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 PaddedObjectMonitor* volatile ObjectSynchronizer::g_block_list = NULL;
 121 // Global ObjectMonitor free list. Newly allocated and deflated
 122 // ObjectMonitors are prepended here.
 123 ObjectMonitor* volatile ObjectSynchronizer::g_free_list = NULL;
 124 // Global ObjectMonitor in-use list. When a JavaThread is exiting,
 125 // ObjectMonitors on its per-thread in-use list are prepended here.
 126 ObjectMonitor* volatile ObjectSynchronizer::g_om_in_use_list = NULL;
 127 int ObjectSynchronizer::g_om_in_use_count = 0;  // # on g_om_in_use_list
 128 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
 129 bool volatile ObjectSynchronizer::_is_special_deflation_requested = false;
 130 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
 131 
 132 static volatile intptr_t gListLock = 0;   // protects global monitor lists
 133 static volatile int g_om_free_count = 0;  // # on g_free_list
 134 static volatile int g_om_population = 0;  // # Extant -- in circulation
 135 
 136 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
 137 
 138 
 139 // =====================> Quick functions
 140 
 141 // The quick_* forms are special fast-path variants used to improve
 142 // performance.  In the simplest case, a "quick_*" implementation could
 143 // simply return false, in which case the caller will perform the necessary
 144 // state transitions and call the slow-path form.
 145 // The fast-path is designed to handle frequently arising cases in an efficient
 146 // manner and is just a degenerate "optimistic" variant of the slow-path.
 147 // returns true  -- to indicate the call was satisfied.
 148 // returns false -- to indicate the call needs the services of the slow-path.
 149 // A no-loitering ordinance is in effect for code in the quick_* family
 150 // operators: safepoints or indefinite blocking (blocking that might span a
 151 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
 152 // entry.
 153 //
 154 // Consider: An interesting optimization is to have the JIT recognize the
 155 // following common idiom:
 156 //   synchronized (someobj) { .... ; notify(); }
 157 // That is, we find a notify() or notifyAll() call that immediately precedes
 158 // the monitorexit operation.  In that case the JIT could fuse the operations
 159 // into a single notifyAndExit() runtime primitive.
 160 
 161 bool ObjectSynchronizer::quick_notify(oopDesc* obj, Thread* self, bool all) {
 162   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 163   assert(self->is_Java_thread(), "invariant");
 164   assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
 165   NoSafepointVerifier nsv;
 166   if (obj == NULL) return false;  // slow-path for invalid obj
 167   const markWord mark = obj->mark();
 168 
 169   if (mark.has_locker() && self->is_lock_owned((address)mark.locker())) {
 170     // Degenerate notify
 171     // stack-locked by caller so by definition the implied waitset is empty.
 172     return true;
 173   }
 174 
 175   if (mark.has_monitor()) {
 176     ObjectMonitor* const mon = mark.monitor();
 177     assert(oopDesc::equals((oop) mon->object(), obj), "invariant");
 178     if (mon->owner() != self) return false;  // slow-path for IMS exception
 179 
 180     if (mon->first_waiter() != NULL) {
 181       // We have one or more waiters. Since this is an inflated monitor
 182       // that we own, we can transfer one or more threads from the waitset
 183       // to the entrylist here and now, avoiding the slow-path.
 184       if (all) {
 185         DTRACE_MONITOR_PROBE(notifyAll, mon, obj, self);
 186       } else {
 187         DTRACE_MONITOR_PROBE(notify, mon, obj, self);
 188       }
 189       int free_count = 0;
 190       do {
 191         mon->INotify(self);
 192         ++free_count;
 193       } while (mon->first_waiter() != NULL && all);
 194       OM_PERFDATA_OP(Notifications, inc(free_count));
 195     }
 196     return true;
 197   }
 198 
 199   // biased locking and any other IMS exception states take the slow-path
 200   return false;
 201 }
 202 
 203 
 204 // The LockNode emitted directly at the synchronization site would have
 205 // been too big if it were to have included support for the cases of inflated
 206 // recursive enter and exit, so they go here instead.
 207 // Note that we can't safely call AsyncPrintJavaStack() from within
 208 // quick_enter() as our thread state remains _in_Java.
 209 
 210 bool ObjectSynchronizer::quick_enter(oop obj, Thread* self,
 211                                      BasicLock * lock) {
 212   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 213   assert(self->is_Java_thread(), "invariant");
 214   assert(((JavaThread *) self)->thread_state() == _thread_in_Java, "invariant");
 215   NoSafepointVerifier nsv;
 216   if (obj == NULL) return false;       // Need to throw NPE
 217 
 218   while (true) {
 219     const markWord mark = obj->mark();
 220 
 221     if (mark.has_monitor()) {
 222       ObjectMonitorHandle omh;
 223       if (!omh.save_om_ptr(obj, mark)) {
 224         // Lost a race with async deflation so try again.
 225         assert(AsyncDeflateIdleMonitors, "sanity check");
 226         continue;
 227       }
 228       ObjectMonitor* const m = omh.om_ptr();
 229       assert(oopDesc::equals((oop) m->object(), obj), "invariant");
 230       Thread* const owner = (Thread *) m->_owner;
 231 
 232       // Lock contention and Transactional Lock Elision (TLE) diagnostics
 233       // and observability
 234       // Case: light contention possibly amenable to TLE
 235       // Case: TLE inimical operations such as nested/recursive synchronization
 236 
 237       if (owner == self) {
 238         m->_recursions++;
 239         return true;
 240       }
 241 
 242       // This Java Monitor is inflated so obj's header will never be
 243       // displaced to this thread's BasicLock. Make the displaced header
 244       // non-NULL so this BasicLock is not seen as recursive nor as
 245       // being locked. We do this unconditionally so that this thread's
 246       // BasicLock cannot be mis-interpreted by any stack walkers. For
 247       // performance reasons, stack walkers generally first check for
 248       // Biased Locking in the object's header, the second check is for
 249       // stack-locking in the object's header, the third check is for
 250       // recursive stack-locking in the displaced header in the BasicLock,
 251       // and last are the inflated Java Monitor (ObjectMonitor) checks.
 252       lock->set_displaced_header(markWord::unused_mark());
 253 
 254       if (owner == NULL && Atomic::replace_if_null(self, &(m->_owner))) {
 255         assert(m->_recursions == 0, "invariant");
 256         return true;
 257       }
 258 
 259       if (AsyncDeflateIdleMonitors &&
 260           Atomic::cmpxchg(self, &m->_owner, DEFLATER_MARKER) == DEFLATER_MARKER) {
 261         // The deflation protocol finished the first part (setting owner),
 262         // but it failed the second part (making ref_count negative) and
 263         // bailed. Or the ObjectMonitor was async deflated and reused.
 264         // Acquired the monitor.
 265         assert(m->_recursions == 0, "invariant");
 266         return true;
 267       }
 268     }
 269     break;
 270   }
 271 
 272   // Note that we could inflate in quick_enter.
 273   // This is likely a useful optimization
 274   // Critically, in quick_enter() we must not:
 275   // -- perform bias revocation, or
 276   // -- block indefinitely, or
 277   // -- reach a safepoint
 278 
 279   return false;        // revert to slow-path
 280 }
 281 
 282 // -----------------------------------------------------------------------------
 283 //  Fast Monitor Enter/Exit
 284 // This the fast monitor enter. The interpreter and compiler use
 285 // some assembly copies of this code. Make sure update those code
 286 // if the following function is changed. The implementation is
 287 // extremely sensitive to race condition. Be careful.
 288 
 289 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
 290                                     bool attempt_rebias, TRAPS) {
 291   if (UseBiasedLocking) {
 292     if (!SafepointSynchronize::is_at_safepoint()) {
 293       BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
 294       if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
 295         return;
 296       }
 297     } else {
 298       assert(!attempt_rebias, "can not rebias toward VM thread");
 299       BiasedLocking::revoke_at_safepoint(obj);
 300     }
 301     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 302   }
 303 
 304   slow_enter(obj, lock, THREAD);
 305 }
 306 
 307 void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
 308   markWord mark = object->mark();
 309   // We cannot check for Biased Locking if we are racing an inflation.
 310   assert(mark == markWord::INFLATING() ||
 311          !mark.has_bias_pattern(), "should not see bias pattern here");
 312 
 313   markWord dhw = lock->displaced_header();
 314   if (dhw.value() == 0) {
 315     // If the displaced header is NULL, then this exit matches up with
 316     // a recursive enter. No real work to do here except for diagnostics.
 317 #ifndef PRODUCT
 318     if (mark != markWord::INFLATING()) {
 319       // Only do diagnostics if we are not racing an inflation. Simply
 320       // exiting a recursive enter of a Java Monitor that is being
 321       // inflated is safe; see the has_monitor() comment below.
 322       assert(!mark.is_neutral(), "invariant");
 323       assert(!mark.has_locker() ||
 324              THREAD->is_lock_owned((address)mark.locker()), "invariant");
 325       if (mark.has_monitor()) {
 326         // The BasicLock's displaced_header is marked as a recursive
 327         // enter and we have an inflated Java Monitor (ObjectMonitor).
 328         // This is a special case where the Java Monitor was inflated
 329         // after this thread entered the stack-lock recursively. When a
 330         // Java Monitor is inflated, we cannot safely walk the Java
 331         // Monitor owner's stack and update the BasicLocks because a
 332         // Java Monitor can be asynchronously inflated by a thread that
 333         // does not own the Java Monitor.
 334         ObjectMonitor* m = mark.monitor();
 335         assert(((oop)(m->object()))->mark() == mark, "invariant");
 336         assert(m->is_entered(THREAD), "invariant");
 337       }
 338     }
 339 #endif
 340     return;
 341   }
 342 
 343   if (mark == markWord::from_pointer(lock)) {
 344     // If the object is stack-locked by the current thread, try to
 345     // swing the displaced header from the BasicLock back to the mark.
 346     assert(dhw.is_neutral(), "invariant");
 347     if (object->cas_set_mark(dhw, mark) == mark) {
 348       return;
 349     }
 350   }
 351 
 352   // We have to take the slow-path of possible inflation and then exit.
 353   ObjectMonitorHandle omh;
 354   inflate(&omh, THREAD, object, inflate_cause_vm_internal);
 355   omh.om_ptr()->exit(true, THREAD);
 356 }
 357 
 358 // -----------------------------------------------------------------------------
 359 // Interpreter/Compiler Slow Case
 360 // This routine is used to handle interpreter/compiler slow case
 361 // We don't need to use fast path here, because it must have been
 362 // failed in the interpreter/compiler code.
 363 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
 364   markWord mark = obj->mark();
 365   assert(!mark.has_bias_pattern(), "should not see bias pattern here");
 366 
 367   if (mark.is_neutral()) {
 368     // Anticipate successful CAS -- the ST of the displaced mark must
 369     // be visible <= the ST performed by the CAS.
 370     lock->set_displaced_header(mark);
 371     if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
 372       return;
 373     }
 374     // Fall through to inflate() ...
 375   } else if (mark.has_locker() &&
 376              THREAD->is_lock_owned((address)mark.locker())) {
 377     assert(lock != mark.locker(), "must not re-lock the same lock");
 378     assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
 379     lock->set_displaced_header(markWord::from_pointer(NULL));
 380     return;
 381   }
 382 
 383   // The object header will never be displaced to this lock,
 384   // so it does not matter what the value is, except that it
 385   // must be non-zero to avoid looking like a re-entrant lock,
 386   // and must not look locked either.
 387   lock->set_displaced_header(markWord::unused_mark());
 388   ObjectMonitorHandle omh;
 389   inflate(&omh, THREAD, obj(), inflate_cause_monitor_enter);
 390   omh.om_ptr()->enter(THREAD);
 391 }
 392 
 393 // This routine is used to handle interpreter/compiler slow case
 394 // We don't need to use fast path here, because it must have
 395 // failed in the interpreter/compiler code. Simply use the heavy
 396 // weight monitor should be ok, unless someone find otherwise.
 397 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
 398   fast_exit(object, lock, THREAD);
 399 }
 400 
 401 // -----------------------------------------------------------------------------
 402 // Class Loader  support to workaround deadlocks on the class loader lock objects
 403 // Also used by GC
 404 // complete_exit()/reenter() are used to wait on a nested lock
 405 // i.e. to give up an outer lock completely and then re-enter
 406 // Used when holding nested locks - lock acquisition order: lock1 then lock2
 407 //  1) complete_exit lock1 - saving recursion count
 408 //  2) wait on lock2
 409 //  3) when notified on lock2, unlock lock2
 410 //  4) reenter lock1 with original recursion count
 411 //  5) lock lock2
 412 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 413 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
 414   if (UseBiasedLocking) {
 415     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 416     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 417   }
 418 
 419   ObjectMonitorHandle omh;
 420   inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
 421   intptr_t ret_code = omh.om_ptr()->complete_exit(THREAD);
 422   return ret_code;
 423 }
 424 
 425 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 426 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
 427   if (UseBiasedLocking) {
 428     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 429     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 430   }
 431 
 432   ObjectMonitorHandle omh;
 433   inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
 434   omh.om_ptr()->reenter(recursion, THREAD);
 435 }
 436 // -----------------------------------------------------------------------------
 437 // JNI locks on java objects
 438 // NOTE: must use heavy weight monitor to handle jni monitor enter
 439 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
 440   // the current locking is from JNI instead of Java code
 441   if (UseBiasedLocking) {
 442     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 443     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 444   }
 445   THREAD->set_current_pending_monitor_is_from_java(false);
 446   ObjectMonitorHandle omh;
 447   inflate(&omh, THREAD, obj(), inflate_cause_jni_enter);
 448   omh.om_ptr()->enter(THREAD);
 449   THREAD->set_current_pending_monitor_is_from_java(true);
 450 }
 451 
 452 // NOTE: must use heavy weight monitor to handle jni monitor exit
 453 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
 454   if (UseBiasedLocking) {
 455     Handle h_obj(THREAD, obj);
 456     BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
 457     obj = h_obj();
 458   }
 459   assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 460 
 461   ObjectMonitorHandle omh;
 462   inflate(&omh, THREAD, obj, inflate_cause_jni_exit);
 463   ObjectMonitor* monitor = omh.om_ptr();
 464   // If this thread has locked the object, exit the monitor. We
 465   // intentionally do not use CHECK here because we must exit the
 466   // monitor even if an exception is pending.
 467   if (monitor->check_owner(THREAD)) {
 468     monitor->exit(true, THREAD);
 469   }
 470 }
 471 
 472 // -----------------------------------------------------------------------------
 473 // Internal VM locks on java objects
 474 // standard constructor, allows locking failures
 475 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool do_lock) {
 476   _dolock = do_lock;
 477   _thread = thread;
 478   _thread->check_for_valid_safepoint_state(false);
 479   _obj = obj;
 480 
 481   if (_dolock) {
 482     ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
 483   }
 484 }
 485 
 486 ObjectLocker::~ObjectLocker() {
 487   if (_dolock) {
 488     ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
 489   }
 490 }
 491 
 492 
 493 // -----------------------------------------------------------------------------
 494 //  Wait/Notify/NotifyAll
 495 // NOTE: must use heavy weight monitor to handle wait()
 496 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 497   if (UseBiasedLocking) {
 498     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 499     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 500   }
 501   if (millis < 0) {
 502     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 503   }
 504   ObjectMonitorHandle omh;
 505   inflate(&omh, THREAD, obj(), inflate_cause_wait);
 506   ObjectMonitor* monitor = omh.om_ptr();
 507 
 508   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
 509   monitor->wait(millis, true, THREAD);
 510 
 511   // This dummy call is in place to get around dtrace bug 6254741.  Once
 512   // that's fixed we can uncomment the following line, remove the call
 513   // and change this function back into a "void" func.
 514   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 515   int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
 516   return ret_code;
 517 }
 518 
 519 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, jlong millis, TRAPS) {
 520   if (UseBiasedLocking) {
 521     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 522     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 523   }
 524   if (millis < 0) {
 525     THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 526   }
 527   ObjectMonitorHandle omh;
 528   inflate(&omh, THREAD, obj(), inflate_cause_wait);
 529   omh.om_ptr()->wait(millis, false, THREAD);
 530 }
 531 
 532 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 533   if (UseBiasedLocking) {
 534     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 535     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 536   }
 537 
 538   markWord mark = obj->mark();
 539   if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
 540     return;
 541   }
 542   ObjectMonitorHandle omh;
 543   inflate(&omh, THREAD, obj(), inflate_cause_notify);
 544   omh.om_ptr()->notify(THREAD);
 545 }
 546 
 547 // NOTE: see comment of notify()
 548 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 549   if (UseBiasedLocking) {
 550     BiasedLocking::revoke_and_rebias(obj, false, THREAD);
 551     assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 552   }
 553 
 554   markWord mark = obj->mark();
 555   if (mark.has_locker() && THREAD->is_lock_owned((address)mark.locker())) {
 556     return;
 557   }
 558   ObjectMonitorHandle omh;
 559   inflate(&omh, THREAD, obj(), inflate_cause_notify);
 560   omh.om_ptr()->notifyAll(THREAD);
 561 }
 562 
 563 // -----------------------------------------------------------------------------
 564 // Hash Code handling
 565 //
 566 // Performance concern:
 567 // OrderAccess::storestore() calls release() which at one time stored 0
 568 // into the global volatile OrderAccess::dummy variable. This store was
 569 // unnecessary for correctness. Many threads storing into a common location
 570 // causes considerable cache migration or "sloshing" on large SMP systems.
 571 // As such, I avoided using OrderAccess::storestore(). In some cases
 572 // OrderAccess::fence() -- which incurs local latency on the executing
 573 // processor -- is a better choice as it scales on SMP systems.
 574 //
 575 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
 576 // a discussion of coherency costs. Note that all our current reference
 577 // platforms provide strong ST-ST order, so the issue is moot on IA32,
 578 // x64, and SPARC.
 579 //
 580 // As a general policy we use "volatile" to control compiler-based reordering
 581 // and explicit fences (barriers) to control for architectural reordering
 582 // performed by the CPU(s) or platform.
 583 
 584 struct SharedGlobals {
 585   char         _pad_prefix[DEFAULT_CACHE_LINE_SIZE];
 586   // These are highly shared mostly-read variables.
 587   // To avoid false-sharing they need to be the sole occupants of a cache line.
 588   volatile int stw_random;
 589   volatile int stw_cycle;
 590   DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int) * 2);
 591   // Hot RW variable -- Sequester to avoid false-sharing
 592   volatile int hc_sequence;
 593   DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
 594 };
 595 
 596 static SharedGlobals GVars;
 597 static int MonitorScavengeThreshold = 1000000;
 598 static volatile int ForceMonitorScavenge = 0; // Scavenge required and pending
 599 
 600 static markWord read_stable_mark(oop obj) {
 601   markWord mark = obj->mark();
 602   if (!mark.is_being_inflated()) {
 603     return mark;       // normal fast-path return
 604   }
 605 
 606   int its = 0;
 607   for (;;) {
 608     markWord mark = obj->mark();
 609     if (!mark.is_being_inflated()) {
 610       return mark;    // normal fast-path return
 611     }
 612 
 613     // The object is being inflated by some other thread.
 614     // The caller of read_stable_mark() must wait for inflation to complete.
 615     // Avoid live-lock
 616     // TODO: consider calling SafepointSynchronize::do_call_back() while
 617     // spinning to see if there's a safepoint pending.  If so, immediately
 618     // yielding or blocking would be appropriate.  Avoid spinning while
 619     // there is a safepoint pending.
 620     // TODO: add inflation contention performance counters.
 621     // TODO: restrict the aggregate number of spinners.
 622 
 623     ++its;
 624     if (its > 10000 || !os::is_MP()) {
 625       if (its & 1) {
 626         os::naked_yield();
 627       } else {
 628         // Note that the following code attenuates the livelock problem but is not
 629         // a complete remedy.  A more complete solution would require that the inflating
 630         // thread hold the associated inflation lock.  The following code simply restricts
 631         // the number of spinners to at most one.  We'll have N-2 threads blocked
 632         // on the inflationlock, 1 thread holding the inflation lock and using
 633         // a yield/park strategy, and 1 thread in the midst of inflation.
 634         // A more refined approach would be to change the encoding of INFLATING
 635         // to allow encapsulation of a native thread pointer.  Threads waiting for
 636         // inflation to complete would use CAS to push themselves onto a singly linked
 637         // list rooted at the markword.  Once enqueued, they'd loop, checking a per-thread flag
 638         // and calling park().  When inflation was complete the thread that accomplished inflation
 639         // would detach the list and set the markword to inflated with a single CAS and
 640         // then for each thread on the list, set the flag and unpark() the thread.
 641         // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
 642         // wakes at most one thread whereas we need to wake the entire list.
 643         int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
 644         int YieldThenBlock = 0;
 645         assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
 646         assert((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant");
 647         Thread::muxAcquire(gInflationLocks + ix, "gInflationLock");
 648         while (obj->mark() == markWord::INFLATING()) {
 649           // Beware: NakedYield() is advisory and has almost no effect on some platforms
 650           // so we periodically call self->_ParkEvent->park(1).
 651           // We use a mixed spin/yield/block mechanism.
 652           if ((YieldThenBlock++) >= 16) {
 653             Thread::current()->_ParkEvent->park(1);
 654           } else {
 655             os::naked_yield();
 656           }
 657         }
 658         Thread::muxRelease(gInflationLocks + ix);
 659       }
 660     } else {
 661       SpinPause();       // SMP-polite spinning
 662     }
 663   }
 664 }
 665 
 666 // hashCode() generation :
 667 //
 668 // Possibilities:
 669 // * MD5Digest of {obj,stw_random}
 670 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
 671 // * A DES- or AES-style SBox[] mechanism
 672 // * One of the Phi-based schemes, such as:
 673 //   2654435761 = 2^32 * Phi (golden ratio)
 674 //   HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
 675 // * A variation of Marsaglia's shift-xor RNG scheme.
 676 // * (obj ^ stw_random) is appealing, but can result
 677 //   in undesirable regularity in the hashCode values of adjacent objects
 678 //   (objects allocated back-to-back, in particular).  This could potentially
 679 //   result in hashtable collisions and reduced hashtable efficiency.
 680 //   There are simple ways to "diffuse" the middle address bits over the
 681 //   generated hashCode values:
 682 
 683 static inline intptr_t get_next_hash(Thread* self, oop obj) {
 684   intptr_t value = 0;
 685   if (hashCode == 0) {
 686     // This form uses global Park-Miller RNG.
 687     // On MP system we'll have lots of RW access to a global, so the
 688     // mechanism induces lots of coherency traffic.
 689     value = os::random();
 690   } else if (hashCode == 1) {
 691     // This variation has the property of being stable (idempotent)
 692     // between STW operations.  This can be useful in some of the 1-0
 693     // synchronization schemes.
 694     intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
 695     value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
 696   } else if (hashCode == 2) {
 697     value = 1;            // for sensitivity testing
 698   } else if (hashCode == 3) {
 699     value = ++GVars.hc_sequence;
 700   } else if (hashCode == 4) {
 701     value = cast_from_oop<intptr_t>(obj);
 702   } else {
 703     // Marsaglia's xor-shift scheme with thread-specific state
 704     // This is probably the best overall implementation -- we'll
 705     // likely make this the default in future releases.
 706     unsigned t = self->_hashStateX;
 707     t ^= (t << 11);
 708     self->_hashStateX = self->_hashStateY;
 709     self->_hashStateY = self->_hashStateZ;
 710     self->_hashStateZ = self->_hashStateW;
 711     unsigned v = self->_hashStateW;
 712     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
 713     self->_hashStateW = v;
 714     value = v;
 715   }
 716 
 717   value &= markWord::hash_mask;
 718   if (value == 0) value = 0xBAD;
 719   assert(value != markWord::no_hash, "invariant");
 720   return value;
 721 }
 722 
 723 intptr_t ObjectSynchronizer::FastHashCode(Thread* self, oop obj) {
 724   if (UseBiasedLocking) {
 725     // NOTE: many places throughout the JVM do not expect a safepoint
 726     // to be taken here, in particular most operations on perm gen
 727     // objects. However, we only ever bias Java instances and all of
 728     // the call sites of identity_hash that might revoke biases have
 729     // been checked to make sure they can handle a safepoint. The
 730     // added check of the bias pattern is to avoid useless calls to
 731     // thread-local storage.
 732     if (obj->mark().has_bias_pattern()) {
 733       // Handle for oop obj in case of STW safepoint
 734       Handle hobj(self, obj);
 735       // Relaxing assertion for bug 6320749.
 736       assert(Universe::verify_in_progress() ||
 737              !SafepointSynchronize::is_at_safepoint(),
 738              "biases should not be seen by VM thread here");
 739       BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
 740       obj = hobj();
 741       assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
 742     }
 743   }
 744 
 745   // hashCode() is a heap mutator ...
 746   // Relaxing assertion for bug 6320749.
 747   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 748          !SafepointSynchronize::is_at_safepoint(), "invariant");
 749   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 750          self->is_Java_thread() , "invariant");
 751   assert(Universe::verify_in_progress() || DumpSharedSpaces ||
 752          ((JavaThread *)self)->thread_state() != _thread_blocked, "invariant");
 753 
 754   while (true) {
 755     ObjectMonitor* monitor = NULL;
 756     markWord temp, test;
 757     intptr_t hash;
 758     markWord mark = read_stable_mark(obj);
 759 
 760     // object should remain ineligible for biased locking
 761     assert(!mark.has_bias_pattern(), "invariant");
 762 
 763     if (mark.is_neutral()) {
 764       hash = mark.hash();              // this is a normal header
 765       if (hash != 0) {                  // if it has hash, just return it
 766         return hash;
 767       }
 768       hash = get_next_hash(self, obj);  // allocate a new hash code
 769       temp = mark.copy_set_hash(hash); // merge the hash code into header
 770       // use (machine word version) atomic operation to install the hash
 771       test = obj->cas_set_mark(temp, mark);
 772       if (test == mark) {
 773         return hash;
 774       }
 775       // If atomic operation failed, we must inflate the header
 776       // into heavy weight monitor. We could add more code here
 777       // for fast path, but it does not worth the complexity.
 778     } else if (mark.has_monitor()) {
 779       ObjectMonitorHandle omh;
 780       if (!omh.save_om_ptr(obj, mark)) {
 781         // Lost a race with async deflation so try again.
 782         assert(AsyncDeflateIdleMonitors, "sanity check");
 783         continue;
 784       }
 785       monitor = omh.om_ptr();
 786       temp = monitor->header();
 787       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 788       hash = temp.hash();
 789       if (hash != 0) {
 790         return hash;
 791       }
 792       // Skip to the following code to reduce code size
 793     } else if (self->is_lock_owned((address)mark.locker())) {
 794       temp = mark.displaced_mark_helper(); // this is a lightweight monitor owned
 795       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 796       hash = temp.hash();              // by current thread, check if the displaced
 797       if (hash != 0) {                  // header contains hash code
 798         return hash;
 799       }
 800       // WARNING:
 801       // The displaced header in the BasicLock on a thread's stack
 802       // is strictly immutable. It CANNOT be changed in ANY cases.
 803       // So we have to inflate the stack lock into an ObjectMonitor
 804       // even if the current thread owns the lock. The BasicLock on
 805       // a thread's stack can be asynchronously read by other threads
 806       // during an inflate() call so any change to that stack memory
 807       // may not propagate to other threads correctly.
 808     }
 809 
 810     // Inflate the monitor to set hash code
 811     ObjectMonitorHandle omh;
 812     inflate(&omh, self, obj, inflate_cause_hash_code);
 813     monitor = omh.om_ptr();
 814     // Load displaced header and check it has hash code
 815     mark = monitor->header();
 816     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
 817     hash = mark.hash();
 818     if (hash == 0) {
 819       hash = get_next_hash(self, obj);
 820       temp = mark.copy_set_hash(hash); // merge hash code into header
 821       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 822       uintptr_t v = Atomic::cmpxchg(temp.value(), (volatile uintptr_t*)monitor->header_addr(), mark.value());
 823       test = markWord(v);
 824       if (test != mark) {
 825         // The only non-deflation update to the ObjectMonitor's
 826         // header/dmw field is to merge in the hash code. If someone
 827         // adds a new usage of the header/dmw field, please update
 828         // this code.
 829         // ObjectMonitor::install_displaced_markword_in_object()
 830         // does mark the header/dmw field as part of async deflation,
 831         // but that protocol cannot happen now due to the
 832         // ObjectMonitorHandle above.
 833         hash = test.hash();
 834         assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
 835         assert(hash != 0, "Trivial unexpected object/monitor header usage.");
 836       }
 837     }
 838     // We finally get the hash
 839     return hash;
 840   }
 841 }
 842 
 843 // Deprecated -- use FastHashCode() instead.
 844 
 845 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
 846   return FastHashCode(Thread::current(), obj());
 847 }
 848 
 849 
 850 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
 851                                                    Handle h_obj) {
 852   if (UseBiasedLocking) {
 853     BiasedLocking::revoke_and_rebias(h_obj, false, thread);
 854     assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
 855   }
 856 
 857   assert(thread == JavaThread::current(), "Can only be called on current thread");
 858   oop obj = h_obj();
 859 
 860   while (true) {
 861     markWord mark = read_stable_mark(obj);
 862 
 863     // Uncontended case, header points to stack
 864     if (mark.has_locker()) {
 865       return thread->is_lock_owned((address)mark.locker());
 866     }
 867     // Contended case, header points to ObjectMonitor (tagged pointer)
 868     if (mark.has_monitor()) {
 869       ObjectMonitorHandle omh;
 870       if (!omh.save_om_ptr(obj, mark)) {
 871         // Lost a race with async deflation so try again.
 872         assert(AsyncDeflateIdleMonitors, "sanity check");
 873         continue;
 874       }
 875       bool ret_code = omh.om_ptr()->is_entered(thread) != 0;
 876       return ret_code;
 877     }
 878     // Unlocked case, header in place
 879     assert(mark.is_neutral(), "sanity check");
 880     return false;
 881   }
 882 }
 883 
 884 // Be aware of this method could revoke bias of the lock object.
 885 // This method queries the ownership of the lock handle specified by 'h_obj'.
 886 // If the current thread owns the lock, it returns owner_self. If no
 887 // thread owns the lock, it returns owner_none. Otherwise, it will return
 888 // owner_other.
 889 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
 890 (JavaThread *self, Handle h_obj) {
 891   // The caller must beware this method can revoke bias, and
 892   // revocation can result in a safepoint.
 893   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 894   assert(self->thread_state() != _thread_blocked, "invariant");
 895 
 896   // Possible mark states: neutral, biased, stack-locked, inflated
 897 
 898   if (UseBiasedLocking && h_obj()->mark().has_bias_pattern()) {
 899     // CASE: biased
 900     BiasedLocking::revoke_and_rebias(h_obj, false, self);
 901     assert(!h_obj->mark().has_bias_pattern(),
 902            "biases should be revoked by now");
 903   }
 904 
 905   assert(self == JavaThread::current(), "Can only be called on current thread");
 906   oop obj = h_obj();
 907 
 908   while (true) {
 909     markWord mark = read_stable_mark(obj);
 910 
 911     // CASE: stack-locked.  Mark points to a BasicLock on the owner's stack.
 912     if (mark.has_locker()) {
 913       return self->is_lock_owned((address)mark.locker()) ?
 914         owner_self : owner_other;
 915     }
 916 
 917     // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
 918     // The Object:ObjectMonitor relationship is stable as long as we're
 919     // not at a safepoint and AsyncDeflateIdleMonitors is false.
 920     if (mark.has_monitor()) {
 921       ObjectMonitorHandle omh;
 922       if (!omh.save_om_ptr(obj, mark)) {
 923         // Lost a race with async deflation so try again.
 924         assert(AsyncDeflateIdleMonitors, "sanity check");
 925         continue;
 926       }
 927       ObjectMonitor* monitor = omh.om_ptr();
 928       void* owner = monitor->_owner;
 929       if (owner == NULL) return owner_none;
 930       return (owner == self ||
 931               self->is_lock_owned((address)owner)) ? owner_self : owner_other;
 932     }
 933 
 934     // CASE: neutral
 935     assert(mark.is_neutral(), "sanity check");
 936     return owner_none;           // it's unlocked
 937   }
 938 }
 939 
 940 // FIXME: jvmti should call this
 941 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
 942   if (UseBiasedLocking) {
 943     if (SafepointSynchronize::is_at_safepoint()) {
 944       BiasedLocking::revoke_at_safepoint(h_obj);
 945     } else {
 946       BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
 947     }
 948     assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
 949   }
 950 
 951   oop obj = h_obj();
 952 
 953   while (true) {
 954     address owner = NULL;
 955     markWord mark = read_stable_mark(obj);
 956 
 957     // Uncontended case, header points to stack
 958     if (mark.has_locker()) {
 959       owner = (address) mark.locker();
 960     }
 961 
 962     // Contended case, header points to ObjectMonitor (tagged pointer)
 963     else if (mark.has_monitor()) {
 964       ObjectMonitorHandle omh;
 965       if (!omh.save_om_ptr(obj, mark)) {
 966         // Lost a race with async deflation so try again.
 967         assert(AsyncDeflateIdleMonitors, "sanity check");
 968         continue;
 969       }
 970       ObjectMonitor* monitor = omh.om_ptr();
 971       assert(monitor != NULL, "monitor should be non-null");
 972       owner = (address) monitor->owner();
 973     }
 974 
 975     if (owner != NULL) {
 976       // owning_thread_from_monitor_owner() may also return NULL here
 977       return Threads::owning_thread_from_monitor_owner(t_list, owner);
 978     }
 979 
 980     // Unlocked case, header in place
 981     // Cannot have assertion since this object may have been
 982     // locked by another thread when reaching here.
 983     // assert(mark.is_neutral(), "sanity check");
 984 
 985     return NULL;
 986   }
 987 }
 988 
 989 // Visitors ...
 990 
 991 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
 992   PaddedObjectMonitor* block = OrderAccess::load_acquire(&g_block_list);
 993   while (block != NULL) {
 994     assert(block->object() == CHAINMARKER, "must be a block header");
 995     for (int i = _BLOCKSIZE - 1; i > 0; i--) {
 996       ObjectMonitor* mid = (ObjectMonitor *)(block + i);
 997       if (mid->is_active()) {
 998         ObjectMonitorHandle omh(mid);
 999 
1000         if (mid->object() == NULL ||
1001             (AsyncDeflateIdleMonitors && mid->_owner == DEFLATER_MARKER)) {
1002           // Only process with closure if the object is set.
1003           // For async deflation, race here if monitor is not owned!
1004           // The above ref_count bump (in ObjectMonitorHandle ctr)
1005           // will cause subsequent async deflation to skip it.
1006           // However, previous or concurrent async deflation is a race.
1007           continue;
1008         }
1009         closure->do_monitor(mid);
1010       }
1011     }
1012     block = (PaddedObjectMonitor*)block->_next_om;
1013   }
1014 }
1015 
1016 static bool monitors_used_above_threshold() {
1017   if (g_om_population == 0) {
1018     return false;
1019   }
1020   if (MonitorUsedDeflationThreshold > 0) {
1021     int monitors_used = g_om_population - g_om_free_count;
1022     int monitor_usage = (monitors_used * 100LL) / g_om_population;
1023     return monitor_usage > MonitorUsedDeflationThreshold;
1024   }
1025   return false;
1026 }
1027 
1028 // Returns true if MonitorBound is set (> 0) and if the specified
1029 // cnt is > MonitorBound. Otherwise returns false.
1030 static bool is_MonitorBound_exceeded(const int cnt) {
1031   const int mx = MonitorBound;
1032   return mx > 0 && cnt > mx;
1033 }
1034 
1035 bool ObjectSynchronizer::is_async_deflation_needed() {
1036   if (!AsyncDeflateIdleMonitors) {
1037     return false;
1038   }
1039   if (is_async_deflation_requested()) {
1040     // Async deflation request.
1041     return true;
1042   }
1043   if (AsyncDeflationInterval > 0 &&
1044       time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1045       monitors_used_above_threshold()) {
1046     // It's been longer than our specified deflate interval and there
1047     // are too many monitors in use. We don't deflate more frequently
1048     // than AsyncDeflationInterval (unless is_async_deflation_requested)
1049     // in order to not swamp the ServiceThread.
1050     _last_async_deflation_time_ns = os::javaTimeNanos();
1051     return true;
1052   }
1053   if (is_MonitorBound_exceeded(g_om_population - g_om_free_count)) {
1054     // Not enough ObjectMonitors on the global free list.
1055     return true;
1056   }
1057   return false;
1058 }
1059 
1060 bool ObjectSynchronizer::is_safepoint_deflation_needed() {
1061   if (!AsyncDeflateIdleMonitors) {
1062     if (monitors_used_above_threshold()) {
1063       // Too many monitors in use.
1064       return true;
1065     }
1066     return false;
1067   }
1068   if (is_special_deflation_requested()) {
1069     // For AsyncDeflateIdleMonitors only do a safepoint deflation
1070     // if there is a special deflation request.
1071     return true;
1072   }
1073   return false;
1074 }
1075 
1076 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1077   return (os::javaTimeNanos() - _last_async_deflation_time_ns) / (NANOUNITS / MILLIUNITS);
1078 }
1079 
1080 void ObjectSynchronizer::oops_do(OopClosure* f) {
1081   // We only scan the global used list here (for moribund threads), and
1082   // the thread-local monitors in Thread::oops_do().
1083   global_used_oops_do(f);
1084 }
1085 
1086 void ObjectSynchronizer::global_used_oops_do(OopClosure* f) {
1087   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1088   list_oops_do(g_om_in_use_list, f);
1089 }
1090 
1091 void ObjectSynchronizer::thread_local_used_oops_do(Thread* thread, OopClosure* f) {
1092   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1093   list_oops_do(thread->om_in_use_list, f);
1094 }
1095 
1096 void ObjectSynchronizer::list_oops_do(ObjectMonitor* list, OopClosure* f) {
1097   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1098   ObjectMonitor* mid;
1099   for (mid = list; mid != NULL; mid = mid->_next_om) {
1100     if (mid->object() != NULL) {
1101       f->do_oop((oop*)mid->object_addr());
1102     }
1103   }
1104 }
1105 
1106 
1107 // -----------------------------------------------------------------------------
1108 // ObjectMonitor Lifecycle
1109 // -----------------------
1110 // Inflation unlinks monitors from the global g_free_list and
1111 // associates them with objects.  Deflation -- which occurs at
1112 // STW-time -- disassociates idle monitors from objects.  Such
1113 // scavenged monitors are returned to the g_free_list.
1114 //
1115 // The global list is protected by gListLock.  All the critical sections
1116 // are short and operate in constant-time.
1117 //
1118 // ObjectMonitors reside in type-stable memory (TSM) and are immortal.
1119 //
1120 // Lifecycle:
1121 // --   unassigned and on the global free list
1122 // --   unassigned and on a thread's private om_free_list
1123 // --   assigned to an object.  The object is inflated and the mark refers
1124 //      to the objectmonitor.
1125 
1126 
1127 // Constraining monitor pool growth via MonitorBound ...
1128 //
1129 // If MonitorBound is not set (<= 0), MonitorBound checks are disabled.
1130 //
1131 // When safepoint deflation is being used (!AsyncDeflateIdleMonitors):
1132 // The monitor pool is grow-only.  We scavenge at STW safepoint-time, but the
1133 // the rate of scavenging is driven primarily by GC.  As such,  we can find
1134 // an inordinate number of monitors in circulation.
1135 // To avoid that scenario we can artificially induce a STW safepoint
1136 // if the pool appears to be growing past some reasonable bound.
1137 // Generally we favor time in space-time tradeoffs, but as there's no
1138 // natural back-pressure on the # of extant monitors we need to impose some
1139 // type of limit.  Beware that if MonitorBound is set to too low a value
1140 // we could just loop. In addition, if MonitorBound is set to a low value
1141 // we'll incur more safepoints, which are harmful to performance.
1142 // See also: GuaranteedSafepointInterval
1143 //
1144 // The current implementation uses asynchronous VM operations.
1145 //
1146 // When safepoint deflation is being used and MonitorBound is set, the
1147 // boundry applies to
1148 //     (g_om_population - g_om_free_count)
1149 // i.e., if there are not enough ObjectMonitors on the global free list,
1150 // then a safepoint deflation is induced. Picking a good MonitorBound value
1151 // is non-trivial.
1152 //
1153 // When async deflation is being used:
1154 // The monitor pool is still grow-only. Async deflation is requested
1155 // by a safepoint's cleanup phase or by the ServiceThread at periodic
1156 // intervals when is_async_deflation_needed() returns true. In
1157 // addition to other policies that are checked, if there are not
1158 // enough ObjectMonitors on the global free list, then
1159 // is_async_deflation_needed() will return true. The ServiceThread
1160 // calls deflate_global_idle_monitors_using_JT() and also sets the
1161 // per-thread om_request_deflation flag as needed.
1162 
1163 static void InduceScavenge(Thread* self, const char * Whence) {
1164   assert(!AsyncDeflateIdleMonitors, "is not used by async deflation");
1165 
1166   // Induce STW safepoint to trim monitors
1167   // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1168   // More precisely, trigger an asynchronous STW safepoint as the number
1169   // of active monitors passes the specified threshold.
1170   // TODO: assert thread state is reasonable
1171 
1172   if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1173     // Induce a 'null' safepoint to scavenge monitors
1174     // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1175     // to the VMthread and have a lifespan longer than that of this activation record.
1176     // The VMThread will delete the op when completed.
1177     VMThread::execute(new VM_ScavengeMonitors());
1178   }
1179 }
1180 
1181 ObjectMonitor* ObjectSynchronizer::om_alloc(Thread* self,
1182                                            const InflateCause cause) {
1183   // A large MAXPRIVATE value reduces both list lock contention
1184   // and list coherency traffic, but also tends to increase the
1185   // number of ObjectMonitors in circulation as well as the STW
1186   // scavenge costs.  As usual, we lean toward time in space-time
1187   // tradeoffs.
1188   const int MAXPRIVATE = 1024;
1189 
1190   if (AsyncDeflateIdleMonitors) {
1191     JavaThread* jt = (JavaThread *)self;
1192     if (jt->om_request_deflation && jt->om_in_use_count > 0 &&
1193         cause != inflate_cause_vm_internal) {
1194       // Deflate any per-thread idle monitors for this JavaThread if
1195       // this is not an internal inflation; internal inflations can
1196       // occur in places where it is not safe to pause for a safepoint.
1197       // Clean up your own mess (Gibbs Rule 45). Otherwise, skip this
1198       // deflation. deflate_global_idle_monitors_using_JT() is called
1199       // by the ServiceThread. Per-thread async deflation is triggered
1200       // by the ServiceThread via om_request_deflation.
1201       debug_only(jt->check_for_valid_safepoint_state(false);)
1202       ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT();
1203     }
1204   }
1205 
1206   stringStream ss;
1207   for (;;) {
1208     ObjectMonitor* m;
1209 
1210     // 1: try to allocate from the thread's local om_free_list.
1211     // Threads will attempt to allocate first from their local list, then
1212     // from the global list, and only after those attempts fail will the thread
1213     // attempt to instantiate new monitors.   Thread-local free lists take
1214     // heat off the gListLock and improve allocation latency, as well as reducing
1215     // coherency traffic on the shared global list.
1216     m = self->om_free_list;
1217     if (m != NULL) {
1218       self->om_free_list = m->_next_om;
1219       self->om_free_count--;
1220       guarantee(m->object() == NULL, "invariant");
1221       m->set_allocation_state(ObjectMonitor::New);
1222       m->_next_om = self->om_in_use_list;
1223       self->om_in_use_list = m;
1224       self->om_in_use_count++;
1225       return m;
1226     }
1227 
1228     // 2: try to allocate from the global g_free_list
1229     // CONSIDER: use muxTry() instead of muxAcquire().
1230     // If the muxTry() fails then drop immediately into case 3.
1231     // If we're using thread-local free lists then try
1232     // to reprovision the caller's free list.
1233     if (g_free_list != NULL) {
1234       // Reprovision the thread's om_free_list.
1235       // Use bulk transfers to reduce the allocation rate and heat
1236       // on various locks.
1237       Thread::muxAcquire(&gListLock, "om_alloc(1)");
1238       for (int i = self->om_free_provision; --i >= 0 && g_free_list != NULL;) {
1239         g_om_free_count--;
1240         ObjectMonitor* take = g_free_list;
1241         g_free_list = take->_next_om;
1242         guarantee(take->object() == NULL, "invariant");
1243         if (AsyncDeflateIdleMonitors) {
1244           // We allowed 3 field values to linger during async deflation.
1245           // We clear header and restore ref_count here, but we leave
1246           // owner == DEFLATER_MARKER so the simple C2 ObjectMonitor
1247           // enter optimization can no longer race with async deflation
1248           // and reuse.
1249           take->set_header(markWord::zero());
1250           if (take->ref_count() < 0) {
1251             // Add back max_jint to restore the ref_count field to its
1252             // proper value.
1253             Atomic::add(max_jint, &take->_ref_count);
1254 
1255             assert(take->ref_count() >= 0, "must not be negative: ref_count=%d",
1256                    take->ref_count());
1257           }
1258         }
1259         take->Recycle();
1260         assert(take->is_free(), "invariant");
1261         om_release(self, take, false);
1262       }
1263       Thread::muxRelease(&gListLock);
1264       self->om_free_provision += 1 + (self->om_free_provision/2);
1265       if (self->om_free_provision > MAXPRIVATE) self->om_free_provision = MAXPRIVATE;
1266 
1267       if (!AsyncDeflateIdleMonitors &&
1268           is_MonitorBound_exceeded(g_om_population - g_om_free_count)) {
1269         // Not enough ObjectMonitors on the global free list.
1270         // We can't safely induce a STW safepoint from om_alloc() as our thread
1271         // state may not be appropriate for such activities and callers may hold
1272         // naked oops, so instead we defer the action.
1273         InduceScavenge(self, "om_alloc");
1274       }
1275       continue;
1276     }
1277 
1278     // 3: allocate a block of new ObjectMonitors
1279     // Both the local and global free lists are empty -- resort to malloc().
1280     // In the current implementation ObjectMonitors are TSM - immortal.
1281     // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1282     // each ObjectMonitor to start at the beginning of a cache line,
1283     // so we use align_up().
1284     // A better solution would be to use C++ placement-new.
1285     // BEWARE: As it stands currently, we don't run the ctors!
1286     assert(_BLOCKSIZE > 1, "invariant");
1287     size_t neededsize = sizeof(PaddedObjectMonitor) * _BLOCKSIZE;
1288     PaddedObjectMonitor* temp;
1289     size_t aligned_size = neededsize + (DEFAULT_CACHE_LINE_SIZE - 1);
1290     void* real_malloc_addr = (void*)NEW_C_HEAP_ARRAY(char, aligned_size,
1291                                                      mtInternal);
1292     temp = (PaddedObjectMonitor*)align_up(real_malloc_addr, DEFAULT_CACHE_LINE_SIZE);
1293 
1294     // NOTE: (almost) no way to recover if allocation failed.
1295     // We might be able to induce a STW safepoint and scavenge enough
1296     // ObjectMonitors to permit progress.
1297     if (temp == NULL) {
1298       vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1299                             "Allocate ObjectMonitors");
1300     }
1301     (void)memset((void *) temp, 0, neededsize);
1302 
1303     // Format the block.
1304     // initialize the linked list, each monitor points to its next
1305     // forming the single linked free list, the very first monitor
1306     // will points to next block, which forms the block list.
1307     // The trick of using the 1st element in the block as g_block_list
1308     // linkage should be reconsidered.  A better implementation would
1309     // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1310 
1311     for (int i = 1; i < _BLOCKSIZE; i++) {
1312       temp[i]._next_om = (ObjectMonitor *)&temp[i+1];
1313       assert(temp[i].is_free(), "invariant");
1314     }
1315 
1316     // terminate the last monitor as the end of list
1317     temp[_BLOCKSIZE - 1]._next_om = NULL;
1318 
1319     // Element [0] is reserved for global list linkage
1320     temp[0].set_object(CHAINMARKER);
1321 
1322     // Consider carving out this thread's current request from the
1323     // block in hand.  This avoids some lock traffic and redundant
1324     // list activity.
1325 
1326     // Acquire the gListLock to manipulate g_block_list and g_free_list.
1327     // An Oyama-Taura-Yonezawa scheme might be more efficient.
1328     Thread::muxAcquire(&gListLock, "om_alloc(2)");
1329     g_om_population += _BLOCKSIZE-1;
1330     g_om_free_count += _BLOCKSIZE-1;
1331 
1332     // Add the new block to the list of extant blocks (g_block_list).
1333     // The very first ObjectMonitor in a block is reserved and dedicated.
1334     // It serves as blocklist "next" linkage.
1335     temp[0]._next_om = g_block_list;
1336     // There are lock-free uses of g_block_list so make sure that
1337     // the previous stores happen before we update g_block_list.
1338     OrderAccess::release_store(&g_block_list, temp);
1339 
1340     // Add the new string of ObjectMonitors to the global free list
1341     temp[_BLOCKSIZE - 1]._next_om = g_free_list;
1342     g_free_list = temp + 1;
1343     Thread::muxRelease(&gListLock);
1344   }
1345 }
1346 
1347 // Place "m" on the caller's private per-thread om_free_list.
1348 // In practice there's no need to clamp or limit the number of
1349 // monitors on a thread's om_free_list as the only non-allocation time
1350 // we'll call om_release() is to return a monitor to the free list after
1351 // a CAS attempt failed. This doesn't allow unbounded #s of monitors to
1352 // accumulate on a thread's free list.
1353 //
1354 // Key constraint: all ObjectMonitors on a thread's free list and the global
1355 // free list must have their object field set to null. This prevents the
1356 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1357 // -- from reclaiming them while we are trying to release them.
1358 
1359 void ObjectSynchronizer::om_release(Thread* self, ObjectMonitor* m,
1360                                     bool from_per_thread_alloc) {
1361   guarantee(m->header().value() == 0, "invariant");
1362   guarantee(m->object() == NULL, "invariant");
1363   stringStream ss;
1364   guarantee((m->is_busy() | m->_recursions) == 0, "freeing in-use monitor: "
1365             "%s, recursions=" INTPTR_FORMAT, m->is_busy_to_string(&ss),
1366             m->_recursions);
1367   m->set_allocation_state(ObjectMonitor::Free);
1368   // _next_om is used for both per-thread in-use and free lists so
1369   // we have to remove 'm' from the in-use list first (as needed).
1370   if (from_per_thread_alloc) {
1371     // Need to remove 'm' from om_in_use_list.
1372     ObjectMonitor* cur_mid_in_use = NULL;
1373     bool extracted = false;
1374     for (ObjectMonitor* mid = self->om_in_use_list; mid != NULL; cur_mid_in_use = mid, mid = mid->_next_om) {
1375       if (m == mid) {
1376         // extract from per-thread in-use list
1377         if (mid == self->om_in_use_list) {
1378           self->om_in_use_list = mid->_next_om;
1379         } else if (cur_mid_in_use != NULL) {
1380           cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
1381         }
1382         extracted = true;
1383         self->om_in_use_count--;
1384         break;
1385       }
1386     }
1387     assert(extracted, "Should have extracted from in-use list");
1388   }
1389 
1390   m->_next_om = self->om_free_list;
1391   guarantee(m->is_free(), "invariant");
1392   self->om_free_list = m;
1393   self->om_free_count++;
1394 }
1395 
1396 // Return ObjectMonitors on a moribund thread's free and in-use
1397 // lists to the appropriate global lists. The ObjectMonitors on the
1398 // per-thread in-use list may still be in use by other threads.
1399 //
1400 // We currently call om_flush() from Threads::remove() before the
1401 // thread has been excised from the thread list and is no longer a
1402 // mutator. This means that om_flush() cannot run concurrently with
1403 // a safepoint and interleave with deflate_idle_monitors(). In
1404 // particular, this ensures that the thread's in-use monitors are
1405 // scanned by a GC safepoint, either via Thread::oops_do() (before
1406 // om_flush() is called) or via ObjectSynchronizer::oops_do() (after
1407 // om_flush() is called).
1408 //
1409 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1410 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1411 // run at the same time as om_flush() so we have to be careful.
1412 
1413 void ObjectSynchronizer::om_flush(Thread* self) {
1414   ObjectMonitor* free_list = self->om_free_list;
1415   ObjectMonitor* free_tail = NULL;
1416   int free_count = 0;
1417   if (free_list != NULL) {
1418     ObjectMonitor* s;
1419     // The thread is going away. Set 'free_tail' to the last per-thread free
1420     // monitor which will be linked to g_free_list below under the gListLock.
1421     stringStream ss;
1422     for (s = free_list; s != NULL; s = s->_next_om) {
1423       free_count++;
1424       free_tail = s;
1425       guarantee(s->object() == NULL, "invariant");
1426       guarantee(!s->is_busy(), "must be !is_busy: %s", s->is_busy_to_string(&ss));
1427     }
1428     guarantee(free_tail != NULL, "invariant");
1429     ADIM_guarantee(self->om_free_count == free_count, "free-count off");
1430     self->om_free_list = NULL;
1431     self->om_free_count = 0;
1432   }
1433 
1434   ObjectMonitor* in_use_list = self->om_in_use_list;
1435   ObjectMonitor* in_use_tail = NULL;
1436   int in_use_count = 0;
1437   if (in_use_list != NULL) {
1438     // The thread is going away, however the ObjectMonitors on the
1439     // om_in_use_list may still be in-use by other threads. Link
1440     // them to in_use_tail, which will be linked into the global
1441     // in-use list g_om_in_use_list below, under the gListLock.
1442     ObjectMonitor *cur_om;
1443     for (cur_om = in_use_list; cur_om != NULL; cur_om = cur_om->_next_om) {
1444       in_use_tail = cur_om;
1445       in_use_count++;
1446       ADIM_guarantee(cur_om->is_active(), "invariant");
1447     }
1448     guarantee(in_use_tail != NULL, "invariant");
1449     ADIM_guarantee(self->om_in_use_count == in_use_count, "in-use count off");
1450     self->om_in_use_list = NULL;
1451     self->om_in_use_count = 0;
1452   }
1453 
1454   Thread::muxAcquire(&gListLock, "om_flush");
1455   if (free_tail != NULL) {
1456     free_tail->_next_om = g_free_list;
1457     g_free_list = free_list;
1458     g_om_free_count += free_count;
1459   }
1460 
1461   if (in_use_tail != NULL) {
1462     in_use_tail->_next_om = g_om_in_use_list;
1463     g_om_in_use_list = in_use_list;
1464     g_om_in_use_count += in_use_count;
1465   }
1466 
1467   Thread::muxRelease(&gListLock);
1468 
1469   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1470   LogStreamHandle(Info, monitorinflation) lsh_info;
1471   LogStream* ls = NULL;
1472   if (log_is_enabled(Debug, monitorinflation)) {
1473     ls = &lsh_debug;
1474   } else if ((free_count != 0 || in_use_count != 0) &&
1475              log_is_enabled(Info, monitorinflation)) {
1476     ls = &lsh_info;
1477   }
1478   if (ls != NULL) {
1479     ls->print_cr("om_flush: jt=" INTPTR_FORMAT ", free_count=%d"
1480                  ", in_use_count=%d" ", om_free_provision=%d",
1481                  p2i(self), free_count, in_use_count, self->om_free_provision);
1482   }
1483 }
1484 
1485 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1486                                        const oop obj,
1487                                        ObjectSynchronizer::InflateCause cause) {
1488   assert(event != NULL, "invariant");
1489   assert(event->should_commit(), "invariant");
1490   event->set_monitorClass(obj->klass());
1491   event->set_address((uintptr_t)(void*)obj);
1492   event->set_cause((u1)cause);
1493   event->commit();
1494 }
1495 
1496 // Fast path code shared by multiple functions
1497 void ObjectSynchronizer::inflate_helper(ObjectMonitorHandle* omh_p, oop obj) {
1498   while (true) {
1499     markWord mark = obj->mark();
1500     if (mark.has_monitor()) {
1501       if (!omh_p->save_om_ptr(obj, mark)) {
1502         // Lost a race with async deflation so try again.
1503         assert(AsyncDeflateIdleMonitors, "sanity check");
1504         continue;
1505       }
1506       ObjectMonitor* monitor = omh_p->om_ptr();
1507       assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor is invalid");
1508       markWord dmw = monitor->header();
1509       assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1510       return;
1511     }
1512     inflate(omh_p, Thread::current(), obj, inflate_cause_vm_internal);
1513     return;
1514   }
1515 }
1516 
1517 void ObjectSynchronizer::inflate(ObjectMonitorHandle* omh_p, Thread* self,
1518                                  oop object, const InflateCause cause) {
1519   // Inflate mutates the heap ...
1520   // Relaxing assertion for bug 6320749.
1521   assert(Universe::verify_in_progress() ||
1522          !SafepointSynchronize::is_at_safepoint(), "invariant");
1523 
1524   EventJavaMonitorInflate event;
1525 
1526   for (;;) {
1527     const markWord mark = object->mark();
1528     assert(!mark.has_bias_pattern(), "invariant");
1529 
1530     // The mark can be in one of the following states:
1531     // *  Inflated     - just return
1532     // *  Stack-locked - coerce it to inflated
1533     // *  INFLATING    - busy wait for conversion to complete
1534     // *  Neutral      - aggressively inflate the object.
1535     // *  BIASED       - Illegal.  We should never see this
1536 
1537     // CASE: inflated
1538     if (mark.has_monitor()) {
1539       if (!omh_p->save_om_ptr(object, mark)) {
1540         // Lost a race with async deflation so try again.
1541         assert(AsyncDeflateIdleMonitors, "sanity check");
1542         continue;
1543       }
1544       ObjectMonitor* inf = omh_p->om_ptr();
1545       markWord dmw = inf->header();
1546       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1547       assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1548       assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1549       return;
1550     }
1551 
1552     // CASE: inflation in progress - inflating over a stack-lock.
1553     // Some other thread is converting from stack-locked to inflated.
1554     // Only that thread can complete inflation -- other threads must wait.
1555     // The INFLATING value is transient.
1556     // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1557     // We could always eliminate polling by parking the thread on some auxiliary list.
1558     if (mark == markWord::INFLATING()) {
1559       read_stable_mark(object);
1560       continue;
1561     }
1562 
1563     // CASE: stack-locked
1564     // Could be stack-locked either by this thread or by some other thread.
1565     //
1566     // Note that we allocate the objectmonitor speculatively, _before_ attempting
1567     // to install INFLATING into the mark word.  We originally installed INFLATING,
1568     // allocated the objectmonitor, and then finally STed the address of the
1569     // objectmonitor into the mark.  This was correct, but artificially lengthened
1570     // the interval in which INFLATED appeared in the mark, thus increasing
1571     // the odds of inflation contention.
1572     //
1573     // We now use per-thread private objectmonitor free lists.
1574     // These list are reprovisioned from the global free list outside the
1575     // critical INFLATING...ST interval.  A thread can transfer
1576     // multiple objectmonitors en-mass from the global free list to its local free list.
1577     // This reduces coherency traffic and lock contention on the global free list.
1578     // Using such local free lists, it doesn't matter if the om_alloc() call appears
1579     // before or after the CAS(INFLATING) operation.
1580     // See the comments in om_alloc().
1581 
1582     LogStreamHandle(Trace, monitorinflation) lsh;
1583 
1584     if (mark.has_locker()) {
1585       ObjectMonitor* m;
1586       if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1587         // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1588         // we won't stop for a potential safepoint in om_alloc.
1589         m = om_alloc(self, cause);
1590       } else {
1591         // If AsyncDeflateIdleMonitors and not an internal inflation, then
1592         // we may stop for a safepoint in om_alloc() so protect object.
1593         Handle h_obj(self, object);
1594         m = om_alloc(self, cause);
1595         object = h_obj();  // Refresh object.
1596       }
1597       // Optimistically prepare the objectmonitor - anticipate successful CAS
1598       // We do this before the CAS in order to minimize the length of time
1599       // in which INFLATING appears in the mark.
1600       m->Recycle();
1601       m->_Responsible  = NULL;
1602       m->_SpinDuration = ObjectMonitor::Knob_SpinLimit;   // Consider: maintain by type/class
1603 
1604       markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1605       if (cmp != mark) {
1606         om_release(self, m, true);
1607         continue;       // Interference -- just retry
1608       }
1609 
1610       // We've successfully installed INFLATING (0) into the mark-word.
1611       // This is the only case where 0 will appear in a mark-word.
1612       // Only the singular thread that successfully swings the mark-word
1613       // to 0 can perform (or more precisely, complete) inflation.
1614       //
1615       // Why do we CAS a 0 into the mark-word instead of just CASing the
1616       // mark-word from the stack-locked value directly to the new inflated state?
1617       // Consider what happens when a thread unlocks a stack-locked object.
1618       // It attempts to use CAS to swing the displaced header value from the
1619       // on-stack BasicLock back into the object header.  Recall also that the
1620       // header value (hash code, etc) can reside in (a) the object header, or
1621       // (b) a displaced header associated with the stack-lock, or (c) a displaced
1622       // header in an ObjectMonitor.  The inflate() routine must copy the header
1623       // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1624       // the while preserving the hashCode stability invariants.  If the owner
1625       // decides to release the lock while the value is 0, the unlock will fail
1626       // and control will eventually pass from slow_exit() to inflate.  The owner
1627       // will then spin, waiting for the 0 value to disappear.   Put another way,
1628       // the 0 causes the owner to stall if the owner happens to try to
1629       // drop the lock (restoring the header from the BasicLock to the object)
1630       // while inflation is in-progress.  This protocol avoids races that might
1631       // would otherwise permit hashCode values to change or "flicker" for an object.
1632       // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1633       // 0 serves as a "BUSY" inflate-in-progress indicator.
1634 
1635 
1636       // fetch the displaced mark from the owner's stack.
1637       // The owner can't die or unwind past the lock while our INFLATING
1638       // object is in the mark.  Furthermore the owner can't complete
1639       // an unlock on the object, either.
1640       markWord dmw = mark.displaced_mark_helper();
1641       // Catch if the object's header is not neutral (not locked and
1642       // not marked is what we care about here).
1643       ADIM_guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1644 
1645       // Setup monitor fields to proper values -- prepare the monitor
1646       m->set_header(dmw);
1647 
1648       // Optimization: if the mark.locker stack address is associated
1649       // with this thread we could simply set m->_owner = self.
1650       // Note that a thread can inflate an object
1651       // that it has stack-locked -- as might happen in wait() -- directly
1652       // with CAS.  That is, we can avoid the xchg-NULL .... ST idiom.
1653       m->set_owner(mark.locker());
1654       m->set_object(object);
1655       // TODO-FIXME: assert BasicLock->dhw != 0.
1656 
1657       omh_p->set_om_ptr(m);
1658       assert(m->is_new(), "freshly allocated monitor must be new");
1659       m->set_allocation_state(ObjectMonitor::Old);
1660 
1661       // Must preserve store ordering. The monitor state must
1662       // be stable at the time of publishing the monitor address.
1663       guarantee(object->mark() == markWord::INFLATING(), "invariant");
1664       object->release_set_mark(markWord::encode(m));
1665 
1666       // Hopefully the performance counters are allocated on distinct cache lines
1667       // to avoid false sharing on MP systems ...
1668       OM_PERFDATA_OP(Inflations, inc());
1669       if (log_is_enabled(Trace, monitorinflation)) {
1670         ResourceMark rm(self);
1671         lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1672                      INTPTR_FORMAT ", type='%s'", p2i(object),
1673                      object->mark().value(), object->klass()->external_name());
1674       }
1675       if (event.should_commit()) {
1676         post_monitor_inflate_event(&event, object, cause);
1677       }
1678       ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
1679       return;
1680     }
1681 
1682     // CASE: neutral
1683     // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1684     // If we know we're inflating for entry it's better to inflate by swinging a
1685     // pre-locked ObjectMonitor pointer into the object header.   A successful
1686     // CAS inflates the object *and* confers ownership to the inflating thread.
1687     // In the current implementation we use a 2-step mechanism where we CAS()
1688     // to inflate and then CAS() again to try to swing _owner from NULL to self.
1689     // An inflateTry() method that we could call from fast_enter() and slow_enter()
1690     // would be useful.
1691 
1692     // Catch if the object's header is not neutral (not locked and
1693     // not marked is what we care about here).
1694     ADIM_guarantee(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1695     ObjectMonitor* m;
1696     if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1697       // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1698       // we won't stop for a potential safepoint in om_alloc.
1699       m = om_alloc(self, cause);
1700     } else {
1701       // If AsyncDeflateIdleMonitors and not an internal inflation, then
1702       // we may stop for a safepoint in om_alloc() so protect object.
1703       Handle h_obj(self, object);
1704       m = om_alloc(self, cause);
1705       object = h_obj();  // Refresh object.
1706     }
1707     // prepare m for installation - set monitor to initial state
1708     m->Recycle();
1709     m->set_header(mark);
1710     // If we leave _owner == DEFLATER_MARKER here, then the simple C2
1711     // ObjectMonitor enter optimization can no longer race with async
1712     // deflation and reuse.
1713     m->set_object(object);
1714     m->_Responsible  = NULL;
1715     m->_SpinDuration = ObjectMonitor::Knob_SpinLimit;       // consider: keep metastats by type/class
1716 
1717     omh_p->set_om_ptr(m);
1718     assert(m->is_new(), "freshly allocated monitor must be new");
1719     m->set_allocation_state(ObjectMonitor::Old);
1720 
1721     if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1722       m->set_header(markWord::zero());
1723       m->set_object(NULL);
1724       m->Recycle();
1725       omh_p->set_om_ptr(NULL);
1726       // om_release() will reset the allocation state
1727       om_release(self, m, true);
1728       m = NULL;
1729       continue;
1730       // interference - the markword changed - just retry.
1731       // The state-transitions are one-way, so there's no chance of
1732       // live-lock -- "Inflated" is an absorbing state.
1733     }
1734 
1735     // Hopefully the performance counters are allocated on distinct
1736     // cache lines to avoid false sharing on MP systems ...
1737     OM_PERFDATA_OP(Inflations, inc());
1738     if (log_is_enabled(Trace, monitorinflation)) {
1739       ResourceMark rm(self);
1740       lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1741                    INTPTR_FORMAT ", type='%s'", p2i(object),
1742                    object->mark().value(), object->klass()->external_name());
1743     }
1744     if (event.should_commit()) {
1745       post_monitor_inflate_event(&event, object, cause);
1746     }
1747     ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
1748     return;
1749   }
1750 }
1751 
1752 
1753 // We maintain a list of in-use monitors for each thread.
1754 //
1755 // For safepoint based deflation:
1756 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1757 // deflate_idle_monitors() scans only a global list of in-use monitors which
1758 // is populated only as a thread dies (see om_flush()).
1759 //
1760 // These operations are called at all safepoints, immediately after mutators
1761 // are stopped, but before any objects have moved. Collectively they traverse
1762 // the population of in-use monitors, deflating where possible. The scavenged
1763 // monitors are returned to the global monitor free list.
1764 //
1765 // Beware that we scavenge at *every* stop-the-world point. Having a large
1766 // number of monitors in-use could negatively impact performance. We also want
1767 // to minimize the total # of monitors in circulation, as they incur a small
1768 // footprint penalty.
1769 //
1770 // Perversely, the heap size -- and thus the STW safepoint rate --
1771 // typically drives the scavenge rate.  Large heaps can mean infrequent GC,
1772 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1773 // This is an unfortunate aspect of this design.
1774 //
1775 // For async deflation:
1776 // If a special deflation request is made, then the safepoint based
1777 // deflation mechanism is used. Otherwise, an async deflation request
1778 // is registered with the ServiceThread and it is notified.
1779 
1780 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* _counters) {
1781   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1782 
1783   // The per-thread in-use lists are handled in
1784   // ParallelSPCleanupThreadClosure::do_thread().
1785 
1786   if (!AsyncDeflateIdleMonitors || is_special_deflation_requested()) {
1787     // Use the older mechanism for the global in-use list or if a
1788     // special deflation has been requested before the safepoint.
1789     ObjectSynchronizer::deflate_idle_monitors(_counters);
1790     return;
1791   }
1792 
1793   log_debug(monitorinflation)("requesting async deflation of idle monitors.");
1794   // Request deflation of idle monitors by the ServiceThread:
1795   set_is_async_deflation_requested(true);
1796   MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
1797   ml.notify_all();
1798 }
1799 
1800 // Deflate a single monitor if not in-use
1801 // Return true if deflated, false if in-use
1802 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1803                                          ObjectMonitor** free_head_p,
1804                                          ObjectMonitor** free_tail_p) {
1805   bool deflated;
1806   // Normal case ... The monitor is associated with obj.
1807   const markWord mark = obj->mark();
1808   guarantee(mark == markWord::encode(mid), "should match: mark="
1809             INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, mark.value(),
1810             markWord::encode(mid).value());
1811   // Make sure that mark.monitor() and markWord::encode() agree:
1812   guarantee(mark.monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1813             ", mid=" INTPTR_FORMAT, p2i(mark.monitor()), p2i(mid));
1814   const markWord dmw = mid->header();
1815   guarantee(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1816 
1817   if (mid->is_busy() || mid->ref_count() != 0) {
1818     // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor*
1819     // is in use so no deflation.
1820     deflated = false;
1821   } else {
1822     // Deflate the monitor if it is no longer being used
1823     // It's idle - scavenge and return to the global free list
1824     // plain old deflation ...
1825     if (log_is_enabled(Trace, monitorinflation)) {
1826       ResourceMark rm;
1827       log_trace(monitorinflation)("deflate_monitor: "
1828                                   "object=" INTPTR_FORMAT ", mark="
1829                                   INTPTR_FORMAT ", type='%s'", p2i(obj),
1830                                   mark.value(), obj->klass()->external_name());
1831     }
1832 
1833     // Restore the header back to obj
1834     obj->release_set_mark(dmw);
1835     if (AsyncDeflateIdleMonitors) {
1836       // clear() expects the owner field to be NULL and we won't race
1837       // with the simple C2 ObjectMonitor enter optimization since
1838       // we're at a safepoint.
1839       mid->set_owner(NULL);
1840     }
1841     mid->clear();
1842 
1843     assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1844            p2i(mid->object()));
1845     assert(mid->is_free(), "invariant");
1846 
1847     // Move the deflated ObjectMonitor to the working free list
1848     // defined by free_head_p and free_tail_p.
1849     if (*free_head_p == NULL) *free_head_p = mid;
1850     if (*free_tail_p != NULL) {
1851       // We append to the list so the caller can use mid->_next_om
1852       // to fix the linkages in its context.
1853       ObjectMonitor* prevtail = *free_tail_p;
1854       // Should have been cleaned up by the caller:
1855       assert(prevtail->_next_om == NULL, "cleaned up deflated?");
1856       prevtail->_next_om = mid;
1857     }
1858     *free_tail_p = mid;
1859     // At this point, mid->_next_om still refers to its current
1860     // value and another ObjectMonitor's _next_om field still
1861     // refers to this ObjectMonitor. Those linkages have to be
1862     // cleaned up by the caller who has the complete context.
1863     deflated = true;
1864   }
1865   return deflated;
1866 }
1867 
1868 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
1869 // Returns true if it was deflated and false otherwise.
1870 //
1871 // The async deflation protocol sets owner to DEFLATER_MARKER and
1872 // makes ref_count negative as signals to contending threads that
1873 // an async deflation is in progress. There are a number of checks
1874 // as part of the protocol to make sure that the calling thread has
1875 // not lost the race to a contending thread or to a thread that just
1876 // wants to use the ObjectMonitor*.
1877 //
1878 // The ObjectMonitor has been successfully async deflated when:
1879 // (owner == DEFLATER_MARKER && ref_count < 0)
1880 // Contending threads or ObjectMonitor* using threads that see those
1881 // values know to retry their operation.
1882 //
1883 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
1884                                                   ObjectMonitor** free_head_p,
1885                                                   ObjectMonitor** free_tail_p) {
1886   assert(AsyncDeflateIdleMonitors, "sanity check");
1887   assert(Thread::current()->is_Java_thread(), "precondition");
1888   // A newly allocated ObjectMonitor should not be seen here so we
1889   // avoid an endless inflate/deflate cycle.
1890   assert(mid->is_old(), "must be old: allocation_state=%d",
1891          (int) mid->allocation_state());
1892 
1893   if (mid->is_busy() || mid->ref_count() != 0) {
1894     // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor*
1895     // is in use so no deflation.
1896     return false;
1897   }
1898 
1899   if (Atomic::replace_if_null(DEFLATER_MARKER, &(mid->_owner))) {
1900     // ObjectMonitor is not owned by another thread. Our setting
1901     // owner to DEFLATER_MARKER forces any contending thread through
1902     // the slow path. This is just the first part of the async
1903     // deflation dance.
1904 
1905     if (mid->_contentions != 0 || mid->_waiters != 0) {
1906       // Another thread has raced to enter the ObjectMonitor after
1907       // mid->is_busy() above or has already entered and waited on
1908       // it which makes it busy so no deflation. Restore owner to
1909       // NULL if it is still DEFLATER_MARKER.
1910       Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
1911       return false;
1912     }
1913 
1914     if (Atomic::cmpxchg(-max_jint, &mid->_ref_count, (jint)0) == 0) {
1915       // Make ref_count negative to force any contending threads or
1916       // ObjectMonitor* using threads to retry. This is the second
1917       // part of the async deflation dance.
1918 
1919       if (mid->owner_is_DEFLATER_MARKER()) {
1920         // If owner is still DEFLATER_MARKER, then we have successfully
1921         // signaled any contending threads to retry. If it is not, then we
1922         // have lost the race to an entering thread and the ObjectMonitor
1923         // is now busy. This is the third and final part of the async
1924         // deflation dance.
1925         // Note: This owner check solves the ABA problem with ref_count
1926         // where another thread acquired the ObjectMonitor, finished
1927         // using it and restored the ref_count to zero.
1928 
1929         // Sanity checks for the races:
1930         guarantee(mid->_contentions == 0, "must be 0: contentions=%d",
1931                   mid->_contentions);
1932         guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
1933         guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
1934                   INTPTR_FORMAT, p2i(mid->_cxq));
1935         guarantee(mid->_EntryList == NULL,
1936                   "must be no entering threads: EntryList=" INTPTR_FORMAT,
1937                   p2i(mid->_EntryList));
1938 
1939         const oop obj = (oop) mid->object();
1940         if (log_is_enabled(Trace, monitorinflation)) {
1941           ResourceMark rm;
1942           log_trace(monitorinflation)("deflate_monitor_using_JT: "
1943                                       "object=" INTPTR_FORMAT ", mark="
1944                                       INTPTR_FORMAT ", type='%s'",
1945                                       p2i(obj), obj->mark().value(),
1946                                       obj->klass()->external_name());
1947         }
1948 
1949         // Install the old mark word if nobody else has already done it.
1950         mid->install_displaced_markword_in_object(obj);
1951         mid->clear_using_JT();
1952 
1953         assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
1954                p2i(mid->object()));
1955         assert(mid->is_free(), "must be free: allocation_state=%d",
1956                (int) mid->allocation_state());
1957 
1958         // Move the deflated ObjectMonitor to the working free list
1959         // defined by free_head_p and free_tail_p.
1960         if (*free_head_p == NULL) {
1961           // First one on the list.
1962           *free_head_p = mid;
1963         }
1964         if (*free_tail_p != NULL) {
1965           // We append to the list so the caller can use mid->_next_om
1966           // to fix the linkages in its context.
1967           ObjectMonitor* prevtail = *free_tail_p;
1968           // Should have been cleaned up by the caller:
1969           assert(prevtail->_next_om == NULL, "must be NULL: _next_om="
1970                  INTPTR_FORMAT, p2i(prevtail->_next_om));
1971           prevtail->_next_om = mid;
1972         }
1973         *free_tail_p = mid;
1974 
1975         // At this point, mid->_next_om still refers to its current
1976         // value and another ObjectMonitor's _next_om field still
1977         // refers to this ObjectMonitor. Those linkages have to be
1978         // cleaned up by the caller who has the complete context.
1979 
1980         // We leave owner == DEFLATER_MARKER and ref_count < 0
1981         // to force any racing threads to retry.
1982         return true;  // Success, ObjectMonitor has been deflated.
1983       }
1984 
1985       // The owner was changed from DEFLATER_MARKER so we lost the
1986       // race since the ObjectMonitor is now busy.
1987 
1988       // Add back max_jint to restore the ref_count field to its
1989       // proper value (which may not be what we saw above):
1990       Atomic::add(max_jint, &mid->_ref_count);
1991 
1992       assert(mid->ref_count() >= 0, "must not be negative: ref_count=%d",
1993              mid->ref_count());
1994       return false;
1995     }
1996 
1997     // The ref_count was no longer 0 so we lost the race since the
1998     // ObjectMonitor is now busy or the ObjectMonitor* is now is use.
1999     // Restore owner to NULL if it is still DEFLATER_MARKER:
2000     Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
2001   }
2002 
2003   // The owner field is no longer NULL so we lost the race since the
2004   // ObjectMonitor is now busy.
2005   return false;
2006 }
2007 
2008 // Walk a given monitor list, and deflate idle monitors
2009 // The given list could be a per-thread list or a global list
2010 // Caller acquires gListLock as needed.
2011 //
2012 // In the case of parallel processing of thread local monitor lists,
2013 // work is done by Threads::parallel_threads_do() which ensures that
2014 // each Java thread is processed by exactly one worker thread, and
2015 // thus avoid conflicts that would arise when worker threads would
2016 // process the same monitor lists concurrently.
2017 //
2018 // See also ParallelSPCleanupTask and
2019 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
2020 // Threads::parallel_java_threads_do() in thread.cpp.
2021 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** list_p,
2022                                              ObjectMonitor** free_head_p,
2023                                              ObjectMonitor** free_tail_p) {
2024   ObjectMonitor* mid;
2025   ObjectMonitor* next;
2026   ObjectMonitor* cur_mid_in_use = NULL;
2027   int deflated_count = 0;
2028 
2029   for (mid = *list_p; mid != NULL;) {
2030     oop obj = (oop) mid->object();
2031     if (obj != NULL && deflate_monitor(mid, obj, free_head_p, free_tail_p)) {
2032       // Deflation succeeded and already updated free_head_p and
2033       // free_tail_p as needed. Finish the move to the local free list
2034       // by unlinking mid from the global or per-thread in-use list.
2035       if (mid == *list_p) {
2036         *list_p = mid->_next_om;
2037       } else if (cur_mid_in_use != NULL) {
2038         cur_mid_in_use->_next_om = mid->_next_om; // maintain the current thread in-use list
2039       }
2040       next = mid->_next_om;
2041       mid->_next_om = NULL;  // This mid is current tail in the free_head_p list
2042       mid = next;
2043       deflated_count++;
2044     } else {
2045       cur_mid_in_use = mid;
2046       mid = mid->_next_om;
2047     }
2048   }
2049   return deflated_count;
2050 }
2051 
2052 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
2053 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
2054 // list could be a per-thread in-use list or the global in-use list.
2055 // Caller acquires gListLock as appropriate. If a safepoint has started,
2056 // then we save state via saved_mid_in_use_p and return to the caller to
2057 // honor the safepoint.
2058 //
2059 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** list_p,
2060                                                       ObjectMonitor** free_head_p,
2061                                                       ObjectMonitor** free_tail_p,
2062                                                       ObjectMonitor** saved_mid_in_use_p) {
2063   assert(AsyncDeflateIdleMonitors, "sanity check");
2064   assert(Thread::current()->is_Java_thread(), "precondition");
2065 
2066   ObjectMonitor* mid;
2067   ObjectMonitor* next;
2068   ObjectMonitor* cur_mid_in_use = NULL;
2069   int deflated_count = 0;
2070 
2071   if (*saved_mid_in_use_p == NULL) {
2072     // No saved state so start at the beginning.
2073     mid = *list_p;
2074   } else {
2075     // We're restarting after a safepoint so restore the necessary state
2076     // before we resume.
2077     cur_mid_in_use = *saved_mid_in_use_p;
2078     mid = cur_mid_in_use->_next_om;
2079   }
2080   while (mid != NULL) {
2081     // Only try to deflate if there is an associated Java object and if
2082     // mid is old (is not newly allocated and is not newly freed).
2083     if (mid->object() != NULL && mid->is_old() &&
2084         deflate_monitor_using_JT(mid, free_head_p, free_tail_p)) {
2085       // Deflation succeeded so update the in-use list.
2086       if (mid == *list_p) {
2087         *list_p = mid->_next_om;
2088       } else if (cur_mid_in_use != NULL) {
2089         // Maintain the current in-use list.
2090         cur_mid_in_use->_next_om = mid->_next_om;
2091       }
2092       next = mid->_next_om;
2093       mid->_next_om = NULL;
2094       // At this point mid is disconnected from the in-use list
2095       // and is the current tail in the free_head_p list.
2096       mid = next;
2097       deflated_count++;
2098     } else {
2099       // mid is considered in-use if it does not have an associated
2100       // Java object or mid is not old or deflation did not succeed.
2101       // A mid->is_new() node can be seen here when it is freshly
2102       // returned by om_alloc() (and skips the deflation code path).
2103       // A mid->is_old() node can be seen here when deflation failed.
2104       // A mid->is_free() node can be seen here when a fresh node from
2105       // om_alloc() is released by om_release() due to losing the race
2106       // in inflate().
2107 
2108       cur_mid_in_use = mid;
2109       mid = mid->_next_om;
2110 
2111       if (SafepointSynchronize::is_synchronizing() &&
2112           cur_mid_in_use != *list_p && cur_mid_in_use->is_old()) {
2113         // If a safepoint has started and cur_mid_in_use is not the list
2114         // head and is old, then it is safe to use as saved state. Return
2115         // to the caller so gListLock can be dropped as appropriate
2116         // before blocking.
2117         *saved_mid_in_use_p = cur_mid_in_use;
2118         return deflated_count;
2119       }
2120     }
2121   }
2122   // We finished the list without a safepoint starting so there's
2123   // no need to save state.
2124   *saved_mid_in_use_p = NULL;
2125   return deflated_count;
2126 }
2127 
2128 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2129   counters->n_in_use = 0;              // currently associated with objects
2130   counters->n_in_circulation = 0;      // extant
2131   counters->n_scavenged = 0;           // reclaimed (global and per-thread)
2132   counters->per_thread_scavenged = 0;  // per-thread scavenge total
2133   counters->per_thread_times = 0.0;    // per-thread scavenge times
2134 }
2135 
2136 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2137   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2138 
2139   if (AsyncDeflateIdleMonitors) {
2140     // Nothing to do when global idle ObjectMonitors are deflated using
2141     // a JavaThread unless a special deflation has been requested.
2142     if (!is_special_deflation_requested()) {
2143       return;
2144     }
2145   }
2146 
2147   bool deflated = false;
2148 
2149   ObjectMonitor* free_head_p = NULL;  // Local SLL of scavenged monitors
2150   ObjectMonitor* free_tail_p = NULL;
2151   elapsedTimer timer;
2152 
2153   if (log_is_enabled(Info, monitorinflation)) {
2154     timer.start();
2155   }
2156 
2157   // Prevent om_flush from changing mids in Thread dtor's during deflation
2158   // And in case the vm thread is acquiring a lock during a safepoint
2159   // See e.g. 6320749
2160   Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
2161 
2162   // Note: the thread-local monitors lists get deflated in
2163   // a separate pass. See deflate_thread_local_monitors().
2164 
2165   // For moribund threads, scan g_om_in_use_list
2166   int deflated_count = 0;
2167   if (g_om_in_use_list) {
2168     counters->n_in_circulation += g_om_in_use_count;
2169     deflated_count = deflate_monitor_list((ObjectMonitor **)&g_om_in_use_list, &free_head_p, &free_tail_p);
2170     g_om_in_use_count -= deflated_count;
2171     counters->n_scavenged += deflated_count;
2172     counters->n_in_use += g_om_in_use_count;
2173   }
2174 
2175   if (free_head_p != NULL) {
2176     // Move the deflated ObjectMonitors back to the global free list.
2177     guarantee(free_tail_p != NULL && counters->n_scavenged > 0, "invariant");
2178     assert(free_tail_p->_next_om == NULL, "invariant");
2179     // constant-time list splice - prepend scavenged segment to g_free_list
2180     free_tail_p->_next_om = g_free_list;
2181     g_free_list = free_head_p;
2182   }
2183   Thread::muxRelease(&gListLock);
2184   timer.stop();
2185 
2186   LogStreamHandle(Debug, monitorinflation) lsh_debug;
2187   LogStreamHandle(Info, monitorinflation) lsh_info;
2188   LogStream* ls = NULL;
2189   if (log_is_enabled(Debug, monitorinflation)) {
2190     ls = &lsh_debug;
2191   } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2192     ls = &lsh_info;
2193   }
2194   if (ls != NULL) {
2195     ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2196   }
2197 }
2198 
2199 // Deflate global idle ObjectMonitors using a JavaThread.
2200 //
2201 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2202   assert(AsyncDeflateIdleMonitors, "sanity check");
2203   assert(Thread::current()->is_Java_thread(), "precondition");
2204   JavaThread* self = JavaThread::current();
2205 
2206   deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2207 }
2208 
2209 // Deflate per-thread idle ObjectMonitors using a JavaThread.
2210 //
2211 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT() {
2212   assert(AsyncDeflateIdleMonitors, "sanity check");
2213   assert(Thread::current()->is_Java_thread(), "precondition");
2214   JavaThread* self = JavaThread::current();
2215 
2216   self->om_request_deflation = false;
2217 
2218   deflate_common_idle_monitors_using_JT(false /* !is_global */, self);
2219 }
2220 
2221 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2222 //
2223 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread* self) {
2224   int deflated_count = 0;
2225   ObjectMonitor* free_head_p = NULL;  // Local SLL of scavenged ObjectMonitors
2226   ObjectMonitor* free_tail_p = NULL;
2227   ObjectMonitor* saved_mid_in_use_p = NULL;
2228   elapsedTimer timer;
2229 
2230   if (log_is_enabled(Info, monitorinflation)) {
2231     timer.start();
2232   }
2233 
2234   if (is_global) {
2235     Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(1)");
2236     OM_PERFDATA_OP(MonExtant, set_value(g_om_in_use_count));
2237   } else {
2238     OM_PERFDATA_OP(MonExtant, inc(self->om_in_use_count));
2239   }
2240 
2241   do {
2242     int local_deflated_count;
2243     if (is_global) {
2244       local_deflated_count = deflate_monitor_list_using_JT((ObjectMonitor **)&g_om_in_use_list, &free_head_p, &free_tail_p, &saved_mid_in_use_p);
2245       g_om_in_use_count -= local_deflated_count;
2246     } else {
2247       local_deflated_count = deflate_monitor_list_using_JT(self->om_in_use_list_addr(), &free_head_p, &free_tail_p, &saved_mid_in_use_p);
2248       self->om_in_use_count -= local_deflated_count;
2249     }
2250     deflated_count += local_deflated_count;
2251 
2252     if (free_head_p != NULL) {
2253       // Move the scavenged ObjectMonitors to the global free list.
2254       guarantee(free_tail_p != NULL && local_deflated_count > 0, "free_tail_p=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(free_tail_p), local_deflated_count);
2255       assert(free_tail_p->_next_om == NULL, "invariant");
2256 
2257       if (!is_global) {
2258         Thread::muxAcquire(&gListLock, "deflate_per_thread_idle_monitors_using_JT(2)");
2259       }
2260       // Constant-time list splice - prepend scavenged segment to g_free_list.
2261       free_tail_p->_next_om = g_free_list;
2262       g_free_list = free_head_p;
2263 
2264       g_om_free_count += local_deflated_count;
2265       OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2266       if (!is_global) {
2267         Thread::muxRelease(&gListLock);
2268       }
2269     }
2270 
2271     if (saved_mid_in_use_p != NULL) {
2272       // deflate_monitor_list_using_JT() detected a safepoint starting.
2273       if (is_global) {
2274         Thread::muxRelease(&gListLock);
2275       }
2276       timer.stop();
2277       {
2278         if (is_global) {
2279           log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2280         } else {
2281           log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(self));
2282         }
2283         assert(SafepointSynchronize::is_synchronizing(), "sanity check");
2284         ThreadBlockInVM blocker(self);
2285       }
2286       // Prepare for another loop after the safepoint.
2287       free_head_p = NULL;
2288       free_tail_p = NULL;
2289       if (log_is_enabled(Info, monitorinflation)) {
2290         timer.start();
2291       }
2292       if (is_global) {
2293         Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(3)");
2294       }
2295     }
2296   } while (saved_mid_in_use_p != NULL);
2297   if (is_global) {
2298     Thread::muxRelease(&gListLock);
2299   }
2300   timer.stop();
2301 
2302   LogStreamHandle(Debug, monitorinflation) lsh_debug;
2303   LogStreamHandle(Info, monitorinflation) lsh_info;
2304   LogStream* ls = NULL;
2305   if (log_is_enabled(Debug, monitorinflation)) {
2306     ls = &lsh_debug;
2307   } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2308     ls = &lsh_info;
2309   }
2310   if (ls != NULL) {
2311     if (is_global) {
2312       ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2313     } else {
2314       ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(self), timer.seconds(), deflated_count);
2315     }
2316   }
2317 }
2318 
2319 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2320   // Report the cumulative time for deflating each thread's idle
2321   // monitors. Note: if the work is split among more than one
2322   // worker thread, then the reported time will likely be more
2323   // than a beginning to end measurement of the phase.
2324   // Note: AsyncDeflateIdleMonitors only deflates per-thread idle
2325   // monitors at a safepoint when a special deflation has been requested.
2326   log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->per_thread_times, counters->per_thread_scavenged);
2327 
2328   bool needs_special_deflation = is_special_deflation_requested();
2329   if (!AsyncDeflateIdleMonitors || needs_special_deflation) {
2330     // AsyncDeflateIdleMonitors does not use these counters unless
2331     // there is a special deflation request.
2332 
2333     g_om_free_count += counters->n_scavenged;
2334 
2335     OM_PERFDATA_OP(Deflations, inc(counters->n_scavenged));
2336     OM_PERFDATA_OP(MonExtant, set_value(counters->n_in_circulation));
2337   }
2338 
2339   if (log_is_enabled(Debug, monitorinflation)) {
2340     // exit_globals()'s call to audit_and_print_stats() is done
2341     // at the Info level.
2342     ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2343   } else if (log_is_enabled(Info, monitorinflation)) {
2344     Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
2345     log_info(monitorinflation)("g_om_population=%d, g_om_in_use_count=%d, "
2346                                "g_om_free_count=%d", g_om_population,
2347                                g_om_in_use_count, g_om_free_count);
2348     Thread::muxRelease(&gListLock);
2349   }
2350 
2351   ForceMonitorScavenge = 0;    // Reset
2352   GVars.stw_random = os::random();
2353   GVars.stw_cycle++;
2354   if (needs_special_deflation) {
2355     set_is_special_deflation_requested(false);  // special deflation is done
2356   }
2357 }
2358 
2359 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2360   assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2361 
2362   if (AsyncDeflateIdleMonitors) {
2363     if (!is_special_deflation_requested()) {
2364       // Mark the JavaThread for idle monitor deflation if a special
2365       // deflation has NOT been requested.
2366       if (thread->om_in_use_count > 0) {
2367         // This JavaThread is using monitors so mark it.
2368         thread->om_request_deflation = true;
2369       }
2370       return;
2371     }
2372   }
2373 
2374   ObjectMonitor* free_head_p = NULL;  // Local SLL of scavenged monitors
2375   ObjectMonitor* free_tail_p = NULL;
2376   elapsedTimer timer;
2377 
2378   if (log_is_enabled(Info, safepoint, cleanup) ||
2379       log_is_enabled(Info, monitorinflation)) {
2380     timer.start();
2381   }
2382 
2383   int deflated_count = deflate_monitor_list(thread->om_in_use_list_addr(), &free_head_p, &free_tail_p);
2384 
2385   Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
2386 
2387   // Adjust counters
2388   counters->n_in_circulation += thread->om_in_use_count;
2389   thread->om_in_use_count -= deflated_count;
2390   counters->n_scavenged += deflated_count;
2391   counters->n_in_use += thread->om_in_use_count;
2392   counters->per_thread_scavenged += deflated_count;
2393 
2394   if (free_head_p != NULL) {
2395     // Move the deflated ObjectMonitors back to the global free list.
2396     guarantee(free_tail_p != NULL && deflated_count > 0, "invariant");
2397     assert(free_tail_p->_next_om == NULL, "invariant");
2398 
2399     // constant-time list splice - prepend scavenged segment to g_free_list
2400     free_tail_p->_next_om = g_free_list;
2401     g_free_list = free_head_p;
2402   }
2403 
2404   timer.stop();
2405   // Safepoint logging cares about cumulative per_thread_times and
2406   // we'll capture most of the cost, but not the muxRelease() which
2407   // should be cheap.
2408   counters->per_thread_times += timer.seconds();
2409 
2410   Thread::muxRelease(&gListLock);
2411 
2412   LogStreamHandle(Debug, monitorinflation) lsh_debug;
2413   LogStreamHandle(Info, monitorinflation) lsh_info;
2414   LogStream* ls = NULL;
2415   if (log_is_enabled(Debug, monitorinflation)) {
2416     ls = &lsh_debug;
2417   } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2418     ls = &lsh_info;
2419   }
2420   if (ls != NULL) {
2421     ls->print_cr("jt=" INTPTR_FORMAT ": deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(thread), timer.seconds(), deflated_count);
2422   }
2423 }
2424 
2425 // Monitor cleanup on JavaThread::exit
2426 
2427 // Iterate through monitor cache and attempt to release thread's monitors
2428 // Gives up on a particular monitor if an exception occurs, but continues
2429 // the overall iteration, swallowing the exception.
2430 class ReleaseJavaMonitorsClosure: public MonitorClosure {
2431  private:
2432   TRAPS;
2433 
2434  public:
2435   ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
2436   void do_monitor(ObjectMonitor* mid) {
2437     if (mid->owner() == THREAD) {
2438       (void)mid->complete_exit(CHECK);
2439     }
2440   }
2441 };
2442 
2443 // Release all inflated monitors owned by THREAD.  Lightweight monitors are
2444 // ignored.  This is meant to be called during JNI thread detach which assumes
2445 // all remaining monitors are heavyweight.  All exceptions are swallowed.
2446 // Scanning the extant monitor list can be time consuming.
2447 // A simple optimization is to add a per-thread flag that indicates a thread
2448 // called jni_monitorenter() during its lifetime.
2449 //
2450 // Instead of No_Savepoint_Verifier it might be cheaper to
2451 // use an idiom of the form:
2452 //   auto int tmp = SafepointSynchronize::_safepoint_counter ;
2453 //   <code that must not run at safepoint>
2454 //   guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
2455 // Since the tests are extremely cheap we could leave them enabled
2456 // for normal product builds.
2457 
2458 void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
2459   assert(THREAD == JavaThread::current(), "must be current Java thread");
2460   NoSafepointVerifier nsv;
2461   ReleaseJavaMonitorsClosure rjmc(THREAD);
2462   Thread::muxAcquire(&gListLock, "release_monitors_owned_by_thread");
2463   ObjectSynchronizer::monitors_iterate(&rjmc);
2464   Thread::muxRelease(&gListLock);
2465   THREAD->clear_pending_exception();
2466 }
2467 
2468 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
2469   switch (cause) {
2470     case inflate_cause_vm_internal:    return "VM Internal";
2471     case inflate_cause_monitor_enter:  return "Monitor Enter";
2472     case inflate_cause_wait:           return "Monitor Wait";
2473     case inflate_cause_notify:         return "Monitor Notify";
2474     case inflate_cause_hash_code:      return "Monitor Hash Code";
2475     case inflate_cause_jni_enter:      return "JNI Monitor Enter";
2476     case inflate_cause_jni_exit:       return "JNI Monitor Exit";
2477     default:
2478       ShouldNotReachHere();
2479   }
2480   return "Unknown";
2481 }
2482 
2483 //------------------------------------------------------------------------------
2484 // Debugging code
2485 
2486 u_char* ObjectSynchronizer::get_gvars_addr() {
2487   return (u_char*)&GVars;
2488 }
2489 
2490 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
2491   return (u_char*)&GVars.hc_sequence;
2492 }
2493 
2494 size_t ObjectSynchronizer::get_gvars_size() {
2495   return sizeof(SharedGlobals);
2496 }
2497 
2498 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
2499   return (u_char*)&GVars.stw_random;
2500 }
2501 
2502 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2503   assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2504 
2505   LogStreamHandle(Debug, monitorinflation) lsh_debug;
2506   LogStreamHandle(Info, monitorinflation) lsh_info;
2507   LogStreamHandle(Trace, monitorinflation) lsh_trace;
2508   LogStream* ls = NULL;
2509   if (log_is_enabled(Trace, monitorinflation)) {
2510     ls = &lsh_trace;
2511   } else if (log_is_enabled(Debug, monitorinflation)) {
2512     ls = &lsh_debug;
2513   } else if (log_is_enabled(Info, monitorinflation)) {
2514     ls = &lsh_info;
2515   }
2516   assert(ls != NULL, "sanity check");
2517 
2518   if (!on_exit) {
2519     // Not at VM exit so grab the global list lock.
2520     Thread::muxAcquire(&gListLock, "audit_and_print_stats");
2521   }
2522 
2523   // Log counts for the global and per-thread monitor lists:
2524   int chk_om_population = log_monitor_list_counts(ls);
2525   int error_cnt = 0;
2526 
2527   ls->print_cr("Checking global lists:");
2528 
2529   // Check g_om_population:
2530   if (g_om_population == chk_om_population) {
2531     ls->print_cr("g_om_population=%d equals chk_om_population=%d",
2532                  g_om_population, chk_om_population);
2533   } else {
2534     ls->print_cr("ERROR: g_om_population=%d is not equal to "
2535                  "chk_om_population=%d", g_om_population,
2536                  chk_om_population);
2537     error_cnt++;
2538   }
2539 
2540   // Check g_om_in_use_list and g_om_in_use_count:
2541   chk_global_in_use_list_and_count(ls, &error_cnt);
2542 
2543   // Check g_free_list and g_om_free_count:
2544   chk_global_free_list_and_count(ls, &error_cnt);
2545 
2546   if (!on_exit) {
2547     Thread::muxRelease(&gListLock);
2548   }
2549 
2550   ls->print_cr("Checking per-thread lists:");
2551 
2552   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2553     // Check om_in_use_list and om_in_use_count:
2554     chk_per_thread_in_use_list_and_count(jt, ls, &error_cnt);
2555 
2556     // Check om_free_list and om_free_count:
2557     chk_per_thread_free_list_and_count(jt, ls, &error_cnt);
2558   }
2559 
2560   if (error_cnt == 0) {
2561     ls->print_cr("No errors found in monitor list checks.");
2562   } else {
2563     log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2564   }
2565 
2566   if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2567       (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2568     // When exiting this log output is at the Info level. When called
2569     // at a safepoint, this log output is at the Trace level since
2570     // there can be a lot of it.
2571     log_in_use_monitor_details(ls, on_exit);
2572   }
2573 
2574   ls->flush();
2575 
2576   guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2577 }
2578 
2579 // Check a free monitor entry; log any errors.
2580 void ObjectSynchronizer::chk_free_entry(JavaThread* jt, ObjectMonitor* n,
2581                                         outputStream * out, int *error_cnt_p) {
2582   stringStream ss;
2583   if (n->is_busy()) {
2584     if (jt != NULL) {
2585       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2586                     ": free per-thread monitor must not be busy: %s", p2i(jt),
2587                     p2i(n), n->is_busy_to_string(&ss));
2588     } else {
2589       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2590                     "must not be busy: %s", p2i(n), n->is_busy_to_string(&ss));
2591     }
2592     *error_cnt_p = *error_cnt_p + 1;
2593   }
2594   if (n->header().value() != 0) {
2595     if (jt != NULL) {
2596       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2597                     ": free per-thread monitor must have NULL _header "
2598                     "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2599                     n->header().value());
2600       *error_cnt_p = *error_cnt_p + 1;
2601     } else if (!AsyncDeflateIdleMonitors) {
2602       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2603                     "must have NULL _header field: _header=" INTPTR_FORMAT,
2604                     p2i(n), n->header().value());
2605       *error_cnt_p = *error_cnt_p + 1;
2606     }
2607   }
2608   if (n->object() != NULL) {
2609     if (jt != NULL) {
2610       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2611                     ": free per-thread monitor must have NULL _object "
2612                     "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
2613                     p2i(n->object()));
2614     } else {
2615       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2616                     "must have NULL _object field: _object=" INTPTR_FORMAT,
2617                     p2i(n), p2i(n->object()));
2618     }
2619     *error_cnt_p = *error_cnt_p + 1;
2620   }
2621 }
2622 
2623 // Check the global free list and count; log the results of the checks.
2624 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
2625                                                         int *error_cnt_p) {
2626   int chk_om_free_count = 0;
2627   for (ObjectMonitor* n = g_free_list; n != NULL; n = n->_next_om) {
2628     chk_free_entry(NULL /* jt */, n, out, error_cnt_p);
2629     chk_om_free_count++;
2630   }
2631   if (g_om_free_count == chk_om_free_count) {
2632     out->print_cr("g_om_free_count=%d equals chk_om_free_count=%d",
2633                   g_om_free_count, chk_om_free_count);
2634   } else {
2635     out->print_cr("ERROR: g_om_free_count=%d is not equal to "
2636                   "chk_om_free_count=%d", g_om_free_count,
2637                   chk_om_free_count);
2638     *error_cnt_p = *error_cnt_p + 1;
2639   }
2640 }
2641 
2642 // Check the global in-use list and count; log the results of the checks.
2643 void ObjectSynchronizer::chk_global_in_use_list_and_count(outputStream * out,
2644                                                           int *error_cnt_p) {
2645   int chk_om_in_use_count = 0;
2646   for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
2647     chk_in_use_entry(NULL /* jt */, n, out, error_cnt_p);
2648     chk_om_in_use_count++;
2649   }
2650   if (g_om_in_use_count == chk_om_in_use_count) {
2651     out->print_cr("g_om_in_use_count=%d equals chk_om_in_use_count=%d", g_om_in_use_count,
2652                   chk_om_in_use_count);
2653   } else {
2654     out->print_cr("ERROR: g_om_in_use_count=%d is not equal to chk_om_in_use_count=%d",
2655                   g_om_in_use_count, chk_om_in_use_count);
2656     *error_cnt_p = *error_cnt_p + 1;
2657   }
2658 }
2659 
2660 // Check an in-use monitor entry; log any errors.
2661 void ObjectSynchronizer::chk_in_use_entry(JavaThread* jt, ObjectMonitor* n,
2662                                           outputStream * out, int *error_cnt_p) {
2663   if (n->header().value() == 0) {
2664     if (jt != NULL) {
2665       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2666                     ": in-use per-thread monitor must have non-NULL _header "
2667                     "field.", p2i(jt), p2i(n));
2668     } else {
2669       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2670                     "must have non-NULL _header field.", p2i(n));
2671     }
2672     *error_cnt_p = *error_cnt_p + 1;
2673   }
2674   if (n->object() == NULL) {
2675     if (jt != NULL) {
2676       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2677                     ": in-use per-thread monitor must have non-NULL _object "
2678                     "field.", p2i(jt), p2i(n));
2679     } else {
2680       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global monitor "
2681                     "must have non-NULL _object field.", p2i(n));
2682     }
2683     *error_cnt_p = *error_cnt_p + 1;
2684   }
2685   const oop obj = (oop)n->object();
2686   const markWord mark = obj->mark();
2687   if (!mark.has_monitor()) {
2688     if (jt != NULL) {
2689       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2690                     ": in-use per-thread monitor's object does not think "
2691                     "it has a monitor: obj=" INTPTR_FORMAT ", mark="
2692                     INTPTR_FORMAT,  p2i(jt), p2i(n), p2i(obj), mark.value());
2693     } else {
2694       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2695                     "monitor's object does not think it has a monitor: obj="
2696                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2697                     p2i(obj), mark.value());
2698     }
2699     *error_cnt_p = *error_cnt_p + 1;
2700   }
2701   ObjectMonitor* const obj_mon = mark.monitor();
2702   if (n != obj_mon) {
2703     if (jt != NULL) {
2704       out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2705                     ": in-use per-thread monitor's object does not refer "
2706                     "to the same monitor: obj=" INTPTR_FORMAT ", mark="
2707                     INTPTR_FORMAT ", obj_mon=" INTPTR_FORMAT, p2i(jt),
2708                     p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2709     } else {
2710       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use global "
2711                     "monitor's object does not refer to the same monitor: obj="
2712                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2713                     INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2714     }
2715     *error_cnt_p = *error_cnt_p + 1;
2716   }
2717 }
2718 
2719 // Check the thread's free list and count; log the results of the checks.
2720 void ObjectSynchronizer::chk_per_thread_free_list_and_count(JavaThread *jt,
2721                                                             outputStream * out,
2722                                                             int *error_cnt_p) {
2723   int chk_om_free_count = 0;
2724   for (ObjectMonitor* n = jt->om_free_list; n != NULL; n = n->_next_om) {
2725     chk_free_entry(jt, n, out, error_cnt_p);
2726     chk_om_free_count++;
2727   }
2728   if (jt->om_free_count == chk_om_free_count) {
2729     out->print_cr("jt=" INTPTR_FORMAT ": om_free_count=%d equals "
2730                   "chk_om_free_count=%d", p2i(jt), jt->om_free_count, chk_om_free_count);
2731   } else {
2732     out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_free_count=%d is not "
2733                   "equal to chk_om_free_count=%d", p2i(jt), jt->om_free_count,
2734                   chk_om_free_count);
2735     *error_cnt_p = *error_cnt_p + 1;
2736   }
2737 }
2738 
2739 // Check the thread's in-use list and count; log the results of the checks.
2740 void ObjectSynchronizer::chk_per_thread_in_use_list_and_count(JavaThread *jt,
2741                                                               outputStream * out,
2742                                                               int *error_cnt_p) {
2743   int chk_om_in_use_count = 0;
2744   for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
2745     chk_in_use_entry(jt, n, out, error_cnt_p);
2746     chk_om_in_use_count++;
2747   }
2748   if (jt->om_in_use_count == chk_om_in_use_count) {
2749     out->print_cr("jt=" INTPTR_FORMAT ": om_in_use_count=%d equals "
2750                   "chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
2751                   chk_om_in_use_count);
2752   } else {
2753     out->print_cr("ERROR: jt=" INTPTR_FORMAT ": om_in_use_count=%d is not "
2754                   "equal to chk_om_in_use_count=%d", p2i(jt), jt->om_in_use_count,
2755                   chk_om_in_use_count);
2756     *error_cnt_p = *error_cnt_p + 1;
2757   }
2758 }
2759 
2760 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2761 // flags indicate why the entry is in-use, 'object' and 'object type'
2762 // indicate the associated object and its type.
2763 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2764                                                     bool on_exit) {
2765   if (!on_exit) {
2766     // Not at VM exit so grab the global list lock.
2767     Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2768   }
2769 
2770   stringStream ss;
2771   if (g_om_in_use_count > 0) {
2772     out->print_cr("In-use global monitor info:");
2773     out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2774     out->print_cr("%18s  %s  %7s  %18s  %18s",
2775                   "monitor", "BHL", "ref_cnt", "object", "object type");
2776     out->print_cr("==================  ===  =======  ==================  ==================");
2777     for (ObjectMonitor* n = g_om_in_use_list; n != NULL; n = n->_next_om) {
2778       const oop obj = (oop) n->object();
2779       const markWord mark = n->header();
2780       ResourceMark rm;
2781       out->print(INTPTR_FORMAT "  %d%d%d  %7d  " INTPTR_FORMAT "  %s",
2782                  p2i(n), n->is_busy() != 0, mark.hash() != 0,
2783                  n->owner() != NULL, (int)n->ref_count(), p2i(obj),
2784                  obj->klass()->external_name());
2785       if (n->is_busy() != 0) {
2786         out->print(" (%s)", n->is_busy_to_string(&ss));
2787         ss.reset();
2788       }
2789       out->cr();
2790     }
2791   }
2792 
2793   if (!on_exit) {
2794     Thread::muxRelease(&gListLock);
2795   }
2796 
2797   out->print_cr("In-use per-thread monitor info:");
2798   out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2799   out->print_cr("%18s  %18s  %s  %7s  %18s  %18s",
2800                 "jt", "monitor", "BHL", "ref_cnt", "object", "object type");
2801   out->print_cr("==================  ==================  ===  =======  ==================  ==================");
2802   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2803     for (ObjectMonitor* n = jt->om_in_use_list; n != NULL; n = n->_next_om) {
2804       const oop obj = (oop) n->object();
2805       const markWord mark = n->header();
2806       ResourceMark rm;
2807       out->print(INTPTR_FORMAT "  " INTPTR_FORMAT "  %d%d%d  %7d  "
2808                  INTPTR_FORMAT "  %s", p2i(jt), p2i(n), n->is_busy() != 0,
2809                  mark.hash() != 0, n->owner() != NULL, (int)n->ref_count(),
2810                  p2i(obj), obj->klass()->external_name());
2811       if (n->is_busy() != 0) {
2812         out->print(" (%s)", n->is_busy_to_string(&ss));
2813         ss.reset();
2814       }
2815       out->cr();
2816     }
2817   }
2818 
2819   out->flush();
2820 }
2821 
2822 // Log counts for the global and per-thread monitor lists and return
2823 // the population count.
2824 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2825   int pop_count = 0;
2826   out->print_cr("%18s  %10s  %10s  %10s",
2827                 "Global Lists:", "InUse", "Free", "Total");
2828   out->print_cr("==================  ==========  ==========  ==========");
2829   out->print_cr("%18s  %10d  %10d  %10d", "",
2830                 g_om_in_use_count, g_om_free_count, g_om_population);
2831   pop_count += g_om_in_use_count + g_om_free_count;
2832 
2833   out->print_cr("%18s  %10s  %10s  %10s",
2834                 "Per-Thread Lists:", "InUse", "Free", "Provision");
2835   out->print_cr("==================  ==========  ==========  ==========");
2836 
2837   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2838     out->print_cr(INTPTR_FORMAT "  %10d  %10d  %10d", p2i(jt),
2839                   jt->om_in_use_count, jt->om_free_count, jt->om_free_provision);
2840     pop_count += jt->om_in_use_count + jt->om_free_count;
2841   }
2842   return pop_count;
2843 }
2844 
2845 #ifndef PRODUCT
2846 
2847 // Check if monitor belongs to the monitor cache
2848 // The list is grow-only so it's *relatively* safe to traverse
2849 // the list of extant blocks without taking a lock.
2850 
2851 int ObjectSynchronizer::verify_objmon_isinpool(ObjectMonitor *monitor) {
2852   PaddedObjectMonitor* block = OrderAccess::load_acquire(&g_block_list);
2853   while (block != NULL) {
2854     assert(block->object() == CHAINMARKER, "must be a block header");
2855     if (monitor > &block[0] && monitor < &block[_BLOCKSIZE]) {
2856       address mon = (address)monitor;
2857       address blk = (address)block;
2858       size_t diff = mon - blk;
2859       assert((diff % sizeof(PaddedObjectMonitor)) == 0, "must be aligned");
2860       return 1;
2861     }
2862     block = (PaddedObjectMonitor*)block->_next_om;
2863   }
2864   return 0;
2865 }
2866 
2867 #endif