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 "memory/universe.hpp"
  35 #include "oops/markWord.hpp"
  36 #include "oops/oop.inline.hpp"
  37 #include "runtime/atomic.hpp"
  38 #include "runtime/biasedLocking.hpp"
  39 #include "runtime/handles.inline.hpp"
  40 #include "runtime/interfaceSupport.inline.hpp"
  41 #include "runtime/mutexLocker.hpp"
  42 #include "runtime/objectMonitor.hpp"
  43 #include "runtime/objectMonitor.inline.hpp"
  44 #include "runtime/osThread.hpp"
  45 #include "runtime/safepointVerifiers.hpp"
  46 #include "runtime/sharedRuntime.hpp"
  47 #include "runtime/stubRoutines.hpp"
  48 #include "runtime/synchronizer.hpp"
  49 #include "runtime/thread.inline.hpp"
  50 #include "runtime/timer.hpp"
  51 #include "runtime/vframe.hpp"
  52 #include "runtime/vmThread.hpp"
  53 #include "utilities/align.hpp"
  54 #include "utilities/dtrace.hpp"
  55 #include "utilities/events.hpp"
  56 #include "utilities/preserveException.hpp"
  57 
  58 // The "core" versions of monitor enter and exit reside in this file.
  59 // The interpreter and compilers contain specialized transliterated
  60 // variants of the enter-exit fast-path operations.  See i486.ad fast_lock(),
  61 // for instance.  If you make changes here, make sure to modify the
  62 // interpreter, and both C1 and C2 fast-path inline locking code emission.
  63 //
  64 // -----------------------------------------------------------------------------
  65 
  66 #ifdef DTRACE_ENABLED
  67 
  68 // Only bother with this argument setup if dtrace is available
  69 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
  70 
  71 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
  72   char* bytes = NULL;                                                      \
  73   int len = 0;                                                             \
  74   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
  75   Symbol* klassname = ((oop)(obj))->klass()->name();                       \
  76   if (klassname != NULL) {                                                 \
  77     bytes = (char*)klassname->bytes();                                     \
  78     len = klassname->utf8_length();                                        \
  79   }
  80 
  81 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
  82   {                                                                        \
  83     if (DTraceMonitorProbes) {                                             \
  84       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
  85       HOTSPOT_MONITOR_WAIT(jtid,                                           \
  86                            (uintptr_t)(monitor), bytes, len, (millis));    \
  87     }                                                                      \
  88   }
  89 
  90 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
  91 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
  92 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
  93 
  94 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
  95   {                                                                        \
  96     if (DTraceMonitorProbes) {                                             \
  97       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
  98       HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */             \
  99                                     (uintptr_t)(monitor), bytes, len);     \
 100     }                                                                      \
 101   }
 102 
 103 #else //  ndef DTRACE_ENABLED
 104 
 105 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 106 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 107 
 108 #endif // ndef DTRACE_ENABLED
 109 
 110 // This exists only as a workaround of dtrace bug 6254741
 111 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
 112   DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
 113   return 0;
 114 }
 115 
 116 #define NINFLATIONLOCKS 256
 117 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
 118 
 119 // global list of blocks of monitors
 120 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL;
 121 // global monitor free list
 122 ObjectMonitor * volatile ObjectSynchronizer::gFreeList  = NULL;
 123 // global monitor in-use list, for moribund threads,
 124 // monitors they inflated need to be scanned for deflation
 125 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList  = NULL;
 126 // count of entries in gOmInUseList
 127 int ObjectSynchronizer::gOmInUseCount = 0;
 128 
 129 static volatile intptr_t gListLock = 0;      // protects global monitor lists
 130 static volatile int gMonitorFreeCount  = 0;  // # on gFreeList
 131 static volatile int gMonitorPopulation = 0;  // # Extant -- in circulation
 132 
 133 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
 134 
 135 
 136 // =====================> Quick functions
 137 
 138 // The quick_* forms are special fast-path variants used to improve
 139 // performance.  In the simplest case, a "quick_*" implementation could
 140 // simply return false, in which case the caller will perform the necessary
 141 // state transitions and call the slow-path form.
 142 // The fast-path is designed to handle frequently arising cases in an efficient
 143 // manner and is just a degenerate "optimistic" variant of the slow-path.
 144 // returns true  -- to indicate the call was satisfied.
 145 // returns false -- to indicate the call needs the services of the slow-path.
 146 // A no-loitering ordinance is in effect for code in the quick_* family
 147 // operators: safepoints or indefinite blocking (blocking that might span a
 148 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
 149 // entry.
 150 //
 151 // Consider: An interesting optimization is to have the JIT recognize the
 152 // following common idiom:
 153 //   synchronized (someobj) { .... ; notify(); }
 154 // That is, we find a notify() or notifyAll() call that immediately precedes
 155 // the monitorexit operation.  In that case the JIT could fuse the operations
 156 // into a single notifyAndExit() runtime primitive.
 157 
 158 bool ObjectSynchronizer::quick_notify(oopDesc * obj, Thread * self, bool all) {
 159   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 160   assert(self->is_Java_thread(), "invariant");
 161   assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
 162   NoSafepointVerifier nsv;
 163   if (obj == NULL) return false;  // slow-path for invalid obj
 164   const markWord mark = obj->mark();
 165 
 166   if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) {
 167     // Degenerate notify
 168     // stack-locked by caller so by definition the implied waitset is empty.
 169     return true;
 170   }
 171 
 172   if (mark.has_monitor()) {
 173     ObjectMonitor * const mon = mark.monitor();
 174     assert(oopDesc::equals((oop) mon->object(), obj), "invariant");
 175     if (mon->owner() != self) return false;  // slow-path for IMS exception
 176 
 177     if (mon->first_waiter() != NULL) {
 178       // We have one or more waiters. Since this is an inflated monitor
 179       // that we own, we can transfer one or more threads from the waitset
 180       // to the entrylist here and now, avoiding the slow-path.
 181       if (all) {
 182         DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
 183       } else {
 184         DTRACE_MONITOR_PROBE(notify, mon, obj, self);
 185       }
 186       int tally = 0;
 187       do {
 188         mon->INotify(self);
 189         ++tally;
 190       } while (mon->first_waiter() != NULL && all);
 191       OM_PERFDATA_OP(Notifications, inc(tally));
 192     }
 193     return true;
 194   }
 195 
 196   // biased locking and any other IMS exception states take the slow-path
 197   return false;
 198 }
 199 
 200 
 201 // The LockNode emitted directly at the synchronization site would have
 202 // been too big if it were to have included support for the cases of inflated
 203 // recursive enter and exit, so they go here instead.
 204 // Note that we can't safely call AsyncPrintJavaStack() from within
 205 // quick_enter() as our thread state remains _in_Java.
 206 
 207 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
 208                                      BasicLock * lock) {
 209   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 210   assert(Self->is_Java_thread(), "invariant");
 211   assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
 212   NoSafepointVerifier nsv;
 213   if (obj == NULL) return false;       // Need to throw NPE
 214   const markWord mark = obj->mark();
 215 
 216   if (mark.has_monitor()) {
 217     ObjectMonitor * const m = mark.monitor();
 218     assert(oopDesc::equals((oop) m->object(), obj), "invariant");
 219     Thread * const owner = (Thread *) m->_owner;
 220 
 221     // Lock contention and Transactional Lock Elision (TLE) diagnostics
 222     // and observability
 223     // Case: light contention possibly amenable to TLE
 224     // Case: TLE inimical operations such as nested/recursive synchronization
 225 
 226     if (owner == Self) {
 227       m->_recursions++;
 228       return true;
 229     }
 230 
 231     // This Java Monitor is inflated so obj's header will never be
 232     // displaced to this thread's BasicLock. Make the displaced header
 233     // non-NULL so this BasicLock is not seen as recursive nor as
 234     // being locked. We do this unconditionally so that this thread's
 235     // BasicLock cannot be mis-interpreted by any stack walkers. For
 236     // performance reasons, stack walkers generally first check for
 237     // Biased Locking in the object's header, the second check is for
 238     // stack-locking in the object's header, the third check is for
 239     // recursive stack-locking in the displaced header in the BasicLock,
 240     // and last are the inflated Java Monitor (ObjectMonitor) checks.
 241     lock->set_displaced_header(markWord::unused_mark());
 242 
 243     if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
 244       assert(m->_recursions == 0, "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   markWord mark = object->mark();
 286   // We cannot check for Biased Locking if we are racing an inflation.
 287   assert(mark == markWord::INFLATING() ||
 288          !mark.has_bias_pattern(), "should not see bias pattern here");
 289 
 290   markWord dhw = lock->displaced_header();
 291   if (dhw.value() == 0) {
 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 != markWord::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 == markWord::from_pointer(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   markWord 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(markWord::from_pointer(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().value(), "don't relock with same BasicLock");
 354     lock->set_displaced_header(markWord::from_pointer(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(markWord::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. We
 433   // intentionally do not use CHECK here because we must exit the
 434   // monitor even if an exception is pending.
 435   if (monitor->check_owner(THREAD)) {
 436     monitor->exit(true, THREAD);
 437   }
 438 }
 439 
 440 // -----------------------------------------------------------------------------
 441 // Internal VM locks on java objects
 442 // standard constructor, allows locking failures
 443 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
 444   _dolock = doLock;
 445   _thread = thread;
 446   _thread->check_for_valid_safepoint_state(false);
 447   _obj = obj;
 448 
 449   if (_dolock) {
 450     ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
 451   }
 452 }
 453 
 454 ObjectLocker::~ObjectLocker() {
 455   if (_dolock) {
 456     ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
 457   }
 458 }
 459 
 460 
 461 // -----------------------------------------------------------------------------
 462 //  Wait/Notify/NotifyAll
 463 // NOTE: must use heavy weight monitor to handle wait()
 464 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 465   if (UseBiasedLocking) {
 466     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 467     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 468   }
 469   if (millis < 0) {
 470     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 471   }
 472   ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
 473 
 474   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
 475   monitor->wait(millis, true, THREAD);
 476 
 477   // This dummy call is in place to get around dtrace bug 6254741.  Once
 478   // that's fixed we can uncomment the following line, remove the call
 479   // and change this function back into a "void" func.
 480   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 481   return dtrace_waited_probe(monitor, obj, THREAD);
 482 }
 483 
 484 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
 485   if (UseBiasedLocking) {
 486     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 487     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 488   }
 489   if (millis < 0) {
 490     THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 491   }
 492   inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD);
 493 }
 494 
 495 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 496   if (UseBiasedLocking) {
 497     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 498     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 499   }
 500 
 501   markWord mark = obj->mark();
 502   if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
 503     return;
 504   }
 505   inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD);
 506 }
 507 
 508 // NOTE: see comment of notify()
 509 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 510   if (UseBiasedLocking) {
 511     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 512     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 513   }
 514 
 515   markWord mark = obj->mark();
 516   if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
 517     return;
 518   }
 519   inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD);
 520 }
 521 
 522 // -----------------------------------------------------------------------------
 523 // Hash Code handling
 524 //
 525 // Performance concern:
 526 // OrderAccess::storestore() calls release() which at one time stored 0
 527 // into the global volatile OrderAccess::dummy variable. This store was
 528 // unnecessary for correctness. Many threads storing into a common location
 529 // causes considerable cache migration or "sloshing" on large SMP systems.
 530 // As such, I avoided using OrderAccess::storestore(). In some cases
 531 // OrderAccess::fence() -- which incurs local latency on the executing
 532 // processor -- is a better choice as it scales on SMP systems.
 533 //
 534 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
 535 // a discussion of coherency costs. Note that all our current reference
 536 // platforms provide strong ST-ST order, so the issue is moot on IA32,
 537 // x64, and SPARC.
 538 //
 539 // As a general policy we use "volatile" to control compiler-based reordering
 540 // and explicit fences (barriers) to control for architectural reordering
 541 // performed by the CPU(s) or platform.
 542 
 543 struct SharedGlobals {
 544   char         _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
 545   // These are highly shared mostly-read variables.
 546   // To avoid false-sharing they need to be the sole occupants of a cache line.
 547   volatile int stwRandom;
 548   volatile int stwCycle;
 549   DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
 550   // Hot RW variable -- Sequester to avoid false-sharing
 551   volatile int hcSequence;
 552   DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
 553 };
 554 
 555 static SharedGlobals GVars;
 556 static int MonitorScavengeThreshold = 1000000;
 557 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
 558 
 559 static markWord ReadStableMark(oop obj) {
 560   markWord mark = obj->mark();
 561   if (!mark.is_being_inflated()) {
 562     return mark;       // normal fast-path return
 563   }
 564 
 565   int its = 0;
 566   for (;;) {
 567     markWord mark = obj->mark();
 568     if (!mark.is_being_inflated()) {
 569       return mark;    // normal fast-path return
 570     }
 571 
 572     // The object is being inflated by some other thread.
 573     // The caller of ReadStableMark() must wait for inflation to complete.
 574     // Avoid live-lock
 575     // TODO: consider calling SafepointSynchronize::do_call_back() while
 576     // spinning to see if there's a safepoint pending.  If so, immediately
 577     // yielding or blocking would be appropriate.  Avoid spinning while
 578     // there is a safepoint pending.
 579     // TODO: add inflation contention performance counters.
 580     // TODO: restrict the aggregate number of spinners.
 581 
 582     ++its;
 583     if (its > 10000 || !os::is_MP()) {
 584       if (its & 1) {
 585         os::naked_yield();
 586       } else {
 587         // Note that the following code attenuates the livelock problem but is not
 588         // a complete remedy.  A more complete solution would require that the inflating
 589         // thread hold the associated inflation lock.  The following code simply restricts
 590         // the number of spinners to at most one.  We'll have N-2 threads blocked
 591         // on the inflationlock, 1 thread holding the inflation lock and using
 592         // a yield/park strategy, and 1 thread in the midst of inflation.
 593         // A more refined approach would be to change the encoding of INFLATING
 594         // to allow encapsulation of a native thread pointer.  Threads waiting for
 595         // inflation to complete would use CAS to push themselves onto a singly linked
 596         // list rooted at the markword.  Once enqueued, they'd loop, checking a per-thread flag
 597         // and calling park().  When inflation was complete the thread that accomplished inflation
 598         // would detach the list and set the markword to inflated with a single CAS and
 599         // then for each thread on the list, set the flag and unpark() the thread.
 600         // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
 601         // wakes at most one thread whereas we need to wake the entire list.
 602         int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
 603         int YieldThenBlock = 0;
 604         assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
 605         assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
 606         Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
 607         while (obj->mark() == markWord::INFLATING()) {
 608           // Beware: NakedYield() is advisory and has almost no effect on some platforms
 609           // so we periodically call Self->_ParkEvent->park(1).
 610           // We use a mixed spin/yield/block mechanism.
 611           if ((YieldThenBlock++) >= 16) {
 612             Thread::current()->_ParkEvent->park(1);
 613           } else {
 614             os::naked_yield();
 615           }
 616         }
 617         Thread::muxRelease(gInflationLocks + ix);
 618       }
 619     } else {
 620       SpinPause();       // SMP-polite spinning
 621     }
 622   }
 623 }
 624 
 625 // hashCode() generation :
 626 //
 627 // Possibilities:
 628 // * MD5Digest of {obj,stwRandom}
 629 // * CRC32 of {obj,stwRandom} or any linear-feedback shift register function.
 630 // * A DES- or AES-style SBox[] mechanism
 631 // * One of the Phi-based schemes, such as:
 632 //   2654435761 = 2^32 * Phi (golden ratio)
 633 //   HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ;
 634 // * A variation of Marsaglia's shift-xor RNG scheme.
 635 // * (obj ^ stwRandom) is appealing, but can result
 636 //   in undesirable regularity in the hashCode values of adjacent objects
 637 //   (objects allocated back-to-back, in particular).  This could potentially
 638 //   result in hashtable collisions and reduced hashtable efficiency.
 639 //   There are simple ways to "diffuse" the middle address bits over the
 640 //   generated hashCode values:
 641 
 642 static inline intptr_t get_next_hash(Thread * Self, oop obj) {
 643   intptr_t value = 0;
 644   if (hashCode == 0) {
 645     // This form uses global Park-Miller RNG.
 646     // On MP system we'll have lots of RW access to a global, so the
 647     // mechanism induces lots of coherency traffic.
 648     value = os::random();
 649   } else if (hashCode == 1) {
 650     // This variation has the property of being stable (idempotent)
 651     // between STW operations.  This can be useful in some of the 1-0
 652     // synchronization schemes.
 653     intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3;
 654     value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom;
 655   } else if (hashCode == 2) {
 656     value = 1;            // for sensitivity testing
 657   } else if (hashCode == 3) {
 658     value = ++GVars.hcSequence;
 659   } else if (hashCode == 4) {
 660     value = cast_from_oop<intptr_t>(obj);
 661   } else {
 662     // Marsaglia's xor-shift scheme with thread-specific state
 663     // This is probably the best overall implementation -- we'll
 664     // likely make this the default in future releases.
 665     unsigned t = Self->_hashStateX;
 666     t ^= (t << 11);
 667     Self->_hashStateX = Self->_hashStateY;
 668     Self->_hashStateY = Self->_hashStateZ;
 669     Self->_hashStateZ = Self->_hashStateW;
 670     unsigned v = Self->_hashStateW;
 671     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
 672     Self->_hashStateW = v;
 673     value = v;
 674   }
 675 
 676   value &= markWord::hash_mask;
 677   if (value == 0) value = 0xBAD;
 678   assert(value != markWord::no_hash, "invariant");
 679   return value;
 680 }
 681 
 682 intptr_t ObjectSynchronizer::FastHashCode(Thread * Self, oop obj) {
 683   if (UseBiasedLocking) {
 684     // NOTE: many places throughout the JVM do not expect a safepoint
 685     // to be taken here, in particular most operations on perm gen
 686     // objects. However, we only ever bias Java instances and all of
 687     // the call sites of identity_hash that might revoke biases have
 688     // been checked to make sure they can handle a safepoint. The
 689     // added check of the bias pattern is to avoid useless calls to
 690     // thread-local storage.
 691     if (obj->mark().has_bias_pattern()) {
 692       // Handle for oop obj in case of STW safepoint
 693       Handle hobj(Self, obj);
 694       // Relaxing assertion for bug 6320749.
 695       assert(Universe::verify_in_progress() ||
 696              !SafepointSynchronize::is_at_safepoint(),
 697              "biases should not be seen by VM thread here");
 698       BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
 699       obj = hobj();
 700       assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 701     }
 702   }
 703 
 704   // hashCode() is a heap mutator ...
 705   // Relaxing assertion for bug 6320749.
 706   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 707          !SafepointSynchronize::is_at_safepoint(), "invariant");
 708   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 709          Self->is_Java_thread() , "invariant");
 710   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 711          ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
 712 
 713   ObjectMonitor* monitor = NULL;
 714   markWord temp, test;
 715   intptr_t hash;
 716   markWord mark = ReadStableMark(obj);
 717 
 718   // object should remain ineligible for biased locking
 719   assert(!mark.has_bias_pattern(), "invariant");
 720 
 721   if (mark.is_neutral()) {
 722     hash = mark.hash();               // this is a normal header
 723     if (hash != 0) {                  // if it has hash, just return it
 724       return hash;
 725     }
 726     hash = get_next_hash(Self, obj);  // allocate a new hash code
 727     temp = mark.copy_set_hash(hash);  // merge the hash code into header
 728     // use (machine word version) atomic operation to install the hash
 729     test = obj->cas_set_mark(temp, mark);
 730     if (test == mark) {
 731       return hash;
 732     }
 733     // If atomic operation failed, we must inflate the header
 734     // into heavy weight monitor. We could add more code here
 735     // for fast path, but it does not worth the complexity.
 736   } else if (mark.has_monitor()) {
 737     monitor = mark.monitor();
 738     temp = monitor->header();
 739     assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 740     hash = temp.hash();
 741     if (hash != 0) {
 742       return hash;
 743     }
 744     // Skip to the following code to reduce code size
 745   } else if (Self->is_lock_owned((address)mark.locker())) {
 746     temp = mark.displaced_mark_helper(); // this is a lightweight monitor owned
 747     assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 748     hash = temp.hash();                  // by current thread, check if the displaced
 749     if (hash != 0) {                     // header contains hash code
 750       return hash;
 751     }
 752     // WARNING:
 753     // The displaced header in the BasicLock on a thread's stack
 754     // is strictly immutable. It CANNOT be changed in ANY cases.
 755     // So we have to inflate the stack lock into an ObjectMonitor
 756     // even if the current thread owns the lock. The BasicLock on
 757     // a thread's stack can be asynchronously read by other threads
 758     // during an inflate() call so any change to that stack memory
 759     // may not propagate to other threads 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, mark.value());
 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, temp.value());
 772     uintptr_t v = Atomic::cmpxchg(temp.value(), (volatile uintptr_t*)monitor->header_addr(), mark.value());
 773     test = markWord(v);
 774     if (test != mark) {
 775       // The only update to the ObjectMonitor's header/dmw field
 776       // is to merge in the hash code. If someone adds a new usage
 777       // of the header/dmw field, please update this code.
 778       hash = test.hash();
 779       assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
 780       assert(hash != 0, "Trivial unexpected object/monitor header usage.");
 781     }
 782   }
 783   // We finally get the hash
 784   return hash;
 785 }
 786 
 787 // Deprecated -- use FastHashCode() instead.
 788 
 789 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
 790   return FastHashCode(Thread::current(), obj());
 791 }
 792 
 793 
 794 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
 795                                                    Handle h_obj) {
 796   if (UseBiasedLocking) {
 797     BiasedLocking::revoke_and_rebias(h_obj, false, thread);
 798     assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
 799   }
 800 
 801   assert(thread == JavaThread::current(), "Can only be called on current thread");
 802   oop obj = h_obj();
 803 
 804   markWord mark = ReadStableMark(obj);
 805 
 806   // Uncontended case, header points to stack
 807   if (mark.has_locker()) {
 808     return thread->is_lock_owned((address)mark.locker());
 809   }
 810   // Contended case, header points to ObjectMonitor (tagged pointer)
 811   if (mark.has_monitor()) {
 812     ObjectMonitor* monitor = mark.monitor();
 813     return monitor->is_entered(thread) != 0;
 814   }
 815   // Unlocked case, header in place
 816   assert(mark.is_neutral(), "sanity check");
 817   return false;
 818 }
 819 
 820 // Be aware of this method could revoke bias of the lock object.
 821 // This method queries the ownership of the lock handle specified by 'h_obj'.
 822 // If the current thread owns the lock, it returns owner_self. If no
 823 // thread owns the lock, it returns owner_none. Otherwise, it will return
 824 // owner_other.
 825 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
 826 (JavaThread *self, Handle h_obj) {
 827   // The caller must beware this method can revoke bias, and
 828   // revocation can result in a safepoint.
 829   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 830   assert(self->thread_state() != _thread_blocked, "invariant");
 831 
 832   // Possible mark states: neutral, biased, stack-locked, inflated
 833 
 834   if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
 835     // CASE: biased
 836     BiasedLocking::revoke_and_rebias(h_obj, false, self);
 837     assert(!h_obj->mark().has_bias_pattern(),
 838            "biases should be revoked by now");
 839   }
 840 
 841   assert(self == JavaThread::current(), "Can only be called on current thread");
 842   oop obj = h_obj();
 843   markWord mark = ReadStableMark(obj);
 844 
 845   // CASE: stack-locked.  Mark points to a BasicLock on the owner's stack.
 846   if (mark.has_locker()) {
 847     return self->is_lock_owned((address)mark.locker()) ?
 848       owner_self : owner_other;
 849   }
 850 
 851   // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
 852   // The Object:ObjectMonitor relationship is stable as long as we're
 853   // not at a safepoint.
 854   if (mark.has_monitor()) {
 855     void * owner = mark.monitor()->_owner;
 856     if (owner == NULL) return owner_none;
 857     return (owner == self ||
 858             self->is_lock_owned((address)owner)) ? owner_self : owner_other;
 859   }
 860 
 861   // CASE: neutral
 862   assert(mark.is_neutral(), "sanity check");
 863   return owner_none;           // it's unlocked
 864 }
 865 
 866 // FIXME: jvmti should call this
 867 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
 868   if (UseBiasedLocking) {
 869     if (SafepointSynchronize::is_at_safepoint()) {
 870       BiasedLocking::revoke_at_safepoint(h_obj);
 871     } else {
 872       BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
 873     }
 874     assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
 875   }
 876 
 877   oop obj = h_obj();
 878   address owner = NULL;
 879 
 880   markWord mark = ReadStableMark(obj);
 881 
 882   // Uncontended case, header points to stack
 883   if (mark.has_locker()) {
 884     owner = (address) mark.locker();
 885   }
 886 
 887   // Contended case, header points to ObjectMonitor (tagged pointer)
 888   else if (mark.has_monitor()) {
 889     ObjectMonitor* monitor = mark.monitor();
 890     assert(monitor != NULL, "monitor should be non-null");
 891     owner = (address) monitor->owner();
 892   }
 893 
 894   if (owner != NULL) {
 895     // owning_thread_from_monitor_owner() may also return NULL here
 896     return Threads::owning_thread_from_monitor_owner(t_list, owner);
 897   }
 898 
 899   // Unlocked case, header in place
 900   // Cannot have assertion since this object may have been
 901   // locked by another thread when reaching here.
 902   // assert(mark.is_neutral(), "sanity check");
 903 
 904   return NULL;
 905 }
 906 
 907 // Visitors ...
 908 
 909 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
 910   PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
 911   while (block != NULL) {
 912     assert(block->object() == CHAINMARKER, "must be a block header");
 913     for (int i = _BLOCKSIZE - 1; i > 0; i--) {
 914       ObjectMonitor* mid = (ObjectMonitor *)(block + i);
 915       oop object = (oop)mid->object();
 916       if (object != NULL) {
 917         closure->do_monitor(mid);
 918       }
 919     }
 920     block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
 921   }
 922 }
 923 
 924 // Get the next block in the block list.
 925 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
 926   assert(block->object() == CHAINMARKER, "must be a block header");
 927   block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
 928   assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
 929   return block;
 930 }
 931 
 932 static bool monitors_used_above_threshold() {
 933   if (gMonitorPopulation == 0) {
 934     return false;
 935   }
 936   int monitors_used = gMonitorPopulation - gMonitorFreeCount;
 937   int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
 938   return monitor_usage > MonitorUsedDeflationThreshold;
 939 }
 940 
 941 bool ObjectSynchronizer::is_cleanup_needed() {
 942   if (MonitorUsedDeflationThreshold > 0) {
 943     return monitors_used_above_threshold();
 944   }
 945   return false;
 946 }
 947 
 948 void ObjectSynchronizer::oops_do(OopClosure* f) {
 949   // We only scan the global used list here (for moribund threads), and
 950   // the thread-local monitors in Thread::oops_do().
 951   global_used_oops_do(f);
 952 }
 953 
 954 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
 955   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
 956   list_oops_do(gOmInUseList, f);
 957 }
 958 
 959 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
 960   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
 961   list_oops_do(thread->omInUseList, f);
 962 }
 963 
 964 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
 965   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
 966   ObjectMonitor* mid;
 967   for (mid = list; mid != NULL; mid = mid->FreeNext) {
 968     if (mid->object() != NULL) {
 969       f->do_oop((oop*)mid->object_addr());
 970     }
 971   }
 972 }
 973 
 974 
 975 // -----------------------------------------------------------------------------
 976 // ObjectMonitor Lifecycle
 977 // -----------------------
 978 // Inflation unlinks monitors from the global gFreeList and
 979 // associates them with objects.  Deflation -- which occurs at
 980 // STW-time -- disassociates idle monitors from objects.  Such
 981 // scavenged monitors are returned to the gFreeList.
 982 //
 983 // The global list is protected by gListLock.  All the critical sections
 984 // are short and operate in constant-time.
 985 //
 986 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
 987 //
 988 // Lifecycle:
 989 // --   unassigned and on the global free list
 990 // --   unassigned and on a thread's private omFreeList
 991 // --   assigned to an object.  The object is inflated and the mark refers
 992 //      to the objectmonitor.
 993 
 994 
 995 // Constraining monitor pool growth via MonitorBound ...
 996 //
 997 // The monitor pool is grow-only.  We scavenge at STW safepoint-time, but the
 998 // the rate of scavenging is driven primarily by GC.  As such,  we can find
 999 // an inordinate number of monitors in circulation.
1000 // To avoid that scenario we can artificially induce a STW safepoint
1001 // if the pool appears to be growing past some reasonable bound.
1002 // Generally we favor time in space-time tradeoffs, but as there's no
1003 // natural back-pressure on the # of extant monitors we need to impose some
1004 // type of limit.  Beware that if MonitorBound is set to too low a value
1005 // we could just loop. In addition, if MonitorBound is set to a low value
1006 // we'll incur more safepoints, which are harmful to performance.
1007 // See also: GuaranteedSafepointInterval
1008 //
1009 // The current implementation uses asynchronous VM operations.
1010 
1011 static void InduceScavenge(Thread * Self, const char * Whence) {
1012   // Induce STW safepoint to trim monitors
1013   // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1014   // More precisely, trigger an asynchronous STW safepoint as the number
1015   // of active monitors passes the specified threshold.
1016   // TODO: assert thread state is reasonable
1017 
1018   if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1019     // Induce a 'null' safepoint to scavenge monitors
1020     // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1021     // to the VMthread and have a lifespan longer than that of this activation record.
1022     // The VMThread will delete the op when completed.
1023     VMThread::execute(new VM_ScavengeMonitors());
1024   }
1025 }
1026 
1027 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self) {
1028   // A large MAXPRIVATE value reduces both list lock contention
1029   // and list coherency traffic, but also tends to increase the
1030   // number of objectMonitors in circulation as well as the STW
1031   // scavenge costs.  As usual, we lean toward time in space-time
1032   // tradeoffs.
1033   const int MAXPRIVATE = 1024;
1034   stringStream ss;
1035   for (;;) {
1036     ObjectMonitor * m;
1037 
1038     // 1: try to allocate from the thread's local omFreeList.
1039     // Threads will attempt to allocate first from their local list, then
1040     // from the global list, and only after those attempts fail will the thread
1041     // attempt to instantiate new monitors.   Thread-local free lists take
1042     // heat off the gListLock and improve allocation latency, as well as reducing
1043     // coherency traffic on the shared global list.
1044     m = Self->omFreeList;
1045     if (m != NULL) {
1046       Self->omFreeList = m->FreeNext;
1047       Self->omFreeCount--;
1048       guarantee(m->object() == NULL, "invariant");
1049       m->FreeNext = Self->omInUseList;
1050       Self->omInUseList = m;
1051       Self->omInUseCount++;
1052       return m;
1053     }
1054 
1055     // 2: try to allocate from the global gFreeList
1056     // CONSIDER: use muxTry() instead of muxAcquire().
1057     // If the muxTry() fails then drop immediately into case 3.
1058     // If we're using thread-local free lists then try
1059     // to reprovision the caller's free list.
1060     if (gFreeList != NULL) {
1061       // Reprovision the thread's omFreeList.
1062       // Use bulk transfers to reduce the allocation rate and heat
1063       // on various locks.
1064       Thread::muxAcquire(&gListLock, "omAlloc(1)");
1065       for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1066         gMonitorFreeCount--;
1067         ObjectMonitor * take = gFreeList;
1068         gFreeList = take->FreeNext;
1069         guarantee(take->object() == NULL, "invariant");
1070         take->Recycle();
1071         omRelease(Self, take, false);
1072       }
1073       Thread::muxRelease(&gListLock);
1074       Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1075       if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1076 
1077       const int mx = MonitorBound;
1078       if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1079         // We can't safely induce a STW safepoint from omAlloc() as our thread
1080         // state may not be appropriate for such activities and callers may hold
1081         // naked oops, so instead we defer the action.
1082         InduceScavenge(Self, "omAlloc");
1083       }
1084       continue;
1085     }
1086 
1087     // 3: allocate a block of new ObjectMonitors
1088     // Both the local and global free lists are empty -- resort to malloc().
1089     // In the current implementation objectMonitors are TSM - immortal.
1090     // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1091     // each ObjectMonitor to start at the beginning of a cache line,
1092     // so we use align_up().
1093     // A better solution would be to use C++ placement-new.
1094     // BEWARE: As it stands currently, we don't run the ctors!
1095     assert(_BLOCKSIZE > 1, "invariant");
1096     size_t neededsize = sizeof(PaddedEnd<ObjectMonitor>) * _BLOCKSIZE;
1097     PaddedEnd<ObjectMonitor> * temp;
1098     size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1099     void* real_malloc_addr = (void *)NEW_C_HEAP_ARRAY(char, aligned_size,
1100                                                       mtInternal);
1101     temp = (PaddedEnd<ObjectMonitor> *)
1102              align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1103 
1104     // NOTE: (almost) no way to recover if allocation failed.
1105     // We might be able to induce a STW safepoint and scavenge enough
1106     // objectMonitors to permit progress.
1107     if (temp == NULL) {
1108       vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1109                             "Allocate ObjectMonitors");
1110     }
1111     (void)memset((void *) temp, 0, neededsize);
1112 
1113     // Format the block.
1114     // initialize the linked list, each monitor points to its next
1115     // forming the single linked free list, the very first monitor
1116     // will points to next block, which forms the block list.
1117     // The trick of using the 1st element in the block as gBlockList
1118     // linkage should be reconsidered.  A better implementation would
1119     // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1120 
1121     for (int i = 1; i < _BLOCKSIZE; i++) {
1122       temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1123     }
1124 
1125     // terminate the last monitor as the end of list
1126     temp[_BLOCKSIZE - 1].FreeNext = NULL;
1127 
1128     // Element [0] is reserved for global list linkage
1129     temp[0].set_object(CHAINMARKER);
1130 
1131     // Consider carving out this thread's current request from the
1132     // block in hand.  This avoids some lock traffic and redundant
1133     // list activity.
1134 
1135     // Acquire the gListLock to manipulate gBlockList and gFreeList.
1136     // An Oyama-Taura-Yonezawa scheme might be more efficient.
1137     Thread::muxAcquire(&gListLock, "omAlloc(2)");
1138     gMonitorPopulation += _BLOCKSIZE-1;
1139     gMonitorFreeCount += _BLOCKSIZE-1;
1140 
1141     // Add the new block to the list of extant blocks (gBlockList).
1142     // The very first objectMonitor in a block is reserved and dedicated.
1143     // It serves as blocklist "next" linkage.
1144     temp[0].FreeNext = gBlockList;
1145     // There are lock-free uses of gBlockList so make sure that
1146     // the previous stores happen before we update gBlockList.
1147     OrderAccess::release_store(&gBlockList, temp);
1148 
1149     // Add the new string of objectMonitors to the global free list
1150     temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1151     gFreeList = temp + 1;
1152     Thread::muxRelease(&gListLock);
1153   }
1154 }
1155 
1156 // Place "m" on the caller's private per-thread omFreeList.
1157 // In practice there's no need to clamp or limit the number of
1158 // monitors on a thread's omFreeList as the only time we'll call
1159 // omRelease is to return a monitor to the free list after a CAS
1160 // attempt failed.  This doesn't allow unbounded #s of monitors to
1161 // accumulate on a thread's free list.
1162 //
1163 // Key constraint: all ObjectMonitors on a thread's free list and the global
1164 // free list must have their object field set to null. This prevents the
1165 // scavenger -- deflate_monitor_list() -- from reclaiming them.
1166 
1167 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1168                                    bool fromPerThreadAlloc) {
1169   guarantee(m->header().value() == 0, "invariant");
1170   guarantee(m->object() == NULL, "invariant");
1171   stringStream ss;
1172   guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1173             "%s, recursions=" INTPTR_FORMAT, m->is_busy_to_string(&ss),
1174             m->_recursions);
1175   // Remove from omInUseList
1176   if (fromPerThreadAlloc) {
1177     ObjectMonitor* cur_mid_in_use = NULL;
1178     bool extracted = false;
1179     for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1180       if (m == mid) {
1181         // extract from per-thread in-use list
1182         if (mid == Self->omInUseList) {
1183           Self->omInUseList = mid->FreeNext;
1184         } else if (cur_mid_in_use != NULL) {
1185           cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1186         }
1187         extracted = true;
1188         Self->omInUseCount--;
1189         break;
1190       }
1191     }
1192     assert(extracted, "Should have extracted from in-use list");
1193   }
1194 
1195   // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1196   m->FreeNext = Self->omFreeList;
1197   Self->omFreeList = m;
1198   Self->omFreeCount++;
1199 }
1200 
1201 // Return the monitors of a moribund thread's local free list to
1202 // the global free list.  Typically a thread calls omFlush() when
1203 // it's dying.  We could also consider having the VM thread steal
1204 // monitors from threads that have not run java code over a few
1205 // consecutive STW safepoints.  Relatedly, we might decay
1206 // omFreeProvision at STW safepoints.
1207 //
1208 // Also return the monitors of a moribund thread's omInUseList to
1209 // a global gOmInUseList under the global list lock so these
1210 // will continue to be scanned.
1211 //
1212 // We currently call omFlush() from Threads::remove() _before the thread
1213 // has been excised from the thread list and is no longer a mutator.
1214 // This means that omFlush() cannot run concurrently with a safepoint and
1215 // interleave with the deflate_idle_monitors scavenge operator. In particular,
1216 // this ensures that the thread's monitors are scanned by a GC safepoint,
1217 // either via Thread::oops_do() (if safepoint happens before omFlush()) or via
1218 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1219 // monitors have been transferred to the global in-use list).
1220 
1221 void ObjectSynchronizer::omFlush(Thread * Self) {
1222   ObjectMonitor * list = Self->omFreeList;  // Null-terminated SLL
1223   ObjectMonitor * tail = NULL;
1224   int tally = 0;
1225   if (list != NULL) {
1226     ObjectMonitor * s;
1227     // The thread is going away. Set 'tail' to the last per-thread free
1228     // monitor which will be linked to gFreeList below under the gListLock.
1229     stringStream ss;
1230     for (s = list; s != NULL; s = s->FreeNext) {
1231       tally++;
1232       tail = s;
1233       guarantee(s->object() == NULL, "invariant");
1234       guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1235     }
1236     guarantee(tail != NULL, "invariant");
1237     assert(Self->omFreeCount == tally, "free-count off");
1238     Self->omFreeList = NULL;
1239     Self->omFreeCount = 0;
1240   }
1241 
1242   ObjectMonitor * inUseList = Self->omInUseList;
1243   ObjectMonitor * inUseTail = NULL;
1244   int inUseTally = 0;
1245   if (inUseList != NULL) {
1246     ObjectMonitor *cur_om;
1247     // The thread is going away, however the omInUseList inflated
1248     // monitors may still be in-use by other threads.
1249     // Link them to inUseTail, which will be linked into the global in-use list
1250     // gOmInUseList below, under the gListLock
1251     for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1252       inUseTail = cur_om;
1253       inUseTally++;
1254     }
1255     guarantee(inUseTail != NULL, "invariant");
1256     assert(Self->omInUseCount == inUseTally, "in-use count off");
1257     Self->omInUseList = NULL;
1258     Self->omInUseCount = 0;
1259   }
1260 
1261   Thread::muxAcquire(&gListLock, "omFlush");
1262   if (tail != NULL) {
1263     tail->FreeNext = gFreeList;
1264     gFreeList = list;
1265     gMonitorFreeCount += tally;
1266   }
1267 
1268   if (inUseTail != NULL) {
1269     inUseTail->FreeNext = gOmInUseList;
1270     gOmInUseList = inUseList;
1271     gOmInUseCount += inUseTally;
1272   }
1273 
1274   Thread::muxRelease(&gListLock);
1275 
1276   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1277   LogStreamHandle(Info, monitorinflation) lsh_info;
1278   LogStream * ls = NULL;
1279   if (log_is_enabled(Debug, monitorinflation)) {
1280     ls = &lsh_debug;
1281   } else if ((tally != 0 || inUseTally != 0) &&
1282              log_is_enabled(Info, monitorinflation)) {
1283     ls = &lsh_info;
1284   }
1285   if (ls != NULL) {
1286     ls->print_cr("omFlush: jt=" INTPTR_FORMAT ", free_monitor_tally=%d"
1287                  ", in_use_monitor_tally=%d" ", omFreeProvision=%d",
1288                  p2i(Self), tally, inUseTally, Self->omFreeProvision);
1289   }
1290 }
1291 
1292 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1293                                        const oop obj,
1294                                        ObjectSynchronizer::InflateCause cause) {
1295   assert(event != NULL, "invariant");
1296   assert(event->should_commit(), "invariant");
1297   event->set_monitorClass(obj->klass());
1298   event->set_address((uintptr_t)(void*)obj);
1299   event->set_cause((u1)cause);
1300   event->commit();
1301 }
1302 
1303 // Fast path code shared by multiple functions
1304 void ObjectSynchronizer::inflate_helper(oop obj) {
1305   markWord mark = obj->mark();
1306   if (mark.has_monitor()) {
1307     assert(ObjectSynchronizer::verify_objmon_isinpool(mark.monitor()), "monitor is invalid");
1308     assert(mark.monitor()->header().is_neutral(), "monitor must record a good object header");
1309     return;
1310   }
1311   inflate(Thread::current(), obj, inflate_cause_vm_internal);
1312 }
1313 
1314 ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self,
1315                                            oop object,
1316                                            const InflateCause cause) {
1317   // Inflate mutates the heap ...
1318   // Relaxing assertion for bug 6320749.
1319   assert(Universe::verify_in_progress() ||
1320          !SafepointSynchronize::is_at_safepoint(), "invariant");
1321 
1322   EventJavaMonitorInflate event;
1323 
1324   for (;;) {
1325     const markWord mark = object->mark();
1326     assert(!mark.has_bias_pattern(), "invariant");
1327 
1328     // The mark can be in one of the following states:
1329     // *  Inflated     - just return
1330     // *  Stack-locked - coerce it to inflated
1331     // *  INFLATING    - busy wait for conversion to complete
1332     // *  Neutral      - aggressively inflate the object.
1333     // *  BIASED       - Illegal.  We should never see this
1334 
1335     // CASE: inflated
1336     if (mark.has_monitor()) {
1337       ObjectMonitor * inf = mark.monitor();
1338       markWord dmw = inf->header();
1339       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1340       assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1341       assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1342       return inf;
1343     }
1344 
1345     // CASE: inflation in progress - inflating over a stack-lock.
1346     // Some other thread is converting from stack-locked to inflated.
1347     // Only that thread can complete inflation -- other threads must wait.
1348     // The INFLATING value is transient.
1349     // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1350     // We could always eliminate polling by parking the thread on some auxiliary list.
1351     if (mark == markWord::INFLATING()) {
1352       ReadStableMark(object);
1353       continue;
1354     }
1355 
1356     // CASE: stack-locked
1357     // Could be stack-locked either by this thread or by some other thread.
1358     //
1359     // Note that we allocate the objectmonitor speculatively, _before_ attempting
1360     // to install INFLATING into the mark word.  We originally installed INFLATING,
1361     // allocated the objectmonitor, and then finally STed the address of the
1362     // objectmonitor into the mark.  This was correct, but artificially lengthened
1363     // the interval in which INFLATED appeared in the mark, thus increasing
1364     // the odds of inflation contention.
1365     //
1366     // We now use per-thread private objectmonitor free lists.
1367     // These list are reprovisioned from the global free list outside the
1368     // critical INFLATING...ST interval.  A thread can transfer
1369     // multiple objectmonitors en-mass from the global free list to its local free list.
1370     // This reduces coherency traffic and lock contention on the global free list.
1371     // Using such local free lists, it doesn't matter if the omAlloc() call appears
1372     // before or after the CAS(INFLATING) operation.
1373     // See the comments in omAlloc().
1374 
1375     LogStreamHandle(Trace, monitorinflation) lsh;
1376 
1377     if (mark.has_locker()) {
1378       ObjectMonitor * m = omAlloc(Self);
1379       // Optimistically prepare the objectmonitor - anticipate successful CAS
1380       // We do this before the CAS in order to minimize the length of time
1381       // in which INFLATING appears in the mark.
1382       m->Recycle();
1383       m->_Responsible  = NULL;
1384       m->_SpinDuration = ObjectMonitor::Knob_SpinLimit;   // Consider: maintain by type/class
1385 
1386       markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1387       if (cmp != mark) {
1388         omRelease(Self, m, true);
1389         continue;       // Interference -- just retry
1390       }
1391 
1392       // We've successfully installed INFLATING (0) into the mark-word.
1393       // This is the only case where 0 will appear in a mark-word.
1394       // Only the singular thread that successfully swings the mark-word
1395       // to 0 can perform (or more precisely, complete) inflation.
1396       //
1397       // Why do we CAS a 0 into the mark-word instead of just CASing the
1398       // mark-word from the stack-locked value directly to the new inflated state?
1399       // Consider what happens when a thread unlocks a stack-locked object.
1400       // It attempts to use CAS to swing the displaced header value from the
1401       // on-stack basiclock back into the object header.  Recall also that the
1402       // header value (hash code, etc) can reside in (a) the object header, or
1403       // (b) a displaced header associated with the stack-lock, or (c) a displaced
1404       // header in an objectMonitor.  The inflate() routine must copy the header
1405       // value from the basiclock on the owner's stack to the objectMonitor, all
1406       // the while preserving the hashCode stability invariants.  If the owner
1407       // decides to release the lock while the value is 0, the unlock will fail
1408       // and control will eventually pass from slow_exit() to inflate.  The owner
1409       // will then spin, waiting for the 0 value to disappear.   Put another way,
1410       // the 0 causes the owner to stall if the owner happens to try to
1411       // drop the lock (restoring the header from the basiclock to the object)
1412       // while inflation is in-progress.  This protocol avoids races that might
1413       // would otherwise permit hashCode values to change or "flicker" for an object.
1414       // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1415       // 0 serves as a "BUSY" inflate-in-progress indicator.
1416 
1417 
1418       // fetch the displaced mark from the owner's stack.
1419       // The owner can't die or unwind past the lock while our INFLATING
1420       // object is in the mark.  Furthermore the owner can't complete
1421       // an unlock on the object, either.
1422       markWord dmw = mark.displaced_mark_helper();
1423       // Catch if the object's header is not neutral (not locked and
1424       // not marked is what we care about here).
1425       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1426 
1427       // Setup monitor fields to proper values -- prepare the monitor
1428       m->set_header(dmw);
1429 
1430       // Optimization: if the mark.locker stack address is associated
1431       // with this thread we could simply set m->_owner = Self.
1432       // Note that a thread can inflate an object
1433       // that it has stack-locked -- as might happen in wait() -- directly
1434       // with CAS.  That is, we can avoid the xchg-NULL .... ST idiom.
1435       m->set_owner(mark.locker());
1436       m->set_object(object);
1437       // TODO-FIXME: assert BasicLock->dhw != 0.
1438 
1439       // Must preserve store ordering. The monitor state must
1440       // be stable at the time of publishing the monitor address.
1441       guarantee(object->mark() == markWord::INFLATING(), "invariant");
1442       object->release_set_mark(markWord::encode(m));
1443 
1444       // Hopefully the performance counters are allocated on distinct cache lines
1445       // to avoid false sharing on MP systems ...
1446       OM_PERFDATA_OP(Inflations, inc());
1447       if (log_is_enabled(Trace, monitorinflation)) {
1448         ResourceMark rm(Self);
1449         lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1450                      INTPTR_FORMAT ", type='%s'", p2i(object),
1451                      object->mark().value(), object->klass()->external_name());
1452       }
1453       if (event.should_commit()) {
1454         post_monitor_inflate_event(&event, object, cause);
1455       }
1456       return m;
1457     }
1458 
1459     // CASE: neutral
1460     // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1461     // If we know we're inflating for entry it's better to inflate by swinging a
1462     // pre-locked objectMonitor pointer into the object header.   A successful
1463     // CAS inflates the object *and* confers ownership to the inflating thread.
1464     // In the current implementation we use a 2-step mechanism where we CAS()
1465     // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1466     // An inflateTry() method that we could call from fast_enter() and slow_enter()
1467     // would be useful.
1468 
1469     // Catch if the object's header is not neutral (not locked and
1470     // not marked is what we care about here).
1471     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1472     ObjectMonitor * m = omAlloc(Self);
1473     // prepare m for installation - set monitor to initial state
1474     m->Recycle();
1475     m->set_header(mark);
1476     m->set_object(object);
1477     m->_Responsible  = NULL;
1478     m->_SpinDuration = ObjectMonitor::Knob_SpinLimit;       // consider: keep metastats by type/class
1479 
1480     if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1481       m->set_header(markWord::zero());
1482       m->set_object(NULL);
1483       m->Recycle();
1484       omRelease(Self, m, true);
1485       m = NULL;
1486       continue;
1487       // interference - the markword changed - just retry.
1488       // The state-transitions are one-way, so there's no chance of
1489       // live-lock -- "Inflated" is an absorbing state.
1490     }
1491 
1492     // Hopefully the performance counters are allocated on distinct
1493     // cache lines to avoid false sharing on MP systems ...
1494     OM_PERFDATA_OP(Inflations, inc());
1495     if (log_is_enabled(Trace, monitorinflation)) {
1496       ResourceMark rm(Self);
1497       lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1498                    INTPTR_FORMAT ", type='%s'", p2i(object),
1499                    object->mark().value(), object->klass()->external_name());
1500     }
1501     if (event.should_commit()) {
1502       post_monitor_inflate_event(&event, object, cause);
1503     }
1504     return m;
1505   }
1506 }
1507 
1508 
1509 // We maintain a list of in-use monitors for each thread.
1510 //
1511 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1512 // deflate_idle_monitors() scans only a global list of in-use monitors which
1513 // is populated only as a thread dies (see omFlush()).
1514 //
1515 // These operations are called at all safepoints, immediately after mutators
1516 // are stopped, but before any objects have moved. Collectively they traverse
1517 // the population of in-use monitors, deflating where possible. The scavenged
1518 // monitors are returned to the global monitor free list.
1519 //
1520 // Beware that we scavenge at *every* stop-the-world point. Having a large
1521 // number of monitors in-use could negatively impact performance. We also want
1522 // to minimize the total # of monitors in circulation, as they incur a small
1523 // footprint penalty.
1524 //
1525 // Perversely, the heap size -- and thus the STW safepoint rate --
1526 // typically drives the scavenge rate.  Large heaps can mean infrequent GC,
1527 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1528 // This is an unfortunate aspect of this design.
1529 
1530 // Deflate a single monitor if not in-use
1531 // Return true if deflated, false if in-use
1532 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1533                                          ObjectMonitor** freeHeadp,
1534                                          ObjectMonitor** freeTailp) {
1535   bool deflated;
1536   // Normal case ... The monitor is associated with obj.
1537   const markWord mark = obj->mark();
1538   guarantee(mark == markWord::encode(mid), "should match: mark="
1539             INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
1540             markWord::encode(mid).value());
1541   // Make sure that mark.monitor() and markWord::encode() agree:
1542   guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1543             ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
1544   const markWord dmw = mid->header();
1545   guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1546 
1547   if (mid->is_busy()) {
1548     deflated = false;
1549   } else {
1550     // Deflate the monitor if it is no longer being used
1551     // It's idle - scavenge and return to the global free list
1552     // plain old deflation ...
1553     if (log_is_enabled(Trace, monitorinflation)) {
1554       ResourceMark rm;
1555       log_trace(monitorinflation)("deflate_monitor: "
1556                                   "object=" INTPTR_FORMAT ", mark="
1557                                   INTPTR_FORMAT ", type='%s'", p2i(obj),
1558                                   mark.value(), obj->klass()->external_name());
1559     }
1560 
1561     // Restore the header back to obj
1562     obj->release_set_mark(dmw);
1563     mid->clear();
1564 
1565     assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1566            p2i(mid->object()));
1567 
1568     // Move the object to the working free list defined by freeHeadp, freeTailp
1569     if (*freeHeadp == NULL) *freeHeadp = mid;
1570     if (*freeTailp != NULL) {
1571       ObjectMonitor * prevtail = *freeTailp;
1572       assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1573       prevtail->FreeNext = mid;
1574     }
1575     *freeTailp = mid;
1576     deflated = true;
1577   }
1578   return deflated;
1579 }
1580 
1581 // Walk a given monitor list, and deflate idle monitors
1582 // The given list could be a per-thread list or a global list
1583 // Caller acquires gListLock as needed.
1584 //
1585 // In the case of parallel processing of thread local monitor lists,
1586 // work is done by Threads::parallel_threads_do() which ensures that
1587 // each Java thread is processed by exactly one worker thread, and
1588 // thus avoid conflicts that would arise when worker threads would
1589 // process the same monitor lists concurrently.
1590 //
1591 // See also ParallelSPCleanupTask and
1592 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1593 // Threads::parallel_java_threads_do() in thread.cpp.
1594 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1595                                              ObjectMonitor** freeHeadp,
1596                                              ObjectMonitor** freeTailp) {
1597   ObjectMonitor* mid;
1598   ObjectMonitor* next;
1599   ObjectMonitor* cur_mid_in_use = NULL;
1600   int deflated_count = 0;
1601 
1602   for (mid = *listHeadp; mid != NULL;) {
1603     oop obj = (oop) mid->object();
1604     if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1605       // if deflate_monitor succeeded,
1606       // extract from per-thread in-use list
1607       if (mid == *listHeadp) {
1608         *listHeadp = mid->FreeNext;
1609       } else if (cur_mid_in_use != NULL) {
1610         cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1611       }
1612       next = mid->FreeNext;
1613       mid->FreeNext = NULL;  // This mid is current tail in the freeHeadp list
1614       mid = next;
1615       deflated_count++;
1616     } else {
1617       cur_mid_in_use = mid;
1618       mid = mid->FreeNext;
1619     }
1620   }
1621   return deflated_count;
1622 }
1623 
1624 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1625   counters->nInuse = 0;              // currently associated with objects
1626   counters->nInCirculation = 0;      // extant
1627   counters->nScavenged = 0;          // reclaimed (global and per-thread)
1628   counters->perThreadScavenged = 0;  // per-thread scavenge total
1629   counters->perThreadTimes = 0.0;    // per-thread scavenge times
1630 }
1631 
1632 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1633   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1634   bool deflated = false;
1635 
1636   ObjectMonitor * freeHeadp = NULL;  // Local SLL of scavenged monitors
1637   ObjectMonitor * freeTailp = NULL;
1638   elapsedTimer timer;
1639 
1640   if (log_is_enabled(Info, monitorinflation)) {
1641     timer.start();
1642   }
1643 
1644   // Prevent omFlush from changing mids in Thread dtor's during deflation
1645   // And in case the vm thread is acquiring a lock during a safepoint
1646   // See e.g. 6320749
1647   Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
1648 
1649   // Note: the thread-local monitors lists get deflated in
1650   // a separate pass. See deflate_thread_local_monitors().
1651 
1652   // For moribund threads, scan gOmInUseList
1653   int deflated_count = 0;
1654   if (gOmInUseList) {
1655     counters->nInCirculation += gOmInUseCount;
1656     deflated_count = deflate_monitor_list((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp);
1657     gOmInUseCount -= deflated_count;
1658     counters->nScavenged += deflated_count;
1659     counters->nInuse += gOmInUseCount;
1660   }
1661 
1662   // Move the scavenged monitors back to the global free list.
1663   if (freeHeadp != NULL) {
1664     guarantee(freeTailp != NULL && counters->nScavenged > 0, "invariant");
1665     assert(freeTailp->FreeNext == NULL, "invariant");
1666     // constant-time list splice - prepend scavenged segment to gFreeList
1667     freeTailp->FreeNext = gFreeList;
1668     gFreeList = freeHeadp;
1669   }
1670   Thread::muxRelease(&gListLock);
1671   timer.stop();
1672 
1673   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1674   LogStreamHandle(Info, monitorinflation) lsh_info;
1675   LogStream * ls = NULL;
1676   if (log_is_enabled(Debug, monitorinflation)) {
1677     ls = &lsh_debug;
1678   } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1679     ls = &lsh_info;
1680   }
1681   if (ls != NULL) {
1682     ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
1683   }
1684 }
1685 
1686 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1687   // Report the cumulative time for deflating each thread's idle
1688   // monitors. Note: if the work is split among more than one
1689   // worker thread, then the reported time will likely be more
1690   // than a beginning to end measurement of the phase.
1691   log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->perThreadTimes, counters->perThreadScavenged);
1692 
1693   gMonitorFreeCount += counters->nScavenged;
1694 
1695   if (log_is_enabled(Debug, monitorinflation)) {
1696     // exit_globals()'s call to audit_and_print_stats() is done
1697     // at the Info level.
1698     ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
1699   } else if (log_is_enabled(Info, monitorinflation)) {
1700     Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
1701     log_info(monitorinflation)("gMonitorPopulation=%d, gOmInUseCount=%d, "
1702                                "gMonitorFreeCount=%d", gMonitorPopulation,
1703                                gOmInUseCount, gMonitorFreeCount);
1704     Thread::muxRelease(&gListLock);
1705   }
1706 
1707   ForceMonitorScavenge = 0;    // Reset
1708 
1709   OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
1710   OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
1711 
1712   GVars.stwRandom = os::random();
1713   GVars.stwCycle++;
1714 }
1715 
1716 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1717   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1718 
1719   ObjectMonitor * freeHeadp = NULL;  // Local SLL of scavenged monitors
1720   ObjectMonitor * freeTailp = NULL;
1721   elapsedTimer timer;
1722 
1723   if (log_is_enabled(Info, safepoint, cleanup) ||
1724       log_is_enabled(Info, monitorinflation)) {
1725     timer.start();
1726   }
1727 
1728   int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
1729 
1730   Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
1731 
1732   // Adjust counters
1733   counters->nInCirculation += thread->omInUseCount;
1734   thread->omInUseCount -= deflated_count;
1735   counters->nScavenged += deflated_count;
1736   counters->nInuse += thread->omInUseCount;
1737   counters->perThreadScavenged += deflated_count;
1738 
1739   // Move the scavenged monitors back to the global free list.
1740   if (freeHeadp != NULL) {
1741     guarantee(freeTailp != NULL && deflated_count > 0, "invariant");
1742     assert(freeTailp->FreeNext == NULL, "invariant");
1743 
1744     // constant-time list splice - prepend scavenged segment to gFreeList
1745     freeTailp->FreeNext = gFreeList;
1746     gFreeList = freeHeadp;
1747   }
1748 
1749   timer.stop();
1750   // Safepoint logging cares about cumulative perThreadTimes and
1751   // we'll capture most of the cost, but not the muxRelease() which
1752   // should be cheap.
1753   counters->perThreadTimes += timer.seconds();
1754 
1755   Thread::muxRelease(&gListLock);
1756 
1757   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1758   LogStreamHandle(Info, monitorinflation) lsh_info;
1759   LogStream * ls = NULL;
1760   if (log_is_enabled(Debug, monitorinflation)) {
1761     ls = &lsh_debug;
1762   } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1763     ls = &lsh_info;
1764   }
1765   if (ls != NULL) {
1766     ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
1767   }
1768 }
1769 
1770 // Monitor cleanup on JavaThread::exit
1771 
1772 // Iterate through monitor cache and attempt to release thread's monitors
1773 // Gives up on a particular monitor if an exception occurs, but continues
1774 // the overall iteration, swallowing the exception.
1775 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1776  private:
1777   TRAPS;
1778 
1779  public:
1780   ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1781   void do_monitor(ObjectMonitor* mid) {
1782     if (mid->owner() == THREAD) {
1783       (void)mid->complete_exit(CHECK);
1784     }
1785   }
1786 };
1787 
1788 // Release all inflated monitors owned by THREAD.  Lightweight monitors are
1789 // ignored.  This is meant to be called during JNI thread detach which assumes
1790 // all remaining monitors are heavyweight.  All exceptions are swallowed.
1791 // Scanning the extant monitor list can be time consuming.
1792 // A simple optimization is to add a per-thread flag that indicates a thread
1793 // called jni_monitorenter() during its lifetime.
1794 //
1795 // Instead of No_Savepoint_Verifier it might be cheaper to
1796 // use an idiom of the form:
1797 //   auto int tmp = SafepointSynchronize::_safepoint_counter ;
1798 //   <code that must not run at safepoint>
1799 //   guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1800 // Since the tests are extremely cheap we could leave them enabled
1801 // for normal product builds.
1802 
1803 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1804   assert(THREAD == JavaThread::current(), "must be current Java thread");
1805   NoSafepointVerifier nsv;
1806   ReleaseJavaMonitorsClosure rjmc(THREAD);
1807   Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
1808   ObjectSynchronizer::monitors_iterate(&rjmc);
1809   Thread::muxRelease(&gListLock);
1810   THREAD->clear_pending_exception();
1811 }
1812 
1813 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1814   switch (cause) {
1815     case inflate_cause_vm_internal:    return "VM Internal";
1816     case inflate_cause_monitor_enter:  return "Monitor Enter";
1817     case inflate_cause_wait:           return "Monitor Wait";
1818     case inflate_cause_notify:         return "Monitor Notify";
1819     case inflate_cause_hash_code:      return "Monitor Hash Code";
1820     case inflate_cause_jni_enter:      return "JNI Monitor Enter";
1821     case inflate_cause_jni_exit:       return "JNI Monitor Exit";
1822     default:
1823       ShouldNotReachHere();
1824   }
1825   return "Unknown";
1826 }
1827 
1828 //------------------------------------------------------------------------------
1829 // Debugging code
1830 
1831 u_char* ObjectSynchronizer::get_gvars_addr() {
1832   return (u_char*)&GVars;
1833 }
1834 
1835 u_char* ObjectSynchronizer::get_gvars_hcSequence_addr() {
1836   return (u_char*)&GVars.hcSequence;
1837 }
1838 
1839 size_t ObjectSynchronizer::get_gvars_size() {
1840   return sizeof(SharedGlobals);
1841 }
1842 
1843 u_char* ObjectSynchronizer::get_gvars_stwRandom_addr() {
1844   return (u_char*)&GVars.stwRandom;
1845 }
1846 
1847 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1848   assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1849 
1850   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1851   LogStreamHandle(Info, monitorinflation) lsh_info;
1852   LogStreamHandle(Trace, monitorinflation) lsh_trace;
1853   LogStream * ls = NULL;
1854   if (log_is_enabled(Trace, monitorinflation)) {
1855     ls = &lsh_trace;
1856   } else if (log_is_enabled(Debug, monitorinflation)) {
1857     ls = &lsh_debug;
1858   } else if (log_is_enabled(Info, monitorinflation)) {
1859     ls = &lsh_info;
1860   }
1861   assert(ls != NULL, "sanity check");
1862 
1863   if (!on_exit) {
1864     // Not at VM exit so grab the global list lock.
1865     Thread::muxAcquire(&gListLock, "audit_and_print_stats");
1866   }
1867 
1868   // Log counts for the global and per-thread monitor lists:
1869   int chkMonitorPopulation = log_monitor_list_counts(ls);
1870   int error_cnt = 0;
1871 
1872   ls->print_cr("Checking global lists:");
1873 
1874   // Check gMonitorPopulation:
1875   if (gMonitorPopulation == chkMonitorPopulation) {
1876     ls->print_cr("gMonitorPopulation=%d equals chkMonitorPopulation=%d",
1877                  gMonitorPopulation, chkMonitorPopulation);
1878   } else {
1879     ls->print_cr("ERROR: gMonitorPopulation=%d is not equal to "
1880                  "chkMonitorPopulation=%d", gMonitorPopulation,
1881                  chkMonitorPopulation);
1882     error_cnt++;
1883   }
1884 
1885   // Check gOmInUseList and gOmInUseCount:
1886   chk_global_in_use_list_and_count(ls, &error_cnt);
1887 
1888   // Check gFreeList and gMonitorFreeCount:
1889   chk_global_free_list_and_count(ls, &error_cnt);
1890 
1891   if (!on_exit) {
1892     Thread::muxRelease(&gListLock);
1893   }
1894 
1895   ls->print_cr("Checking per-thread lists:");
1896 
1897   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
1898     // Check omInUseList and omInUseCount:
1899     chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
1900 
1901     // Check omFreeList and omFreeCount:
1902     chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
1903   }
1904 
1905   if (error_cnt == 0) {
1906     ls->print_cr("No errors found in monitor list checks.");
1907   } else {
1908     log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
1909   }
1910 
1911   if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1912       (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1913     // When exiting this log output is at the Info level. When called
1914     // at a safepoint, this log output is at the Trace level since
1915     // there can be a lot of it.
1916     log_in_use_monitor_details(ls, on_exit);
1917   }
1918 
1919   ls->flush();
1920 
1921   guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1922 }
1923 
1924 // Check a free monitor entry; log any errors.
1925 void ObjectSynchronizer::chk_free_entry(JavaThread * jt, ObjectMonitor * n,
1926                                         outputStream * out, int *error_cnt_p) {
1927   stringStream ss;
1928   if (n->is_busy()) {
1929     if (jt != NULL) {
1930       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1931                     ": free per-thread monitor must not be busy: %s", p2i(jt),
1932                     p2i(n), n->is_busy_to_string(&ss));
1933     } else {
1934       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1935                     "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
1936     }
1937     *error_cnt_p = *error_cnt_p + 1;
1938   }
1939   if (n->header().value() != 0) {
1940     if (jt != NULL) {
1941       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1942                     ": free per-thread monitor must have NULL _header "
1943                     "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
1944                     n->header().value());
1945     } else {
1946       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1947                     "must have NULL _header field: _header=" INTPTR_FORMAT,
1948                     p2i(n), n->header().value());
1949     }
1950     *error_cnt_p = *error_cnt_p + 1;
1951   }
1952   if (n->object() != NULL) {
1953     if (jt != NULL) {
1954       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1955                     ": free per-thread monitor must have NULL _object "
1956                     "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
1957                     p2i(n->object()));
1958     } else {
1959       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1960                     "must have NULL _object field: _object=" INTPTR_FORMAT,
1961                     p2i(n), p2i(n->object()));
1962     }
1963     *error_cnt_p = *error_cnt_p + 1;
1964   }
1965 }
1966 
1967 // Check the global free list and count; log the results of the checks.
1968 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
1969                                                         int *error_cnt_p) {
1970   int chkMonitorFreeCount = 0;
1971   for (ObjectMonitor * n = gFreeList; n != NULL; n = n->FreeNext) {
1972     chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
1973     chkMonitorFreeCount++;
1974   }
1975   if (gMonitorFreeCount == chkMonitorFreeCount) {
1976     out->print_cr("gMonitorFreeCount=%d equals chkMonitorFreeCount=%d",
1977                   gMonitorFreeCount, chkMonitorFreeCount);
1978   } else {
1979     out->print_cr("ERROR: gMonitorFreeCount=%d is not equal to "
1980                   "chkMonitorFreeCount=%d", gMonitorFreeCount,
1981                   chkMonitorFreeCount);
1982     *error_cnt_p = *error_cnt_p + 1;
1983   }
1984 }
1985 
1986 // Check the global in-use list and count; log the results of the checks.
1987 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
1988                                                           int *error_cnt_p) {
1989   int chkOmInUseCount = 0;
1990   for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
1991     chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
1992     chkOmInUseCount++;
1993   }
1994   if (gOmInUseCount == chkOmInUseCount) {
1995     out->print_cr("gOmInUseCount=%d equals chkOmInUseCount=%d", gOmInUseCount,
1996                   chkOmInUseCount);
1997   } else {
1998     out->print_cr("ERROR: gOmInUseCount=%d is not equal to chkOmInUseCount=%d",
1999                   gOmInUseCount, chkOmInUseCount);
2000     *error_cnt_p = *error_cnt_p + 1;
2001   }
2002 }
2003 
2004 // Check an in-use monitor entry; log any errors.
2005 void ObjectSynchronizer::chk_in_use_entry(JavaThread * jt, ObjectMonitor * n,
2006                                           outputStream * out, int *error_cnt_p) {
2007   if (n->header().value() == 0) {
2008     if (jt != NULL) {
2009       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2010                     ": in-use per-thread monitor must have non-NULL _header "
2011                     "field.", p2i(jt), p2i(n));
2012     } else {
2013       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2014                     "must have non-NULL _header field.", p2i(n));
2015     }
2016     *error_cnt_p = *error_cnt_p + 1;
2017   }
2018   if (n->object() == NULL) {
2019     if (jt != NULL) {
2020       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2021                     ": in-use per-thread monitor must have non-NULL _object "
2022                     "field.", p2i(jt), p2i(n));
2023     } else {
2024       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2025                     "must have non-NULL _object field.", p2i(n));
2026     }
2027     *error_cnt_p = *error_cnt_p + 1;
2028   }
2029   const oop obj = (oop)n->object();
2030   const markWord mark = obj->mark();
2031   if (!mark.has_monitor()) {
2032     if (jt != NULL) {
2033       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2034                     ": in-use per-thread monitor's object does not think "
2035                     "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2036                     INTPTR_FORMAT,  p2i(jt), p2i(n), p2i(obj), mark.value());
2037     } else {
2038       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2039                     "monitor's object does not think it has a monitor: obj="
2040                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2041                     p2i(obj), mark.value());
2042     }
2043     *error_cnt_p = *error_cnt_p + 1;
2044   }
2045   ObjectMonitor * const obj_mon = mark.monitor();
2046   if (n != obj_mon) {
2047     if (jt != NULL) {
2048       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2049                     ": in-use per-thread monitor's object does not refer "
2050                     "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2051                     INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2052                     p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2053     } else {
2054       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2055                     "monitor's object does not refer to the same monitor: obj="
2056                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2057                     INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2058     }
2059     *error_cnt_p = *error_cnt_p + 1;
2060   }
2061 }
2062 
2063 // Check the thread's free list and count; log the results of the checks.
2064 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2065                                                             outputStream * out,
2066                                                             int *error_cnt_p) {
2067   int chkOmFreeCount = 0;
2068   for (ObjectMonitor * n = jt->omFreeList; n != NULL; n = n->FreeNext) {
2069     chk_free_entry(jt, n, out, error_cnt_p);
2070     chkOmFreeCount++;
2071   }
2072   if (jt->omFreeCount == chkOmFreeCount) {
2073     out->print_cr("jt=" INTPTR_FORMAT ": omFreeCount=%d equals "
2074                   "chkOmFreeCount=%d", p2i(jt), jt->omFreeCount, chkOmFreeCount);
2075   } else {
2076     out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omFreeCount=%d is not "
2077                   "equal to chkOmFreeCount=%d", p2i(jt), jt->omFreeCount,
2078                   chkOmFreeCount);
2079     *error_cnt_p = *error_cnt_p + 1;
2080   }
2081 }
2082 
2083 // Check the thread's in-use list and count; log the results of the checks.
2084 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2085                                                               outputStream * out,
2086                                                               int *error_cnt_p) {
2087   int chkOmInUseCount = 0;
2088   for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2089     chk_in_use_entry(jt, n, out, error_cnt_p);
2090     chkOmInUseCount++;
2091   }
2092   if (jt->omInUseCount == chkOmInUseCount) {
2093     out->print_cr("jt=" INTPTR_FORMAT ": omInUseCount=%d equals "
2094                   "chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2095                   chkOmInUseCount);
2096   } else {
2097     out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omInUseCount=%d is not "
2098                   "equal to chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2099                   chkOmInUseCount);
2100     *error_cnt_p = *error_cnt_p + 1;
2101   }
2102 }
2103 
2104 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2105 // flags indicate why the entry is in-use, 'object' and 'object type'
2106 // indicate the associated object and its type.
2107 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2108                                                     bool on_exit) {
2109   if (!on_exit) {
2110     // Not at VM exit so grab the global list lock.
2111     Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2112   }
2113 
2114   stringStream ss;
2115   if (gOmInUseCount > 0) {
2116     out->print_cr("In-use global monitor info:");
2117     out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2118     out->print_cr("%18s  %s  %18s  %18s",
2119                   "monitor", "BHL", "object", "object type");
2120     out->print_cr("==================  ===  ==================  ==================");
2121     for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2122       const oop obj = (oop) n->object();
2123       const markWord mark = n->header();
2124       ResourceMark rm;
2125       out->print(INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT "  %s", p2i(n),
2126                  n->is_busy() != 0, mark.hash() != 0, n->owner() != NULL,
2127                  p2i(obj), obj->klass()->external_name());
2128       if (n->is_busy() != 0) {
2129         out->print(" (%s)", n->is_busy_to_string(&ss));
2130         ss.reset();
2131       }
2132       out->cr();
2133     }
2134   }
2135 
2136   if (!on_exit) {
2137     Thread::muxRelease(&gListLock);
2138   }
2139 
2140   out->print_cr("In-use per-thread monitor info:");
2141   out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2142   out->print_cr("%18s  %18s  %s  %18s  %18s",
2143                 "jt", "monitor", "BHL", "object", "object type");
2144   out->print_cr("==================  ==================  ===  ==================  ==================");
2145   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2146     for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2147       const oop obj = (oop) n->object();
2148       const markWord mark = n->header();
2149       ResourceMark rm;
2150       out->print(INTPTR_FORMAT "  " INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT
2151                  "  %s", p2i(jt), p2i(n), n->is_busy() != 0,
2152                  mark.hash() != 0, n->owner() != NULL, p2i(obj),
2153                  obj->klass()->external_name());
2154       if (n->is_busy() != 0) {
2155         out->print(" (%s)", n->is_busy_to_string(&ss));
2156         ss.reset();
2157       }
2158       out->cr();
2159     }
2160   }
2161 
2162   out->flush();
2163 }
2164 
2165 // Log counts for the global and per-thread monitor lists and return
2166 // the population count.
2167 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2168   int popCount = 0;
2169   out->print_cr("%18s  %10s  %10s  %10s",
2170                 "Global Lists:", "InUse", "Free", "Total");
2171   out->print_cr("==================  ==========  ==========  ==========");
2172   out->print_cr("%18s  %10d  %10d  %10d", "",
2173                 gOmInUseCount, gMonitorFreeCount, gMonitorPopulation);
2174   popCount += gOmInUseCount + gMonitorFreeCount;
2175 
2176   out->print_cr("%18s  %10s  %10s  %10s",
2177                 "Per-Thread Lists:", "InUse", "Free", "Provision");
2178   out->print_cr("==================  ==========  ==========  ==========");
2179 
2180   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2181     out->print_cr(INTPTR_FORMAT "  %10d  %10d  %10d", p2i(jt),
2182                   jt->omInUseCount, jt->omFreeCount, jt->omFreeProvision);
2183     popCount += jt->omInUseCount + jt->omFreeCount;
2184   }
2185   return popCount;
2186 }
2187 
2188 #ifndef PRODUCT
2189 
2190 // Check if monitor belongs to the monitor cache
2191 // The list is grow-only so it's *relatively* safe to traverse
2192 // the list of extant blocks without taking a lock.
2193 
2194 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2195   PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
2196   while (block != NULL) {
2197     assert(block->object() == CHAINMARKER, "must be a block header");
2198     if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2199       address mon = (address)monitor;
2200       address blk = (address)block;
2201       size_t diff = mon - blk;
2202       assert((diff % sizeof(PaddedEnd<ObjectMonitor>)) == 0, "must be aligned");
2203       return 1;
2204     }
2205     block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
2206   }
2207   return 0;
2208 }
2209 
2210 #endif
--- EOF ---