1 /*
   2  * Copyright (c) 1998, 2022, 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 "gc/shared/oopStorage.hpp"
  28 #include "gc/shared/oopStorageSet.hpp"
  29 #include "jfr/jfrEvents.hpp"
  30 #include "jfr/support/jfrThreadId.hpp"
  31 #include "logging/log.hpp"
  32 #include "logging/logStream.hpp"
  33 #include "memory/allocation.inline.hpp"
  34 #include "memory/resourceArea.hpp"
  35 #include "oops/markWord.hpp"
  36 #include "oops/oop.inline.hpp"
  37 #include "oops/oopHandle.inline.hpp"
  38 #include "oops/weakHandle.inline.hpp"
  39 #include "prims/jvmtiDeferredUpdates.hpp"
  40 #include "prims/jvmtiExport.hpp"
  41 #include "runtime/atomic.hpp"
  42 #include "runtime/handles.inline.hpp"
  43 #include "runtime/interfaceSupport.inline.hpp"
  44 #include "runtime/javaThread.inline.hpp"
  45 #include "runtime/mutexLocker.hpp"
  46 #include "runtime/objectMonitor.hpp"
  47 #include "runtime/objectMonitor.inline.hpp"
  48 #include "runtime/orderAccess.hpp"
  49 #include "runtime/osThread.hpp"
  50 #include "runtime/perfData.hpp"
  51 #include "runtime/safefetch.hpp"
  52 #include "runtime/safepointMechanism.inline.hpp"
  53 #include "runtime/sharedRuntime.hpp"
  54 #include "services/threadService.hpp"
  55 #include "utilities/dtrace.hpp"
  56 #include "utilities/macros.hpp"
  57 #include "utilities/preserveException.hpp"
  58 #if INCLUDE_JFR
  59 #include "jfr/support/jfrFlush.hpp"
  60 #endif
  61 
  62 #ifdef DTRACE_ENABLED
  63 
  64 // Only bother with this argument setup if dtrace is available
  65 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
  66 
  67 
  68 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
  69   char* bytes = NULL;                                                      \
  70   int len = 0;                                                             \
  71   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
  72   Symbol* klassname = obj->klass()->name();                                \
  73   if (klassname != NULL) {                                                 \
  74     bytes = (char*)klassname->bytes();                                     \
  75     len = klassname->utf8_length();                                        \
  76   }
  77 
  78 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
  79   {                                                                        \
  80     if (DTraceMonitorProbes) {                                             \
  81       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
  82       HOTSPOT_MONITOR_WAIT(jtid,                                           \
  83                            (monitor), bytes, len, (millis));               \
  84     }                                                                      \
  85   }
  86 
  87 #define HOTSPOT_MONITOR_contended__enter HOTSPOT_MONITOR_CONTENDED_ENTER
  88 #define HOTSPOT_MONITOR_contended__entered HOTSPOT_MONITOR_CONTENDED_ENTERED
  89 #define HOTSPOT_MONITOR_contended__exit HOTSPOT_MONITOR_CONTENDED_EXIT
  90 #define HOTSPOT_MONITOR_notify HOTSPOT_MONITOR_NOTIFY
  91 #define HOTSPOT_MONITOR_notifyAll HOTSPOT_MONITOR_NOTIFYALL
  92 
  93 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
  94   {                                                                        \
  95     if (DTraceMonitorProbes) {                                             \
  96       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
  97       HOTSPOT_MONITOR_##probe(jtid,                                        \
  98                               (uintptr_t)(monitor), bytes, len);           \
  99     }                                                                      \
 100   }
 101 
 102 #else //  ndef DTRACE_ENABLED
 103 
 104 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 105 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 106 
 107 #endif // ndef DTRACE_ENABLED
 108 
 109 // Tunables ...
 110 // The knob* variables are effectively final.  Once set they should
 111 // never be modified hence.  Consider using __read_mostly with GCC.
 112 
 113 int ObjectMonitor::Knob_SpinLimit    = 5000;    // derived by an external tool -
 114 
 115 static int Knob_Bonus               = 100;     // spin success bonus
 116 static int Knob_BonusB              = 100;     // spin success bonus
 117 static int Knob_Penalty             = 200;     // spin failure penalty
 118 static int Knob_Poverty             = 1000;
 119 static int Knob_FixedSpin           = 0;
 120 static int Knob_PreSpin             = 10;      // 20-100 likely better
 121 
 122 DEBUG_ONLY(static volatile bool InitDone = false;)
 123 
 124 OopStorage* ObjectMonitor::_oop_storage = NULL;
 125 
 126 // -----------------------------------------------------------------------------
 127 // Theory of operations -- Monitors lists, thread residency, etc:
 128 //
 129 // * A thread acquires ownership of a monitor by successfully
 130 //   CAS()ing the _owner field from null to non-null.
 131 //
 132 // * Invariant: A thread appears on at most one monitor list --
 133 //   cxq, EntryList or WaitSet -- at any one time.
 134 //
 135 // * Contending threads "push" themselves onto the cxq with CAS
 136 //   and then spin/park.
 137 //
 138 // * After a contending thread eventually acquires the lock it must
 139 //   dequeue itself from either the EntryList or the cxq.
 140 //
 141 // * The exiting thread identifies and unparks an "heir presumptive"
 142 //   tentative successor thread on the EntryList.  Critically, the
 143 //   exiting thread doesn't unlink the successor thread from the EntryList.
 144 //   After having been unparked, the wakee will recontend for ownership of
 145 //   the monitor.   The successor (wakee) will either acquire the lock or
 146 //   re-park itself.
 147 //
 148 //   Succession is provided for by a policy of competitive handoff.
 149 //   The exiting thread does _not_ grant or pass ownership to the
 150 //   successor thread.  (This is also referred to as "handoff" succession").
 151 //   Instead the exiting thread releases ownership and possibly wakes
 152 //   a successor, so the successor can (re)compete for ownership of the lock.
 153 //   If the EntryList is empty but the cxq is populated the exiting
 154 //   thread will drain the cxq into the EntryList.  It does so by
 155 //   by detaching the cxq (installing null with CAS) and folding
 156 //   the threads from the cxq into the EntryList.  The EntryList is
 157 //   doubly linked, while the cxq is singly linked because of the
 158 //   CAS-based "push" used to enqueue recently arrived threads (RATs).
 159 //
 160 // * Concurrency invariants:
 161 //
 162 //   -- only the monitor owner may access or mutate the EntryList.
 163 //      The mutex property of the monitor itself protects the EntryList
 164 //      from concurrent interference.
 165 //   -- Only the monitor owner may detach the cxq.
 166 //
 167 // * The monitor entry list operations avoid locks, but strictly speaking
 168 //   they're not lock-free.  Enter is lock-free, exit is not.
 169 //   For a description of 'Methods and apparatus providing non-blocking access
 170 //   to a resource,' see U.S. Pat. No. 7844973.
 171 //
 172 // * The cxq can have multiple concurrent "pushers" but only one concurrent
 173 //   detaching thread.  This mechanism is immune from the ABA corruption.
 174 //   More precisely, the CAS-based "push" onto cxq is ABA-oblivious.
 175 //
 176 // * Taken together, the cxq and the EntryList constitute or form a
 177 //   single logical queue of threads stalled trying to acquire the lock.
 178 //   We use two distinct lists to improve the odds of a constant-time
 179 //   dequeue operation after acquisition (in the ::enter() epilogue) and
 180 //   to reduce heat on the list ends.  (c.f. Michael Scott's "2Q" algorithm).
 181 //   A key desideratum is to minimize queue & monitor metadata manipulation
 182 //   that occurs while holding the monitor lock -- that is, we want to
 183 //   minimize monitor lock holds times.  Note that even a small amount of
 184 //   fixed spinning will greatly reduce the # of enqueue-dequeue operations
 185 //   on EntryList|cxq.  That is, spinning relieves contention on the "inner"
 186 //   locks and monitor metadata.
 187 //
 188 //   Cxq points to the set of Recently Arrived Threads attempting entry.
 189 //   Because we push threads onto _cxq with CAS, the RATs must take the form of
 190 //   a singly-linked LIFO.  We drain _cxq into EntryList  at unlock-time when
 191 //   the unlocking thread notices that EntryList is null but _cxq is != null.
 192 //
 193 //   The EntryList is ordered by the prevailing queue discipline and
 194 //   can be organized in any convenient fashion, such as a doubly-linked list or
 195 //   a circular doubly-linked list.  Critically, we want insert and delete operations
 196 //   to operate in constant-time.  If we need a priority queue then something akin
 197 //   to Solaris' sleepq would work nicely.  Viz.,
 198 //   http://agg.eng/ws/on10_nightly/source/usr/src/uts/common/os/sleepq.c.
 199 //   Queue discipline is enforced at ::exit() time, when the unlocking thread
 200 //   drains the cxq into the EntryList, and orders or reorders the threads on the
 201 //   EntryList accordingly.
 202 //
 203 //   Barring "lock barging", this mechanism provides fair cyclic ordering,
 204 //   somewhat similar to an elevator-scan.
 205 //
 206 // * The monitor synchronization subsystem avoids the use of native
 207 //   synchronization primitives except for the narrow platform-specific
 208 //   park-unpark abstraction.  See the comments in os_solaris.cpp regarding
 209 //   the semantics of park-unpark.  Put another way, this monitor implementation
 210 //   depends only on atomic operations and park-unpark.  The monitor subsystem
 211 //   manages all RUNNING->BLOCKED and BLOCKED->READY transitions while the
 212 //   underlying OS manages the READY<->RUN transitions.
 213 //
 214 // * Waiting threads reside on the WaitSet list -- wait() puts
 215 //   the caller onto the WaitSet.
 216 //
 217 // * notify() or notifyAll() simply transfers threads from the WaitSet to
 218 //   either the EntryList or cxq.  Subsequent exit() operations will
 219 //   unpark the notifyee.  Unparking a notifee in notify() is inefficient -
 220 //   it's likely the notifyee would simply impale itself on the lock held
 221 //   by the notifier.
 222 //
 223 // * An interesting alternative is to encode cxq as (List,LockByte) where
 224 //   the LockByte is 0 iff the monitor is owned.  _owner is simply an auxiliary
 225 //   variable, like _recursions, in the scheme.  The threads or Events that form
 226 //   the list would have to be aligned in 256-byte addresses.  A thread would
 227 //   try to acquire the lock or enqueue itself with CAS, but exiting threads
 228 //   could use a 1-0 protocol and simply STB to set the LockByte to 0.
 229 //   Note that is is *not* word-tearing, but it does presume that full-word
 230 //   CAS operations are coherent with intermix with STB operations.  That's true
 231 //   on most common processors.
 232 //
 233 // * See also http://blogs.sun.com/dave
 234 
 235 
 236 // Check that object() and set_object() are called from the right context:
 237 static void check_object_context() {
 238 #ifdef ASSERT
 239   Thread* self = Thread::current();
 240   if (self->is_Java_thread()) {
 241     // Mostly called from JavaThreads so sanity check the thread state.
 242     JavaThread* jt = JavaThread::cast(self);
 243     switch (jt->thread_state()) {
 244     case _thread_in_vm:    // the usual case
 245     case _thread_in_Java:  // during deopt
 246       break;
 247     default:
 248       fatal("called from an unsafe thread state");
 249     }
 250     assert(jt->is_active_Java_thread(), "must be active JavaThread");
 251   } else {
 252     // However, ThreadService::get_current_contended_monitor()
 253     // can call here via the VMThread so sanity check it.
 254     assert(self->is_VM_thread(), "must be");
 255   }
 256 #endif // ASSERT
 257 }
 258 
 259 ObjectMonitor::ObjectMonitor(oop object) :
 260   _header(markWord::zero()),
 261   _object(_oop_storage, object),
 262   _owner(NULL),
 263   _previous_owner_tid(0),
 264   _next_om(NULL),
 265   _recursions(0),
 266   _EntryList(NULL),
 267   _cxq(NULL),
 268   _succ(NULL),
 269   _Responsible(NULL),
 270   _Spinner(0),
 271   _SpinDuration(ObjectMonitor::Knob_SpinLimit),
 272   _contentions(0),
 273   _WaitSet(NULL),
 274   _waiters(0),
 275   _WaitSetLock(0)
 276 { }
 277 
 278 ObjectMonitor::~ObjectMonitor() {
 279   _object.release(_oop_storage);
 280 }
 281 
 282 oop ObjectMonitor::object() const {
 283   check_object_context();
 284   if (_object.is_null()) {
 285     return NULL;
 286   }
 287   return _object.resolve();
 288 }
 289 
 290 oop ObjectMonitor::object_peek() const {
 291   if (_object.is_null()) {
 292     return NULL;
 293   }
 294   return _object.peek();
 295 }
 296 
 297 void ObjectMonitor::ExitOnSuspend::operator()(JavaThread* current) {
 298   if (current->is_suspended()) {
 299     _om->_recursions = 0;
 300     _om->_succ = NULL;
 301     // Don't need a full fence after clearing successor here because of the call to exit().
 302     _om->exit(current, false /* not_suspended */);
 303     _om_exited = true;
 304 
 305     current->set_current_pending_monitor(_om);
 306   }
 307 }
 308 
 309 void ObjectMonitor::ClearSuccOnSuspend::operator()(JavaThread* current) {
 310   if (current->is_suspended()) {
 311     if (_om->_succ == current) {
 312       _om->_succ = NULL;
 313       OrderAccess::fence(); // always do a full fence when successor is cleared
 314     }
 315   }
 316 }
 317 
 318 // -----------------------------------------------------------------------------
 319 // Enter support
 320 
 321 bool ObjectMonitor::enter(JavaThread* current) {
 322   // The following code is ordered to check the most common cases first
 323   // and to reduce RTS->RTO cache line upgrades on SPARC and IA32 processors.
 324 
 325   void* cur = try_set_owner_from(NULL, current);
 326   if (cur == NULL) {
 327     assert(_recursions == 0, "invariant");
 328     return true;
 329   }
 330 
 331   if (cur == current) {
 332     // TODO-FIXME: check for integer overflow!  BUGID 6557169.
 333     _recursions++;
 334     return true;
 335   }
 336 
 337   assert(cur == ANONYMOUS_OWNER || !current->is_lock_owned((address)cur), "precondition");
 338 
 339   // We've encountered genuine contention.
 340   assert(current->_Stalled == 0, "invariant");
 341   current->_Stalled = intptr_t(this);
 342 
 343   // Try one round of spinning *before* enqueueing current
 344   // and before going through the awkward and expensive state
 345   // transitions.  The following spin is strictly optional ...
 346   // Note that if we acquire the monitor from an initial spin
 347   // we forgo posting JVMTI events and firing DTRACE probes.
 348   if (TrySpin(current) > 0) {
 349     assert(owner_raw() == current, "must be current: owner=" INTPTR_FORMAT, p2i(owner_raw()));
 350     assert(_recursions == 0, "must be 0: recursions=" INTX_FORMAT, _recursions);
 351     assert(object()->mark() == markWord::encode(this),
 352            "object mark must match encoded this: mark=" INTPTR_FORMAT
 353            ", encoded this=" INTPTR_FORMAT, object()->mark().value(),
 354            markWord::encode(this).value());
 355     current->_Stalled = 0;
 356     return true;
 357   }
 358 
 359   assert(owner_raw() != current, "invariant");
 360   assert(_succ != current, "invariant");
 361   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 362   assert(current->thread_state() != _thread_blocked, "invariant");
 363 
 364   // Keep track of contention for JVM/TI and M&M queries.
 365   add_to_contentions(1);
 366   if (is_being_async_deflated()) {
 367     // Async deflation is in progress and our contentions increment
 368     // above lost the race to async deflation. Undo the work and
 369     // force the caller to retry.
 370     const oop l_object = object();
 371     if (l_object != NULL) {
 372       // Attempt to restore the header/dmw to the object's header so that
 373       // we only retry once if the deflater thread happens to be slow.
 374       install_displaced_markword_in_object(l_object);
 375     }
 376     current->_Stalled = 0;
 377     add_to_contentions(-1);
 378     return false;
 379   }
 380 
 381   JFR_ONLY(JfrConditionalFlushWithStacktrace<EventJavaMonitorEnter> flush(current);)
 382   EventJavaMonitorEnter event;
 383   if (event.is_started()) {
 384     event.set_monitorClass(object()->klass());
 385     // Set an address that is 'unique enough', such that events close in
 386     // time and with the same address are likely (but not guaranteed) to
 387     // belong to the same object.
 388     event.set_address((uintptr_t)this);
 389   }
 390 
 391   { // Change java thread status to indicate blocked on monitor enter.
 392     JavaThreadBlockedOnMonitorEnterState jtbmes(current, this);
 393 
 394     assert(current->current_pending_monitor() == NULL, "invariant");
 395     current->set_current_pending_monitor(this);
 396 
 397     DTRACE_MONITOR_PROBE(contended__enter, this, object(), current);
 398     if (JvmtiExport::should_post_monitor_contended_enter()) {
 399       JvmtiExport::post_monitor_contended_enter(current, this);
 400 
 401       // The current thread does not yet own the monitor and does not
 402       // yet appear on any queues that would get it made the successor.
 403       // This means that the JVMTI_EVENT_MONITOR_CONTENDED_ENTER event
 404       // handler cannot accidentally consume an unpark() meant for the
 405       // ParkEvent associated with this ObjectMonitor.
 406     }
 407 
 408     OSThreadContendState osts(current->osthread());
 409 
 410     assert(current->thread_state() == _thread_in_vm, "invariant");
 411 
 412     for (;;) {
 413       ExitOnSuspend eos(this);
 414       {
 415         ThreadBlockInVMPreprocess<ExitOnSuspend> tbivs(current, eos, true /* allow_suspend */);
 416         EnterI(current);
 417         current->set_current_pending_monitor(NULL);
 418         // We can go to a safepoint at the end of this block. If we
 419         // do a thread dump during that safepoint, then this thread will show
 420         // as having "-locked" the monitor, but the OS and java.lang.Thread
 421         // states will still report that the thread is blocked trying to
 422         // acquire it.
 423         // If there is a suspend request, ExitOnSuspend will exit the OM
 424         // and set the OM as pending.
 425       }
 426       if (!eos.exited()) {
 427         // ExitOnSuspend did not exit the OM
 428         assert(owner_raw() == current, "invariant");
 429         break;
 430       }
 431     }
 432 
 433     // We've just gotten past the enter-check-for-suspend dance and we now own
 434     // the monitor free and clear.
 435   }
 436 
 437   add_to_contentions(-1);
 438   assert(contentions() >= 0, "must not be negative: contentions=%d", contentions());
 439   current->_Stalled = 0;
 440 
 441   // Must either set _recursions = 0 or ASSERT _recursions == 0.
 442   assert(_recursions == 0, "invariant");
 443   assert(owner_raw() == current, "invariant");
 444   assert(_succ != current, "invariant");
 445   assert(object()->mark() == markWord::encode(this), "invariant");
 446 
 447   // The thread -- now the owner -- is back in vm mode.
 448   // Report the glorious news via TI,DTrace and jvmstat.
 449   // The probe effect is non-trivial.  All the reportage occurs
 450   // while we hold the monitor, increasing the length of the critical
 451   // section.  Amdahl's parallel speedup law comes vividly into play.
 452   //
 453   // Another option might be to aggregate the events (thread local or
 454   // per-monitor aggregation) and defer reporting until a more opportune
 455   // time -- such as next time some thread encounters contention but has
 456   // yet to acquire the lock.  While spinning that thread could
 457   // spinning we could increment JVMStat counters, etc.
 458 
 459   DTRACE_MONITOR_PROBE(contended__entered, this, object(), current);
 460   if (JvmtiExport::should_post_monitor_contended_entered()) {
 461     JvmtiExport::post_monitor_contended_entered(current, this);
 462 
 463     // The current thread already owns the monitor and is not going to
 464     // call park() for the remainder of the monitor enter protocol. So
 465     // it doesn't matter if the JVMTI_EVENT_MONITOR_CONTENDED_ENTERED
 466     // event handler consumed an unpark() issued by the thread that
 467     // just exited the monitor.
 468   }
 469   if (event.should_commit()) {
 470     event.set_previousOwner(_previous_owner_tid);
 471     event.commit();
 472   }
 473   OM_PERFDATA_OP(ContendedLockAttempts, inc());
 474   return true;
 475 }
 476 
 477 // Caveat: TryLock() is not necessarily serializing if it returns failure.
 478 // Callers must compensate as needed.
 479 
 480 int ObjectMonitor::TryLock(JavaThread* current) {
 481   void* own = owner_raw();
 482   if (own != NULL) return 0;
 483   if (try_set_owner_from(NULL, current) == NULL) {
 484     assert(_recursions == 0, "invariant");
 485     return 1;
 486   }
 487   // The lock had been free momentarily, but we lost the race to the lock.
 488   // Interference -- the CAS failed.
 489   // We can either return -1 or retry.
 490   // Retry doesn't make as much sense because the lock was just acquired.
 491   return -1;
 492 }
 493 
 494 // Deflate the specified ObjectMonitor if not in-use. Returns true if it
 495 // was deflated and false otherwise.
 496 //
 497 // The async deflation protocol sets owner to DEFLATER_MARKER and
 498 // makes contentions negative as signals to contending threads that
 499 // an async deflation is in progress. There are a number of checks
 500 // as part of the protocol to make sure that the calling thread has
 501 // not lost the race to a contending thread.
 502 //
 503 // The ObjectMonitor has been successfully async deflated when:
 504 //   (contentions < 0)
 505 // Contending threads that see that condition know to retry their operation.
 506 //
 507 bool ObjectMonitor::deflate_monitor() {
 508   if (is_busy()) {
 509     // Easy checks are first - the ObjectMonitor is busy so no deflation.
 510     return false;
 511   }
 512 
 513   if (ObjectSynchronizer::is_final_audit() && owner_is_DEFLATER_MARKER()) {
 514     // The final audit can see an already deflated ObjectMonitor on the
 515     // in-use list because MonitorList::unlink_deflated() might have
 516     // blocked for the final safepoint before unlinking all the deflated
 517     // monitors.
 518     assert(contentions() < 0, "must be negative: contentions=%d", contentions());
 519     // Already returned 'true' when it was originally deflated.
 520     return false;
 521   }
 522 
 523   const oop obj = object_peek();
 524 
 525   if (obj == NULL) {
 526     // If the object died, we can recycle the monitor without racing with
 527     // Java threads. The GC already broke the association with the object.
 528     set_owner_from(NULL, DEFLATER_MARKER);
 529     assert(contentions() >= 0, "must be non-negative: contentions=%d", contentions());
 530     _contentions = INT_MIN; // minimum negative int
 531   } else {
 532     // Attempt async deflation protocol.
 533 
 534     // Set a NULL owner to DEFLATER_MARKER to force any contending thread
 535     // through the slow path. This is just the first part of the async
 536     // deflation dance.
 537     if (try_set_owner_from(NULL, DEFLATER_MARKER) != NULL) {
 538       // The owner field is no longer NULL so we lost the race since the
 539       // ObjectMonitor is now busy.
 540       return false;
 541     }
 542 
 543     if (contentions() > 0 || _waiters != 0) {
 544       // Another thread has raced to enter the ObjectMonitor after
 545       // is_busy() above or has already entered and waited on
 546       // it which makes it busy so no deflation. Restore owner to
 547       // NULL if it is still DEFLATER_MARKER.
 548       if (try_set_owner_from(DEFLATER_MARKER, NULL) != DEFLATER_MARKER) {
 549         // Deferred decrement for the JT EnterI() that cancelled the async deflation.
 550         add_to_contentions(-1);
 551       }
 552       return false;
 553     }
 554 
 555     // Make a zero contentions field negative to force any contending threads
 556     // to retry. This is the second part of the async deflation dance.
 557     if (Atomic::cmpxchg(&_contentions, 0, INT_MIN) != 0) {
 558       // Contentions was no longer 0 so we lost the race since the
 559       // ObjectMonitor is now busy. Restore owner to NULL if it is
 560       // still DEFLATER_MARKER:
 561       if (try_set_owner_from(DEFLATER_MARKER, NULL) != DEFLATER_MARKER) {
 562         // Deferred decrement for the JT EnterI() that cancelled the async deflation.
 563         add_to_contentions(-1);
 564       }
 565       return false;
 566     }
 567   }
 568 
 569   // Sanity checks for the races:
 570   guarantee(owner_is_DEFLATER_MARKER(), "must be deflater marker");
 571   guarantee(contentions() < 0, "must be negative: contentions=%d",
 572             contentions());
 573   guarantee(_waiters == 0, "must be 0: waiters=%d", _waiters);
 574   guarantee(_cxq == NULL, "must be no contending threads: cxq="
 575             INTPTR_FORMAT, p2i(_cxq));
 576   guarantee(_EntryList == NULL,
 577             "must be no entering threads: EntryList=" INTPTR_FORMAT,
 578             p2i(_EntryList));
 579 
 580   if (obj != NULL) {
 581     if (log_is_enabled(Trace, monitorinflation)) {
 582       ResourceMark rm;
 583       log_trace(monitorinflation)("deflate_monitor: object=" INTPTR_FORMAT
 584                                   ", mark=" INTPTR_FORMAT ", type='%s'",
 585                                   p2i(obj), obj->mark().value(),
 586                                   obj->klass()->external_name());
 587     }
 588 
 589     // Install the old mark word if nobody else has already done it.
 590     install_displaced_markword_in_object(obj);
 591   }
 592 
 593   // We leave owner == DEFLATER_MARKER and contentions < 0
 594   // to force any racing threads to retry.
 595   return true;  // Success, ObjectMonitor has been deflated.
 596 }
 597 
 598 // We might access the dead object headers for parsable heap walk, make sure
 599 // headers are in correct shape, e.g. monitors deflated.
 600 void ObjectMonitor::maybe_deflate_dead(oop* p) {
 601   oop obj = *p;
 602   assert(obj != NULL, "must not yet been cleared");
 603   markWord mark = obj->mark();
 604   if (mark.has_monitor()) {
 605     ObjectMonitor* monitor = mark.monitor();
 606     if (p == monitor->_object.ptr_raw()) {
 607       assert(monitor->object_peek() == obj, "lock object must match");
 608       markWord dmw = monitor->header();
 609       obj->set_mark(dmw);
 610     }
 611   }
 612 }
 613 
 614 // Install the displaced mark word (dmw) of a deflating ObjectMonitor
 615 // into the header of the object associated with the monitor. This
 616 // idempotent method is called by a thread that is deflating a
 617 // monitor and by other threads that have detected a race with the
 618 // deflation process.
 619 void ObjectMonitor::install_displaced_markword_in_object(const oop obj) {
 620   // This function must only be called when (owner == DEFLATER_MARKER
 621   // && contentions <= 0), but we can't guarantee that here because
 622   // those values could change when the ObjectMonitor gets moved from
 623   // the global free list to a per-thread free list.
 624 
 625   guarantee(obj != NULL, "must be non-NULL");
 626 
 627   // Separate loads in is_being_async_deflated(), which is almost always
 628   // called before this function, from the load of dmw/header below.
 629 
 630   // _contentions and dmw/header may get written by different threads.
 631   // Make sure to observe them in the same order when having several observers.
 632   OrderAccess::loadload_for_IRIW();
 633 
 634   const oop l_object = object_peek();
 635   if (l_object == NULL) {
 636     // ObjectMonitor's object ref has already been cleared by async
 637     // deflation or GC so we're done here.
 638     return;
 639   }
 640   assert(l_object == obj, "object=" INTPTR_FORMAT " must equal obj="
 641          INTPTR_FORMAT, p2i(l_object), p2i(obj));
 642 
 643   markWord dmw = header();
 644   // The dmw has to be neutral (not NULL, not locked and not marked).
 645   assert(dmw.is_neutral(), "must be neutral: dmw=" INTPTR_FORMAT, dmw.value());
 646 
 647   // Install displaced mark word if the object's header still points
 648   // to this ObjectMonitor. More than one racing caller to this function
 649   // can rarely reach this point, but only one can win.
 650   markWord res = obj->cas_set_mark(dmw, markWord::encode(this));
 651   if (res != markWord::encode(this)) {
 652     // This should be rare so log at the Info level when it happens.
 653     log_info(monitorinflation)("install_displaced_markword_in_object: "
 654                                "failed cas_set_mark: new_mark=" INTPTR_FORMAT
 655                                ", old_mark=" INTPTR_FORMAT ", res=" INTPTR_FORMAT,
 656                                dmw.value(), markWord::encode(this).value(),
 657                                res.value());
 658   }
 659 
 660   // Note: It does not matter which thread restored the header/dmw
 661   // into the object's header. The thread deflating the monitor just
 662   // wanted the object's header restored and it is. The threads that
 663   // detected a race with the deflation process also wanted the
 664   // object's header restored before they retry their operation and
 665   // because it is restored they will only retry once.
 666 }
 667 
 668 // Convert the fields used by is_busy() to a string that can be
 669 // used for diagnostic output.
 670 const char* ObjectMonitor::is_busy_to_string(stringStream* ss) {
 671   ss->print("is_busy: waiters=%d, ", _waiters);
 672   if (contentions() > 0) {
 673     ss->print("contentions=%d, ", contentions());
 674   } else {
 675     ss->print("contentions=0");
 676   }
 677   if (!owner_is_DEFLATER_MARKER()) {
 678     ss->print("owner=" INTPTR_FORMAT, p2i(owner_raw()));
 679   } else {
 680     // We report NULL instead of DEFLATER_MARKER here because is_busy()
 681     // ignores DEFLATER_MARKER values.
 682     ss->print("owner=" INTPTR_FORMAT, NULL_WORD);
 683   }
 684   ss->print(", cxq=" INTPTR_FORMAT ", EntryList=" INTPTR_FORMAT, p2i(_cxq),
 685             p2i(_EntryList));
 686   return ss->base();
 687 }
 688 
 689 #define MAX_RECHECK_INTERVAL 1000
 690 
 691 void ObjectMonitor::EnterI(JavaThread* current) {
 692   assert(current->thread_state() == _thread_blocked, "invariant");
 693 
 694   // Try the lock - TATAS
 695   if (TryLock (current) > 0) {
 696     assert(_succ != current, "invariant");
 697     assert(owner_raw() == current, "invariant");
 698     assert(_Responsible != current, "invariant");
 699     return;
 700   }
 701 
 702   if (try_set_owner_from(DEFLATER_MARKER, current) == DEFLATER_MARKER) {
 703     // Cancelled the in-progress async deflation by changing owner from
 704     // DEFLATER_MARKER to current. As part of the contended enter protocol,
 705     // contentions was incremented to a positive value before EnterI()
 706     // was called and that prevents the deflater thread from winning the
 707     // last part of the 2-part async deflation protocol. After EnterI()
 708     // returns to enter(), contentions is decremented because the caller
 709     // now owns the monitor. We bump contentions an extra time here to
 710     // prevent the deflater thread from winning the last part of the
 711     // 2-part async deflation protocol after the regular decrement
 712     // occurs in enter(). The deflater thread will decrement contentions
 713     // after it recognizes that the async deflation was cancelled.
 714     add_to_contentions(1);
 715     assert(_succ != current, "invariant");
 716     assert(_Responsible != current, "invariant");
 717     return;
 718   }
 719 
 720   assert(InitDone, "Unexpectedly not initialized");
 721 
 722   // We try one round of spinning *before* enqueueing current.
 723   //
 724   // If the _owner is ready but OFFPROC we could use a YieldTo()
 725   // operation to donate the remainder of this thread's quantum
 726   // to the owner.  This has subtle but beneficial affinity
 727   // effects.
 728 
 729   if (TrySpin(current) > 0) {
 730     assert(owner_raw() == current, "invariant");
 731     assert(_succ != current, "invariant");
 732     assert(_Responsible != current, "invariant");
 733     return;
 734   }
 735 
 736   // The Spin failed -- Enqueue and park the thread ...
 737   assert(_succ != current, "invariant");
 738   assert(owner_raw() != current, "invariant");
 739   assert(_Responsible != current, "invariant");
 740 
 741   // Enqueue "current" on ObjectMonitor's _cxq.
 742   //
 743   // Node acts as a proxy for current.
 744   // As an aside, if were to ever rewrite the synchronization code mostly
 745   // in Java, WaitNodes, ObjectMonitors, and Events would become 1st-class
 746   // Java objects.  This would avoid awkward lifecycle and liveness issues,
 747   // as well as eliminate a subset of ABA issues.
 748   // TODO: eliminate ObjectWaiter and enqueue either Threads or Events.
 749 
 750   ObjectWaiter node(current);
 751   current->_ParkEvent->reset();
 752   node._prev   = (ObjectWaiter*) 0xBAD;
 753   node.TState  = ObjectWaiter::TS_CXQ;
 754 
 755   // Push "current" onto the front of the _cxq.
 756   // Once on cxq/EntryList, current stays on-queue until it acquires the lock.
 757   // Note that spinning tends to reduce the rate at which threads
 758   // enqueue and dequeue on EntryList|cxq.
 759   ObjectWaiter* nxt;
 760   for (;;) {
 761     node._next = nxt = _cxq;
 762     if (Atomic::cmpxchg(&_cxq, nxt, &node) == nxt) break;
 763 
 764     // Interference - the CAS failed because _cxq changed.  Just retry.
 765     // As an optional optimization we retry the lock.
 766     if (TryLock (current) > 0) {
 767       assert(_succ != current, "invariant");
 768       assert(owner_raw() == current, "invariant");
 769       assert(_Responsible != current, "invariant");
 770       return;
 771     }
 772   }
 773 
 774   // Check for cxq|EntryList edge transition to non-null.  This indicates
 775   // the onset of contention.  While contention persists exiting threads
 776   // will use a ST:MEMBAR:LD 1-1 exit protocol.  When contention abates exit
 777   // operations revert to the faster 1-0 mode.  This enter operation may interleave
 778   // (race) a concurrent 1-0 exit operation, resulting in stranding, so we
 779   // arrange for one of the contending thread to use a timed park() operations
 780   // to detect and recover from the race.  (Stranding is form of progress failure
 781   // where the monitor is unlocked but all the contending threads remain parked).
 782   // That is, at least one of the contended threads will periodically poll _owner.
 783   // One of the contending threads will become the designated "Responsible" thread.
 784   // The Responsible thread uses a timed park instead of a normal indefinite park
 785   // operation -- it periodically wakes and checks for and recovers from potential
 786   // strandings admitted by 1-0 exit operations.   We need at most one Responsible
 787   // thread per-monitor at any given moment.  Only threads on cxq|EntryList may
 788   // be responsible for a monitor.
 789   //
 790   // Currently, one of the contended threads takes on the added role of "Responsible".
 791   // A viable alternative would be to use a dedicated "stranding checker" thread
 792   // that periodically iterated over all the threads (or active monitors) and unparked
 793   // successors where there was risk of stranding.  This would help eliminate the
 794   // timer scalability issues we see on some platforms as we'd only have one thread
 795   // -- the checker -- parked on a timer.
 796 
 797   if (nxt == NULL && _EntryList == NULL) {
 798     // Try to assume the role of responsible thread for the monitor.
 799     // CONSIDER:  ST vs CAS vs { if (Responsible==null) Responsible=current }
 800     Atomic::replace_if_null(&_Responsible, current);
 801   }
 802 
 803   // The lock might have been released while this thread was occupied queueing
 804   // itself onto _cxq.  To close the race and avoid "stranding" and
 805   // progress-liveness failure we must resample-retry _owner before parking.
 806   // Note the Dekker/Lamport duality: ST cxq; MEMBAR; LD Owner.
 807   // In this case the ST-MEMBAR is accomplished with CAS().
 808   //
 809   // TODO: Defer all thread state transitions until park-time.
 810   // Since state transitions are heavy and inefficient we'd like
 811   // to defer the state transitions until absolutely necessary,
 812   // and in doing so avoid some transitions ...
 813 
 814   int nWakeups = 0;
 815   int recheckInterval = 1;
 816 
 817   for (;;) {
 818 
 819     if (TryLock(current) > 0) break;
 820     assert(owner_raw() != current, "invariant");
 821 
 822     // park self
 823     if (_Responsible == current) {
 824       current->_ParkEvent->park((jlong) recheckInterval);
 825       // Increase the recheckInterval, but clamp the value.
 826       recheckInterval *= 8;
 827       if (recheckInterval > MAX_RECHECK_INTERVAL) {
 828         recheckInterval = MAX_RECHECK_INTERVAL;
 829       }
 830     } else {
 831       current->_ParkEvent->park();
 832     }
 833 
 834     if (TryLock(current) > 0) break;
 835 
 836     if (try_set_owner_from(DEFLATER_MARKER, current) == DEFLATER_MARKER) {
 837       // Cancelled the in-progress async deflation by changing owner from
 838       // DEFLATER_MARKER to current. As part of the contended enter protocol,
 839       // contentions was incremented to a positive value before EnterI()
 840       // was called and that prevents the deflater thread from winning the
 841       // last part of the 2-part async deflation protocol. After EnterI()
 842       // returns to enter(), contentions is decremented because the caller
 843       // now owns the monitor. We bump contentions an extra time here to
 844       // prevent the deflater thread from winning the last part of the
 845       // 2-part async deflation protocol after the regular decrement
 846       // occurs in enter(). The deflater thread will decrement contentions
 847       // after it recognizes that the async deflation was cancelled.
 848       add_to_contentions(1);
 849       break;
 850     }
 851 
 852     // The lock is still contested.
 853     // Keep a tally of the # of futile wakeups.
 854     // Note that the counter is not protected by a lock or updated by atomics.
 855     // That is by design - we trade "lossy" counters which are exposed to
 856     // races during updates for a lower probe effect.
 857 
 858     // This PerfData object can be used in parallel with a safepoint.
 859     // See the work around in PerfDataManager::destroy().
 860     OM_PERFDATA_OP(FutileWakeups, inc());
 861     ++nWakeups;
 862 
 863     // Assuming this is not a spurious wakeup we'll normally find _succ == current.
 864     // We can defer clearing _succ until after the spin completes
 865     // TrySpin() must tolerate being called with _succ == current.
 866     // Try yet another round of adaptive spinning.
 867     if (TrySpin(current) > 0) break;
 868 
 869     // We can find that we were unpark()ed and redesignated _succ while
 870     // we were spinning.  That's harmless.  If we iterate and call park(),
 871     // park() will consume the event and return immediately and we'll
 872     // just spin again.  This pattern can repeat, leaving _succ to simply
 873     // spin on a CPU.
 874 
 875     if (_succ == current) _succ = NULL;
 876 
 877     // Invariant: after clearing _succ a thread *must* retry _owner before parking.
 878     OrderAccess::fence();
 879   }
 880 
 881   // Egress :
 882   // current has acquired the lock -- Unlink current from the cxq or EntryList.
 883   // Normally we'll find current on the EntryList .
 884   // From the perspective of the lock owner (this thread), the
 885   // EntryList is stable and cxq is prepend-only.
 886   // The head of cxq is volatile but the interior is stable.
 887   // In addition, current.TState is stable.
 888 
 889   assert(owner_raw() == current, "invariant");
 890 
 891   UnlinkAfterAcquire(current, &node);
 892   if (_succ == current) _succ = NULL;
 893 
 894   assert(_succ != current, "invariant");
 895   if (_Responsible == current) {
 896     _Responsible = NULL;
 897     OrderAccess::fence(); // Dekker pivot-point
 898 
 899     // We may leave threads on cxq|EntryList without a designated
 900     // "Responsible" thread.  This is benign.  When this thread subsequently
 901     // exits the monitor it can "see" such preexisting "old" threads --
 902     // threads that arrived on the cxq|EntryList before the fence, above --
 903     // by LDing cxq|EntryList.  Newly arrived threads -- that is, threads
 904     // that arrive on cxq after the ST:MEMBAR, above -- will set Responsible
 905     // non-null and elect a new "Responsible" timer thread.
 906     //
 907     // This thread executes:
 908     //    ST Responsible=null; MEMBAR    (in enter epilogue - here)
 909     //    LD cxq|EntryList               (in subsequent exit)
 910     //
 911     // Entering threads in the slow/contended path execute:
 912     //    ST cxq=nonnull; MEMBAR; LD Responsible (in enter prolog)
 913     //    The (ST cxq; MEMBAR) is accomplished with CAS().
 914     //
 915     // The MEMBAR, above, prevents the LD of cxq|EntryList in the subsequent
 916     // exit operation from floating above the ST Responsible=null.
 917   }
 918 
 919   // We've acquired ownership with CAS().
 920   // CAS is serializing -- it has MEMBAR/FENCE-equivalent semantics.
 921   // But since the CAS() this thread may have also stored into _succ,
 922   // EntryList, cxq or Responsible.  These meta-data updates must be
 923   // visible __before this thread subsequently drops the lock.
 924   // Consider what could occur if we didn't enforce this constraint --
 925   // STs to monitor meta-data and user-data could reorder with (become
 926   // visible after) the ST in exit that drops ownership of the lock.
 927   // Some other thread could then acquire the lock, but observe inconsistent
 928   // or old monitor meta-data and heap data.  That violates the JMM.
 929   // To that end, the 1-0 exit() operation must have at least STST|LDST
 930   // "release" barrier semantics.  Specifically, there must be at least a
 931   // STST|LDST barrier in exit() before the ST of null into _owner that drops
 932   // the lock.   The barrier ensures that changes to monitor meta-data and data
 933   // protected by the lock will be visible before we release the lock, and
 934   // therefore before some other thread (CPU) has a chance to acquire the lock.
 935   // See also: http://gee.cs.oswego.edu/dl/jmm/cookbook.html.
 936   //
 937   // Critically, any prior STs to _succ or EntryList must be visible before
 938   // the ST of null into _owner in the *subsequent* (following) corresponding
 939   // monitorexit.  Recall too, that in 1-0 mode monitorexit does not necessarily
 940   // execute a serializing instruction.
 941 
 942   return;
 943 }
 944 
 945 // ReenterI() is a specialized inline form of the latter half of the
 946 // contended slow-path from EnterI().  We use ReenterI() only for
 947 // monitor reentry in wait().
 948 //
 949 // In the future we should reconcile EnterI() and ReenterI().
 950 
 951 void ObjectMonitor::ReenterI(JavaThread* current, ObjectWaiter* currentNode) {
 952   assert(current != NULL, "invariant");
 953   assert(currentNode != NULL, "invariant");
 954   assert(currentNode->_thread == current, "invariant");
 955   assert(_waiters > 0, "invariant");
 956   assert(object()->mark() == markWord::encode(this), "invariant");
 957 
 958   assert(current->thread_state() != _thread_blocked, "invariant");
 959 
 960   int nWakeups = 0;
 961   for (;;) {
 962     ObjectWaiter::TStates v = currentNode->TState;
 963     guarantee(v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant");
 964     assert(owner_raw() != current, "invariant");
 965 
 966     if (TryLock(current) > 0) break;
 967     if (TrySpin(current) > 0) break;
 968 
 969     {
 970       OSThreadContendState osts(current->osthread());
 971 
 972       assert(current->thread_state() == _thread_in_vm, "invariant");
 973 
 974       {
 975         ClearSuccOnSuspend csos(this);
 976         ThreadBlockInVMPreprocess<ClearSuccOnSuspend> tbivs(current, csos, true /* allow_suspend */);
 977         current->_ParkEvent->park();
 978       }
 979     }
 980 
 981     // Try again, but just so we distinguish between futile wakeups and
 982     // successful wakeups.  The following test isn't algorithmically
 983     // necessary, but it helps us maintain sensible statistics.
 984     if (TryLock(current) > 0) break;
 985 
 986     // The lock is still contested.
 987     // Keep a tally of the # of futile wakeups.
 988     // Note that the counter is not protected by a lock or updated by atomics.
 989     // That is by design - we trade "lossy" counters which are exposed to
 990     // races during updates for a lower probe effect.
 991     ++nWakeups;
 992 
 993     // Assuming this is not a spurious wakeup we'll normally
 994     // find that _succ == current.
 995     if (_succ == current) _succ = NULL;
 996 
 997     // Invariant: after clearing _succ a contending thread
 998     // *must* retry  _owner before parking.
 999     OrderAccess::fence();
1000 
1001     // This PerfData object can be used in parallel with a safepoint.
1002     // See the work around in PerfDataManager::destroy().
1003     OM_PERFDATA_OP(FutileWakeups, inc());
1004   }
1005 
1006   // current has acquired the lock -- Unlink current from the cxq or EntryList .
1007   // Normally we'll find current on the EntryList.
1008   // Unlinking from the EntryList is constant-time and atomic-free.
1009   // From the perspective of the lock owner (this thread), the
1010   // EntryList is stable and cxq is prepend-only.
1011   // The head of cxq is volatile but the interior is stable.
1012   // In addition, current.TState is stable.
1013 
1014   assert(owner_raw() == current, "invariant");
1015   assert(object()->mark() == markWord::encode(this), "invariant");
1016   UnlinkAfterAcquire(current, currentNode);
1017   if (_succ == current) _succ = NULL;
1018   assert(_succ != current, "invariant");
1019   currentNode->TState = ObjectWaiter::TS_RUN;
1020   OrderAccess::fence();      // see comments at the end of EnterI()
1021 }
1022 
1023 // By convention we unlink a contending thread from EntryList|cxq immediately
1024 // after the thread acquires the lock in ::enter().  Equally, we could defer
1025 // unlinking the thread until ::exit()-time.
1026 
1027 void ObjectMonitor::UnlinkAfterAcquire(JavaThread* current, ObjectWaiter* currentNode) {
1028   assert(owner_raw() == current, "invariant");
1029   assert(currentNode->_thread == current, "invariant");
1030 
1031   if (currentNode->TState == ObjectWaiter::TS_ENTER) {
1032     // Normal case: remove current from the DLL EntryList .
1033     // This is a constant-time operation.
1034     ObjectWaiter* nxt = currentNode->_next;
1035     ObjectWaiter* prv = currentNode->_prev;
1036     if (nxt != NULL) nxt->_prev = prv;
1037     if (prv != NULL) prv->_next = nxt;
1038     if (currentNode == _EntryList) _EntryList = nxt;
1039     assert(nxt == NULL || nxt->TState == ObjectWaiter::TS_ENTER, "invariant");
1040     assert(prv == NULL || prv->TState == ObjectWaiter::TS_ENTER, "invariant");
1041   } else {
1042     assert(currentNode->TState == ObjectWaiter::TS_CXQ, "invariant");
1043     // Inopportune interleaving -- current is still on the cxq.
1044     // This usually means the enqueue of self raced an exiting thread.
1045     // Normally we'll find current near the front of the cxq, so
1046     // dequeueing is typically fast.  If needbe we can accelerate
1047     // this with some MCS/CHL-like bidirectional list hints and advisory
1048     // back-links so dequeueing from the interior will normally operate
1049     // in constant-time.
1050     // Dequeue current from either the head (with CAS) or from the interior
1051     // with a linear-time scan and normal non-atomic memory operations.
1052     // CONSIDER: if current is on the cxq then simply drain cxq into EntryList
1053     // and then unlink current from EntryList.  We have to drain eventually,
1054     // so it might as well be now.
1055 
1056     ObjectWaiter* v = _cxq;
1057     assert(v != NULL, "invariant");
1058     if (v != currentNode || Atomic::cmpxchg(&_cxq, v, currentNode->_next) != v) {
1059       // The CAS above can fail from interference IFF a "RAT" arrived.
1060       // In that case current must be in the interior and can no longer be
1061       // at the head of cxq.
1062       if (v == currentNode) {
1063         assert(_cxq != v, "invariant");
1064         v = _cxq;          // CAS above failed - start scan at head of list
1065       }
1066       ObjectWaiter* p;
1067       ObjectWaiter* q = NULL;
1068       for (p = v; p != NULL && p != currentNode; p = p->_next) {
1069         q = p;
1070         assert(p->TState == ObjectWaiter::TS_CXQ, "invariant");
1071       }
1072       assert(v != currentNode, "invariant");
1073       assert(p == currentNode, "Node not found on cxq");
1074       assert(p != _cxq, "invariant");
1075       assert(q != NULL, "invariant");
1076       assert(q->_next == p, "invariant");
1077       q->_next = p->_next;
1078     }
1079   }
1080 
1081 #ifdef ASSERT
1082   // Diagnostic hygiene ...
1083   currentNode->_prev  = (ObjectWaiter*) 0xBAD;
1084   currentNode->_next  = (ObjectWaiter*) 0xBAD;
1085   currentNode->TState = ObjectWaiter::TS_RUN;
1086 #endif
1087 }
1088 
1089 // -----------------------------------------------------------------------------
1090 // Exit support
1091 //
1092 // exit()
1093 // ~~~~~~
1094 // Note that the collector can't reclaim the objectMonitor or deflate
1095 // the object out from underneath the thread calling ::exit() as the
1096 // thread calling ::exit() never transitions to a stable state.
1097 // This inhibits GC, which in turn inhibits asynchronous (and
1098 // inopportune) reclamation of "this".
1099 //
1100 // We'd like to assert that: (THREAD->thread_state() != _thread_blocked) ;
1101 // There's one exception to the claim above, however.  EnterI() can call
1102 // exit() to drop a lock if the acquirer has been externally suspended.
1103 // In that case exit() is called with _thread_state == _thread_blocked,
1104 // but the monitor's _contentions field is > 0, which inhibits reclamation.
1105 //
1106 // 1-0 exit
1107 // ~~~~~~~~
1108 // ::exit() uses a canonical 1-1 idiom with a MEMBAR although some of
1109 // the fast-path operators have been optimized so the common ::exit()
1110 // operation is 1-0, e.g., see macroAssembler_x86.cpp: fast_unlock().
1111 // The code emitted by fast_unlock() elides the usual MEMBAR.  This
1112 // greatly improves latency -- MEMBAR and CAS having considerable local
1113 // latency on modern processors -- but at the cost of "stranding".  Absent the
1114 // MEMBAR, a thread in fast_unlock() can race a thread in the slow
1115 // ::enter() path, resulting in the entering thread being stranding
1116 // and a progress-liveness failure.   Stranding is extremely rare.
1117 // We use timers (timed park operations) & periodic polling to detect
1118 // and recover from stranding.  Potentially stranded threads periodically
1119 // wake up and poll the lock.  See the usage of the _Responsible variable.
1120 //
1121 // The CAS() in enter provides for safety and exclusion, while the CAS or
1122 // MEMBAR in exit provides for progress and avoids stranding.  1-0 locking
1123 // eliminates the CAS/MEMBAR from the exit path, but it admits stranding.
1124 // We detect and recover from stranding with timers.
1125 //
1126 // If a thread transiently strands it'll park until (a) another
1127 // thread acquires the lock and then drops the lock, at which time the
1128 // exiting thread will notice and unpark the stranded thread, or, (b)
1129 // the timer expires.  If the lock is high traffic then the stranding latency
1130 // will be low due to (a).  If the lock is low traffic then the odds of
1131 // stranding are lower, although the worst-case stranding latency
1132 // is longer.  Critically, we don't want to put excessive load in the
1133 // platform's timer subsystem.  We want to minimize both the timer injection
1134 // rate (timers created/sec) as well as the number of timers active at
1135 // any one time.  (more precisely, we want to minimize timer-seconds, which is
1136 // the integral of the # of active timers at any instant over time).
1137 // Both impinge on OS scalability.  Given that, at most one thread parked on
1138 // a monitor will use a timer.
1139 //
1140 // There is also the risk of a futile wake-up. If we drop the lock
1141 // another thread can reacquire the lock immediately, and we can
1142 // then wake a thread unnecessarily. This is benign, and we've
1143 // structured the code so the windows are short and the frequency
1144 // of such futile wakups is low.
1145 
1146 void ObjectMonitor::exit(JavaThread* current, bool not_suspended) {
1147   void* cur = owner_raw();
1148   if (current != cur) {
1149     assert(!current->is_lock_owned((address)cur), "no stack-locking");
1150     // Apparent unbalanced locking ...
1151     // Naively we'd like to throw IllegalMonitorStateException.
1152     // As a practical matter we can neither allocate nor throw an
1153     // exception as ::exit() can be called from leaf routines.
1154     // see x86_32.ad Fast_Unlock() and the I1 and I2 properties.
1155     // Upon deeper reflection, however, in a properly run JVM the only
1156     // way we should encounter this situation is in the presence of
1157     // unbalanced JNI locking. TODO: CheckJNICalls.
1158     // See also: CR4414101
1159 #ifdef ASSERT
1160     LogStreamHandle(Error, monitorinflation) lsh;
1161     lsh.print_cr("ERROR: ObjectMonitor::exit(): thread=" INTPTR_FORMAT
1162                   " is exiting an ObjectMonitor it does not own.", p2i(current));
1163     lsh.print_cr("The imbalance is possibly caused by JNI locking.");
1164     print_debug_style_on(&lsh);
1165     assert(false, "Non-balanced monitor enter/exit! " PTR_FORMAT, p2i(object()));
1166 #endif
1167     return;
1168   }
1169 
1170   if (_recursions != 0) {
1171     _recursions--;        // this is simple recursive enter
1172     return;
1173   }
1174 
1175   // Invariant: after setting Responsible=null an thread must execute
1176   // a MEMBAR or other serializing instruction before fetching EntryList|cxq.
1177   _Responsible = NULL;
1178 
1179 #if INCLUDE_JFR
1180   // get the owner's thread id for the MonitorEnter event
1181   // if it is enabled and the thread isn't suspended
1182   if (not_suspended && EventJavaMonitorEnter::is_enabled()) {
1183     _previous_owner_tid = JFR_THREAD_ID(current);
1184   }
1185 #endif
1186 
1187   for (;;) {
1188     assert(current == owner_raw(), "invariant");
1189 
1190     // Drop the lock.
1191     // release semantics: prior loads and stores from within the critical section
1192     // must not float (reorder) past the following store that drops the lock.
1193     // Uses a storeload to separate release_store(owner) from the
1194     // successor check. The try_set_owner() below uses cmpxchg() so
1195     // we get the fence down there.
1196     release_clear_owner(current);
1197     OrderAccess::storeload();
1198 
1199     if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) {
1200       return;
1201     }
1202     // Other threads are blocked trying to acquire the lock.
1203 
1204     // Normally the exiting thread is responsible for ensuring succession,
1205     // but if other successors are ready or other entering threads are spinning
1206     // then this thread can simply store NULL into _owner and exit without
1207     // waking a successor.  The existence of spinners or ready successors
1208     // guarantees proper succession (liveness).  Responsibility passes to the
1209     // ready or running successors.  The exiting thread delegates the duty.
1210     // More precisely, if a successor already exists this thread is absolved
1211     // of the responsibility of waking (unparking) one.
1212     //
1213     // The _succ variable is critical to reducing futile wakeup frequency.
1214     // _succ identifies the "heir presumptive" thread that has been made
1215     // ready (unparked) but that has not yet run.  We need only one such
1216     // successor thread to guarantee progress.
1217     // See http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf
1218     // section 3.3 "Futile Wakeup Throttling" for details.
1219     //
1220     // Note that spinners in Enter() also set _succ non-null.
1221     // In the current implementation spinners opportunistically set
1222     // _succ so that exiting threads might avoid waking a successor.
1223     // Another less appealing alternative would be for the exiting thread
1224     // to drop the lock and then spin briefly to see if a spinner managed
1225     // to acquire the lock.  If so, the exiting thread could exit
1226     // immediately without waking a successor, otherwise the exiting
1227     // thread would need to dequeue and wake a successor.
1228     // (Note that we'd need to make the post-drop spin short, but no
1229     // shorter than the worst-case round-trip cache-line migration time.
1230     // The dropped lock needs to become visible to the spinner, and then
1231     // the acquisition of the lock by the spinner must become visible to
1232     // the exiting thread).
1233 
1234     // It appears that an heir-presumptive (successor) must be made ready.
1235     // Only the current lock owner can manipulate the EntryList or
1236     // drain _cxq, so we need to reacquire the lock.  If we fail
1237     // to reacquire the lock the responsibility for ensuring succession
1238     // falls to the new owner.
1239     //
1240     if (try_set_owner_from(NULL, current) != NULL) {
1241       return;
1242     }
1243 
1244     guarantee(owner_raw() == current, "invariant");
1245 
1246     ObjectWaiter* w = NULL;
1247 
1248     w = _EntryList;
1249     if (w != NULL) {
1250       // I'd like to write: guarantee (w->_thread != current).
1251       // But in practice an exiting thread may find itself on the EntryList.
1252       // Let's say thread T1 calls O.wait().  Wait() enqueues T1 on O's waitset and
1253       // then calls exit().  Exit release the lock by setting O._owner to NULL.
1254       // Let's say T1 then stalls.  T2 acquires O and calls O.notify().  The
1255       // notify() operation moves T1 from O's waitset to O's EntryList. T2 then
1256       // release the lock "O".  T2 resumes immediately after the ST of null into
1257       // _owner, above.  T2 notices that the EntryList is populated, so it
1258       // reacquires the lock and then finds itself on the EntryList.
1259       // Given all that, we have to tolerate the circumstance where "w" is
1260       // associated with current.
1261       assert(w->TState == ObjectWaiter::TS_ENTER, "invariant");
1262       ExitEpilog(current, w);
1263       return;
1264     }
1265 
1266     // If we find that both _cxq and EntryList are null then just
1267     // re-run the exit protocol from the top.
1268     w = _cxq;
1269     if (w == NULL) continue;
1270 
1271     // Drain _cxq into EntryList - bulk transfer.
1272     // First, detach _cxq.
1273     // The following loop is tantamount to: w = swap(&cxq, NULL)
1274     for (;;) {
1275       assert(w != NULL, "Invariant");
1276       ObjectWaiter* u = Atomic::cmpxchg(&_cxq, w, (ObjectWaiter*)NULL);
1277       if (u == w) break;
1278       w = u;
1279     }
1280 
1281     assert(w != NULL, "invariant");
1282     assert(_EntryList == NULL, "invariant");
1283 
1284     // Convert the LIFO SLL anchored by _cxq into a DLL.
1285     // The list reorganization step operates in O(LENGTH(w)) time.
1286     // It's critical that this step operate quickly as
1287     // "current" still holds the outer-lock, restricting parallelism
1288     // and effectively lengthening the critical section.
1289     // Invariant: s chases t chases u.
1290     // TODO-FIXME: consider changing EntryList from a DLL to a CDLL so
1291     // we have faster access to the tail.
1292 
1293     _EntryList = w;
1294     ObjectWaiter* q = NULL;
1295     ObjectWaiter* p;
1296     for (p = w; p != NULL; p = p->_next) {
1297       guarantee(p->TState == ObjectWaiter::TS_CXQ, "Invariant");
1298       p->TState = ObjectWaiter::TS_ENTER;
1299       p->_prev = q;
1300       q = p;
1301     }
1302 
1303     // In 1-0 mode we need: ST EntryList; MEMBAR #storestore; ST _owner = NULL
1304     // The MEMBAR is satisfied by the release_store() operation in ExitEpilog().
1305 
1306     // See if we can abdicate to a spinner instead of waking a thread.
1307     // A primary goal of the implementation is to reduce the
1308     // context-switch rate.
1309     if (_succ != NULL) continue;
1310 
1311     w = _EntryList;
1312     if (w != NULL) {
1313       guarantee(w->TState == ObjectWaiter::TS_ENTER, "invariant");
1314       ExitEpilog(current, w);
1315       return;
1316     }
1317   }
1318 }
1319 
1320 void ObjectMonitor::ExitEpilog(JavaThread* current, ObjectWaiter* Wakee) {
1321   assert(owner_raw() == current, "invariant");
1322 
1323   // Exit protocol:
1324   // 1. ST _succ = wakee
1325   // 2. membar #loadstore|#storestore;
1326   // 2. ST _owner = NULL
1327   // 3. unpark(wakee)
1328 
1329   _succ = Wakee->_thread;
1330   ParkEvent * Trigger = Wakee->_event;
1331 
1332   // Hygiene -- once we've set _owner = NULL we can't safely dereference Wakee again.
1333   // The thread associated with Wakee may have grabbed the lock and "Wakee" may be
1334   // out-of-scope (non-extant).
1335   Wakee  = NULL;
1336 
1337   // Drop the lock.
1338   // Uses a fence to separate release_store(owner) from the LD in unpark().
1339   release_clear_owner(current);
1340   OrderAccess::fence();
1341 
1342   DTRACE_MONITOR_PROBE(contended__exit, this, object(), current);
1343   Trigger->unpark();
1344 
1345   // Maintain stats and report events to JVMTI
1346   OM_PERFDATA_OP(Parks, inc());
1347 }
1348 
1349 
1350 // -----------------------------------------------------------------------------
1351 // Class Loader deadlock handling.
1352 //
1353 // complete_exit exits a lock returning recursion count
1354 // complete_exit/reenter operate as a wait without waiting
1355 // complete_exit requires an inflated monitor
1356 // The _owner field is not always the Thread addr even with an
1357 // inflated monitor, e.g. the monitor can be inflated by a non-owning
1358 // thread due to contention.
1359 intx ObjectMonitor::complete_exit(JavaThread* current) {
1360   assert(InitDone, "Unexpectedly not initialized");
1361 
1362   void* cur = owner_raw();
1363   if (current != cur) {
1364     assert(!current->is_lock_owned((address)cur), "no stack-locking");
1365   }
1366 
1367   guarantee(current == owner_raw(), "complete_exit not owner");
1368   intx save = _recursions; // record the old recursion count
1369   _recursions = 0;         // set the recursion level to be 0
1370   exit(current);           // exit the monitor
1371   guarantee(owner_raw() != current, "invariant");
1372   return save;
1373 }
1374 
1375 // reenter() enters a lock and sets recursion count
1376 // complete_exit/reenter operate as a wait without waiting
1377 bool ObjectMonitor::reenter(intx recursions, JavaThread* current) {
1378 
1379   guarantee(owner_raw() != current, "reenter already owner");
1380   if (!enter(current)) {
1381     return false;
1382   }
1383   // Entered the monitor.
1384   guarantee(_recursions == 0, "reenter recursion");
1385   _recursions = recursions;
1386   return true;
1387 }
1388 
1389 // Checks that the current THREAD owns this monitor and causes an
1390 // immediate return if it doesn't. We don't use the CHECK macro
1391 // because we want the IMSE to be the only exception that is thrown
1392 // from the call site when false is returned. Any other pending
1393 // exception is ignored.
1394 #define CHECK_OWNER()                                                  \
1395   do {                                                                 \
1396     if (!check_owner(THREAD)) {                                        \
1397        assert(HAS_PENDING_EXCEPTION, "expected a pending IMSE here."); \
1398        return;                                                         \
1399      }                                                                 \
1400   } while (false)
1401 
1402 // Returns true if the specified thread owns the ObjectMonitor.
1403 // Otherwise returns false and throws IllegalMonitorStateException
1404 // (IMSE). If there is a pending exception and the specified thread
1405 // is not the owner, that exception will be replaced by the IMSE.
1406 bool ObjectMonitor::check_owner(TRAPS) {
1407   JavaThread* current = THREAD;
1408   void* cur = owner_raw();
1409   assert(cur != ANONYMOUS_OWNER, "no anon owner here");
1410   if (cur == current) {
1411     return true;
1412   }
1413   THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
1414              "current thread is not owner", false);
1415 }
1416 
1417 static void post_monitor_wait_event(EventJavaMonitorWait* event,
1418                                     ObjectMonitor* monitor,
1419                                     uint64_t notifier_tid,
1420                                     jlong timeout,
1421                                     bool timedout) {
1422   assert(event != NULL, "invariant");
1423   assert(monitor != NULL, "invariant");
1424   event->set_monitorClass(monitor->object()->klass());
1425   event->set_timeout(timeout);
1426   // Set an address that is 'unique enough', such that events close in
1427   // time and with the same address are likely (but not guaranteed) to
1428   // belong to the same object.
1429   event->set_address((uintptr_t)monitor);
1430   event->set_notifier(notifier_tid);
1431   event->set_timedOut(timedout);
1432   event->commit();
1433 }
1434 
1435 // -----------------------------------------------------------------------------
1436 // Wait/Notify/NotifyAll
1437 //
1438 // Note: a subset of changes to ObjectMonitor::wait()
1439 // will need to be replicated in complete_exit
1440 void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
1441   JavaThread* current = THREAD;
1442 
1443   assert(InitDone, "Unexpectedly not initialized");
1444 
1445   CHECK_OWNER();  // Throws IMSE if not owner.
1446 
1447   EventJavaMonitorWait event;
1448 
1449   // check for a pending interrupt
1450   if (interruptible && current->is_interrupted(true) && !HAS_PENDING_EXCEPTION) {
1451     // post monitor waited event.  Note that this is past-tense, we are done waiting.
1452     if (JvmtiExport::should_post_monitor_waited()) {
1453       // Note: 'false' parameter is passed here because the
1454       // wait was not timed out due to thread interrupt.
1455       JvmtiExport::post_monitor_waited(current, this, false);
1456 
1457       // In this short circuit of the monitor wait protocol, the
1458       // current thread never drops ownership of the monitor and
1459       // never gets added to the wait queue so the current thread
1460       // cannot be made the successor. This means that the
1461       // JVMTI_EVENT_MONITOR_WAITED event handler cannot accidentally
1462       // consume an unpark() meant for the ParkEvent associated with
1463       // this ObjectMonitor.
1464     }
1465     if (event.should_commit()) {
1466       post_monitor_wait_event(&event, this, 0, millis, false);
1467     }
1468     THROW(vmSymbols::java_lang_InterruptedException());
1469     return;
1470   }
1471 
1472   assert(current->_Stalled == 0, "invariant");
1473   current->_Stalled = intptr_t(this);
1474   current->set_current_waiting_monitor(this);
1475 
1476   // create a node to be put into the queue
1477   // Critically, after we reset() the event but prior to park(), we must check
1478   // for a pending interrupt.
1479   ObjectWaiter node(current);
1480   node.TState = ObjectWaiter::TS_WAIT;
1481   current->_ParkEvent->reset();
1482   OrderAccess::fence();          // ST into Event; membar ; LD interrupted-flag
1483 
1484   // Enter the waiting queue, which is a circular doubly linked list in this case
1485   // but it could be a priority queue or any data structure.
1486   // _WaitSetLock protects the wait queue.  Normally the wait queue is accessed only
1487   // by the owner of the monitor *except* in the case where park()
1488   // returns because of a timeout of interrupt.  Contention is exceptionally rare
1489   // so we use a simple spin-lock instead of a heavier-weight blocking lock.
1490 
1491   Thread::SpinAcquire(&_WaitSetLock, "WaitSet - add");
1492   AddWaiter(&node);
1493   Thread::SpinRelease(&_WaitSetLock);
1494 
1495   _Responsible = NULL;
1496 
1497   intx save = _recursions;     // record the old recursion count
1498   _waiters++;                  // increment the number of waiters
1499   _recursions = 0;             // set the recursion level to be 1
1500   exit(current);               // exit the monitor
1501   guarantee(owner_raw() != current, "invariant");
1502 
1503   // The thread is on the WaitSet list - now park() it.
1504   // On MP systems it's conceivable that a brief spin before we park
1505   // could be profitable.
1506   //
1507   // TODO-FIXME: change the following logic to a loop of the form
1508   //   while (!timeout && !interrupted && _notified == 0) park()
1509 
1510   int ret = OS_OK;
1511   int WasNotified = 0;
1512 
1513   // Need to check interrupt state whilst still _thread_in_vm
1514   bool interrupted = interruptible && current->is_interrupted(false);
1515 
1516   { // State transition wrappers
1517     OSThread* osthread = current->osthread();
1518     OSThreadWaitState osts(osthread, true);
1519 
1520     assert(current->thread_state() == _thread_in_vm, "invariant");
1521 
1522     {
1523       ClearSuccOnSuspend csos(this);
1524       ThreadBlockInVMPreprocess<ClearSuccOnSuspend> tbivs(current, csos, true /* allow_suspend */);
1525       if (interrupted || HAS_PENDING_EXCEPTION) {
1526         // Intentionally empty
1527       } else if (node._notified == 0) {
1528         if (millis <= 0) {
1529           current->_ParkEvent->park();
1530         } else {
1531           ret = current->_ParkEvent->park(millis);
1532         }
1533       }
1534     }
1535 
1536     // Node may be on the WaitSet, the EntryList (or cxq), or in transition
1537     // from the WaitSet to the EntryList.
1538     // See if we need to remove Node from the WaitSet.
1539     // We use double-checked locking to avoid grabbing _WaitSetLock
1540     // if the thread is not on the wait queue.
1541     //
1542     // Note that we don't need a fence before the fetch of TState.
1543     // In the worst case we'll fetch a old-stale value of TS_WAIT previously
1544     // written by the is thread. (perhaps the fetch might even be satisfied
1545     // by a look-aside into the processor's own store buffer, although given
1546     // the length of the code path between the prior ST and this load that's
1547     // highly unlikely).  If the following LD fetches a stale TS_WAIT value
1548     // then we'll acquire the lock and then re-fetch a fresh TState value.
1549     // That is, we fail toward safety.
1550 
1551     if (node.TState == ObjectWaiter::TS_WAIT) {
1552       Thread::SpinAcquire(&_WaitSetLock, "WaitSet - unlink");
1553       if (node.TState == ObjectWaiter::TS_WAIT) {
1554         DequeueSpecificWaiter(&node);       // unlink from WaitSet
1555         assert(node._notified == 0, "invariant");
1556         node.TState = ObjectWaiter::TS_RUN;
1557       }
1558       Thread::SpinRelease(&_WaitSetLock);
1559     }
1560 
1561     // The thread is now either on off-list (TS_RUN),
1562     // on the EntryList (TS_ENTER), or on the cxq (TS_CXQ).
1563     // The Node's TState variable is stable from the perspective of this thread.
1564     // No other threads will asynchronously modify TState.
1565     guarantee(node.TState != ObjectWaiter::TS_WAIT, "invariant");
1566     OrderAccess::loadload();
1567     if (_succ == current) _succ = NULL;
1568     WasNotified = node._notified;
1569 
1570     // Reentry phase -- reacquire the monitor.
1571     // re-enter contended monitor after object.wait().
1572     // retain OBJECT_WAIT state until re-enter successfully completes
1573     // Thread state is thread_in_vm and oop access is again safe,
1574     // although the raw address of the object may have changed.
1575     // (Don't cache naked oops over safepoints, of course).
1576 
1577     // post monitor waited event. Note that this is past-tense, we are done waiting.
1578     if (JvmtiExport::should_post_monitor_waited()) {
1579       JvmtiExport::post_monitor_waited(current, this, ret == OS_TIMEOUT);
1580 
1581       if (node._notified != 0 && _succ == current) {
1582         // In this part of the monitor wait-notify-reenter protocol it
1583         // is possible (and normal) for another thread to do a fastpath
1584         // monitor enter-exit while this thread is still trying to get
1585         // to the reenter portion of the protocol.
1586         //
1587         // The ObjectMonitor was notified and the current thread is
1588         // the successor which also means that an unpark() has already
1589         // been done. The JVMTI_EVENT_MONITOR_WAITED event handler can
1590         // consume the unpark() that was done when the successor was
1591         // set because the same ParkEvent is shared between Java
1592         // monitors and JVM/TI RawMonitors (for now).
1593         //
1594         // We redo the unpark() to ensure forward progress, i.e., we
1595         // don't want all pending threads hanging (parked) with none
1596         // entering the unlocked monitor.
1597         node._event->unpark();
1598       }
1599     }
1600 
1601     if (event.should_commit()) {
1602       post_monitor_wait_event(&event, this, node._notifier_tid, millis, ret == OS_TIMEOUT);
1603     }
1604 
1605     OrderAccess::fence();
1606 
1607     assert(current->_Stalled != 0, "invariant");
1608     current->_Stalled = 0;
1609 
1610     assert(owner_raw() != current, "invariant");
1611     ObjectWaiter::TStates v = node.TState;
1612     if (v == ObjectWaiter::TS_RUN) {
1613       enter(current);
1614     } else {
1615       guarantee(v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant");
1616       ReenterI(current, &node);
1617       node.wait_reenter_end(this);
1618     }
1619 
1620     // current has reacquired the lock.
1621     // Lifecycle - the node representing current must not appear on any queues.
1622     // Node is about to go out-of-scope, but even if it were immortal we wouldn't
1623     // want residual elements associated with this thread left on any lists.
1624     guarantee(node.TState == ObjectWaiter::TS_RUN, "invariant");
1625     assert(owner_raw() == current, "invariant");
1626     assert(_succ != current, "invariant");
1627   } // OSThreadWaitState()
1628 
1629   current->set_current_waiting_monitor(NULL);
1630 
1631   guarantee(_recursions == 0, "invariant");
1632   int relock_count = JvmtiDeferredUpdates::get_and_reset_relock_count_after_wait(current);
1633   _recursions =   save          // restore the old recursion count
1634                 + relock_count; //  increased by the deferred relock count
1635   current->inc_held_monitor_count(relock_count); // Deopt never entered these counts.
1636   _waiters--;             // decrement the number of waiters
1637 
1638   // Verify a few postconditions
1639   assert(owner_raw() == current, "invariant");
1640   assert(_succ != current, "invariant");
1641   assert(object()->mark() == markWord::encode(this), "invariant");
1642 
1643   // check if the notification happened
1644   if (!WasNotified) {
1645     // no, it could be timeout or Thread.interrupt() or both
1646     // check for interrupt event, otherwise it is timeout
1647     if (interruptible && current->is_interrupted(true) && !HAS_PENDING_EXCEPTION) {
1648       THROW(vmSymbols::java_lang_InterruptedException());
1649     }
1650   }
1651 
1652   // NOTE: Spurious wake up will be consider as timeout.
1653   // Monitor notify has precedence over thread interrupt.
1654 }
1655 
1656 
1657 // Consider:
1658 // If the lock is cool (cxq == null && succ == null) and we're on an MP system
1659 // then instead of transferring a thread from the WaitSet to the EntryList
1660 // we might just dequeue a thread from the WaitSet and directly unpark() it.
1661 
1662 void ObjectMonitor::INotify(JavaThread* current) {
1663   Thread::SpinAcquire(&_WaitSetLock, "WaitSet - notify");
1664   ObjectWaiter* iterator = DequeueWaiter();
1665   if (iterator != NULL) {
1666     guarantee(iterator->TState == ObjectWaiter::TS_WAIT, "invariant");
1667     guarantee(iterator->_notified == 0, "invariant");
1668     // Disposition - what might we do with iterator ?
1669     // a.  add it directly to the EntryList - either tail (policy == 1)
1670     //     or head (policy == 0).
1671     // b.  push it onto the front of the _cxq (policy == 2).
1672     // For now we use (b).
1673 
1674     iterator->TState = ObjectWaiter::TS_ENTER;
1675 
1676     iterator->_notified = 1;
1677     iterator->_notifier_tid = JFR_THREAD_ID(current);
1678 
1679     ObjectWaiter* list = _EntryList;
1680     if (list != NULL) {
1681       assert(list->_prev == NULL, "invariant");
1682       assert(list->TState == ObjectWaiter::TS_ENTER, "invariant");
1683       assert(list != iterator, "invariant");
1684     }
1685 
1686     // prepend to cxq
1687     if (list == NULL) {
1688       iterator->_next = iterator->_prev = NULL;
1689       _EntryList = iterator;
1690     } else {
1691       iterator->TState = ObjectWaiter::TS_CXQ;
1692       for (;;) {
1693         ObjectWaiter* front = _cxq;
1694         iterator->_next = front;
1695         if (Atomic::cmpxchg(&_cxq, front, iterator) == front) {
1696           break;
1697         }
1698       }
1699     }
1700 
1701     // _WaitSetLock protects the wait queue, not the EntryList.  We could
1702     // move the add-to-EntryList operation, above, outside the critical section
1703     // protected by _WaitSetLock.  In practice that's not useful.  With the
1704     // exception of  wait() timeouts and interrupts the monitor owner
1705     // is the only thread that grabs _WaitSetLock.  There's almost no contention
1706     // on _WaitSetLock so it's not profitable to reduce the length of the
1707     // critical section.
1708 
1709     iterator->wait_reenter_begin(this);
1710   }
1711   Thread::SpinRelease(&_WaitSetLock);
1712 }
1713 
1714 // Consider: a not-uncommon synchronization bug is to use notify() when
1715 // notifyAll() is more appropriate, potentially resulting in stranded
1716 // threads; this is one example of a lost wakeup. A useful diagnostic
1717 // option is to force all notify() operations to behave as notifyAll().
1718 //
1719 // Note: We can also detect many such problems with a "minimum wait".
1720 // When the "minimum wait" is set to a small non-zero timeout value
1721 // and the program does not hang whereas it did absent "minimum wait",
1722 // that suggests a lost wakeup bug.
1723 
1724 void ObjectMonitor::notify(TRAPS) {
1725   JavaThread* current = THREAD;
1726   CHECK_OWNER();  // Throws IMSE if not owner.
1727   if (_WaitSet == NULL) {
1728     return;
1729   }
1730   DTRACE_MONITOR_PROBE(notify, this, object(), current);
1731   INotify(current);
1732   OM_PERFDATA_OP(Notifications, inc(1));
1733 }
1734 
1735 
1736 // The current implementation of notifyAll() transfers the waiters one-at-a-time
1737 // from the waitset to the EntryList. This could be done more efficiently with a
1738 // single bulk transfer but in practice it's not time-critical. Beware too,
1739 // that in prepend-mode we invert the order of the waiters. Let's say that the
1740 // waitset is "ABCD" and the EntryList is "XYZ". After a notifyAll() in prepend
1741 // mode the waitset will be empty and the EntryList will be "DCBAXYZ".
1742 
1743 void ObjectMonitor::notifyAll(TRAPS) {
1744   JavaThread* current = THREAD;
1745   CHECK_OWNER();  // Throws IMSE if not owner.
1746   if (_WaitSet == NULL) {
1747     return;
1748   }
1749 
1750   DTRACE_MONITOR_PROBE(notifyAll, this, object(), current);
1751   int tally = 0;
1752   while (_WaitSet != NULL) {
1753     tally++;
1754     INotify(current);
1755   }
1756 
1757   OM_PERFDATA_OP(Notifications, inc(tally));
1758 }
1759 
1760 // -----------------------------------------------------------------------------
1761 // Adaptive Spinning Support
1762 //
1763 // Adaptive spin-then-block - rational spinning
1764 //
1765 // Note that we spin "globally" on _owner with a classic SMP-polite TATAS
1766 // algorithm.  On high order SMP systems it would be better to start with
1767 // a brief global spin and then revert to spinning locally.  In the spirit of MCS/CLH,
1768 // a contending thread could enqueue itself on the cxq and then spin locally
1769 // on a thread-specific variable such as its ParkEvent._Event flag.
1770 // That's left as an exercise for the reader.  Note that global spinning is
1771 // not problematic on Niagara, as the L2 cache serves the interconnect and
1772 // has both low latency and massive bandwidth.
1773 //
1774 // Broadly, we can fix the spin frequency -- that is, the % of contended lock
1775 // acquisition attempts where we opt to spin --  at 100% and vary the spin count
1776 // (duration) or we can fix the count at approximately the duration of
1777 // a context switch and vary the frequency.   Of course we could also
1778 // vary both satisfying K == Frequency * Duration, where K is adaptive by monitor.
1779 // For a description of 'Adaptive spin-then-block mutual exclusion in
1780 // multi-threaded processing,' see U.S. Pat. No. 8046758.
1781 //
1782 // This implementation varies the duration "D", where D varies with
1783 // the success rate of recent spin attempts. (D is capped at approximately
1784 // length of a round-trip context switch).  The success rate for recent
1785 // spin attempts is a good predictor of the success rate of future spin
1786 // attempts.  The mechanism adapts automatically to varying critical
1787 // section length (lock modality), system load and degree of parallelism.
1788 // D is maintained per-monitor in _SpinDuration and is initialized
1789 // optimistically.  Spin frequency is fixed at 100%.
1790 //
1791 // Note that _SpinDuration is volatile, but we update it without locks
1792 // or atomics.  The code is designed so that _SpinDuration stays within
1793 // a reasonable range even in the presence of races.  The arithmetic
1794 // operations on _SpinDuration are closed over the domain of legal values,
1795 // so at worst a race will install and older but still legal value.
1796 // At the very worst this introduces some apparent non-determinism.
1797 // We might spin when we shouldn't or vice-versa, but since the spin
1798 // count are relatively short, even in the worst case, the effect is harmless.
1799 //
1800 // Care must be taken that a low "D" value does not become an
1801 // an absorbing state.  Transient spinning failures -- when spinning
1802 // is overall profitable -- should not cause the system to converge
1803 // on low "D" values.  We want spinning to be stable and predictable
1804 // and fairly responsive to change and at the same time we don't want
1805 // it to oscillate, become metastable, be "too" non-deterministic,
1806 // or converge on or enter undesirable stable absorbing states.
1807 //
1808 // We implement a feedback-based control system -- using past behavior
1809 // to predict future behavior.  We face two issues: (a) if the
1810 // input signal is random then the spin predictor won't provide optimal
1811 // results, and (b) if the signal frequency is too high then the control
1812 // system, which has some natural response lag, will "chase" the signal.
1813 // (b) can arise from multimodal lock hold times.  Transient preemption
1814 // can also result in apparent bimodal lock hold times.
1815 // Although sub-optimal, neither condition is particularly harmful, as
1816 // in the worst-case we'll spin when we shouldn't or vice-versa.
1817 // The maximum spin duration is rather short so the failure modes aren't bad.
1818 // To be conservative, I've tuned the gain in system to bias toward
1819 // _not spinning.  Relatedly, the system can sometimes enter a mode where it
1820 // "rings" or oscillates between spinning and not spinning.  This happens
1821 // when spinning is just on the cusp of profitability, however, so the
1822 // situation is not dire.  The state is benign -- there's no need to add
1823 // hysteresis control to damp the transition rate between spinning and
1824 // not spinning.
1825 
1826 // Spinning: Fixed frequency (100%), vary duration
1827 int ObjectMonitor::TrySpin(JavaThread* current) {
1828   // Dumb, brutal spin.  Good for comparative measurements against adaptive spinning.
1829   int ctr = Knob_FixedSpin;
1830   if (ctr != 0) {
1831     while (--ctr >= 0) {
1832       if (TryLock(current) > 0) return 1;
1833       SpinPause();
1834     }
1835     return 0;
1836   }
1837 
1838   for (ctr = Knob_PreSpin + 1; --ctr >= 0;) {
1839     if (TryLock(current) > 0) {
1840       // Increase _SpinDuration ...
1841       // Note that we don't clamp SpinDuration precisely at SpinLimit.
1842       // Raising _SpurDuration to the poverty line is key.
1843       int x = _SpinDuration;
1844       if (x < Knob_SpinLimit) {
1845         if (x < Knob_Poverty) x = Knob_Poverty;
1846         _SpinDuration = x + Knob_BonusB;
1847       }
1848       return 1;
1849     }
1850     SpinPause();
1851   }
1852 
1853   // Admission control - verify preconditions for spinning
1854   //
1855   // We always spin a little bit, just to prevent _SpinDuration == 0 from
1856   // becoming an absorbing state.  Put another way, we spin briefly to
1857   // sample, just in case the system load, parallelism, contention, or lock
1858   // modality changed.
1859   //
1860   // Consider the following alternative:
1861   // Periodically set _SpinDuration = _SpinLimit and try a long/full
1862   // spin attempt.  "Periodically" might mean after a tally of
1863   // the # of failed spin attempts (or iterations) reaches some threshold.
1864   // This takes us into the realm of 1-out-of-N spinning, where we
1865   // hold the duration constant but vary the frequency.
1866 
1867   ctr = _SpinDuration;
1868   if (ctr <= 0) return 0;
1869 
1870   if (NotRunnable(current, (JavaThread*) owner_raw())) {
1871     return 0;
1872   }
1873 
1874   // We're good to spin ... spin ingress.
1875   // CONSIDER: use Prefetch::write() to avoid RTS->RTO upgrades
1876   // when preparing to LD...CAS _owner, etc and the CAS is likely
1877   // to succeed.
1878   if (_succ == NULL) {
1879     _succ = current;
1880   }
1881   Thread* prv = NULL;
1882 
1883   // There are three ways to exit the following loop:
1884   // 1.  A successful spin where this thread has acquired the lock.
1885   // 2.  Spin failure with prejudice
1886   // 3.  Spin failure without prejudice
1887 
1888   while (--ctr >= 0) {
1889 
1890     // Periodic polling -- Check for pending GC
1891     // Threads may spin while they're unsafe.
1892     // We don't want spinning threads to delay the JVM from reaching
1893     // a stop-the-world safepoint or to steal cycles from GC.
1894     // If we detect a pending safepoint we abort in order that
1895     // (a) this thread, if unsafe, doesn't delay the safepoint, and (b)
1896     // this thread, if safe, doesn't steal cycles from GC.
1897     // This is in keeping with the "no loitering in runtime" rule.
1898     // We periodically check to see if there's a safepoint pending.
1899     if ((ctr & 0xFF) == 0) {
1900       // Can't call SafepointMechanism::should_process() since that
1901       // might update the poll values and we could be in a thread_blocked
1902       // state here which is not allowed so just check the poll.
1903       if (SafepointMechanism::local_poll_armed(current)) {
1904         goto Abort;           // abrupt spin egress
1905       }
1906       SpinPause();
1907     }
1908 
1909     // Probe _owner with TATAS
1910     // If this thread observes the monitor transition or flicker
1911     // from locked to unlocked to locked, then the odds that this
1912     // thread will acquire the lock in this spin attempt go down
1913     // considerably.  The same argument applies if the CAS fails
1914     // or if we observe _owner change from one non-null value to
1915     // another non-null value.   In such cases we might abort
1916     // the spin without prejudice or apply a "penalty" to the
1917     // spin count-down variable "ctr", reducing it by 100, say.
1918 
1919     JavaThread* ox = (JavaThread*) owner_raw();
1920     if (ox == NULL) {
1921       ox = (JavaThread*)try_set_owner_from(NULL, current);
1922       if (ox == NULL) {
1923         // The CAS succeeded -- this thread acquired ownership
1924         // Take care of some bookkeeping to exit spin state.
1925         if (_succ == current) {
1926           _succ = NULL;
1927         }
1928 
1929         // Increase _SpinDuration :
1930         // The spin was successful (profitable) so we tend toward
1931         // longer spin attempts in the future.
1932         // CONSIDER: factor "ctr" into the _SpinDuration adjustment.
1933         // If we acquired the lock early in the spin cycle it
1934         // makes sense to increase _SpinDuration proportionally.
1935         // Note that we don't clamp SpinDuration precisely at SpinLimit.
1936         int x = _SpinDuration;
1937         if (x < Knob_SpinLimit) {
1938           if (x < Knob_Poverty) x = Knob_Poverty;
1939           _SpinDuration = x + Knob_Bonus;
1940         }
1941         return 1;
1942       }
1943 
1944       // The CAS failed ... we can take any of the following actions:
1945       // * penalize: ctr -= CASPenalty
1946       // * exit spin with prejudice -- goto Abort;
1947       // * exit spin without prejudice.
1948       // * Since CAS is high-latency, retry again immediately.
1949       prv = ox;
1950       goto Abort;
1951     }
1952 
1953     // Did lock ownership change hands ?
1954     if (ox != prv && prv != NULL) {
1955       goto Abort;
1956     }
1957     prv = ox;
1958 
1959     // Abort the spin if the owner is not executing.
1960     // The owner must be executing in order to drop the lock.
1961     // Spinning while the owner is OFFPROC is idiocy.
1962     // Consider: ctr -= RunnablePenalty ;
1963     if (NotRunnable(current, ox)) {
1964       goto Abort;
1965     }
1966     if (_succ == NULL) {
1967       _succ = current;
1968     }
1969   }
1970 
1971   // Spin failed with prejudice -- reduce _SpinDuration.
1972   // TODO: Use an AIMD-like policy to adjust _SpinDuration.
1973   // AIMD is globally stable.
1974   {
1975     int x = _SpinDuration;
1976     if (x > 0) {
1977       // Consider an AIMD scheme like: x -= (x >> 3) + 100
1978       // This is globally sample and tends to damp the response.
1979       x -= Knob_Penalty;
1980       if (x < 0) x = 0;
1981       _SpinDuration = x;
1982     }
1983   }
1984 
1985  Abort:
1986   if (_succ == current) {
1987     _succ = NULL;
1988     // Invariant: after setting succ=null a contending thread
1989     // must recheck-retry _owner before parking.  This usually happens
1990     // in the normal usage of TrySpin(), but it's safest
1991     // to make TrySpin() as foolproof as possible.
1992     OrderAccess::fence();
1993     if (TryLock(current) > 0) return 1;
1994   }
1995   return 0;
1996 }
1997 
1998 // NotRunnable() -- informed spinning
1999 //
2000 // Don't bother spinning if the owner is not eligible to drop the lock.
2001 // Spin only if the owner thread is _thread_in_Java or _thread_in_vm.
2002 // The thread must be runnable in order to drop the lock in timely fashion.
2003 // If the _owner is not runnable then spinning will not likely be
2004 // successful (profitable).
2005 //
2006 // Beware -- the thread referenced by _owner could have died
2007 // so a simply fetch from _owner->_thread_state might trap.
2008 // Instead, we use SafeFetchXX() to safely LD _owner->_thread_state.
2009 // Because of the lifecycle issues, the _thread_state values
2010 // observed by NotRunnable() might be garbage.  NotRunnable must
2011 // tolerate this and consider the observed _thread_state value
2012 // as advisory.
2013 //
2014 // Checking _thread_state isn't perfect.  Even if the thread is
2015 // in_java it might be blocked on a page-fault or have been preempted
2016 // and sitting on a ready/dispatch queue.
2017 //
2018 // The return value from NotRunnable() is *advisory* -- the
2019 // result is based on sampling and is not necessarily coherent.
2020 // The caller must tolerate false-negative and false-positive errors.
2021 // Spinning, in general, is probabilistic anyway.
2022 
2023 
2024 int ObjectMonitor::NotRunnable(JavaThread* current, JavaThread* ox) {
2025   // Check ox->TypeTag == 2BAD.
2026   if (ox == NULL) return 0;
2027 
2028   // Avoid transitive spinning ...
2029   // Say T1 spins or blocks trying to acquire L.  T1._Stalled is set to L.
2030   // Immediately after T1 acquires L it's possible that T2, also
2031   // spinning on L, will see L.Owner=T1 and T1._Stalled=L.
2032   // This occurs transiently after T1 acquired L but before
2033   // T1 managed to clear T1.Stalled.  T2 does not need to abort
2034   // its spin in this circumstance.
2035   intptr_t BlockedOn = SafeFetchN((intptr_t *) &ox->_Stalled, intptr_t(1));
2036 
2037   if (BlockedOn == 1) return 1;
2038   if (BlockedOn != 0) {
2039     return BlockedOn != intptr_t(this) && owner_raw() == ox;
2040   }
2041 
2042   assert(sizeof(ox->_thread_state == sizeof(int)), "invariant");
2043   int jst = SafeFetch32((int *) &ox->_thread_state, -1);;
2044   // consider also: jst != _thread_in_Java -- but that's overspecific.
2045   return jst == _thread_blocked || jst == _thread_in_native;
2046 }
2047 
2048 
2049 // -----------------------------------------------------------------------------
2050 // WaitSet management ...
2051 
2052 ObjectWaiter::ObjectWaiter(JavaThread* current) {
2053   _next     = NULL;
2054   _prev     = NULL;
2055   _notified = 0;
2056   _notifier_tid = 0;
2057   TState    = TS_RUN;
2058   _thread   = current;
2059   _event    = _thread->_ParkEvent;
2060   _active   = false;
2061   assert(_event != NULL, "invariant");
2062 }
2063 
2064 void ObjectWaiter::wait_reenter_begin(ObjectMonitor * const mon) {
2065   _active = JavaThreadBlockedOnMonitorEnterState::wait_reenter_begin(_thread, mon);
2066 }
2067 
2068 void ObjectWaiter::wait_reenter_end(ObjectMonitor * const mon) {
2069   JavaThreadBlockedOnMonitorEnterState::wait_reenter_end(_thread, _active);
2070 }
2071 
2072 inline void ObjectMonitor::AddWaiter(ObjectWaiter* node) {
2073   assert(node != NULL, "should not add NULL node");
2074   assert(node->_prev == NULL, "node already in list");
2075   assert(node->_next == NULL, "node already in list");
2076   // put node at end of queue (circular doubly linked list)
2077   if (_WaitSet == NULL) {
2078     _WaitSet = node;
2079     node->_prev = node;
2080     node->_next = node;
2081   } else {
2082     ObjectWaiter* head = _WaitSet;
2083     ObjectWaiter* tail = head->_prev;
2084     assert(tail->_next == head, "invariant check");
2085     tail->_next = node;
2086     head->_prev = node;
2087     node->_next = head;
2088     node->_prev = tail;
2089   }
2090 }
2091 
2092 inline ObjectWaiter* ObjectMonitor::DequeueWaiter() {
2093   // dequeue the very first waiter
2094   ObjectWaiter* waiter = _WaitSet;
2095   if (waiter) {
2096     DequeueSpecificWaiter(waiter);
2097   }
2098   return waiter;
2099 }
2100 
2101 inline void ObjectMonitor::DequeueSpecificWaiter(ObjectWaiter* node) {
2102   assert(node != NULL, "should not dequeue NULL node");
2103   assert(node->_prev != NULL, "node already removed from list");
2104   assert(node->_next != NULL, "node already removed from list");
2105   // when the waiter has woken up because of interrupt,
2106   // timeout or other spurious wake-up, dequeue the
2107   // waiter from waiting list
2108   ObjectWaiter* next = node->_next;
2109   if (next == node) {
2110     assert(node->_prev == node, "invariant check");
2111     _WaitSet = NULL;
2112   } else {
2113     ObjectWaiter* prev = node->_prev;
2114     assert(prev->_next == node, "invariant check");
2115     assert(next->_prev == node, "invariant check");
2116     next->_prev = prev;
2117     prev->_next = next;
2118     if (_WaitSet == node) {
2119       _WaitSet = next;
2120     }
2121   }
2122   node->_next = NULL;
2123   node->_prev = NULL;
2124 }
2125 
2126 // -----------------------------------------------------------------------------
2127 // PerfData support
2128 PerfCounter * ObjectMonitor::_sync_ContendedLockAttempts       = NULL;
2129 PerfCounter * ObjectMonitor::_sync_FutileWakeups               = NULL;
2130 PerfCounter * ObjectMonitor::_sync_Parks                       = NULL;
2131 PerfCounter * ObjectMonitor::_sync_Notifications               = NULL;
2132 PerfCounter * ObjectMonitor::_sync_Inflations                  = NULL;
2133 PerfCounter * ObjectMonitor::_sync_Deflations                  = NULL;
2134 PerfLongVariable * ObjectMonitor::_sync_MonExtant              = NULL;
2135 
2136 // One-shot global initialization for the sync subsystem.
2137 // We could also defer initialization and initialize on-demand
2138 // the first time we call ObjectSynchronizer::inflate().
2139 // Initialization would be protected - like so many things - by
2140 // the MonitorCache_lock.
2141 
2142 void ObjectMonitor::Initialize() {
2143   assert(!InitDone, "invariant");
2144 
2145   if (!os::is_MP()) {
2146     Knob_SpinLimit = 0;
2147     Knob_PreSpin   = 0;
2148     Knob_FixedSpin = -1;
2149   }
2150 
2151   if (UsePerfData) {
2152     EXCEPTION_MARK;
2153 #define NEWPERFCOUNTER(n)                                                \
2154   {                                                                      \
2155     n = PerfDataManager::create_counter(SUN_RT, #n, PerfData::U_Events,  \
2156                                         CHECK);                          \
2157   }
2158 #define NEWPERFVARIABLE(n)                                                \
2159   {                                                                       \
2160     n = PerfDataManager::create_variable(SUN_RT, #n, PerfData::U_Events,  \
2161                                          CHECK);                          \
2162   }
2163     NEWPERFCOUNTER(_sync_Inflations);
2164     NEWPERFCOUNTER(_sync_Deflations);
2165     NEWPERFCOUNTER(_sync_ContendedLockAttempts);
2166     NEWPERFCOUNTER(_sync_FutileWakeups);
2167     NEWPERFCOUNTER(_sync_Parks);
2168     NEWPERFCOUNTER(_sync_Notifications);
2169     NEWPERFVARIABLE(_sync_MonExtant);
2170 #undef NEWPERFCOUNTER
2171 #undef NEWPERFVARIABLE
2172   }
2173 
2174   _oop_storage = OopStorageSet::create_weak("ObjectSynchronizer Weak", mtSynchronizer);
2175 
2176   DEBUG_ONLY(InitDone = true;)
2177 }
2178 
2179 void ObjectMonitor::print_on(outputStream* st) const {
2180   // The minimal things to print for markWord printing, more can be added for debugging and logging.
2181   st->print("{contentions=0x%08x,waiters=0x%08x"
2182             ",recursions=" INTX_FORMAT ",owner=" INTPTR_FORMAT "}",
2183             contentions(), waiters(), recursions(),
2184             p2i(owner()));
2185 }
2186 void ObjectMonitor::print() const { print_on(tty); }
2187 
2188 #ifdef ASSERT
2189 // Print the ObjectMonitor like a debugger would:
2190 //
2191 // (ObjectMonitor) 0x00007fdfb6012e40 = {
2192 //   _header = 0x0000000000000001
2193 //   _object = 0x000000070ff45fd0
2194 //   _pad_buf0 = {
2195 //     [0] = '\0'
2196 //     ...
2197 //     [43] = '\0'
2198 //   }
2199 //   _owner = 0x0000000000000000
2200 //   _previous_owner_tid = 0
2201 //   _pad_buf1 = {
2202 //     [0] = '\0'
2203 //     ...
2204 //     [47] = '\0'
2205 //   }
2206 //   _next_om = 0x0000000000000000
2207 //   _recursions = 0
2208 //   _EntryList = 0x0000000000000000
2209 //   _cxq = 0x0000000000000000
2210 //   _succ = 0x0000000000000000
2211 //   _Responsible = 0x0000000000000000
2212 //   _Spinner = 0
2213 //   _SpinDuration = 5000
2214 //   _contentions = 0
2215 //   _WaitSet = 0x0000700009756248
2216 //   _waiters = 1
2217 //   _WaitSetLock = 0
2218 // }
2219 //
2220 void ObjectMonitor::print_debug_style_on(outputStream* st) const {
2221   st->print_cr("(ObjectMonitor*) " INTPTR_FORMAT " = {", p2i(this));
2222   st->print_cr("  _header = " INTPTR_FORMAT, header().value());
2223   st->print_cr("  _object = " INTPTR_FORMAT, p2i(object_peek()));
2224   st->print_cr("  _pad_buf0 = {");
2225   st->print_cr("    [0] = '\\0'");
2226   st->print_cr("    ...");
2227   st->print_cr("    [%d] = '\\0'", (int)sizeof(_pad_buf0) - 1);
2228   st->print_cr("  }");
2229   st->print_cr("  _owner = " INTPTR_FORMAT, p2i(owner_raw()));
2230   st->print_cr("  _previous_owner_tid = " UINT64_FORMAT, _previous_owner_tid);
2231   st->print_cr("  _pad_buf1 = {");
2232   st->print_cr("    [0] = '\\0'");
2233   st->print_cr("    ...");
2234   st->print_cr("    [%d] = '\\0'", (int)sizeof(_pad_buf1) - 1);
2235   st->print_cr("  }");
2236   st->print_cr("  _next_om = " INTPTR_FORMAT, p2i(next_om()));
2237   st->print_cr("  _recursions = " INTX_FORMAT, _recursions);
2238   st->print_cr("  _EntryList = " INTPTR_FORMAT, p2i(_EntryList));
2239   st->print_cr("  _cxq = " INTPTR_FORMAT, p2i(_cxq));
2240   st->print_cr("  _succ = " INTPTR_FORMAT, p2i(_succ));
2241   st->print_cr("  _Responsible = " INTPTR_FORMAT, p2i(_Responsible));
2242   st->print_cr("  _Spinner = %d", _Spinner);
2243   st->print_cr("  _SpinDuration = %d", _SpinDuration);
2244   st->print_cr("  _contentions = %d", contentions());
2245   st->print_cr("  _WaitSet = " INTPTR_FORMAT, p2i(_WaitSet));
2246   st->print_cr("  _waiters = %d", _waiters);
2247   st->print_cr("  _WaitSetLock = %d", _WaitSetLock);
2248   st->print_cr("}");
2249 }
2250 #endif