR: gMonitorPopulation=%d is not equal to "
1873                  "chkMonitorPopulation=%d", gMonitorPopulation,
1874                  chkMonitorPopulation);
1875     error_cnt++;
1876   }
1877 
1878   // Check gOmInUseList and gOmInUseCount:
1879   chk_global_in_use_list_and_count(ls, &error_cnt);
1880 
1881   // Check gFreeList and gMonitorFreeCount:
1882   chk_global_free_list_and_count(ls, &error_cnt);
1883 
1884   if (!on_exit) {
1885     Thread::muxRelease(&gListLock);
1886   }
1887 
1888   ls->print_cr("Checking per-thread lists:");
1889 
1890   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
1891     // Check omInUseList and omInUseCount:
1892     chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
1893 
1894     // Check omFreeList and omFreeCount:
1895     chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
1896   }
1897 
1898   if (error_cnt == 0) {
1899     ls->print_cr("No errors found in monitor list checks.");
1900   } else {
1901     log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
1902   }
1903 
1904   if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1905       (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1906     // When exiting this log output is at the Info level. When called
1907     // at a safepoint, this log output is at the Trace level since
1908     // there can be a lot of it.
1909     log_in_use_monitor_details(ls, on_exit);
1910   }
1911 
1912   ls->flush();
1913 
1914   guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1915 }
1916 
1917 // Check a free monitor entry; log any errors.
1918 void ObjectSynchronizer::chk_free_entry(JavaThread * jt, ObjectMonitor * n,
1919                                         outputStream * out, int *error_cnt_p) {
1920   if (n->is_busy()) {
1921     if (jt != NULL) {
1922       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1923                     ": free per-thread monitor must not be busy.", p2i(jt),
1924                     p2i(n));
1925     } else {
1926       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1927                     "must not be busy.", p2i(n));
1928     }
1929     *error_cnt_p = *error_cnt_p + 1;
1930   }
1931   if (n->header() != NULL) {
1932     if (jt != NULL) {
1933       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1934                     ": free per-thread monitor must have NULL _header "
1935                     "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
1936                     p2i(n->header()));
1937     } else {
1938       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1939                     "must have NULL _header field: _header=" INTPTR_FORMAT,
1940                     p2i(n), p2i(n->header()));
1941     }
1942     *error_cnt_p = *error_cnt_p + 1;
1943   }
1944   if (n->object() != NULL) {
1945     if (jt != NULL) {
1946       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1947                     ": free per-thread monitor must have NULL _object "
1948                     "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
1949                     p2i(n->object()));
1950     } else {
1951       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1952                     "must have NULL _object field: _object=" INTPTR_FORMAT,
1953                     p2i(n), p2i(n->object()));
1954     }
1955     *error_cnt_p = *error_cnt_p + 1;
1956   }
1957 }
1958 
1959 // Check the global free list and count; log the results of the checks.
1960 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
1961                                                         int *error_cnt_p) {
1962   int chkMonitorFreeCount = 0;
1963   for (ObjectMonitor * n = gFreeList; n != NULL; n = n->FreeNext) {
1964     chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
1965     chkMonitorFreeCount++;
1966   }
1967   if (gMonitorFreeCount == chkMonitorFreeCount) {
1968     out->print_cr("gMonitorFreeCount=%d equals chkMonitorFreeCount=%d",
1969                   gMonitorFreeCount, chkMonitorFreeCount);
1970   } else {
1971     out->print_cr("ERROR: gMonitorFreeCount=%d is not equal to "
1972                   "chkMonitorFreeCount=%d", gMonitorFreeCount,
1973                   chkMonitorFreeCount);
1974     *error_cnt_p = *error_cnt_p + 1;
1975   }
1976 }
1977 
1978 // Check the global in-use list and count; log the results of the checks.
1979 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
1980                                                           int *error_cnt_p) {
1981   int chkOmInUseCount = 0;
1982   for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
1983     chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
1984     chkOmInUseCount++;
1985   }
1986   if (gOmInUseCount == chkOmInUseCount) {
1987     out->print_cr("gOmInUseCount=%d equals chkOmInUseCount=%d", gOmInUseCount,
1988                   chkOmInUseCount);
1989   } else {
1990     out->print_cr("ERROR: gOmInUseCount=%d is not equal to chkOmInUseCount=%d",
1991                   gOmInUseCount, chkOmInUseCount);
1992     *error_cnt_p = *error_cnt_p + 1;
1993   }
1994 }
1995 
1996 // Check an in-use monitor entry; log any errors.
1997 void ObjectSynchronizer::chk_in_use_entry(JavaThread * jt, ObjectMonitor * n,
1998                                           outputStream * out, int *error_cnt_p) {
1999   if (n->header() == NULL) {
2000     if (jt != NULL) {
2001       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2002                     ": in-use per-thread monitor must have non-NULL _header "
2003                     "field.", p2i(jt), p2i(n));
2004     } else {
2005       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2006                     "must have non-NULL _header field.", p2i(n));
2007     }
2008     *error_cnt_p = *error_cnt_p + 1;
2009   }
2010   if (n->object() == NULL) {
2011     if (jt != NULL) {
2012       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2013                     ": in-use per-thread monitor must have non-NULL _object "
2014                     "field.", p2i(jt), p2i(n));
2015     } else {
2016       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2017                     "must have non-NULL _object field.", p2i(n));
2018     }
2019     *error_cnt_p = *error_cnt_p + 1;
2020   }
2021   const oop obj = (oop)n->object();
2022   const markOop mark = obj->mark();
2023   if (!mark->has_monitor()) {
2024     if (jt != NULL) {
2025       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2026                     ": in-use per-thread monitor's object does not think "
2027                     "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2028                     INTPTR_FORMAT,  p2i(jt), p2i(n), p2i((address)obj),
2029                     p2i((address)mark));
2030     } else {
2031       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2032                     "monitor's object does not think it has a monitor: obj="
2033                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2034                     p2i((address)obj), p2i((address)mark));
2035     }
2036     *error_cnt_p = *error_cnt_p + 1;
2037   }
2038   ObjectMonitor * const obj_mon = mark->monitor();
2039   if (n != obj_mon) {
2040     if (jt != NULL) {
2041       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2042                     ": in-use per-thread monitor's object does not refer "
2043                     "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2044                     INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2045                     p2i(n), p2i((address)obj), p2i((address)mark),
2046                     p2i((address)obj_mon));
2047     } else {
2048       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2049                     "monitor's object does not refer to the same monitor: obj="
2050                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2051                     INTPTR_FORMAT, p2i(n), p2i((address)obj),
2052                     p2i((address)mark), p2i((address)obj_mon));
2053     }
2054     *error_cnt_p = *error_cnt_p + 1;
2055   }
2056 }
2057 
2058 // Check the thread's free list and count; log the results of the checks.
2059 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2060                                                             outputStream * out,
2061                                                             int *error_cnt_p) {
2062   int chkOmFreeCount = 0;
2063   for (ObjectMonitor * n = jt->omFreeList; n != NULL; n = n->FreeNext) {
2064     chk_free_entry(jt, n, out, error_cnt_p);
2065     chkOmFreeCount++;
2066   }
2067   if (jt->omFreeCount == chkOmFreeCount) {
2068     out->print_cr("jt=" INTPTR_FORMAT ": omFreeCount=%d equals "
2069                   "chkOmFreeCount=%d", p2i(jt), jt->omFreeCount, chkOmFreeCount);
2070   } else {
2071     out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omFreeCount=%d is not "
2072                   "equal to chkOmFreeCount=%d", p2i(jt), jt->omFreeCount,
2073                   chkOmFreeCount);
2074     *error_cnt_p = *error_cnt_p + 1;
2075   }
2076 }
2077 
2078 // Check the thread's in-use list and count; log the results of the checks.
2079 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2080                                                               outputStream * out,
2081                                                               int *error_cnt_p) {
2082   int chkOmInUseCount = 0;
2083   for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2084     chk_in_use_entry(jt, n, out, error_cnt_p);
2085     chkOmInUseCount++;
2086   }
2087   if (jt->omInUseCount == chkOmInUseCount) {
2088     out->print_cr("jt=" INTPTR_FORMAT ": omInUseCount=%d equals "
2089                   "chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2090                   chkOmInUseCount);
2091   } else {
2092     out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omInUseCount=%d is not "
2093                   "equal to chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2094                   chkOmInUseCount);
2095     *error_cnt_p = *error_cnt_p + 1;
2096   }
2097 }
2098 
2099 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2100 // flags indicate why the entry is in-use, 'object' and 'object type'
2101 // indicate the associated object and its type.
2102 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2103                                                     bool on_exit) {
2104   if (!on_exit) {
2105     // Not at VM exit so grab the global list lock.
2106     Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2107   }
2108 
2109   if (gOmInUseCount > 0) {
2110     out->print_cr("In-use global monitor info:");
2111     out->print_cr("(B -> is_busy, H -> has hashcode, L -> lock status)");
2112     out->print_cr("%18s  %s  %18s  %18s",
2113                   "monitor", "BHL", "object", "object type");
2114     out->print_cr("==================  ===  ==================  ==================");
2115     for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2116       const oop obj = (oop) n->object();
2117       const markOop mark = n->header();
2118       ResourceMark rm;
2119       out->print_cr(INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT "  %s", p2i(n),
2120                     n->is_busy() != 0, mark->hash() != 0, n->owner() != NULL,
2121                     p2i(obj), obj->klass()->external_name());
2122     }
2123   }
2124 
2125   if (!on_exit) {
2126     Thread::muxRelease(&gListLock);
2127   }
2128 
2129   out->print_cr("In-use per-thread monitor info:");
2130   out->print_cr("(B -> is_busy, H -> has hashcode, L -> lock status)");
2131   out->print_cr("%18s  %18s  %s  %18s  %18s",
2132                 "jt", "monitor", "BHL", "object", "object type");
2133   out->print_cr("==================  ==================  ===  ==================  ==================");
2134   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2135     for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2136       const oop obj = (oop) n->object();
2137       const markOop mark = n->header();
2138       ResourceMark rm;
2139       out->print_cr(INTPTR_FORMAT "  " INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT
2140                     "  %s", p2i(jt), p2i(n), n->is_busy() != 0,
2141                     mark->hash() != 0, n->owner() != NULL, p2i(obj),
2142                     obj->klass()->external_name());
2143     }
2144   }
2145 
2146   out->flush();
2147 }
2148 
2149 // Log counts for the global and per-thread monitor lists and return
2150 // the population count.
2151 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2152   int popCount = 0;
2153   out->print_cr("%18s  %10s  %10s  %10s",
2154                 "Global Lists:", "InUse", "Free", "Total");
2155   out->print_cr("==================  ==========  ==========  ==========");
2156   out->print_cr("%18s  %10d  %10d  %10d", "",
2157                 gOmInUseCount, gMonitorFreeCount, gMonitorPopulation);
2158   popCount += gOmInUseCount + gMonitorFreeCount;
2159 
2160   out->print_cr("%18s  %10s  %10s  %10s",
2161                 "Per-Thread Lists:", "InUse", "Free", "Provision");
2162   out->print_cr("==================  ==========  ==========  ==========");
2163 
2164   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2165     out->print_cr(INTPTR_FORMAT "  %10d  %10d  %10d", p2i(jt),
2166                   jt->omInUseCount, jt->omFreeCount, jt->omFreeProvision);
2167     popCount += jt->omInUseCount + jt->omFreeCount;
2168   }
2169   return popCount;
2170 }
2171 
2172 #ifndef PRODUCT
2173 
2174 // Check if monitor belongs to the monitor cache
2175 // The list is grow-only so it's *relatively* safe to traverse
2176 // the list of extant blocks without taking a lock.
2177 
2178 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2179   PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
2180   while (block != NULL) {
2181     assert(block->object() == CHAINMARKER, "must be a block header");
2182     if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2183       address mon = (address)monitor;
2184       address blk = (address)block;
2185       size_t diff = mon - blk;
2186       assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
2187       return 1;
2188     }
2189     block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
2190   }
2191   return 0;
2192 }
2193 
2194 #endif