1 /*
   2  * Copyright (c) 1998, 2024, 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/globals.hpp"
  43 #include "runtime/handles.inline.hpp"
  44 #include "runtime/interfaceSupport.inline.hpp"
  45 #include "runtime/javaThread.inline.hpp"
  46 #include "runtime/mutexLocker.hpp"
  47 #include "runtime/objectMonitor.hpp"
  48 #include "runtime/objectMonitor.inline.hpp"
  49 #include "runtime/orderAccess.hpp"
  50 #include "runtime/osThread.hpp"
  51 #include "runtime/perfData.hpp"
  52 #include "runtime/safefetch.hpp"
  53 #include "runtime/safepointMechanism.inline.hpp"
  54 #include "runtime/sharedRuntime.hpp"

  55 #include "services/threadService.hpp"
  56 #include "utilities/dtrace.hpp"
  57 #include "utilities/globalDefinitions.hpp"
  58 #include "utilities/macros.hpp"
  59 #include "utilities/preserveException.hpp"
  60 #if INCLUDE_JFR
  61 #include "jfr/support/jfrFlush.hpp"
  62 #endif
  63 
  64 #ifdef DTRACE_ENABLED
  65 
  66 // Only bother with this argument setup if dtrace is available
  67 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
  68 
  69 
  70 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
  71   char* bytes = nullptr;                                                   \
  72   int len = 0;                                                             \
  73   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
  74   Symbol* klassname = obj->klass()->name();                                \
  75   if (klassname != nullptr) {                                              \
  76     bytes = (char*)klassname->bytes();                                     \
  77     len = klassname->utf8_length();                                        \
  78   }
  79 
  80 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
  81   {                                                                        \
  82     if (DTraceMonitorProbes) {                                             \
  83       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
  84       HOTSPOT_MONITOR_WAIT(jtid,                                           \
  85                            (monitor), bytes, len, (millis));               \
  86     }                                                                      \
  87   }
  88 
  89 #define HOTSPOT_MONITOR_contended__enter HOTSPOT_MONITOR_CONTENDED_ENTER
  90 #define HOTSPOT_MONITOR_contended__entered HOTSPOT_MONITOR_CONTENDED_ENTERED
  91 #define HOTSPOT_MONITOR_contended__exit HOTSPOT_MONITOR_CONTENDED_EXIT
  92 #define HOTSPOT_MONITOR_notify HOTSPOT_MONITOR_NOTIFY
  93 #define HOTSPOT_MONITOR_notifyAll HOTSPOT_MONITOR_NOTIFYALL
  94 
  95 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
  96   {                                                                        \
  97     if (DTraceMonitorProbes) {                                             \
  98       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
  99       HOTSPOT_MONITOR_##probe(jtid,                                        \
 100                               (uintptr_t)(monitor), bytes, len);           \
 101     }                                                                      \
 102   }
 103 
 104 #else //  ndef DTRACE_ENABLED
 105 
 106 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 107 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 108 
 109 #endif // ndef DTRACE_ENABLED
 110 
 111 // Tunables ...
 112 // The knob* variables are effectively final.  Once set they should
 113 // never be modified hence.  Consider using __read_mostly with GCC.
 114 
 115 int ObjectMonitor::Knob_SpinLimit    = 5000;    // derived by an external tool -
 116 
 117 static int Knob_Bonus               = 100;     // spin success bonus
 118 static int Knob_BonusB              = 100;     // spin success bonus
 119 static int Knob_Penalty             = 200;     // spin failure penalty
 120 static int Knob_Poverty             = 1000;
 121 static int Knob_FixedSpin           = 0;
 122 static int Knob_PreSpin             = 10;      // 20-100 likely better
 123 
 124 DEBUG_ONLY(static volatile bool InitDone = false;)
 125 
 126 OopStorage* ObjectMonitor::_oop_storage = nullptr;
 127 



 128 // -----------------------------------------------------------------------------
 129 // Theory of operations -- Monitors lists, thread residency, etc:
 130 //
 131 // * A thread acquires ownership of a monitor by successfully
 132 //   CAS()ing the _owner field from null to non-null.
 133 //
 134 // * Invariant: A thread appears on at most one monitor list --
 135 //   cxq, EntryList or WaitSet -- at any one time.
 136 //
 137 // * Contending threads "push" themselves onto the cxq with CAS
 138 //   and then spin/park.
 139 //
 140 // * After a contending thread eventually acquires the lock it must
 141 //   dequeue itself from either the EntryList or the cxq.
 142 //
 143 // * The exiting thread identifies and unparks an "heir presumptive"
 144 //   tentative successor thread on the EntryList.  Critically, the
 145 //   exiting thread doesn't unlink the successor thread from the EntryList.
 146 //   After having been unparked, the wakee will recontend for ownership of
 147 //   the monitor.   The successor (wakee) will either acquire the lock or
 148 //   re-park itself.
 149 //
 150 //   Succession is provided for by a policy of competitive handoff.
 151 //   The exiting thread does _not_ grant or pass ownership to the
 152 //   successor thread.  (This is also referred to as "handoff" succession").
 153 //   Instead the exiting thread releases ownership and possibly wakes
 154 //   a successor, so the successor can (re)compete for ownership of the lock.
 155 //   If the EntryList is empty but the cxq is populated the exiting
 156 //   thread will drain the cxq into the EntryList.  It does so by
 157 //   by detaching the cxq (installing null with CAS) and folding
 158 //   the threads from the cxq into the EntryList.  The EntryList is
 159 //   doubly linked, while the cxq is singly linked because of the
 160 //   CAS-based "push" used to enqueue recently arrived threads (RATs).
 161 //
 162 // * Concurrency invariants:
 163 //
 164 //   -- only the monitor owner may access or mutate the EntryList.
 165 //      The mutex property of the monitor itself protects the EntryList
 166 //      from concurrent interference.
 167 //   -- Only the monitor owner may detach the cxq.
 168 //
 169 // * The monitor entry list operations avoid locks, but strictly speaking
 170 //   they're not lock-free.  Enter is lock-free, exit is not.
 171 //   For a description of 'Methods and apparatus providing non-blocking access
 172 //   to a resource,' see U.S. Pat. No. 7844973.
 173 //
 174 // * The cxq can have multiple concurrent "pushers" but only one concurrent
 175 //   detaching thread.  This mechanism is immune from the ABA corruption.
 176 //   More precisely, the CAS-based "push" onto cxq is ABA-oblivious.
 177 //
 178 // * Taken together, the cxq and the EntryList constitute or form a
 179 //   single logical queue of threads stalled trying to acquire the lock.
 180 //   We use two distinct lists to improve the odds of a constant-time
 181 //   dequeue operation after acquisition (in the ::enter() epilogue) and
 182 //   to reduce heat on the list ends.  (c.f. Michael Scott's "2Q" algorithm).
 183 //   A key desideratum is to minimize queue & monitor metadata manipulation
 184 //   that occurs while holding the monitor lock -- that is, we want to
 185 //   minimize monitor lock holds times.  Note that even a small amount of
 186 //   fixed spinning will greatly reduce the # of enqueue-dequeue operations
 187 //   on EntryList|cxq.  That is, spinning relieves contention on the "inner"
 188 //   locks and monitor metadata.
 189 //
 190 //   Cxq points to the set of Recently Arrived Threads attempting entry.
 191 //   Because we push threads onto _cxq with CAS, the RATs must take the form of
 192 //   a singly-linked LIFO.  We drain _cxq into EntryList  at unlock-time when
 193 //   the unlocking thread notices that EntryList is null but _cxq is != null.
 194 //
 195 //   The EntryList is ordered by the prevailing queue discipline and
 196 //   can be organized in any convenient fashion, such as a doubly-linked list or
 197 //   a circular doubly-linked list.  Critically, we want insert and delete operations
 198 //   to operate in constant-time.  If we need a priority queue then something akin
 199 //   to Solaris' sleepq would work nicely.  Viz.,
 200 //   http://agg.eng/ws/on10_nightly/source/usr/src/uts/common/os/sleepq.c.
 201 //   Queue discipline is enforced at ::exit() time, when the unlocking thread
 202 //   drains the cxq into the EntryList, and orders or reorders the threads on the
 203 //   EntryList accordingly.
 204 //
 205 //   Barring "lock barging", this mechanism provides fair cyclic ordering,
 206 //   somewhat similar to an elevator-scan.
 207 //
 208 // * The monitor synchronization subsystem avoids the use of native
 209 //   synchronization primitives except for the narrow platform-specific
 210 //   park-unpark abstraction.  See the comments in os_solaris.cpp regarding
 211 //   the semantics of park-unpark.  Put another way, this monitor implementation
 212 //   depends only on atomic operations and park-unpark.  The monitor subsystem
 213 //   manages all RUNNING->BLOCKED and BLOCKED->READY transitions while the
 214 //   underlying OS manages the READY<->RUN transitions.
 215 //
 216 // * Waiting threads reside on the WaitSet list -- wait() puts
 217 //   the caller onto the WaitSet.
 218 //
 219 // * notify() or notifyAll() simply transfers threads from the WaitSet to
 220 //   either the EntryList or cxq.  Subsequent exit() operations will
 221 //   unpark the notifyee.  Unparking a notifee in notify() is inefficient -
 222 //   it's likely the notifyee would simply impale itself on the lock held
 223 //   by the notifier.
 224 //
 225 // * An interesting alternative is to encode cxq as (List,LockByte) where
 226 //   the LockByte is 0 iff the monitor is owned.  _owner is simply an auxiliary
 227 //   variable, like _recursions, in the scheme.  The threads or Events that form
 228 //   the list would have to be aligned in 256-byte addresses.  A thread would
 229 //   try to acquire the lock or enqueue itself with CAS, but exiting threads
 230 //   could use a 1-0 protocol and simply STB to set the LockByte to 0.
 231 //   Note that is is *not* word-tearing, but it does presume that full-word
 232 //   CAS operations are coherent with intermix with STB operations.  That's true
 233 //   on most common processors.
 234 //
 235 // * See also http://blogs.sun.com/dave
 236 
 237 
 238 // Check that object() and set_object() are called from the right context:
 239 static void check_object_context() {
 240 #ifdef ASSERT
 241   Thread* self = Thread::current();
 242   if (self->is_Java_thread()) {
 243     // Mostly called from JavaThreads so sanity check the thread state.
 244     JavaThread* jt = JavaThread::cast(self);
 245     switch (jt->thread_state()) {
 246     case _thread_in_vm:    // the usual case
 247     case _thread_in_Java:  // during deopt
 248       break;
 249     default:
 250       fatal("called from an unsafe thread state");
 251     }
 252     assert(jt->is_active_Java_thread(), "must be active JavaThread");
 253   } else {
 254     // However, ThreadService::get_current_contended_monitor()
 255     // can call here via the VMThread so sanity check it.
 256     assert(self->is_VM_thread(), "must be");
 257   }
 258 #endif // ASSERT
 259 }
 260 
 261 ObjectMonitor::ObjectMonitor(oop object) :
 262   _header(markWord::zero()),
 263   _object(_oop_storage, object),
 264   _owner(nullptr),

 265   _previous_owner_tid(0),
 266   _next_om(nullptr),
 267   _recursions(0),
 268   _EntryList(nullptr),
 269   _cxq(nullptr),
 270   _succ(nullptr),
 271   _Responsible(nullptr),
 272   _SpinDuration(ObjectMonitor::Knob_SpinLimit),
 273   _contentions(0),
 274   _WaitSet(nullptr),
 275   _waiters(0),
 276   _WaitSetLock(0)
 277 { }
 278 
 279 ObjectMonitor::~ObjectMonitor() {
 280   _object.release(_oop_storage);
 281 }
 282 
 283 oop ObjectMonitor::object() const {
 284   check_object_context();
 285   return _object.resolve();
 286 }
 287 
 288 oop ObjectMonitor::object_peek() const {
 289   return _object.peek();
 290 }
 291 
 292 void ObjectMonitor::ExitOnSuspend::operator()(JavaThread* current) {
 293   if (current->is_suspended()) {
 294     _om->_recursions = 0;
 295     _om->_succ = nullptr;
 296     // Don't need a full fence after clearing successor here because of the call to exit().
 297     _om->exit(current, false /* not_suspended */);
 298     _om_exited = true;
 299 
 300     current->set_current_pending_monitor(_om);
 301   }
 302 }
 303 
 304 void ObjectMonitor::ClearSuccOnSuspend::operator()(JavaThread* current) {
 305   if (current->is_suspended()) {
 306     if (_om->_succ == current) {
 307       _om->_succ = nullptr;
 308       OrderAccess::fence(); // always do a full fence when successor is cleared
 309     }
 310   }
 311 }
 312 
 313 // -----------------------------------------------------------------------------
 314 // Enter support
 315 
 316 bool ObjectMonitor::enter_for(JavaThread* locking_thread) {
 317   // Used by ObjectSynchronizer::enter_for to enter for another thread.
 318   // The monitor is private to or already owned by locking_thread which must be suspended.
 319   // So this code may only contend with deflation.
 320   assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
 321 
 322   // Block out deflation as soon as possible.
 323   add_to_contentions(1);
 324 
 325   bool success = false;
 326   if (!is_being_async_deflated()) {
 327     void* prev_owner = try_set_owner_from(nullptr, locking_thread);
 328 
 329     if (prev_owner == nullptr) {
 330       assert(_recursions == 0, "invariant");
 331       success = true;
 332     } else if (prev_owner == locking_thread) {
 333       _recursions++;
 334       success = true;
 335     } else if (prev_owner == DEFLATER_MARKER) {
 336       // Racing with deflation.
 337       prev_owner = try_set_owner_from(DEFLATER_MARKER, locking_thread);
 338       if (prev_owner == DEFLATER_MARKER) {
 339         // Cancelled deflation. Increment contentions as part of the deflation protocol.
 340         add_to_contentions(1);
 341         success = true;
 342       } else if (prev_owner == nullptr) {
 343         // At this point we cannot race with deflation as we have both incremented
 344         // contentions, seen contention > 0 and seen a DEFLATER_MARKER.
 345         // success will only be false if this races with something other than
 346         // deflation.
 347         prev_owner = try_set_owner_from(nullptr, locking_thread);
 348         success = prev_owner == nullptr;
 349       }
 350     } else if (LockingMode == LM_LEGACY && locking_thread->is_lock_owned((address)prev_owner)) {
 351       assert(_recursions == 0, "must be");
 352       _recursions = 1;
 353       set_owner_from_BasicLock(prev_owner, locking_thread);
 354       success = true;
 355     }
 356     assert(success, "Failed to enter_for: locking_thread=" INTPTR_FORMAT
 357            ", this=" INTPTR_FORMAT "{owner=" INTPTR_FORMAT "}, observed owner: " INTPTR_FORMAT,
 358            p2i(locking_thread), p2i(this), p2i(owner_raw()), p2i(prev_owner));
 359   } else {
 360     // Async deflation is in progress and our contentions increment
 361     // above lost the race to async deflation. Undo the work and
 362     // force the caller to retry.
 363     const oop l_object = object();
 364     if (l_object != nullptr) {
 365       // Attempt to restore the header/dmw to the object's header so that
 366       // we only retry once if the deflater thread happens to be slow.
 367       install_displaced_markword_in_object(l_object);
 368     }
 369   }
 370 
 371   add_to_contentions(-1);
 372 
 373   assert(!success || owner_raw() == locking_thread, "must be");
 374 
 375   return success;
 376 }
 377 
 378 bool ObjectMonitor::enter(JavaThread* current) {
 379   assert(current == JavaThread::current(), "must be");
 380   // The following code is ordered to check the most common cases first
 381   // and to reduce RTS->RTO cache line upgrades on SPARC and IA32 processors.
 382 
 383   void* cur = try_set_owner_from(nullptr, current);
 384   if (cur == nullptr) {
 385     assert(_recursions == 0, "invariant");
 386     return true;
 387   }
 388 
 389   if (cur == current) {
 390     // TODO-FIXME: check for integer overflow!  BUGID 6557169.
 391     _recursions++;
 392     return true;
 393   }
 394 
 395   if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) {
 396     assert(_recursions == 0, "internal state error");
 397     _recursions = 1;
 398     set_owner_from_BasicLock(cur, current);  // Convert from BasicLock* to Thread*.
 399     return true;
 400   }
 401 
 402   // We've encountered genuine contention.
 403 
 404   // Try one round of spinning *before* enqueueing current
 405   // and before going through the awkward and expensive state
 406   // transitions.  The following spin is strictly optional ...
 407   // Note that if we acquire the monitor from an initial spin
 408   // we forgo posting JVMTI events and firing DTRACE probes.
 409   if (TrySpin(current) > 0) {
 410     assert(owner_raw() == current, "must be current: owner=" INTPTR_FORMAT, p2i(owner_raw()));
 411     assert(_recursions == 0, "must be 0: recursions=" INTX_FORMAT, _recursions);
 412     assert(object()->mark() == markWord::encode(this),
 413            "object mark must match encoded this: mark=" INTPTR_FORMAT
 414            ", encoded this=" INTPTR_FORMAT, object()->mark().value(),
 415            markWord::encode(this).value());
 416     return true;
 417   }
 418 
 419   assert(owner_raw() != current, "invariant");
 420   assert(_succ != current, "invariant");
 421   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
 422   assert(current->thread_state() != _thread_blocked, "invariant");
 423 
 424   // Keep track of contention for JVM/TI and M&M queries.
 425   add_to_contentions(1);
 426   if (is_being_async_deflated()) {
 427     // Async deflation is in progress and our contentions increment
 428     // above lost the race to async deflation. Undo the work and
 429     // force the caller to retry.
 430     const oop l_object = object();
 431     if (l_object != nullptr) {
 432       // Attempt to restore the header/dmw to the object's header so that
 433       // we only retry once if the deflater thread happens to be slow.
 434       install_displaced_markword_in_object(l_object);
 435     }
 436     add_to_contentions(-1);
 437     return false;
 438   }
 439 
 440   JFR_ONLY(JfrConditionalFlush<EventJavaMonitorEnter> flush(current);)
 441   EventJavaMonitorEnter event;
 442   if (event.is_started()) {
 443     event.set_monitorClass(object()->klass());
 444     // Set an address that is 'unique enough', such that events close in
 445     // time and with the same address are likely (but not guaranteed) to
 446     // belong to the same object.
 447     event.set_address((uintptr_t)this);
 448   }
 449 
 450   { // Change java thread status to indicate blocked on monitor enter.
 451     JavaThreadBlockedOnMonitorEnterState jtbmes(current, this);
 452 
 453     assert(current->current_pending_monitor() == nullptr, "invariant");
 454     current->set_current_pending_monitor(this);
 455 
 456     DTRACE_MONITOR_PROBE(contended__enter, this, object(), current);
 457     if (JvmtiExport::should_post_monitor_contended_enter()) {
 458       JvmtiExport::post_monitor_contended_enter(current, this);
 459 
 460       // The current thread does not yet own the monitor and does not
 461       // yet appear on any queues that would get it made the successor.
 462       // This means that the JVMTI_EVENT_MONITOR_CONTENDED_ENTER event
 463       // handler cannot accidentally consume an unpark() meant for the
 464       // ParkEvent associated with this ObjectMonitor.
 465     }
 466 




















 467     OSThreadContendState osts(current->osthread());
 468 
 469     assert(current->thread_state() == _thread_in_vm, "invariant");
 470 
 471     for (;;) {
 472       ExitOnSuspend eos(this);
 473       {
 474         ThreadBlockInVMPreprocess<ExitOnSuspend> tbivs(current, eos, true /* allow_suspend */);
 475         EnterI(current);
 476         current->set_current_pending_monitor(nullptr);
 477         // We can go to a safepoint at the end of this block. If we
 478         // do a thread dump during that safepoint, then this thread will show
 479         // as having "-locked" the monitor, but the OS and java.lang.Thread
 480         // states will still report that the thread is blocked trying to
 481         // acquire it.
 482         // If there is a suspend request, ExitOnSuspend will exit the OM
 483         // and set the OM as pending.
 484       }
 485       if (!eos.exited()) {
 486         // ExitOnSuspend did not exit the OM
 487         assert(owner_raw() == current, "invariant");
 488         break;
 489       }
 490     }
 491 
 492     // We've just gotten past the enter-check-for-suspend dance and we now own
 493     // the monitor free and clear.
 494   }
 495 
 496   add_to_contentions(-1);
 497   assert(contentions() >= 0, "must not be negative: contentions=%d", contentions());
 498 
 499   // Must either set _recursions = 0 or ASSERT _recursions == 0.
 500   assert(_recursions == 0, "invariant");
 501   assert(owner_raw() == current, "invariant");
 502   assert(_succ != current, "invariant");
 503   assert(object()->mark() == markWord::encode(this), "invariant");
 504 
 505   // The thread -- now the owner -- is back in vm mode.
 506   // Report the glorious news via TI,DTrace and jvmstat.
 507   // The probe effect is non-trivial.  All the reportage occurs
 508   // while we hold the monitor, increasing the length of the critical
 509   // section.  Amdahl's parallel speedup law comes vividly into play.
 510   //
 511   // Another option might be to aggregate the events (thread local or
 512   // per-monitor aggregation) and defer reporting until a more opportune
 513   // time -- such as next time some thread encounters contention but has
 514   // yet to acquire the lock.  While spinning that thread could
 515   // spinning we could increment JVMStat counters, etc.
 516 
 517   DTRACE_MONITOR_PROBE(contended__entered, this, object(), current);
 518   if (JvmtiExport::should_post_monitor_contended_entered()) {
 519     JvmtiExport::post_monitor_contended_entered(current, this);
 520 
 521     // The current thread already owns the monitor and is not going to
 522     // call park() for the remainder of the monitor enter protocol. So
 523     // it doesn't matter if the JVMTI_EVENT_MONITOR_CONTENDED_ENTERED
 524     // event handler consumed an unpark() issued by the thread that
 525     // just exited the monitor.
 526   }
 527   if (event.should_commit()) {
 528     event.set_previousOwner(_previous_owner_tid);
 529     event.commit();
 530   }
 531   OM_PERFDATA_OP(ContendedLockAttempts, inc());
 532   return true;
 533 }
 534 
 535 // Caveat: TryLock() is not necessarily serializing if it returns failure.
 536 // Callers must compensate as needed.
 537 
 538 int ObjectMonitor::TryLock(JavaThread* current) {
 539   void* own = owner_raw();
 540   if (own != nullptr) return 0;
 541   if (try_set_owner_from(nullptr, current) == nullptr) {
 542     assert(_recursions == 0, "invariant");
 543     return 1;
 544   }
 545   // The lock had been free momentarily, but we lost the race to the lock.
 546   // Interference -- the CAS failed.
 547   // We can either return -1 or retry.
 548   // Retry doesn't make as much sense because the lock was just acquired.
 549   return -1;
 550 }
 551 
 552 // Deflate the specified ObjectMonitor if not in-use. Returns true if it
 553 // was deflated and false otherwise.
 554 //
 555 // The async deflation protocol sets owner to DEFLATER_MARKER and
 556 // makes contentions negative as signals to contending threads that
 557 // an async deflation is in progress. There are a number of checks
 558 // as part of the protocol to make sure that the calling thread has
 559 // not lost the race to a contending thread.
 560 //
 561 // The ObjectMonitor has been successfully async deflated when:
 562 //   (contentions < 0)
 563 // Contending threads that see that condition know to retry their operation.
 564 //
 565 bool ObjectMonitor::deflate_monitor() {
 566   if (is_busy()) {
 567     // Easy checks are first - the ObjectMonitor is busy so no deflation.
 568     return false;
 569   }
 570 
 571   const oop obj = object_peek();
 572 
 573   if (obj == nullptr) {
 574     // If the object died, we can recycle the monitor without racing with
 575     // Java threads. The GC already broke the association with the object.
 576     set_owner_from(nullptr, DEFLATER_MARKER);
 577     assert(contentions() >= 0, "must be non-negative: contentions=%d", contentions());
 578     _contentions = INT_MIN; // minimum negative int
 579   } else {
 580     // Attempt async deflation protocol.
 581 
 582     // Set a null owner to DEFLATER_MARKER to force any contending thread
 583     // through the slow path. This is just the first part of the async
 584     // deflation dance.
 585     if (try_set_owner_from(nullptr, DEFLATER_MARKER) != nullptr) {
 586       // The owner field is no longer null so we lost the race since the
 587       // ObjectMonitor is now busy.
 588       return false;
 589     }
 590 
 591     if (contentions() > 0 || _waiters != 0) {
 592       // Another thread has raced to enter the ObjectMonitor after
 593       // is_busy() above or has already entered and waited on
 594       // it which makes it busy so no deflation. Restore owner to
 595       // null if it is still DEFLATER_MARKER.
 596       if (try_set_owner_from(DEFLATER_MARKER, nullptr) != DEFLATER_MARKER) {
 597         // Deferred decrement for the JT EnterI() that cancelled the async deflation.
 598         add_to_contentions(-1);
 599       }
 600       return false;
 601     }
 602 
 603     // Make a zero contentions field negative to force any contending threads
 604     // to retry. This is the second part of the async deflation dance.
 605     if (Atomic::cmpxchg(&_contentions, 0, INT_MIN) != 0) {
 606       // Contentions was no longer 0 so we lost the race since the
 607       // ObjectMonitor is now busy. Restore owner to null if it is
 608       // still DEFLATER_MARKER:
 609       if (try_set_owner_from(DEFLATER_MARKER, nullptr) != DEFLATER_MARKER) {
 610         // Deferred decrement for the JT EnterI() that cancelled the async deflation.
 611         add_to_contentions(-1);
 612       }
 613       return false;
 614     }
 615   }
 616 
 617   // Sanity checks for the races:
 618   guarantee(owner_is_DEFLATER_MARKER(), "must be deflater marker");
 619   guarantee(contentions() < 0, "must be negative: contentions=%d",
 620             contentions());
 621   guarantee(_waiters == 0, "must be 0: waiters=%d", _waiters);
 622   guarantee(_cxq == nullptr, "must be no contending threads: cxq="
 623             INTPTR_FORMAT, p2i(_cxq));
 624   guarantee(_EntryList == nullptr,
 625             "must be no entering threads: EntryList=" INTPTR_FORMAT,
 626             p2i(_EntryList));
 627 
 628   if (obj != nullptr) {
 629     if (log_is_enabled(Trace, monitorinflation)) {
 630       ResourceMark rm;
 631       log_trace(monitorinflation)("deflate_monitor: object=" INTPTR_FORMAT
 632                                   ", mark=" INTPTR_FORMAT ", type='%s'",
 633                                   p2i(obj), obj->mark().value(),
 634                                   obj->klass()->external_name());
 635     }
 636 
 637     // Install the old mark word if nobody else has already done it.
 638     install_displaced_markword_in_object(obj);
 639   }
 640 
 641   // We leave owner == DEFLATER_MARKER and contentions < 0
 642   // to force any racing threads to retry.
 643   return true;  // Success, ObjectMonitor has been deflated.
 644 }
 645 
 646 // Install the displaced mark word (dmw) of a deflating ObjectMonitor
 647 // into the header of the object associated with the monitor. This
 648 // idempotent method is called by a thread that is deflating a
 649 // monitor and by other threads that have detected a race with the
 650 // deflation process.
 651 void ObjectMonitor::install_displaced_markword_in_object(const oop obj) {
 652   // This function must only be called when (owner == DEFLATER_MARKER
 653   // && contentions <= 0), but we can't guarantee that here because
 654   // those values could change when the ObjectMonitor gets moved from
 655   // the global free list to a per-thread free list.
 656 
 657   guarantee(obj != nullptr, "must be non-null");
 658 
 659   // Separate loads in is_being_async_deflated(), which is almost always
 660   // called before this function, from the load of dmw/header below.
 661 
 662   // _contentions and dmw/header may get written by different threads.
 663   // Make sure to observe them in the same order when having several observers.
 664   OrderAccess::loadload_for_IRIW();
 665 
 666   const oop l_object = object_peek();
 667   if (l_object == nullptr) {
 668     // ObjectMonitor's object ref has already been cleared by async
 669     // deflation or GC so we're done here.
 670     return;
 671   }
 672   assert(l_object == obj, "object=" INTPTR_FORMAT " must equal obj="
 673          INTPTR_FORMAT, p2i(l_object), p2i(obj));
 674 
 675   markWord dmw = header();
 676   // The dmw has to be neutral (not null, not locked and not marked).
 677   assert(dmw.is_neutral(), "must be neutral: dmw=" INTPTR_FORMAT, dmw.value());
 678 
 679   // Install displaced mark word if the object's header still points
 680   // to this ObjectMonitor. More than one racing caller to this function
 681   // can rarely reach this point, but only one can win.
 682   markWord res = obj->cas_set_mark(dmw, markWord::encode(this));
 683   if (res != markWord::encode(this)) {
 684     // This should be rare so log at the Info level when it happens.
 685     log_info(monitorinflation)("install_displaced_markword_in_object: "
 686                                "failed cas_set_mark: new_mark=" INTPTR_FORMAT
 687                                ", old_mark=" INTPTR_FORMAT ", res=" INTPTR_FORMAT,
 688                                dmw.value(), markWord::encode(this).value(),
 689                                res.value());
 690   }
 691 
 692   // Note: It does not matter which thread restored the header/dmw
 693   // into the object's header. The thread deflating the monitor just
 694   // wanted the object's header restored and it is. The threads that
 695   // detected a race with the deflation process also wanted the
 696   // object's header restored before they retry their operation and
 697   // because it is restored they will only retry once.
 698 }
 699 
 700 // Convert the fields used by is_busy() to a string that can be
 701 // used for diagnostic output.
 702 const char* ObjectMonitor::is_busy_to_string(stringStream* ss) {
 703   ss->print("is_busy: waiters=%d"
 704             ", contentions=%d"
 705             ", owner=" PTR_FORMAT
 706             ", cxq=" PTR_FORMAT
 707             ", EntryList=" PTR_FORMAT,
 708             _waiters,
 709             (contentions() > 0 ? contentions() : 0),
 710             owner_is_DEFLATER_MARKER()
 711                 // We report null instead of DEFLATER_MARKER here because is_busy()
 712                 // ignores DEFLATER_MARKER values.
 713                 ? p2i(nullptr)
 714                 : p2i(owner_raw()),
 715             p2i(_cxq),
 716             p2i(_EntryList));
 717   return ss->base();
 718 }
 719 
 720 #define MAX_RECHECK_INTERVAL 1000
 721 
 722 void ObjectMonitor::EnterI(JavaThread* current) {
 723   assert(current->thread_state() == _thread_blocked, "invariant");
 724 
 725   // Try the lock - TATAS
 726   if (TryLock (current) > 0) {
 727     assert(_succ != current, "invariant");
 728     assert(owner_raw() == current, "invariant");
 729     assert(_Responsible != current, "invariant");
 730     return;
 731   }
 732 
 733   if (try_set_owner_from(DEFLATER_MARKER, current) == DEFLATER_MARKER) {
 734     // Cancelled the in-progress async deflation by changing owner from
 735     // DEFLATER_MARKER to current. As part of the contended enter protocol,
 736     // contentions was incremented to a positive value before EnterI()
 737     // was called and that prevents the deflater thread from winning the
 738     // last part of the 2-part async deflation protocol. After EnterI()
 739     // returns to enter(), contentions is decremented because the caller
 740     // now owns the monitor. We bump contentions an extra time here to
 741     // prevent the deflater thread from winning the last part of the
 742     // 2-part async deflation protocol after the regular decrement
 743     // occurs in enter(). The deflater thread will decrement contentions
 744     // after it recognizes that the async deflation was cancelled.
 745     add_to_contentions(1);
 746     assert(_succ != current, "invariant");
 747     assert(_Responsible != current, "invariant");
 748     return;
 749   }
 750 
 751   assert(InitDone, "Unexpectedly not initialized");
 752 
 753   // We try one round of spinning *before* enqueueing current.
 754   //
 755   // If the _owner is ready but OFFPROC we could use a YieldTo()
 756   // operation to donate the remainder of this thread's quantum
 757   // to the owner.  This has subtle but beneficial affinity
 758   // effects.
 759 
 760   if (TrySpin(current) > 0) {
 761     assert(owner_raw() == current, "invariant");
 762     assert(_succ != current, "invariant");
 763     assert(_Responsible != current, "invariant");
 764     return;
 765   }
 766 
 767   // The Spin failed -- Enqueue and park the thread ...
 768   assert(_succ != current, "invariant");
 769   assert(owner_raw() != current, "invariant");
 770   assert(_Responsible != current, "invariant");
 771 
 772   // Enqueue "current" on ObjectMonitor's _cxq.
 773   //
 774   // Node acts as a proxy for current.
 775   // As an aside, if were to ever rewrite the synchronization code mostly
 776   // in Java, WaitNodes, ObjectMonitors, and Events would become 1st-class
 777   // Java objects.  This would avoid awkward lifecycle and liveness issues,
 778   // as well as eliminate a subset of ABA issues.
 779   // TODO: eliminate ObjectWaiter and enqueue either Threads or Events.
 780 
 781   ObjectWaiter node(current);
 782   current->_ParkEvent->reset();
 783   node._prev   = (ObjectWaiter*) 0xBAD;
 784   node.TState  = ObjectWaiter::TS_CXQ;
 785 
 786   // Push "current" onto the front of the _cxq.
 787   // Once on cxq/EntryList, current stays on-queue until it acquires the lock.
 788   // Note that spinning tends to reduce the rate at which threads
 789   // enqueue and dequeue on EntryList|cxq.
 790   ObjectWaiter* nxt;
 791   for (;;) {
 792     node._next = nxt = _cxq;
 793     if (Atomic::cmpxchg(&_cxq, nxt, &node) == nxt) break;
 794 
 795     // Interference - the CAS failed because _cxq changed.  Just retry.
 796     // As an optional optimization we retry the lock.
 797     if (TryLock (current) > 0) {
 798       assert(_succ != current, "invariant");
 799       assert(owner_raw() == current, "invariant");
 800       assert(_Responsible != current, "invariant");
 801       return;
 802     }
 803   }
 804 
 805   // Check for cxq|EntryList edge transition to non-null.  This indicates
 806   // the onset of contention.  While contention persists exiting threads
 807   // will use a ST:MEMBAR:LD 1-1 exit protocol.  When contention abates exit
 808   // operations revert to the faster 1-0 mode.  This enter operation may interleave
 809   // (race) a concurrent 1-0 exit operation, resulting in stranding, so we
 810   // arrange for one of the contending thread to use a timed park() operations
 811   // to detect and recover from the race.  (Stranding is form of progress failure
 812   // where the monitor is unlocked but all the contending threads remain parked).
 813   // That is, at least one of the contended threads will periodically poll _owner.
 814   // One of the contending threads will become the designated "Responsible" thread.
 815   // The Responsible thread uses a timed park instead of a normal indefinite park
 816   // operation -- it periodically wakes and checks for and recovers from potential
 817   // strandings admitted by 1-0 exit operations.   We need at most one Responsible
 818   // thread per-monitor at any given moment.  Only threads on cxq|EntryList may
 819   // be responsible for a monitor.
 820   //
 821   // Currently, one of the contended threads takes on the added role of "Responsible".
 822   // A viable alternative would be to use a dedicated "stranding checker" thread
 823   // that periodically iterated over all the threads (or active monitors) and unparked
 824   // successors where there was risk of stranding.  This would help eliminate the
 825   // timer scalability issues we see on some platforms as we'd only have one thread
 826   // -- the checker -- parked on a timer.
 827 
 828   if (nxt == nullptr && _EntryList == nullptr) {
 829     // Try to assume the role of responsible thread for the monitor.
 830     // CONSIDER:  ST vs CAS vs { if (Responsible==null) Responsible=current }
 831     Atomic::replace_if_null(&_Responsible, current);
 832   }
 833 
 834   // The lock might have been released while this thread was occupied queueing
 835   // itself onto _cxq.  To close the race and avoid "stranding" and
 836   // progress-liveness failure we must resample-retry _owner before parking.
 837   // Note the Dekker/Lamport duality: ST cxq; MEMBAR; LD Owner.
 838   // In this case the ST-MEMBAR is accomplished with CAS().
 839   //
 840   // TODO: Defer all thread state transitions until park-time.
 841   // Since state transitions are heavy and inefficient we'd like
 842   // to defer the state transitions until absolutely necessary,
 843   // and in doing so avoid some transitions ...
 844 
 845   int nWakeups = 0;
 846   int recheckInterval = 1;






 847 
 848   for (;;) {
 849 
 850     if (TryLock(current) > 0) break;
 851     assert(owner_raw() != current, "invariant");
 852 
 853     // park self
 854     if (_Responsible == current) {
 855       current->_ParkEvent->park((jlong) recheckInterval);
 856       // Increase the recheckInterval, but clamp the value.
 857       recheckInterval *= 8;
 858       if (recheckInterval > MAX_RECHECK_INTERVAL) {
 859         recheckInterval = MAX_RECHECK_INTERVAL;
 860       }
 861     } else {
 862       current->_ParkEvent->park();
 863     }
 864 
 865     if (TryLock(current) > 0) break;
 866 
 867     if (try_set_owner_from(DEFLATER_MARKER, current) == DEFLATER_MARKER) {
 868       // Cancelled the in-progress async deflation by changing owner from
 869       // DEFLATER_MARKER to current. As part of the contended enter protocol,
 870       // contentions was incremented to a positive value before EnterI()
 871       // was called and that prevents the deflater thread from winning the
 872       // last part of the 2-part async deflation protocol. After EnterI()
 873       // returns to enter(), contentions is decremented because the caller
 874       // now owns the monitor. We bump contentions an extra time here to
 875       // prevent the deflater thread from winning the last part of the
 876       // 2-part async deflation protocol after the regular decrement
 877       // occurs in enter(). The deflater thread will decrement contentions
 878       // after it recognizes that the async deflation was cancelled.
 879       add_to_contentions(1);
 880       break;
 881     }
 882 
 883     // The lock is still contested.
 884     // Keep a tally of the # of futile wakeups.
 885     // Note that the counter is not protected by a lock or updated by atomics.
 886     // That is by design - we trade "lossy" counters which are exposed to
 887     // races during updates for a lower probe effect.
 888 
 889     // This PerfData object can be used in parallel with a safepoint.
 890     // See the work around in PerfDataManager::destroy().
 891     OM_PERFDATA_OP(FutileWakeups, inc());
 892     ++nWakeups;
 893 
 894     // Assuming this is not a spurious wakeup we'll normally find _succ == current.
 895     // We can defer clearing _succ until after the spin completes
 896     // TrySpin() must tolerate being called with _succ == current.
 897     // Try yet another round of adaptive spinning.
 898     if (TrySpin(current) > 0) break;
 899 
 900     // We can find that we were unpark()ed and redesignated _succ while
 901     // we were spinning.  That's harmless.  If we iterate and call park(),
 902     // park() will consume the event and return immediately and we'll
 903     // just spin again.  This pattern can repeat, leaving _succ to simply
 904     // spin on a CPU.
 905 
 906     if (_succ == current) _succ = nullptr;
 907 
 908     // Invariant: after clearing _succ a thread *must* retry _owner before parking.
 909     OrderAccess::fence();
 910   }
 911 
 912   // Egress :
 913   // current has acquired the lock -- Unlink current from the cxq or EntryList.
 914   // Normally we'll find current on the EntryList .
 915   // From the perspective of the lock owner (this thread), the
 916   // EntryList is stable and cxq is prepend-only.
 917   // The head of cxq is volatile but the interior is stable.
 918   // In addition, current.TState is stable.
 919 
 920   assert(owner_raw() == current, "invariant");
 921 
 922   UnlinkAfterAcquire(current, &node);
 923   if (_succ == current) _succ = nullptr;
 924 
 925   assert(_succ != current, "invariant");
 926   if (_Responsible == current) {
 927     _Responsible = nullptr;
 928     OrderAccess::fence(); // Dekker pivot-point
 929 
 930     // We may leave threads on cxq|EntryList without a designated
 931     // "Responsible" thread.  This is benign.  When this thread subsequently
 932     // exits the monitor it can "see" such preexisting "old" threads --
 933     // threads that arrived on the cxq|EntryList before the fence, above --
 934     // by LDing cxq|EntryList.  Newly arrived threads -- that is, threads
 935     // that arrive on cxq after the ST:MEMBAR, above -- will set Responsible
 936     // non-null and elect a new "Responsible" timer thread.
 937     //
 938     // This thread executes:
 939     //    ST Responsible=null; MEMBAR    (in enter epilogue - here)
 940     //    LD cxq|EntryList               (in subsequent exit)
 941     //
 942     // Entering threads in the slow/contended path execute:
 943     //    ST cxq=nonnull; MEMBAR; LD Responsible (in enter prolog)
 944     //    The (ST cxq; MEMBAR) is accomplished with CAS().
 945     //
 946     // The MEMBAR, above, prevents the LD of cxq|EntryList in the subsequent
 947     // exit operation from floating above the ST Responsible=null.
 948   }
 949 
 950   // We've acquired ownership with CAS().
 951   // CAS is serializing -- it has MEMBAR/FENCE-equivalent semantics.
 952   // But since the CAS() this thread may have also stored into _succ,
 953   // EntryList, cxq or Responsible.  These meta-data updates must be
 954   // visible __before this thread subsequently drops the lock.
 955   // Consider what could occur if we didn't enforce this constraint --
 956   // STs to monitor meta-data and user-data could reorder with (become
 957   // visible after) the ST in exit that drops ownership of the lock.
 958   // Some other thread could then acquire the lock, but observe inconsistent
 959   // or old monitor meta-data and heap data.  That violates the JMM.
 960   // To that end, the 1-0 exit() operation must have at least STST|LDST
 961   // "release" barrier semantics.  Specifically, there must be at least a
 962   // STST|LDST barrier in exit() before the ST of null into _owner that drops
 963   // the lock.   The barrier ensures that changes to monitor meta-data and data
 964   // protected by the lock will be visible before we release the lock, and
 965   // therefore before some other thread (CPU) has a chance to acquire the lock.
 966   // See also: http://gee.cs.oswego.edu/dl/jmm/cookbook.html.
 967   //
 968   // Critically, any prior STs to _succ or EntryList must be visible before
 969   // the ST of null into _owner in the *subsequent* (following) corresponding
 970   // monitorexit.  Recall too, that in 1-0 mode monitorexit does not necessarily
 971   // execute a serializing instruction.
 972 
 973   return;
 974 }
 975 





















































































 976 // ReenterI() is a specialized inline form of the latter half of the
 977 // contended slow-path from EnterI().  We use ReenterI() only for
 978 // monitor reentry in wait().
 979 //
 980 // In the future we should reconcile EnterI() and ReenterI().
 981 
 982 void ObjectMonitor::ReenterI(JavaThread* current, ObjectWaiter* currentNode) {
 983   assert(current != nullptr, "invariant");
 984   assert(currentNode != nullptr, "invariant");
 985   assert(currentNode->_thread == current, "invariant");
 986   assert(_waiters > 0, "invariant");
 987   assert(object()->mark() == markWord::encode(this), "invariant");
 988 
 989   assert(current->thread_state() != _thread_blocked, "invariant");
 990 
 991   int nWakeups = 0;
 992   for (;;) {
 993     ObjectWaiter::TStates v = currentNode->TState;
 994     guarantee(v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant");
 995     assert(owner_raw() != current, "invariant");
 996 
 997     if (TryLock(current) > 0) break;
 998     if (TrySpin(current) > 0) break;
 999 
1000     {
1001       OSThreadContendState osts(current->osthread());
1002 
1003       assert(current->thread_state() == _thread_in_vm, "invariant");
1004 
1005       {
1006         ClearSuccOnSuspend csos(this);
1007         ThreadBlockInVMPreprocess<ClearSuccOnSuspend> tbivs(current, csos, true /* allow_suspend */);
1008         current->_ParkEvent->park();
1009       }
1010     }
1011 
1012     // Try again, but just so we distinguish between futile wakeups and
1013     // successful wakeups.  The following test isn't algorithmically
1014     // necessary, but it helps us maintain sensible statistics.
1015     if (TryLock(current) > 0) break;
1016 
1017     // The lock is still contested.
1018     // Keep a tally of the # of futile wakeups.
1019     // Note that the counter is not protected by a lock or updated by atomics.
1020     // That is by design - we trade "lossy" counters which are exposed to
1021     // races during updates for a lower probe effect.
1022     ++nWakeups;
1023 
1024     // Assuming this is not a spurious wakeup we'll normally
1025     // find that _succ == current.
1026     if (_succ == current) _succ = nullptr;
1027 
1028     // Invariant: after clearing _succ a contending thread
1029     // *must* retry  _owner before parking.
1030     OrderAccess::fence();
1031 
1032     // This PerfData object can be used in parallel with a safepoint.
1033     // See the work around in PerfDataManager::destroy().
1034     OM_PERFDATA_OP(FutileWakeups, inc());
1035   }
1036 
1037   // current has acquired the lock -- Unlink current from the cxq or EntryList .
1038   // Normally we'll find current on the EntryList.
1039   // Unlinking from the EntryList is constant-time and atomic-free.
1040   // From the perspective of the lock owner (this thread), the
1041   // EntryList is stable and cxq is prepend-only.
1042   // The head of cxq is volatile but the interior is stable.
1043   // In addition, current.TState is stable.
1044 
1045   assert(owner_raw() == current, "invariant");
1046   assert(object()->mark() == markWord::encode(this), "invariant");
1047   UnlinkAfterAcquire(current, currentNode);
1048   if (_succ == current) _succ = nullptr;
1049   assert(_succ != current, "invariant");
1050   currentNode->TState = ObjectWaiter::TS_RUN;
1051   OrderAccess::fence();      // see comments at the end of EnterI()
1052 }
1053 



























































1054 // By convention we unlink a contending thread from EntryList|cxq immediately
1055 // after the thread acquires the lock in ::enter().  Equally, we could defer
1056 // unlinking the thread until ::exit()-time.
1057 
1058 void ObjectMonitor::UnlinkAfterAcquire(JavaThread* current, ObjectWaiter* currentNode) {
1059   assert(owner_raw() == current, "invariant");
1060   assert(currentNode->_thread == current, "invariant");
1061 
1062   if (currentNode->TState == ObjectWaiter::TS_ENTER) {
1063     // Normal case: remove current from the DLL EntryList .
1064     // This is a constant-time operation.
1065     ObjectWaiter* nxt = currentNode->_next;
1066     ObjectWaiter* prv = currentNode->_prev;
1067     if (nxt != nullptr) nxt->_prev = prv;
1068     if (prv != nullptr) prv->_next = nxt;
1069     if (currentNode == _EntryList) _EntryList = nxt;
1070     assert(nxt == nullptr || nxt->TState == ObjectWaiter::TS_ENTER, "invariant");
1071     assert(prv == nullptr || prv->TState == ObjectWaiter::TS_ENTER, "invariant");
1072   } else {
1073     assert(currentNode->TState == ObjectWaiter::TS_CXQ, "invariant");
1074     // Inopportune interleaving -- current is still on the cxq.
1075     // This usually means the enqueue of self raced an exiting thread.
1076     // Normally we'll find current near the front of the cxq, so
1077     // dequeueing is typically fast.  If needbe we can accelerate
1078     // this with some MCS/CHL-like bidirectional list hints and advisory
1079     // back-links so dequeueing from the interior will normally operate
1080     // in constant-time.
1081     // Dequeue current from either the head (with CAS) or from the interior
1082     // with a linear-time scan and normal non-atomic memory operations.
1083     // CONSIDER: if current is on the cxq then simply drain cxq into EntryList
1084     // and then unlink current from EntryList.  We have to drain eventually,
1085     // so it might as well be now.
1086 
1087     ObjectWaiter* v = _cxq;
1088     assert(v != nullptr, "invariant");
1089     if (v != currentNode || Atomic::cmpxchg(&_cxq, v, currentNode->_next) != v) {
1090       // The CAS above can fail from interference IFF a "RAT" arrived.
1091       // In that case current must be in the interior and can no longer be
1092       // at the head of cxq.
1093       if (v == currentNode) {
1094         assert(_cxq != v, "invariant");
1095         v = _cxq;          // CAS above failed - start scan at head of list
1096       }
1097       ObjectWaiter* p;
1098       ObjectWaiter* q = nullptr;
1099       for (p = v; p != nullptr && p != currentNode; p = p->_next) {
1100         q = p;
1101         assert(p->TState == ObjectWaiter::TS_CXQ, "invariant");
1102       }
1103       assert(v != currentNode, "invariant");
1104       assert(p == currentNode, "Node not found on cxq");
1105       assert(p != _cxq, "invariant");
1106       assert(q != nullptr, "invariant");
1107       assert(q->_next == p, "invariant");
1108       q->_next = p->_next;
1109     }
1110   }
1111 
1112 #ifdef ASSERT
1113   // Diagnostic hygiene ...
1114   currentNode->_prev  = (ObjectWaiter*) 0xBAD;
1115   currentNode->_next  = (ObjectWaiter*) 0xBAD;
1116   currentNode->TState = ObjectWaiter::TS_RUN;
1117 #endif
1118 }
1119 










1120 // -----------------------------------------------------------------------------
1121 // Exit support
1122 //
1123 // exit()
1124 // ~~~~~~
1125 // Note that the collector can't reclaim the objectMonitor or deflate
1126 // the object out from underneath the thread calling ::exit() as the
1127 // thread calling ::exit() never transitions to a stable state.
1128 // This inhibits GC, which in turn inhibits asynchronous (and
1129 // inopportune) reclamation of "this".
1130 //
1131 // We'd like to assert that: (THREAD->thread_state() != _thread_blocked) ;
1132 // There's one exception to the claim above, however.  EnterI() can call
1133 // exit() to drop a lock if the acquirer has been externally suspended.
1134 // In that case exit() is called with _thread_state == _thread_blocked,
1135 // but the monitor's _contentions field is > 0, which inhibits reclamation.
1136 //
1137 // 1-0 exit
1138 // ~~~~~~~~
1139 // ::exit() uses a canonical 1-1 idiom with a MEMBAR although some of
1140 // the fast-path operators have been optimized so the common ::exit()
1141 // operation is 1-0, e.g., see macroAssembler_x86.cpp: fast_unlock().
1142 // The code emitted by fast_unlock() elides the usual MEMBAR.  This
1143 // greatly improves latency -- MEMBAR and CAS having considerable local
1144 // latency on modern processors -- but at the cost of "stranding".  Absent the
1145 // MEMBAR, a thread in fast_unlock() can race a thread in the slow
1146 // ::enter() path, resulting in the entering thread being stranding
1147 // and a progress-liveness failure.   Stranding is extremely rare.
1148 // We use timers (timed park operations) & periodic polling to detect
1149 // and recover from stranding.  Potentially stranded threads periodically
1150 // wake up and poll the lock.  See the usage of the _Responsible variable.
1151 //
1152 // The CAS() in enter provides for safety and exclusion, while the CAS or
1153 // MEMBAR in exit provides for progress and avoids stranding.  1-0 locking
1154 // eliminates the CAS/MEMBAR from the exit path, but it admits stranding.
1155 // We detect and recover from stranding with timers.
1156 //
1157 // If a thread transiently strands it'll park until (a) another
1158 // thread acquires the lock and then drops the lock, at which time the
1159 // exiting thread will notice and unpark the stranded thread, or, (b)
1160 // the timer expires.  If the lock is high traffic then the stranding latency
1161 // will be low due to (a).  If the lock is low traffic then the odds of
1162 // stranding are lower, although the worst-case stranding latency
1163 // is longer.  Critically, we don't want to put excessive load in the
1164 // platform's timer subsystem.  We want to minimize both the timer injection
1165 // rate (timers created/sec) as well as the number of timers active at
1166 // any one time.  (more precisely, we want to minimize timer-seconds, which is
1167 // the integral of the # of active timers at any instant over time).
1168 // Both impinge on OS scalability.  Given that, at most one thread parked on
1169 // a monitor will use a timer.
1170 //
1171 // There is also the risk of a futile wake-up. If we drop the lock
1172 // another thread can reacquire the lock immediately, and we can
1173 // then wake a thread unnecessarily. This is benign, and we've
1174 // structured the code so the windows are short and the frequency
1175 // of such futile wakups is low.
1176 
1177 void ObjectMonitor::exit(JavaThread* current, bool not_suspended) {
1178   void* cur = owner_raw();
1179   if (current != cur) {
1180     if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) {
1181       assert(_recursions == 0, "invariant");
1182       set_owner_from_BasicLock(cur, current);  // Convert from BasicLock* to Thread*.
1183       _recursions = 0;
1184     } else {
1185       // Apparent unbalanced locking ...
1186       // Naively we'd like to throw IllegalMonitorStateException.
1187       // As a practical matter we can neither allocate nor throw an
1188       // exception as ::exit() can be called from leaf routines.
1189       // see x86_32.ad Fast_Unlock() and the I1 and I2 properties.
1190       // Upon deeper reflection, however, in a properly run JVM the only
1191       // way we should encounter this situation is in the presence of
1192       // unbalanced JNI locking. TODO: CheckJNICalls.
1193       // See also: CR4414101
1194 #ifdef ASSERT
1195       LogStreamHandle(Error, monitorinflation) lsh;
1196       lsh.print_cr("ERROR: ObjectMonitor::exit(): thread=" INTPTR_FORMAT
1197                     " is exiting an ObjectMonitor it does not own.", p2i(current));
1198       lsh.print_cr("The imbalance is possibly caused by JNI locking.");
1199       print_debug_style_on(&lsh);
1200       assert(false, "Non-balanced monitor enter/exit!");
1201 #endif
1202       return;
1203     }
1204   }
1205 
1206   if (_recursions != 0) {
1207     _recursions--;        // this is simple recursive enter
1208     return;
1209   }
1210 
1211   // Invariant: after setting Responsible=null an thread must execute
1212   // a MEMBAR or other serializing instruction before fetching EntryList|cxq.
1213   _Responsible = nullptr;
1214 
1215 #if INCLUDE_JFR
1216   // get the owner's thread id for the MonitorEnter event
1217   // if it is enabled and the thread isn't suspended
1218   if (not_suspended && EventJavaMonitorEnter::is_enabled()) {
1219     _previous_owner_tid = JFR_THREAD_ID(current);
1220   }
1221 #endif
1222 
1223   for (;;) {
1224     assert(current == owner_raw(), "invariant");
1225 
1226     // Drop the lock.
1227     // release semantics: prior loads and stores from within the critical section
1228     // must not float (reorder) past the following store that drops the lock.
1229     // Uses a storeload to separate release_store(owner) from the
1230     // successor check. The try_set_owner() below uses cmpxchg() so
1231     // we get the fence down there.
1232     release_clear_owner(current);
1233     OrderAccess::storeload();
1234 
1235     if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != nullptr) {
1236       return;
1237     }
1238     // Other threads are blocked trying to acquire the lock.
1239 
1240     // Normally the exiting thread is responsible for ensuring succession,
1241     // but if other successors are ready or other entering threads are spinning
1242     // then this thread can simply store null into _owner and exit without
1243     // waking a successor.  The existence of spinners or ready successors
1244     // guarantees proper succession (liveness).  Responsibility passes to the
1245     // ready or running successors.  The exiting thread delegates the duty.
1246     // More precisely, if a successor already exists this thread is absolved
1247     // of the responsibility of waking (unparking) one.
1248     //
1249     // The _succ variable is critical to reducing futile wakeup frequency.
1250     // _succ identifies the "heir presumptive" thread that has been made
1251     // ready (unparked) but that has not yet run.  We need only one such
1252     // successor thread to guarantee progress.
1253     // See http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf
1254     // section 3.3 "Futile Wakeup Throttling" for details.
1255     //
1256     // Note that spinners in Enter() also set _succ non-null.
1257     // In the current implementation spinners opportunistically set
1258     // _succ so that exiting threads might avoid waking a successor.
1259     // Another less appealing alternative would be for the exiting thread
1260     // to drop the lock and then spin briefly to see if a spinner managed
1261     // to acquire the lock.  If so, the exiting thread could exit
1262     // immediately without waking a successor, otherwise the exiting
1263     // thread would need to dequeue and wake a successor.
1264     // (Note that we'd need to make the post-drop spin short, but no
1265     // shorter than the worst-case round-trip cache-line migration time.
1266     // The dropped lock needs to become visible to the spinner, and then
1267     // the acquisition of the lock by the spinner must become visible to
1268     // the exiting thread).
1269 
1270     // It appears that an heir-presumptive (successor) must be made ready.
1271     // Only the current lock owner can manipulate the EntryList or
1272     // drain _cxq, so we need to reacquire the lock.  If we fail
1273     // to reacquire the lock the responsibility for ensuring succession
1274     // falls to the new owner.
1275     //
1276     if (try_set_owner_from(nullptr, current) != nullptr) {
1277       return;
1278     }
1279 
1280     guarantee(owner_raw() == current, "invariant");
1281 
1282     ObjectWaiter* w = nullptr;
1283 
1284     w = _EntryList;
1285     if (w != nullptr) {
1286       // I'd like to write: guarantee (w->_thread != current).
1287       // But in practice an exiting thread may find itself on the EntryList.
1288       // Let's say thread T1 calls O.wait().  Wait() enqueues T1 on O's waitset and
1289       // then calls exit().  Exit release the lock by setting O._owner to null.
1290       // Let's say T1 then stalls.  T2 acquires O and calls O.notify().  The
1291       // notify() operation moves T1 from O's waitset to O's EntryList. T2 then
1292       // release the lock "O".  T2 resumes immediately after the ST of null into
1293       // _owner, above.  T2 notices that the EntryList is populated, so it
1294       // reacquires the lock and then finds itself on the EntryList.
1295       // Given all that, we have to tolerate the circumstance where "w" is
1296       // associated with current.
1297       assert(w->TState == ObjectWaiter::TS_ENTER, "invariant");
1298       ExitEpilog(current, w);
1299       return;
1300     }
1301 
1302     // If we find that both _cxq and EntryList are null then just
1303     // re-run the exit protocol from the top.
1304     w = _cxq;
1305     if (w == nullptr) continue;
1306 
1307     // Drain _cxq into EntryList - bulk transfer.
1308     // First, detach _cxq.
1309     // The following loop is tantamount to: w = swap(&cxq, nullptr)
1310     for (;;) {
1311       assert(w != nullptr, "Invariant");
1312       ObjectWaiter* u = Atomic::cmpxchg(&_cxq, w, (ObjectWaiter*)nullptr);
1313       if (u == w) break;
1314       w = u;
1315     }
1316 
1317     assert(w != nullptr, "invariant");
1318     assert(_EntryList == nullptr, "invariant");
1319 
1320     // Convert the LIFO SLL anchored by _cxq into a DLL.
1321     // The list reorganization step operates in O(LENGTH(w)) time.
1322     // It's critical that this step operate quickly as
1323     // "current" still holds the outer-lock, restricting parallelism
1324     // and effectively lengthening the critical section.
1325     // Invariant: s chases t chases u.
1326     // TODO-FIXME: consider changing EntryList from a DLL to a CDLL so
1327     // we have faster access to the tail.
1328 
1329     _EntryList = w;
1330     ObjectWaiter* q = nullptr;
1331     ObjectWaiter* p;
1332     for (p = w; p != nullptr; p = p->_next) {
1333       guarantee(p->TState == ObjectWaiter::TS_CXQ, "Invariant");
1334       p->TState = ObjectWaiter::TS_ENTER;
1335       p->_prev = q;
1336       q = p;
1337     }
1338 
1339     // In 1-0 mode we need: ST EntryList; MEMBAR #storestore; ST _owner = nullptr
1340     // The MEMBAR is satisfied by the release_store() operation in ExitEpilog().
1341 
1342     // See if we can abdicate to a spinner instead of waking a thread.
1343     // A primary goal of the implementation is to reduce the
1344     // context-switch rate.
1345     if (_succ != nullptr) continue;
1346 
1347     w = _EntryList;
1348     if (w != nullptr) {
1349       guarantee(w->TState == ObjectWaiter::TS_ENTER, "invariant");
1350       ExitEpilog(current, w);
1351       return;
1352     }
1353   }
1354 }
1355 
1356 void ObjectMonitor::ExitEpilog(JavaThread* current, ObjectWaiter* Wakee) {
1357   assert(owner_raw() == current, "invariant");
1358 
1359   // Exit protocol:
1360   // 1. ST _succ = wakee
1361   // 2. membar #loadstore|#storestore;
1362   // 2. ST _owner = nullptr
1363   // 3. unpark(wakee)
1364 
1365   _succ = Wakee->_thread;








1366   ParkEvent * Trigger = Wakee->_event;
1367 
1368   // Hygiene -- once we've set _owner = nullptr we can't safely dereference Wakee again.
1369   // The thread associated with Wakee may have grabbed the lock and "Wakee" may be
1370   // out-of-scope (non-extant).
1371   Wakee  = nullptr;
1372 
1373   // Drop the lock.
1374   // Uses a fence to separate release_store(owner) from the LD in unpark().
1375   release_clear_owner(current);
1376   OrderAccess::fence();
1377 
1378   DTRACE_MONITOR_PROBE(contended__exit, this, object(), current);
1379   Trigger->unpark();






1380 
1381   // Maintain stats and report events to JVMTI
1382   OM_PERFDATA_OP(Parks, inc());
1383 }
1384 
1385 // complete_exit exits a lock returning recursion count
1386 // complete_exit requires an inflated monitor
1387 // The _owner field is not always the Thread addr even with an
1388 // inflated monitor, e.g. the monitor can be inflated by a non-owning
1389 // thread due to contention.
1390 intx ObjectMonitor::complete_exit(JavaThread* current) {
1391   assert(InitDone, "Unexpectedly not initialized");
1392 
1393   void* cur = owner_raw();
1394   if (current != cur) {
1395     if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) {
1396       assert(_recursions == 0, "internal state error");
1397       set_owner_from_BasicLock(cur, current);  // Convert from BasicLock* to Thread*.
1398       _recursions = 0;
1399     }
1400   }
1401 
1402   guarantee(current == owner_raw(), "complete_exit not owner");
1403   intx save = _recursions; // record the old recursion count
1404   _recursions = 0;         // set the recursion level to be 0
1405   exit(current);           // exit the monitor
1406   guarantee(owner_raw() != current, "invariant");
1407   return save;
1408 }
1409 
1410 // Checks that the current THREAD owns this monitor and causes an
1411 // immediate return if it doesn't. We don't use the CHECK macro
1412 // because we want the IMSE to be the only exception that is thrown
1413 // from the call site when false is returned. Any other pending
1414 // exception is ignored.
1415 #define CHECK_OWNER()                                                  \
1416   do {                                                                 \
1417     if (!check_owner(THREAD)) {                                        \
1418        assert(HAS_PENDING_EXCEPTION, "expected a pending IMSE here."); \
1419        return;                                                         \
1420      }                                                                 \
1421   } while (false)
1422 
1423 // Returns true if the specified thread owns the ObjectMonitor.
1424 // Otherwise returns false and throws IllegalMonitorStateException
1425 // (IMSE). If there is a pending exception and the specified thread
1426 // is not the owner, that exception will be replaced by the IMSE.
1427 bool ObjectMonitor::check_owner(TRAPS) {
1428   JavaThread* current = THREAD;
1429   void* cur = owner_raw();
1430   assert(cur != anon_owner_ptr(), "no anon owner here");
1431   if (cur == current) {
1432     return true;
1433   }
1434   if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) {
1435     set_owner_from_BasicLock(cur, current);  // Convert from BasicLock* to Thread*.
1436     _recursions = 0;
1437     return true;
1438   }
1439   THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
1440              "current thread is not owner", false);
1441 }
1442 
1443 static inline bool is_excluded(const Klass* monitor_klass) {
1444   assert(monitor_klass != nullptr, "invariant");
1445   NOT_JFR_RETURN_(false);
1446   JFR_ONLY(return vmSymbols::jfr_chunk_rotation_monitor() == monitor_klass->name();)
1447 }
1448 
1449 static void post_monitor_wait_event(EventJavaMonitorWait* event,
1450                                     ObjectMonitor* monitor,
1451                                     uint64_t notifier_tid,
1452                                     jlong timeout,
1453                                     bool timedout) {
1454   assert(event != nullptr, "invariant");
1455   assert(monitor != nullptr, "invariant");
1456   const Klass* monitor_klass = monitor->object()->klass();
1457   if (is_excluded(monitor_klass)) {
1458     return;
1459   }
1460   event->set_monitorClass(monitor_klass);
1461   event->set_timeout(timeout);
1462   // Set an address that is 'unique enough', such that events close in
1463   // time and with the same address are likely (but not guaranteed) to
1464   // belong to the same object.
1465   event->set_address((uintptr_t)monitor);
1466   event->set_notifier(notifier_tid);
1467   event->set_timedOut(timedout);
1468   event->commit();
1469 }
1470 
1471 // -----------------------------------------------------------------------------
1472 // Wait/Notify/NotifyAll
1473 //
1474 // Note: a subset of changes to ObjectMonitor::wait()
1475 // will need to be replicated in complete_exit
1476 void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
1477   JavaThread* current = THREAD;
1478 
1479   assert(InitDone, "Unexpectedly not initialized");
1480 
1481   CHECK_OWNER();  // Throws IMSE if not owner.
1482 








1483   EventJavaMonitorWait event;
1484 
1485   // check for a pending interrupt
1486   if (interruptible && current->is_interrupted(true) && !HAS_PENDING_EXCEPTION) {
1487     // post monitor waited event.  Note that this is past-tense, we are done waiting.
1488     if (JvmtiExport::should_post_monitor_waited()) {
1489       // Note: 'false' parameter is passed here because the
1490       // wait was not timed out due to thread interrupt.
1491       JvmtiExport::post_monitor_waited(current, this, false);
1492 
1493       // In this short circuit of the monitor wait protocol, the
1494       // current thread never drops ownership of the monitor and
1495       // never gets added to the wait queue so the current thread
1496       // cannot be made the successor. This means that the
1497       // JVMTI_EVENT_MONITOR_WAITED event handler cannot accidentally
1498       // consume an unpark() meant for the ParkEvent associated with
1499       // this ObjectMonitor.
1500     }
1501     if (event.should_commit()) {
1502       post_monitor_wait_event(&event, this, 0, millis, false);
1503     }
1504     THROW(vmSymbols::java_lang_InterruptedException());
1505     return;
1506   }
1507 
1508   current->set_current_waiting_monitor(this);
1509 
1510   // create a node to be put into the queue
1511   // Critically, after we reset() the event but prior to park(), we must check
1512   // for a pending interrupt.
1513   ObjectWaiter node(current);
1514   node.TState = ObjectWaiter::TS_WAIT;
1515   current->_ParkEvent->reset();
1516   OrderAccess::fence();          // ST into Event; membar ; LD interrupted-flag
1517 
1518   // Enter the waiting queue, which is a circular doubly linked list in this case
1519   // but it could be a priority queue or any data structure.
1520   // _WaitSetLock protects the wait queue.  Normally the wait queue is accessed only
1521   // by the owner of the monitor *except* in the case where park()
1522   // returns because of a timeout of interrupt.  Contention is exceptionally rare
1523   // so we use a simple spin-lock instead of a heavier-weight blocking lock.
1524 
1525   Thread::SpinAcquire(&_WaitSetLock, "WaitSet - add");
1526   AddWaiter(&node);
1527   Thread::SpinRelease(&_WaitSetLock);
1528 
1529   _Responsible = nullptr;
1530 
1531   intx save = _recursions;     // record the old recursion count
1532   _waiters++;                  // increment the number of waiters
1533   _recursions = 0;             // set the recursion level to be 1
1534   exit(current);               // exit the monitor
1535   guarantee(owner_raw() != current, "invariant");
1536 
1537   // The thread is on the WaitSet list - now park() it.
1538   // On MP systems it's conceivable that a brief spin before we park
1539   // could be profitable.
1540   //
1541   // TODO-FIXME: change the following logic to a loop of the form
1542   //   while (!timeout && !interrupted && _notified == 0) park()
1543 
1544   int ret = OS_OK;
1545   int WasNotified = 0;
1546 
1547   // Need to check interrupt state whilst still _thread_in_vm
1548   bool interrupted = interruptible && current->is_interrupted(false);
1549 
1550   { // State transition wrappers
1551     OSThread* osthread = current->osthread();
1552     OSThreadWaitState osts(osthread, true);
1553 
1554     assert(current->thread_state() == _thread_in_vm, "invariant");
1555 
1556     {
1557       ClearSuccOnSuspend csos(this);
1558       ThreadBlockInVMPreprocess<ClearSuccOnSuspend> tbivs(current, csos, true /* allow_suspend */);
1559       if (interrupted || HAS_PENDING_EXCEPTION) {
1560         // Intentionally empty
1561       } else if (node._notified == 0) {
1562         if (millis <= 0) {
1563           current->_ParkEvent->park();
1564         } else {
1565           ret = current->_ParkEvent->park(millis);
1566         }
1567       }
1568     }
1569 
1570     // Node may be on the WaitSet, the EntryList (or cxq), or in transition
1571     // from the WaitSet to the EntryList.
1572     // See if we need to remove Node from the WaitSet.
1573     // We use double-checked locking to avoid grabbing _WaitSetLock
1574     // if the thread is not on the wait queue.
1575     //
1576     // Note that we don't need a fence before the fetch of TState.
1577     // In the worst case we'll fetch a old-stale value of TS_WAIT previously
1578     // written by the is thread. (perhaps the fetch might even be satisfied
1579     // by a look-aside into the processor's own store buffer, although given
1580     // the length of the code path between the prior ST and this load that's
1581     // highly unlikely).  If the following LD fetches a stale TS_WAIT value
1582     // then we'll acquire the lock and then re-fetch a fresh TState value.
1583     // That is, we fail toward safety.
1584 
1585     if (node.TState == ObjectWaiter::TS_WAIT) {
1586       Thread::SpinAcquire(&_WaitSetLock, "WaitSet - unlink");
1587       if (node.TState == ObjectWaiter::TS_WAIT) {
1588         DequeueSpecificWaiter(&node);       // unlink from WaitSet
1589         assert(node._notified == 0, "invariant");
1590         node.TState = ObjectWaiter::TS_RUN;
1591       }
1592       Thread::SpinRelease(&_WaitSetLock);
1593     }
1594 
1595     // The thread is now either on off-list (TS_RUN),
1596     // on the EntryList (TS_ENTER), or on the cxq (TS_CXQ).
1597     // The Node's TState variable is stable from the perspective of this thread.
1598     // No other threads will asynchronously modify TState.
1599     guarantee(node.TState != ObjectWaiter::TS_WAIT, "invariant");
1600     OrderAccess::loadload();
1601     if (_succ == current) _succ = nullptr;
1602     WasNotified = node._notified;
1603 
1604     // Reentry phase -- reacquire the monitor.
1605     // re-enter contended monitor after object.wait().
1606     // retain OBJECT_WAIT state until re-enter successfully completes
1607     // Thread state is thread_in_vm and oop access is again safe,
1608     // although the raw address of the object may have changed.
1609     // (Don't cache naked oops over safepoints, of course).
1610 
1611     // post monitor waited event. Note that this is past-tense, we are done waiting.
1612     if (JvmtiExport::should_post_monitor_waited()) {
1613       JvmtiExport::post_monitor_waited(current, this, ret == OS_TIMEOUT);
1614 
1615       if (node._notified != 0 && _succ == current) {
1616         // In this part of the monitor wait-notify-reenter protocol it
1617         // is possible (and normal) for another thread to do a fastpath
1618         // monitor enter-exit while this thread is still trying to get
1619         // to the reenter portion of the protocol.
1620         //
1621         // The ObjectMonitor was notified and the current thread is
1622         // the successor which also means that an unpark() has already
1623         // been done. The JVMTI_EVENT_MONITOR_WAITED event handler can
1624         // consume the unpark() that was done when the successor was
1625         // set because the same ParkEvent is shared between Java
1626         // monitors and JVM/TI RawMonitors (for now).
1627         //
1628         // We redo the unpark() to ensure forward progress, i.e., we
1629         // don't want all pending threads hanging (parked) with none
1630         // entering the unlocked monitor.
1631         node._event->unpark();
1632       }
1633     }
1634 
1635     if (event.should_commit()) {
1636       post_monitor_wait_event(&event, this, node._notifier_tid, millis, ret == OS_TIMEOUT);
1637     }
1638 
1639     OrderAccess::fence();
1640 
1641     assert(owner_raw() != current, "invariant");
1642     ObjectWaiter::TStates v = node.TState;
1643     if (v == ObjectWaiter::TS_RUN) {
1644       enter(current);
1645     } else {
1646       guarantee(v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant");
1647       ReenterI(current, &node);
1648       node.wait_reenter_end(this);
1649     }
1650 
1651     // current has reacquired the lock.
1652     // Lifecycle - the node representing current must not appear on any queues.
1653     // Node is about to go out-of-scope, but even if it were immortal we wouldn't
1654     // want residual elements associated with this thread left on any lists.
1655     guarantee(node.TState == ObjectWaiter::TS_RUN, "invariant");
1656     assert(owner_raw() == current, "invariant");
1657     assert(_succ != current, "invariant");
1658   } // OSThreadWaitState()
1659 
1660   current->set_current_waiting_monitor(nullptr);
1661 
1662   guarantee(_recursions == 0, "invariant");
1663   int relock_count = JvmtiDeferredUpdates::get_and_reset_relock_count_after_wait(current);
1664   _recursions =   save          // restore the old recursion count
1665                 + relock_count; //  increased by the deferred relock count
1666   current->inc_held_monitor_count(relock_count); // Deopt never entered these counts.
1667   _waiters--;             // decrement the number of waiters
1668 
1669   // Verify a few postconditions
1670   assert(owner_raw() == current, "invariant");
1671   assert(_succ != current, "invariant");
1672   assert(object()->mark() == markWord::encode(this), "invariant");
1673 
1674   // check if the notification happened
1675   if (!WasNotified) {
1676     // no, it could be timeout or Thread.interrupt() or both
1677     // check for interrupt event, otherwise it is timeout
1678     if (interruptible && current->is_interrupted(true) && !HAS_PENDING_EXCEPTION) {
1679       THROW(vmSymbols::java_lang_InterruptedException());
1680     }
1681   }
1682 
1683   // NOTE: Spurious wake up will be consider as timeout.
1684   // Monitor notify has precedence over thread interrupt.
1685 }
1686 
1687 
1688 // Consider:
1689 // If the lock is cool (cxq == null && succ == null) and we're on an MP system
1690 // then instead of transferring a thread from the WaitSet to the EntryList
1691 // we might just dequeue a thread from the WaitSet and directly unpark() it.
1692 
1693 void ObjectMonitor::INotify(JavaThread* current) {
1694   Thread::SpinAcquire(&_WaitSetLock, "WaitSet - notify");
1695   ObjectWaiter* iterator = DequeueWaiter();
1696   if (iterator != nullptr) {
1697     guarantee(iterator->TState == ObjectWaiter::TS_WAIT, "invariant");
1698     guarantee(iterator->_notified == 0, "invariant");
1699     // Disposition - what might we do with iterator ?
1700     // a.  add it directly to the EntryList - either tail (policy == 1)
1701     //     or head (policy == 0).
1702     // b.  push it onto the front of the _cxq (policy == 2).
1703     // For now we use (b).
1704 
1705     iterator->TState = ObjectWaiter::TS_ENTER;
1706 
1707     iterator->_notified = 1;
1708     iterator->_notifier_tid = JFR_THREAD_ID(current);
1709 
1710     ObjectWaiter* list = _EntryList;
1711     if (list != nullptr) {
1712       assert(list->_prev == nullptr, "invariant");
1713       assert(list->TState == ObjectWaiter::TS_ENTER, "invariant");
1714       assert(list != iterator, "invariant");
1715     }
1716 
1717     // prepend to cxq
1718     if (list == nullptr) {
1719       iterator->_next = iterator->_prev = nullptr;
1720       _EntryList = iterator;
1721     } else {
1722       iterator->TState = ObjectWaiter::TS_CXQ;
1723       for (;;) {
1724         ObjectWaiter* front = _cxq;
1725         iterator->_next = front;
1726         if (Atomic::cmpxchg(&_cxq, front, iterator) == front) {
1727           break;
1728         }
1729       }
1730     }
1731 
1732     // _WaitSetLock protects the wait queue, not the EntryList.  We could
1733     // move the add-to-EntryList operation, above, outside the critical section
1734     // protected by _WaitSetLock.  In practice that's not useful.  With the
1735     // exception of  wait() timeouts and interrupts the monitor owner
1736     // is the only thread that grabs _WaitSetLock.  There's almost no contention
1737     // on _WaitSetLock so it's not profitable to reduce the length of the
1738     // critical section.
1739 
1740     iterator->wait_reenter_begin(this);
1741   }
1742   Thread::SpinRelease(&_WaitSetLock);
1743 }
1744 
1745 // Consider: a not-uncommon synchronization bug is to use notify() when
1746 // notifyAll() is more appropriate, potentially resulting in stranded
1747 // threads; this is one example of a lost wakeup. A useful diagnostic
1748 // option is to force all notify() operations to behave as notifyAll().
1749 //
1750 // Note: We can also detect many such problems with a "minimum wait".
1751 // When the "minimum wait" is set to a small non-zero timeout value
1752 // and the program does not hang whereas it did absent "minimum wait",
1753 // that suggests a lost wakeup bug.
1754 
1755 void ObjectMonitor::notify(TRAPS) {
1756   JavaThread* current = THREAD;
1757   CHECK_OWNER();  // Throws IMSE if not owner.
1758   if (_WaitSet == nullptr) {
1759     return;
1760   }
1761   DTRACE_MONITOR_PROBE(notify, this, object(), current);
1762   INotify(current);
1763   OM_PERFDATA_OP(Notifications, inc(1));
1764 }
1765 
1766 
1767 // The current implementation of notifyAll() transfers the waiters one-at-a-time
1768 // from the waitset to the EntryList. This could be done more efficiently with a
1769 // single bulk transfer but in practice it's not time-critical. Beware too,
1770 // that in prepend-mode we invert the order of the waiters. Let's say that the
1771 // waitset is "ABCD" and the EntryList is "XYZ". After a notifyAll() in prepend
1772 // mode the waitset will be empty and the EntryList will be "DCBAXYZ".
1773 
1774 void ObjectMonitor::notifyAll(TRAPS) {
1775   JavaThread* current = THREAD;
1776   CHECK_OWNER();  // Throws IMSE if not owner.
1777   if (_WaitSet == nullptr) {
1778     return;
1779   }
1780 
1781   DTRACE_MONITOR_PROBE(notifyAll, this, object(), current);
1782   int tally = 0;
1783   while (_WaitSet != nullptr) {
1784     tally++;
1785     INotify(current);
1786   }
1787 
1788   OM_PERFDATA_OP(Notifications, inc(tally));
1789 }
1790 
1791 // -----------------------------------------------------------------------------
1792 // Adaptive Spinning Support
1793 //
1794 // Adaptive spin-then-block - rational spinning
1795 //
1796 // Note that we spin "globally" on _owner with a classic SMP-polite TATAS
1797 // algorithm.  On high order SMP systems it would be better to start with
1798 // a brief global spin and then revert to spinning locally.  In the spirit of MCS/CLH,
1799 // a contending thread could enqueue itself on the cxq and then spin locally
1800 // on a thread-specific variable such as its ParkEvent._Event flag.
1801 // That's left as an exercise for the reader.  Note that global spinning is
1802 // not problematic on Niagara, as the L2 cache serves the interconnect and
1803 // has both low latency and massive bandwidth.
1804 //
1805 // Broadly, we can fix the spin frequency -- that is, the % of contended lock
1806 // acquisition attempts where we opt to spin --  at 100% and vary the spin count
1807 // (duration) or we can fix the count at approximately the duration of
1808 // a context switch and vary the frequency.   Of course we could also
1809 // vary both satisfying K == Frequency * Duration, where K is adaptive by monitor.
1810 // For a description of 'Adaptive spin-then-block mutual exclusion in
1811 // multi-threaded processing,' see U.S. Pat. No. 8046758.
1812 //
1813 // This implementation varies the duration "D", where D varies with
1814 // the success rate of recent spin attempts. (D is capped at approximately
1815 // length of a round-trip context switch).  The success rate for recent
1816 // spin attempts is a good predictor of the success rate of future spin
1817 // attempts.  The mechanism adapts automatically to varying critical
1818 // section length (lock modality), system load and degree of parallelism.
1819 // D is maintained per-monitor in _SpinDuration and is initialized
1820 // optimistically.  Spin frequency is fixed at 100%.
1821 //
1822 // Note that _SpinDuration is volatile, but we update it without locks
1823 // or atomics.  The code is designed so that _SpinDuration stays within
1824 // a reasonable range even in the presence of races.  The arithmetic
1825 // operations on _SpinDuration are closed over the domain of legal values,
1826 // so at worst a race will install and older but still legal value.
1827 // At the very worst this introduces some apparent non-determinism.
1828 // We might spin when we shouldn't or vice-versa, but since the spin
1829 // count are relatively short, even in the worst case, the effect is harmless.
1830 //
1831 // Care must be taken that a low "D" value does not become an
1832 // an absorbing state.  Transient spinning failures -- when spinning
1833 // is overall profitable -- should not cause the system to converge
1834 // on low "D" values.  We want spinning to be stable and predictable
1835 // and fairly responsive to change and at the same time we don't want
1836 // it to oscillate, become metastable, be "too" non-deterministic,
1837 // or converge on or enter undesirable stable absorbing states.
1838 //
1839 // We implement a feedback-based control system -- using past behavior
1840 // to predict future behavior.  We face two issues: (a) if the
1841 // input signal is random then the spin predictor won't provide optimal
1842 // results, and (b) if the signal frequency is too high then the control
1843 // system, which has some natural response lag, will "chase" the signal.
1844 // (b) can arise from multimodal lock hold times.  Transient preemption
1845 // can also result in apparent bimodal lock hold times.
1846 // Although sub-optimal, neither condition is particularly harmful, as
1847 // in the worst-case we'll spin when we shouldn't or vice-versa.
1848 // The maximum spin duration is rather short so the failure modes aren't bad.
1849 // To be conservative, I've tuned the gain in system to bias toward
1850 // _not spinning.  Relatedly, the system can sometimes enter a mode where it
1851 // "rings" or oscillates between spinning and not spinning.  This happens
1852 // when spinning is just on the cusp of profitability, however, so the
1853 // situation is not dire.  The state is benign -- there's no need to add
1854 // hysteresis control to damp the transition rate between spinning and
1855 // not spinning.
1856 
1857 // Spinning: Fixed frequency (100%), vary duration
1858 int ObjectMonitor::TrySpin(JavaThread* current) {
1859   // Dumb, brutal spin.  Good for comparative measurements against adaptive spinning.
1860   int ctr = Knob_FixedSpin;
1861   if (ctr != 0) {
1862     while (--ctr >= 0) {
1863       if (TryLock(current) > 0) return 1;
1864       SpinPause();
1865     }
1866     return 0;
1867   }
1868 
1869   for (ctr = Knob_PreSpin + 1; --ctr >= 0;) {
1870     if (TryLock(current) > 0) {
1871       // Increase _SpinDuration ...
1872       // Note that we don't clamp SpinDuration precisely at SpinLimit.
1873       // Raising _SpurDuration to the poverty line is key.
1874       int x = _SpinDuration;
1875       if (x < Knob_SpinLimit) {
1876         if (x < Knob_Poverty) x = Knob_Poverty;
1877         _SpinDuration = x + Knob_BonusB;
1878       }
1879       return 1;
1880     }
1881     SpinPause();
1882   }
1883 
1884   // Admission control - verify preconditions for spinning
1885   //
1886   // We always spin a little bit, just to prevent _SpinDuration == 0 from
1887   // becoming an absorbing state.  Put another way, we spin briefly to
1888   // sample, just in case the system load, parallelism, contention, or lock
1889   // modality changed.
1890   //
1891   // Consider the following alternative:
1892   // Periodically set _SpinDuration = _SpinLimit and try a long/full
1893   // spin attempt.  "Periodically" might mean after a tally of
1894   // the # of failed spin attempts (or iterations) reaches some threshold.
1895   // This takes us into the realm of 1-out-of-N spinning, where we
1896   // hold the duration constant but vary the frequency.
1897 
1898   ctr = _SpinDuration;
1899   if (ctr <= 0) return 0;
1900 
1901   // We're good to spin ... spin ingress.
1902   // CONSIDER: use Prefetch::write() to avoid RTS->RTO upgrades
1903   // when preparing to LD...CAS _owner, etc and the CAS is likely
1904   // to succeed.
1905   if (_succ == nullptr) {
1906     _succ = current;
1907   }
1908   Thread* prv = nullptr;
1909 
1910   // There are three ways to exit the following loop:
1911   // 1.  A successful spin where this thread has acquired the lock.
1912   // 2.  Spin failure with prejudice
1913   // 3.  Spin failure without prejudice
1914 
1915   while (--ctr >= 0) {
1916 
1917     // Periodic polling -- Check for pending GC
1918     // Threads may spin while they're unsafe.
1919     // We don't want spinning threads to delay the JVM from reaching
1920     // a stop-the-world safepoint or to steal cycles from GC.
1921     // If we detect a pending safepoint we abort in order that
1922     // (a) this thread, if unsafe, doesn't delay the safepoint, and (b)
1923     // this thread, if safe, doesn't steal cycles from GC.
1924     // This is in keeping with the "no loitering in runtime" rule.
1925     // We periodically check to see if there's a safepoint pending.
1926     if ((ctr & 0xFF) == 0) {
1927       // Can't call SafepointMechanism::should_process() since that
1928       // might update the poll values and we could be in a thread_blocked
1929       // state here which is not allowed so just check the poll.
1930       if (SafepointMechanism::local_poll_armed(current)) {
1931         goto Abort;           // abrupt spin egress
1932       }
1933       SpinPause();
1934     }
1935 
1936     // Probe _owner with TATAS
1937     // If this thread observes the monitor transition or flicker
1938     // from locked to unlocked to locked, then the odds that this
1939     // thread will acquire the lock in this spin attempt go down
1940     // considerably.  The same argument applies if the CAS fails
1941     // or if we observe _owner change from one non-null value to
1942     // another non-null value.   In such cases we might abort
1943     // the spin without prejudice or apply a "penalty" to the
1944     // spin count-down variable "ctr", reducing it by 100, say.
1945 
1946     JavaThread* ox = static_cast<JavaThread*>(owner_raw());
1947     if (ox == nullptr) {
1948       ox = static_cast<JavaThread*>(try_set_owner_from(nullptr, current));
1949       if (ox == nullptr) {
1950         // The CAS succeeded -- this thread acquired ownership
1951         // Take care of some bookkeeping to exit spin state.
1952         if (_succ == current) {
1953           _succ = nullptr;
1954         }
1955 
1956         // Increase _SpinDuration :
1957         // The spin was successful (profitable) so we tend toward
1958         // longer spin attempts in the future.
1959         // CONSIDER: factor "ctr" into the _SpinDuration adjustment.
1960         // If we acquired the lock early in the spin cycle it
1961         // makes sense to increase _SpinDuration proportionally.
1962         // Note that we don't clamp SpinDuration precisely at SpinLimit.
1963         int x = _SpinDuration;
1964         if (x < Knob_SpinLimit) {
1965           if (x < Knob_Poverty) x = Knob_Poverty;
1966           _SpinDuration = x + Knob_Bonus;
1967         }
1968         return 1;
1969       }
1970 
1971       // The CAS failed ... we can take any of the following actions:
1972       // * penalize: ctr -= CASPenalty
1973       // * exit spin with prejudice -- goto Abort;
1974       // * exit spin without prejudice.
1975       // * Since CAS is high-latency, retry again immediately.
1976       prv = ox;
1977       goto Abort;
1978     }
1979 
1980     // Did lock ownership change hands ?
1981     if (ox != prv && prv != nullptr) {
1982       goto Abort;
1983     }
1984     prv = ox;
1985 
1986     if (_succ == nullptr) {
1987       _succ = current;
1988     }
1989   }
1990 
1991   // Spin failed with prejudice -- reduce _SpinDuration.
1992   // TODO: Use an AIMD-like policy to adjust _SpinDuration.
1993   // AIMD is globally stable.
1994   {
1995     int x = _SpinDuration;
1996     if (x > 0) {
1997       // Consider an AIMD scheme like: x -= (x >> 3) + 100
1998       // This is globally sample and tends to damp the response.
1999       x -= Knob_Penalty;
2000       if (x < 0) x = 0;
2001       _SpinDuration = x;
2002     }
2003   }
2004 
2005  Abort:
2006   if (_succ == current) {
2007     _succ = nullptr;
2008     // Invariant: after setting succ=null a contending thread
2009     // must recheck-retry _owner before parking.  This usually happens
2010     // in the normal usage of TrySpin(), but it's safest
2011     // to make TrySpin() as foolproof as possible.
2012     OrderAccess::fence();
2013     if (TryLock(current) > 0) return 1;
2014   }
2015   return 0;
2016 }
2017 
2018 
2019 // -----------------------------------------------------------------------------
2020 // WaitSet management ...
2021 
2022 ObjectWaiter::ObjectWaiter(JavaThread* current) {
2023   _next     = nullptr;
2024   _prev     = nullptr;
2025   _notified = 0;
2026   _notifier_tid = 0;
2027   TState    = TS_RUN;
2028   _thread   = current;
2029   _event    = _thread->_ParkEvent;
2030   _active   = false;
2031   assert(_event != nullptr, "invariant");
2032 }
2033 




2034 void ObjectWaiter::wait_reenter_begin(ObjectMonitor * const mon) {
2035   _active = JavaThreadBlockedOnMonitorEnterState::wait_reenter_begin(_thread, mon);
2036 }
2037 
2038 void ObjectWaiter::wait_reenter_end(ObjectMonitor * const mon) {
2039   JavaThreadBlockedOnMonitorEnterState::wait_reenter_end(_thread, _active);
2040 }
2041 
2042 inline void ObjectMonitor::AddWaiter(ObjectWaiter* node) {
2043   assert(node != nullptr, "should not add null node");
2044   assert(node->_prev == nullptr, "node already in list");
2045   assert(node->_next == nullptr, "node already in list");
2046   // put node at end of queue (circular doubly linked list)
2047   if (_WaitSet == nullptr) {
2048     _WaitSet = node;
2049     node->_prev = node;
2050     node->_next = node;
2051   } else {
2052     ObjectWaiter* head = _WaitSet;
2053     ObjectWaiter* tail = head->_prev;
2054     assert(tail->_next == head, "invariant check");
2055     tail->_next = node;
2056     head->_prev = node;
2057     node->_next = head;
2058     node->_prev = tail;
2059   }
2060 }
2061 
2062 inline ObjectWaiter* ObjectMonitor::DequeueWaiter() {
2063   // dequeue the very first waiter
2064   ObjectWaiter* waiter = _WaitSet;
2065   if (waiter) {
2066     DequeueSpecificWaiter(waiter);
2067   }
2068   return waiter;
2069 }
2070 
2071 inline void ObjectMonitor::DequeueSpecificWaiter(ObjectWaiter* node) {
2072   assert(node != nullptr, "should not dequeue nullptr node");
2073   assert(node->_prev != nullptr, "node already removed from list");
2074   assert(node->_next != nullptr, "node already removed from list");
2075   // when the waiter has woken up because of interrupt,
2076   // timeout or other spurious wake-up, dequeue the
2077   // waiter from waiting list
2078   ObjectWaiter* next = node->_next;
2079   if (next == node) {
2080     assert(node->_prev == node, "invariant check");
2081     _WaitSet = nullptr;
2082   } else {
2083     ObjectWaiter* prev = node->_prev;
2084     assert(prev->_next == node, "invariant check");
2085     assert(next->_prev == node, "invariant check");
2086     next->_prev = prev;
2087     prev->_next = next;
2088     if (_WaitSet == node) {
2089       _WaitSet = next;
2090     }
2091   }
2092   node->_next = nullptr;
2093   node->_prev = nullptr;
2094 }
2095 
2096 // -----------------------------------------------------------------------------
2097 // PerfData support
2098 PerfCounter * ObjectMonitor::_sync_ContendedLockAttempts       = nullptr;
2099 PerfCounter * ObjectMonitor::_sync_FutileWakeups               = nullptr;
2100 PerfCounter * ObjectMonitor::_sync_Parks                       = nullptr;
2101 PerfCounter * ObjectMonitor::_sync_Notifications               = nullptr;
2102 PerfCounter * ObjectMonitor::_sync_Inflations                  = nullptr;
2103 PerfCounter * ObjectMonitor::_sync_Deflations                  = nullptr;
2104 PerfLongVariable * ObjectMonitor::_sync_MonExtant              = nullptr;
2105 
2106 // One-shot global initialization for the sync subsystem.
2107 // We could also defer initialization and initialize on-demand
2108 // the first time we call ObjectSynchronizer::inflate().
2109 // Initialization would be protected - like so many things - by
2110 // the MonitorCache_lock.
2111 
2112 void ObjectMonitor::Initialize() {
2113   assert(!InitDone, "invariant");
2114 
2115   if (!os::is_MP()) {
2116     Knob_SpinLimit = 0;
2117     Knob_PreSpin   = 0;
2118     Knob_FixedSpin = -1;
2119   }
2120 
2121   if (UsePerfData) {
2122     EXCEPTION_MARK;
2123 #define NEWPERFCOUNTER(n)                                                \
2124   {                                                                      \
2125     n = PerfDataManager::create_counter(SUN_RT, #n, PerfData::U_Events,  \
2126                                         CHECK);                          \
2127   }
2128 #define NEWPERFVARIABLE(n)                                                \
2129   {                                                                       \
2130     n = PerfDataManager::create_variable(SUN_RT, #n, PerfData::U_Events,  \
2131                                          CHECK);                          \
2132   }
2133     NEWPERFCOUNTER(_sync_Inflations);
2134     NEWPERFCOUNTER(_sync_Deflations);
2135     NEWPERFCOUNTER(_sync_ContendedLockAttempts);
2136     NEWPERFCOUNTER(_sync_FutileWakeups);
2137     NEWPERFCOUNTER(_sync_Parks);
2138     NEWPERFCOUNTER(_sync_Notifications);
2139     NEWPERFVARIABLE(_sync_MonExtant);
2140 #undef NEWPERFCOUNTER
2141 #undef NEWPERFVARIABLE
2142   }
2143 
2144   _oop_storage = OopStorageSet::create_weak("ObjectSynchronizer Weak", mtSynchronizer);
2145 
2146   DEBUG_ONLY(InitDone = true;)
2147 }
2148 





2149 void ObjectMonitor::print_on(outputStream* st) const {
2150   // The minimal things to print for markWord printing, more can be added for debugging and logging.
2151   st->print("{contentions=0x%08x,waiters=0x%08x"
2152             ",recursions=" INTX_FORMAT ",owner=" INTPTR_FORMAT "}",
2153             contentions(), waiters(), recursions(),
2154             p2i(owner()));
2155 }
2156 void ObjectMonitor::print() const { print_on(tty); }
2157 
2158 #ifdef ASSERT
2159 // Print the ObjectMonitor like a debugger would:
2160 //
2161 // (ObjectMonitor) 0x00007fdfb6012e40 = {
2162 //   _header = 0x0000000000000001
2163 //   _object = 0x000000070ff45fd0
2164 //   _pad_buf0 = {
2165 //     [0] = '\0'
2166 //     ...
2167 //     [43] = '\0'
2168 //   }
2169 //   _owner = 0x0000000000000000
2170 //   _previous_owner_tid = 0
2171 //   _pad_buf1 = {
2172 //     [0] = '\0'
2173 //     ...
2174 //     [47] = '\0'
2175 //   }
2176 //   _next_om = 0x0000000000000000
2177 //   _recursions = 0
2178 //   _EntryList = 0x0000000000000000
2179 //   _cxq = 0x0000000000000000
2180 //   _succ = 0x0000000000000000
2181 //   _Responsible = 0x0000000000000000
2182 //   _SpinDuration = 5000
2183 //   _contentions = 0
2184 //   _WaitSet = 0x0000700009756248
2185 //   _waiters = 1
2186 //   _WaitSetLock = 0
2187 // }
2188 //
2189 void ObjectMonitor::print_debug_style_on(outputStream* st) const {
2190   st->print_cr("(ObjectMonitor*) " INTPTR_FORMAT " = {", p2i(this));
2191   st->print_cr("  _header = " INTPTR_FORMAT, header().value());
2192   st->print_cr("  _object = " INTPTR_FORMAT, p2i(object_peek()));
2193   st->print_cr("  _pad_buf0 = {");
2194   st->print_cr("    [0] = '\\0'");
2195   st->print_cr("    ...");
2196   st->print_cr("    [%d] = '\\0'", (int)sizeof(_pad_buf0) - 1);
2197   st->print_cr("  }");
2198   st->print_cr("  _owner = " INTPTR_FORMAT, p2i(owner_raw()));
2199   st->print_cr("  _previous_owner_tid = " UINT64_FORMAT, _previous_owner_tid);
2200   st->print_cr("  _pad_buf1 = {");
2201   st->print_cr("    [0] = '\\0'");
2202   st->print_cr("    ...");
2203   st->print_cr("    [%d] = '\\0'", (int)sizeof(_pad_buf1) - 1);
2204   st->print_cr("  }");
2205   st->print_cr("  _next_om = " INTPTR_FORMAT, p2i(next_om()));
2206   st->print_cr("  _recursions = " INTX_FORMAT, _recursions);
2207   st->print_cr("  _EntryList = " INTPTR_FORMAT, p2i(_EntryList));
2208   st->print_cr("  _cxq = " INTPTR_FORMAT, p2i(_cxq));
2209   st->print_cr("  _succ = " INTPTR_FORMAT, p2i(_succ));
2210   st->print_cr("  _Responsible = " INTPTR_FORMAT, p2i(_Responsible));
2211   st->print_cr("  _SpinDuration = %d", _SpinDuration);
2212   st->print_cr("  _contentions = %d", contentions());
2213   st->print_cr("  _WaitSet = " INTPTR_FORMAT, p2i(_WaitSet));
2214   st->print_cr("  _waiters = %d", _waiters);
2215   st->print_cr("  _WaitSetLock = %d", _WaitSetLock);
2216   st->print_cr("}");
2217 }
2218 #endif
--- EOF ---