1 /*
   2  * Copyright (c) 1998, 2025, 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 "classfile/vmSymbols.hpp"
  26 #include "gc/shared/collectedHeap.hpp"
  27 #include "jfr/jfrEvents.hpp"
  28 #include "logging/log.hpp"
  29 #include "logging/logStream.hpp"
  30 #include "memory/allocation.inline.hpp"
  31 #include "memory/padded.hpp"
  32 #include "memory/resourceArea.hpp"
  33 #include "memory/universe.hpp"
  34 #include "oops/markWord.hpp"
  35 #include "oops/oop.inline.hpp"
  36 #include "runtime/atomicAccess.hpp"
  37 #include "runtime/basicLock.inline.hpp"
  38 #include "runtime/frame.inline.hpp"
  39 #include "runtime/globals.hpp"
  40 #include "runtime/handles.inline.hpp"
  41 #include "runtime/handshake.hpp"
  42 #include "runtime/interfaceSupport.inline.hpp"
  43 #include "runtime/javaThread.hpp"
  44 #include "runtime/lightweightSynchronizer.hpp"
  45 #include "runtime/lockStack.inline.hpp"
  46 #include "runtime/mutexLocker.hpp"
  47 #include "runtime/objectMonitor.inline.hpp"
  48 #include "runtime/os.inline.hpp"
  49 #include "runtime/osThread.hpp"
  50 #include "runtime/safepointMechanism.inline.hpp"
  51 #include "runtime/safepointVerifiers.hpp"
  52 #include "runtime/sharedRuntime.hpp"
  53 #include "runtime/stubRoutines.hpp"
  54 #include "runtime/synchronizer.inline.hpp"
  55 #include "runtime/threads.hpp"
  56 #include "runtime/timer.hpp"
  57 #include "runtime/trimNativeHeap.hpp"
  58 #include "runtime/vframe.hpp"
  59 #include "runtime/vmThread.hpp"
  60 #include "utilities/align.hpp"
  61 #include "utilities/dtrace.hpp"
  62 #include "utilities/events.hpp"
  63 #include "utilities/globalCounter.inline.hpp"
  64 #include "utilities/globalDefinitions.hpp"
  65 #include "utilities/linkedlist.hpp"
  66 #include "utilities/preserveException.hpp"
  67 
  68 class ObjectMonitorDeflationLogging;
  69 
  70 void MonitorList::add(ObjectMonitor* m) {
  71   ObjectMonitor* head;
  72   do {
  73     head = AtomicAccess::load(&_head);
  74     m->set_next_om(head);
  75   } while (AtomicAccess::cmpxchg(&_head, head, m) != head);
  76 
  77   size_t count = AtomicAccess::add(&_count, 1u, memory_order_relaxed);
  78   size_t old_max;
  79   do {
  80     old_max = AtomicAccess::load(&_max);
  81     if (count <= old_max) {
  82       break;
  83     }
  84   } while (AtomicAccess::cmpxchg(&_max, old_max, count, memory_order_relaxed) != old_max);
  85 }
  86 
  87 size_t MonitorList::count() const {
  88   return AtomicAccess::load(&_count);
  89 }
  90 
  91 size_t MonitorList::max() const {
  92   return AtomicAccess::load(&_max);
  93 }
  94 
  95 class ObjectMonitorDeflationSafepointer : public StackObj {
  96   JavaThread* const                    _current;
  97   ObjectMonitorDeflationLogging* const _log;
  98 
  99 public:
 100   ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
 101     : _current(current), _log(log) {}
 102 
 103   void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
 104 };
 105 
 106 // Walk the in-use list and unlink deflated ObjectMonitors.
 107 // Returns the number of unlinked ObjectMonitors.
 108 size_t MonitorList::unlink_deflated(size_t deflated_count,
 109                                     GrowableArray<ObjectMonitor*>* unlinked_list,
 110                                     ObjectMonitorDeflationSafepointer* safepointer) {
 111   size_t unlinked_count = 0;
 112   ObjectMonitor* prev = nullptr;
 113   ObjectMonitor* m = AtomicAccess::load_acquire(&_head);
 114 
 115   while (m != nullptr) {
 116     if (m->is_being_async_deflated()) {
 117       // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
 118       // modify the list once per batch. The batch starts at "m".
 119       size_t unlinked_batch = 0;
 120       ObjectMonitor* next = m;
 121       // Look for at most MonitorUnlinkBatch monitors, or the number of
 122       // deflated and not unlinked monitors, whatever comes first.
 123       assert(deflated_count >= unlinked_count, "Sanity: underflow");
 124       size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
 125       do {
 126         ObjectMonitor* next_next = next->next_om();
 127         unlinked_batch++;
 128         unlinked_list->append(next);
 129         next = next_next;
 130         if (unlinked_batch >= unlinked_batch_limit) {
 131           // Reached the max batch, so bail out of the gathering loop.
 132           break;
 133         }
 134         if (prev == nullptr && AtomicAccess::load(&_head) != m) {
 135           // Current batch used to be at head, but it is not at head anymore.
 136           // Bail out and figure out where we currently are. This avoids long
 137           // walks searching for new prev during unlink under heavy list inserts.
 138           break;
 139         }
 140       } while (next != nullptr && next->is_being_async_deflated());
 141 
 142       // Unlink the found batch.
 143       if (prev == nullptr) {
 144         // The current batch is the first batch, so there is a chance that it starts at head.
 145         // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
 146         ObjectMonitor* prev_head = AtomicAccess::cmpxchg(&_head, m, next);
 147         if (prev_head != m) {
 148           // Something must have updated the head. Figure out the actual prev for this batch.
 149           for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
 150             prev = n;
 151           }
 152           assert(prev != nullptr, "Should have found the prev for the current batch");
 153           prev->set_next_om(next);
 154         }
 155       } else {
 156         // The current batch is preceded by another batch. This guarantees the current batch
 157         // does not start at head. Unlink the entire current batch without updating the head.
 158         assert(AtomicAccess::load(&_head) != m, "Sanity");
 159         prev->set_next_om(next);
 160       }
 161 
 162       unlinked_count += unlinked_batch;
 163       if (unlinked_count >= deflated_count) {
 164         // Reached the max so bail out of the searching loop.
 165         // There should be no more deflated monitors left.
 166         break;
 167       }
 168       m = next;
 169     } else {
 170       prev = m;
 171       m = m->next_om();
 172     }
 173 
 174     // Must check for a safepoint/handshake and honor it.
 175     safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
 176   }
 177 
 178 #ifdef ASSERT
 179   // Invariant: the code above should unlink all deflated monitors.
 180   // The code that runs after this unlinking does not expect deflated monitors.
 181   // Notably, attempting to deflate the already deflated monitor would break.
 182   {
 183     ObjectMonitor* m = AtomicAccess::load_acquire(&_head);
 184     while (m != nullptr) {
 185       assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
 186       m = m->next_om();
 187     }
 188   }
 189 #endif
 190 
 191   AtomicAccess::sub(&_count, unlinked_count);
 192   return unlinked_count;
 193 }
 194 
 195 MonitorList::Iterator MonitorList::iterator() const {
 196   return Iterator(AtomicAccess::load_acquire(&_head));
 197 }
 198 
 199 ObjectMonitor* MonitorList::Iterator::next() {
 200   ObjectMonitor* current = _current;
 201   _current = current->next_om();
 202   return current;
 203 }
 204 
 205 // The "core" versions of monitor enter and exit reside in this file.
 206 // The interpreter and compilers contain specialized transliterated
 207 // variants of the enter-exit fast-path operations.  See c2_MacroAssembler_x86.cpp
 208 // fast_lock(...) for instance.  If you make changes here, make sure to modify the
 209 // interpreter, and both C1 and C2 fast-path inline locking code emission.
 210 //
 211 // -----------------------------------------------------------------------------
 212 
 213 #ifdef DTRACE_ENABLED
 214 
 215 // Only bother with this argument setup if dtrace is available
 216 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
 217 
 218 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
 219   char* bytes = nullptr;                                                      \
 220   int len = 0;                                                             \
 221   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
 222   Symbol* klassname = obj->klass()->name();                                \
 223   if (klassname != nullptr) {                                                 \
 224     bytes = (char*)klassname->bytes();                                     \
 225     len = klassname->utf8_length();                                        \
 226   }
 227 
 228 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
 229   {                                                                        \
 230     if (DTraceMonitorProbes) {                                             \
 231       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 232       HOTSPOT_MONITOR_WAIT(jtid,                                           \
 233                            (uintptr_t)(monitor), bytes, len, (millis));    \
 234     }                                                                      \
 235   }
 236 
 237 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
 238 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
 239 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
 240 
 241 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
 242   {                                                                        \
 243     if (DTraceMonitorProbes) {                                             \
 244       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 245       HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */             \
 246                                     (uintptr_t)(monitor), bytes, len);     \
 247     }                                                                      \
 248   }
 249 
 250 #else //  ndef DTRACE_ENABLED
 251 
 252 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 253 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 254 
 255 #endif // ndef DTRACE_ENABLED
 256 
 257 // This exists only as a workaround of dtrace bug 6254741
 258 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
 259   DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
 260   return 0;
 261 }
 262 
 263 static constexpr size_t inflation_lock_count() {
 264   return 256;
 265 }
 266 
 267 // Static storage for an array of PlatformMutex.
 268 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
 269 
 270 static inline PlatformMutex* inflation_lock(size_t index) {
 271   return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
 272 }
 273 
 274 void ObjectSynchronizer::initialize() {
 275   for (size_t i = 0; i < inflation_lock_count(); i++) {
 276     ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
 277   }
 278   // Start the ceiling with the estimate for one thread.
 279   set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
 280 
 281   // Start the timer for deflations, so it does not trigger immediately.
 282   _last_async_deflation_time_ns = os::javaTimeNanos();
 283 
 284   LightweightSynchronizer::initialize();
 285 }
 286 
 287 MonitorList ObjectSynchronizer::_in_use_list;
 288 // monitors_used_above_threshold() policy is as follows:
 289 //
 290 // The ratio of the current _in_use_list count to the ceiling is used
 291 // to determine if we are above MonitorUsedDeflationThreshold and need
 292 // to do an async monitor deflation cycle. The ceiling is increased by
 293 // AvgMonitorsPerThreadEstimate when a thread is added to the system
 294 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
 295 // removed from the system.
 296 //
 297 // Note: If the _in_use_list max exceeds the ceiling, then
 298 // monitors_used_above_threshold() will use the in_use_list max instead
 299 // of the thread count derived ceiling because we have used more
 300 // ObjectMonitors than the estimated average.
 301 //
 302 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
 303 // no-progress async monitor deflation cycles in a row, then the ceiling
 304 // is adjusted upwards by monitors_used_above_threshold().
 305 //
 306 // Start the ceiling with the estimate for one thread in initialize()
 307 // which is called after cmd line options are processed.
 308 static size_t _in_use_list_ceiling = 0;
 309 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
 310 bool volatile ObjectSynchronizer::_is_final_audit = false;
 311 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
 312 static uintx _no_progress_cnt = 0;
 313 static bool _no_progress_skip_increment = false;
 314 
 315 // =====================> Quick functions
 316 
 317 // The quick_* forms are special fast-path variants used to improve
 318 // performance.  In the simplest case, a "quick_*" implementation could
 319 // simply return false, in which case the caller will perform the necessary
 320 // state transitions and call the slow-path form.
 321 // The fast-path is designed to handle frequently arising cases in an efficient
 322 // manner and is just a degenerate "optimistic" variant of the slow-path.
 323 // returns true  -- to indicate the call was satisfied.
 324 // returns false -- to indicate the call needs the services of the slow-path.
 325 // A no-loitering ordinance is in effect for code in the quick_* family
 326 // operators: safepoints or indefinite blocking (blocking that might span a
 327 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
 328 // entry.
 329 //
 330 // Consider: An interesting optimization is to have the JIT recognize the
 331 // following common idiom:
 332 //   synchronized (someobj) { .... ; notify(); }
 333 // That is, we find a notify() or notifyAll() call that immediately precedes
 334 // the monitorexit operation.  In that case the JIT could fuse the operations
 335 // into a single notifyAndExit() runtime primitive.
 336 
 337 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
 338   assert(current->thread_state() == _thread_in_Java, "invariant");
 339   NoSafepointVerifier nsv;
 340   if (obj == nullptr) return false;  // slow-path for invalid obj
 341   const markWord mark = obj->mark();
 342 
 343   if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
 344     // Degenerate notify
 345     // fast-locked by caller so by definition the implied waitset is empty.
 346     return true;
 347   }
 348 
 349   if (mark.has_monitor()) {
 350     ObjectMonitor* const mon = read_monitor(current, obj, mark);
 351     if (mon == nullptr) {
 352       // Racing with inflation/deflation go slow path
 353       return false;
 354     }
 355     assert(mon->object() == oop(obj), "invariant");
 356     if (!mon->has_owner(current)) return false;  // slow-path for IMS exception
 357 
 358     if (mon->first_waiter() != nullptr) {
 359       // We have one or more waiters. Since this is an inflated monitor
 360       // that we own, we quickly notify them here and now, avoiding the slow-path.
 361       if (all) {
 362         mon->quick_notifyAll(current);
 363       } else {
 364         mon->quick_notify(current);
 365       }
 366     }
 367     return true;
 368   }
 369 
 370   // other IMS exception states take the slow-path
 371   return false;
 372 }
 373 
 374 // Handle notifications when synchronizing on value based classes
 375 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
 376   assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
 377   frame last_frame = locking_thread->last_frame();
 378   bool bcp_was_adjusted = false;
 379   // Don't decrement bcp if it points to the frame's first instruction.  This happens when
 380   // handle_sync_on_value_based_class() is called because of a synchronized method.  There
 381   // is no actual monitorenter instruction in the byte code in this case.
 382   if (last_frame.is_interpreted_frame() &&
 383       (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
 384     // adjust bcp to point back to monitorenter so that we print the correct line numbers
 385     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
 386     bcp_was_adjusted = true;
 387   }
 388 
 389   if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
 390     ResourceMark rm;
 391     stringStream ss;
 392     locking_thread->print_active_stack_on(&ss);
 393     char* base = (char*)strstr(ss.base(), "at");
 394     char* newline = (char*)strchr(ss.base(), '\n');
 395     if (newline != nullptr) {
 396       *newline = '\0';
 397     }
 398     fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
 399   } else {
 400     assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
 401     ResourceMark rm;
 402     Log(valuebasedclasses) vblog;
 403 
 404     vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
 405     if (locking_thread->has_last_Java_frame()) {
 406       LogStream info_stream(vblog.info());
 407       locking_thread->print_active_stack_on(&info_stream);
 408     } else {
 409       vblog.info("Cannot find the last Java frame");
 410     }
 411 
 412     EventSyncOnValueBasedClass event;
 413     if (event.should_commit()) {
 414       event.set_valueBasedClass(obj->klass());
 415       event.commit();
 416     }
 417   }
 418 
 419   if (bcp_was_adjusted) {
 420     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
 421   }
 422 }
 423 
 424 // -----------------------------------------------------------------------------
 425 // Monitor Enter/Exit
 426 
 427 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
 428   // When called with locking_thread != Thread::current() some mechanism must synchronize
 429   // the locking_thread with respect to the current thread. Currently only used when
 430   // deoptimizing and re-locking locks. See Deoptimization::relock_objects
 431   assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
 432   return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
 433 }
 434 
 435 // -----------------------------------------------------------------------------
 436 // JNI locks on java objects
 437 // NOTE: must use heavy weight monitor to handle jni monitor enter
 438 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
 439   // Top native frames in the stack will not be seen if we attempt
 440   // preemption, since we start walking from the last Java anchor.
 441   NoPreemptMark npm(current);
 442 
 443   if (obj->klass()->is_value_based()) {
 444     handle_sync_on_value_based_class(obj, current);
 445   }
 446 
 447   // the current locking is from JNI instead of Java code
 448   current->set_current_pending_monitor_is_from_java(false);
 449   // An async deflation can race after the inflate() call and before
 450   // enter() can make the ObjectMonitor busy. enter() returns false if
 451   // we have lost the race to async deflation and we simply try again.
 452   while (true) {
 453     BasicLock lock;
 454     if (LightweightSynchronizer::inflate_and_enter(obj(), &lock, inflate_cause_jni_enter, current, current) != nullptr) {
 455       break;
 456     }
 457   }
 458   current->set_current_pending_monitor_is_from_java(true);
 459 }
 460 
 461 // NOTE: must use heavy weight monitor to handle jni monitor exit
 462 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
 463   JavaThread* current = THREAD;
 464 
 465   ObjectMonitor* monitor;
 466   monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
 467   // If this thread has locked the object, exit the monitor. We
 468   // intentionally do not use CHECK on check_owner because we must exit the
 469   // monitor even if an exception was already pending.
 470   if (monitor->check_owner(THREAD)) {
 471     monitor->exit(current);
 472   }
 473 }
 474 
 475 // -----------------------------------------------------------------------------
 476 // Internal VM locks on java objects
 477 // standard constructor, allows locking failures
 478 ObjectLocker::ObjectLocker(Handle obj, TRAPS) : _thread(THREAD), _obj(obj),
 479   _npm(_thread, _thread->at_preemptable_init() /* ignore_mark */), _skip_exit(false) {
 480   assert(!_thread->preempting(), "");
 481 
 482   _thread->check_for_valid_safepoint_state();
 483 
 484   if (_obj() != nullptr) {
 485     ObjectSynchronizer::enter(_obj, &_lock, _thread);
 486 
 487     if (_thread->preempting()) {
 488       // If preemption was cancelled we acquired the monitor after freezing
 489       // the frames. Redoing the vm call laterĀ in thaw will require us to
 490       // release it since the call should look like the original one. We
 491       // do it in ~ObjectLocker to reduce the window of time we hold the
 492       // monitor since we can't do anything useful with it now, and would
 493       // otherwise just force other vthreads to preempt in case they try
 494       // to acquire this monitor.
 495       _skip_exit = !_thread->preemption_cancelled();
 496       ObjectSynchronizer::read_monitor(_thread, _obj())->set_object_strong();
 497       _thread->set_pending_preempted_exception();
 498 
 499     }
 500   }
 501 }
 502 
 503 ObjectLocker::~ObjectLocker() {
 504   if (_obj() != nullptr && !_skip_exit) {
 505     ObjectSynchronizer::exit(_obj(), &_lock, _thread);
 506   }
 507 }
 508 
 509 void ObjectLocker::wait_uninterruptibly(TRAPS) {
 510   ObjectSynchronizer::waitUninterruptibly(_obj, 0, _thread);
 511   if (_thread->preempting()) {
 512     _skip_exit = true;
 513     ObjectSynchronizer::read_monitor(_thread, _obj())->set_object_strong();
 514     _thread->set_pending_preempted_exception();
 515   }
 516 }
 517 
 518 // -----------------------------------------------------------------------------
 519 //  Wait/Notify/NotifyAll
 520 // NOTE: must use heavy weight monitor to handle wait()
 521 
 522 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 523   JavaThread* current = THREAD;
 524   if (millis < 0) {
 525     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 526   }
 527 
 528   ObjectMonitor* monitor;
 529   monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
 530 
 531   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
 532   monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
 533 
 534   // This dummy call is in place to get around dtrace bug 6254741.  Once
 535   // that's fixed we can uncomment the following line, remove the call
 536   // and change this function back into a "void" func.
 537   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 538   int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
 539   return ret_code;
 540 }
 541 
 542 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
 543   assert(millis >= 0, "timeout value is negative");
 544 
 545   ObjectMonitor* monitor;
 546   monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
 547   monitor->wait(millis, false, THREAD);
 548 }
 549 
 550 
 551 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 552   JavaThread* current = THREAD;
 553 
 554   markWord mark = obj->mark();
 555   if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
 556     // Not inflated so there can't be any waiters to notify.
 557     return;
 558   }
 559   ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
 560   monitor->notify(CHECK);
 561 }
 562 
 563 // NOTE: see comment of notify()
 564 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 565   JavaThread* current = THREAD;
 566 
 567   markWord mark = obj->mark();
 568   if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
 569     // Not inflated so there can't be any waiters to notify.
 570     return;
 571   }
 572 
 573   ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
 574   monitor->notifyAll(CHECK);
 575 }
 576 
 577 // -----------------------------------------------------------------------------
 578 // Hash Code handling
 579 
 580 struct SharedGlobals {
 581   char         _pad_prefix[OM_CACHE_LINE_SIZE];
 582   // This is a highly shared mostly-read variable.
 583   // To avoid false-sharing it needs to be the sole occupant of a cache line.
 584   volatile int stw_random;
 585   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 586   // Hot RW variable -- Sequester to avoid false-sharing
 587   volatile int hc_sequence;
 588   DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 589 };
 590 
 591 static SharedGlobals GVars;
 592 
 593 // hashCode() generation :
 594 //
 595 // Possibilities:
 596 // * MD5Digest of {obj,stw_random}
 597 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
 598 // * A DES- or AES-style SBox[] mechanism
 599 // * One of the Phi-based schemes, such as:
 600 //   2654435761 = 2^32 * Phi (golden ratio)
 601 //   HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
 602 // * A variation of Marsaglia's shift-xor RNG scheme.
 603 // * (obj ^ stw_random) is appealing, but can result
 604 //   in undesirable regularity in the hashCode values of adjacent objects
 605 //   (objects allocated back-to-back, in particular).  This could potentially
 606 //   result in hashtable collisions and reduced hashtable efficiency.
 607 //   There are simple ways to "diffuse" the middle address bits over the
 608 //   generated hashCode values:
 609 
 610 static intptr_t get_next_hash(Thread* current, oop obj) {
 611   intptr_t value = 0;
 612   if (hashCode == 0) {
 613     // This form uses global Park-Miller RNG.
 614     // On MP system we'll have lots of RW access to a global, so the
 615     // mechanism induces lots of coherency traffic.
 616     value = os::random();
 617   } else if (hashCode == 1) {
 618     // This variation has the property of being stable (idempotent)
 619     // between STW operations.  This can be useful in some of the 1-0
 620     // synchronization schemes.
 621     intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
 622     value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
 623   } else if (hashCode == 2) {
 624     value = 1;            // for sensitivity testing
 625   } else if (hashCode == 3) {
 626     value = ++GVars.hc_sequence;
 627   } else if (hashCode == 4) {
 628     value = cast_from_oop<intptr_t>(obj);
 629   } else {
 630     // Marsaglia's xor-shift scheme with thread-specific state
 631     // This is probably the best overall implementation -- we'll
 632     // likely make this the default in future releases.
 633     unsigned t = current->_hashStateX;
 634     t ^= (t << 11);
 635     current->_hashStateX = current->_hashStateY;
 636     current->_hashStateY = current->_hashStateZ;
 637     current->_hashStateZ = current->_hashStateW;
 638     unsigned v = current->_hashStateW;
 639     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
 640     current->_hashStateW = v;
 641     value = v;
 642   }
 643 
 644   value &= markWord::hash_mask;
 645   if (value == 0) value = 0xBAD;
 646   assert(value != markWord::no_hash, "invariant");
 647   return value;
 648 }
 649 
 650 static intptr_t install_hash_code(Thread* current, oop obj) {
 651   assert(UseObjectMonitorTable, "must be");
 652 
 653   markWord mark = obj->mark_acquire();
 654   for (;;) {
 655     intptr_t hash = mark.hash();
 656     if (hash != 0) {
 657       return hash;
 658     }
 659 
 660     hash = get_next_hash(current, obj);
 661     const markWord old_mark = mark;
 662     const markWord new_mark = old_mark.copy_set_hash(hash);
 663 
 664     mark = obj->cas_set_mark(new_mark, old_mark);
 665     if (old_mark == mark) {
 666       return hash;
 667     }
 668   }
 669 }
 670 
 671 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
 672   if (UseObjectMonitorTable) {
 673     // Since the monitor isn't in the object header, the hash can simply be
 674     // installed in the object header.
 675     return install_hash_code(current, obj);
 676   }
 677 
 678   while (true) {
 679     ObjectMonitor* monitor = nullptr;
 680     markWord temp, test;
 681     intptr_t hash;
 682     markWord mark = obj->mark_acquire();
 683     if (mark.is_unlocked() || mark.is_fast_locked()) {
 684       hash = mark.hash();
 685       if (hash != 0) {                     // if it has a hash, just return it
 686         return hash;
 687       }
 688       hash = get_next_hash(current, obj);  // get a new hash
 689       temp = mark.copy_set_hash(hash);     // merge the hash into header
 690                                            // try to install the hash
 691       test = obj->cas_set_mark(temp, mark);
 692       if (test == mark) {                  // if the hash was installed, return it
 693         return hash;
 694       }
 695       // CAS failed, retry
 696       continue;
 697 
 698       // Failed to install the hash. It could be that another thread
 699       // installed the hash just before our attempt or inflation has
 700       // occurred or... so we fall thru to inflate the monitor for
 701       // stability and then install the hash.
 702     } else if (mark.has_monitor()) {
 703       monitor = mark.monitor();
 704       temp = monitor->header();
 705       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 706       hash = temp.hash();
 707       if (hash != 0) {
 708         // It has a hash.
 709 
 710         // Separate load of dmw/header above from the loads in
 711         // is_being_async_deflated().
 712 
 713         // dmw/header and _contentions may get written by different threads.
 714         // Make sure to observe them in the same order when having several observers.
 715         OrderAccess::loadload_for_IRIW();
 716 
 717         if (monitor->is_being_async_deflated()) {
 718           // But we can't safely use the hash if we detect that async
 719           // deflation has occurred. So we attempt to restore the
 720           // header/dmw to the object's header so that we only retry
 721           // once if the deflater thread happens to be slow.
 722           monitor->install_displaced_markword_in_object(obj);
 723           continue;
 724         }
 725         return hash;
 726       }
 727       // Fall thru so we only have one place that installs the hash in
 728       // the ObjectMonitor.
 729     }
 730 
 731     // NOTE: an async deflation can race after we get the monitor and
 732     // before we can update the ObjectMonitor's header with the hash
 733     // value below.
 734     assert(mark.has_monitor(), "must be");
 735     monitor = mark.monitor();
 736 
 737     // Load ObjectMonitor's header/dmw field and see if it has a hash.
 738     mark = monitor->header();
 739     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
 740     hash = mark.hash();
 741     if (hash == 0) {                       // if it does not have a hash
 742       hash = get_next_hash(current, obj);  // get a new hash
 743       temp = mark.copy_set_hash(hash)   ;  // merge the hash into header
 744       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 745       uintptr_t v = AtomicAccess::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
 746       test = markWord(v);
 747       if (test != mark) {
 748         // The attempt to update the ObjectMonitor's header/dmw field
 749         // did not work. This can happen if another thread managed to
 750         // merge in the hash just before our cmpxchg().
 751         // If we add any new usages of the header/dmw field, this code
 752         // will need to be updated.
 753         hash = test.hash();
 754         assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
 755         assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
 756       }
 757       if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
 758         // If we detect that async deflation has occurred, then we
 759         // attempt to restore the header/dmw to the object's header
 760         // so that we only retry once if the deflater thread happens
 761         // to be slow.
 762         monitor->install_displaced_markword_in_object(obj);
 763         continue;
 764       }
 765     }
 766     // We finally get the hash.
 767     return hash;
 768   }
 769 }
 770 
 771 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
 772                                                    Handle h_obj) {
 773   assert(current == JavaThread::current(), "Can only be called on current thread");
 774   oop obj = h_obj();
 775 
 776   markWord mark = obj->mark_acquire();
 777 
 778   if (mark.is_fast_locked()) {
 779     // fast-locking case, see if lock is in current's lock stack
 780     return current->lock_stack().contains(h_obj());
 781   }
 782 
 783   while (mark.has_monitor()) {
 784     ObjectMonitor* monitor = read_monitor(current, obj, mark);
 785     if (monitor != nullptr) {
 786       return monitor->is_entered(current) != 0;
 787     }
 788     // Racing with inflation/deflation, retry
 789     mark = obj->mark_acquire();
 790 
 791     if (mark.is_fast_locked()) {
 792       // Some other thread fast_locked, current could not have held the lock
 793       return false;
 794     }
 795   }
 796 
 797   // Unlocked case, header in place
 798   assert(mark.is_unlocked(), "sanity check");
 799   return false;
 800 }
 801 
 802 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
 803   oop obj = h_obj();
 804   markWord mark = obj->mark_acquire();
 805 
 806   if (mark.is_fast_locked()) {
 807     // fast-locked so get owner from the object.
 808     // owning_thread_from_object() may also return null here:
 809     return Threads::owning_thread_from_object(t_list, h_obj());
 810   }
 811 
 812   while (mark.has_monitor()) {
 813     ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
 814     if (monitor != nullptr) {
 815       return Threads::owning_thread_from_monitor(t_list, monitor);
 816     }
 817     // Racing with inflation/deflation, retry
 818     mark = obj->mark_acquire();
 819 
 820     if (mark.is_fast_locked()) {
 821       // Some other thread fast_locked
 822       return Threads::owning_thread_from_object(t_list, h_obj());
 823     }
 824   }
 825 
 826   // Unlocked case, header in place
 827   // Cannot have assertion since this object may have been
 828   // locked by another thread when reaching here.
 829   // assert(mark.is_unlocked(), "sanity check");
 830 
 831   return nullptr;
 832 }
 833 
 834 // Visitors ...
 835 
 836 // Iterate over all ObjectMonitors.
 837 template <typename Function>
 838 void ObjectSynchronizer::monitors_iterate(Function function) {
 839   MonitorList::Iterator iter = _in_use_list.iterator();
 840   while (iter.has_next()) {
 841     ObjectMonitor* monitor = iter.next();
 842     function(monitor);
 843   }
 844 }
 845 
 846 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
 847 // returns true.
 848 template <typename OwnerFilter>
 849 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
 850   monitors_iterate([&](ObjectMonitor* monitor) {
 851     // This function is only called at a safepoint or when the
 852     // target thread is suspended or when the target thread is
 853     // operating on itself. The current closures in use today are
 854     // only interested in an owned ObjectMonitor and ownership
 855     // cannot be dropped under the calling contexts so the
 856     // ObjectMonitor cannot be async deflated.
 857     if (monitor->has_owner() && filter(monitor)) {
 858       assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
 859 
 860       closure->do_monitor(monitor);
 861     }
 862   });
 863 }
 864 
 865 // Iterate ObjectMonitors where the owner == thread; this does NOT include
 866 // ObjectMonitors where owner is set to a stack-lock address in thread.
 867 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
 868   int64_t key = ObjectMonitor::owner_id_from(thread);
 869   auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
 870   return owned_monitors_iterate_filtered(closure, thread_filter);
 871 }
 872 
 873 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
 874   int64_t key = ObjectMonitor::owner_id_from(vthread);
 875   auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
 876   return owned_monitors_iterate_filtered(closure, thread_filter);
 877 }
 878 
 879 // Iterate ObjectMonitors owned by any thread.
 880 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
 881   auto all_filter = [&](ObjectMonitor* monitor) { return true; };
 882   return owned_monitors_iterate_filtered(closure, all_filter);
 883 }
 884 
 885 static bool monitors_used_above_threshold(MonitorList* list) {
 886   if (MonitorUsedDeflationThreshold == 0) {  // disabled case is easy
 887     return false;
 888   }
 889   size_t monitors_used = list->count();
 890   if (monitors_used == 0) {  // empty list is easy
 891     return false;
 892   }
 893   size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
 894   // Make sure that we use a ceiling value that is not lower than
 895   // previous, not lower than the recorded max used by the system, and
 896   // not lower than the current number of monitors in use (which can
 897   // race ahead of max). The result is guaranteed > 0.
 898   size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
 899 
 900   // Check if our monitor usage is above the threshold:
 901   size_t monitor_usage = (monitors_used * 100LL) / ceiling;
 902   if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
 903     // Deflate monitors if over the threshold percentage, unless no
 904     // progress on previous deflations.
 905     bool is_above_threshold = true;
 906 
 907     // Check if it's time to adjust the in_use_list_ceiling up, due
 908     // to too many async deflation attempts without any progress.
 909     if (NoAsyncDeflationProgressMax != 0 &&
 910         _no_progress_cnt >= NoAsyncDeflationProgressMax) {
 911       double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
 912       size_t delta = (size_t)(ceiling * remainder) + 1;
 913       size_t new_ceiling = (ceiling > SIZE_MAX - delta)
 914         ? SIZE_MAX         // Overflow, let's clamp new_ceiling.
 915         : ceiling + delta;
 916 
 917       ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
 918       log_info(monitorinflation)("Too many deflations without progress; "
 919                                  "bumping in_use_list_ceiling from %zu"
 920                                  " to %zu", old_ceiling, new_ceiling);
 921       _no_progress_cnt = 0;
 922       ceiling = new_ceiling;
 923 
 924       // Check if our monitor usage is still above the threshold:
 925       monitor_usage = (monitors_used * 100LL) / ceiling;
 926       is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
 927     }
 928     log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
 929                                ", monitor_usage=%zu, threshold=%d",
 930                                monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
 931     return is_above_threshold;
 932   }
 933 
 934   return false;
 935 }
 936 
 937 size_t ObjectSynchronizer::in_use_list_count() {
 938   return _in_use_list.count();
 939 }
 940 
 941 size_t ObjectSynchronizer::in_use_list_max() {
 942   return _in_use_list.max();
 943 }
 944 
 945 size_t ObjectSynchronizer::in_use_list_ceiling() {
 946   return _in_use_list_ceiling;
 947 }
 948 
 949 void ObjectSynchronizer::dec_in_use_list_ceiling() {
 950   AtomicAccess::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
 951 }
 952 
 953 void ObjectSynchronizer::inc_in_use_list_ceiling() {
 954   AtomicAccess::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
 955 }
 956 
 957 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
 958   _in_use_list_ceiling = new_value;
 959 }
 960 
 961 bool ObjectSynchronizer::is_async_deflation_needed() {
 962   if (is_async_deflation_requested()) {
 963     // Async deflation request.
 964     log_info(monitorinflation)("Async deflation needed: explicit request");
 965     return true;
 966   }
 967 
 968   jlong time_since_last = time_since_last_async_deflation_ms();
 969 
 970   if (AsyncDeflationInterval > 0 &&
 971       time_since_last > AsyncDeflationInterval &&
 972       monitors_used_above_threshold(&_in_use_list)) {
 973     // It's been longer than our specified deflate interval and there
 974     // are too many monitors in use. We don't deflate more frequently
 975     // than AsyncDeflationInterval (unless is_async_deflation_requested)
 976     // in order to not swamp the MonitorDeflationThread.
 977     log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
 978     return true;
 979   }
 980 
 981   if (GuaranteedAsyncDeflationInterval > 0 &&
 982       time_since_last > GuaranteedAsyncDeflationInterval) {
 983     // It's been longer than our specified guaranteed deflate interval.
 984     // We need to clean up the used monitors even if the threshold is
 985     // not reached, to keep the memory utilization at bay when many threads
 986     // touched many monitors.
 987     log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
 988                                "is greater than time since last deflation (" JLONG_FORMAT " ms)",
 989                                GuaranteedAsyncDeflationInterval, time_since_last);
 990 
 991     // If this deflation has no progress, then it should not affect the no-progress
 992     // tracking, otherwise threshold heuristics would think it was triggered, experienced
 993     // no progress, and needs to backoff more aggressively. In this "no progress" case,
 994     // the generic code would bump the no-progress counter, and we compensate for that
 995     // by telling it to skip the update.
 996     //
 997     // If this deflation has progress, then it should let non-progress tracking
 998     // know about this, otherwise the threshold heuristics would kick in, potentially
 999     // experience no-progress due to aggressive cleanup by this deflation, and think
1000     // it is still in no-progress stride. In this "progress" case, the generic code would
1001     // zero the counter, and we allow it to happen.
1002     _no_progress_skip_increment = true;
1003 
1004     return true;
1005   }
1006 
1007   return false;
1008 }
1009 
1010 void ObjectSynchronizer::request_deflate_idle_monitors() {
1011   MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1012   set_is_async_deflation_requested(true);
1013   ml.notify_all();
1014 }
1015 
1016 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1017   JavaThread* current = JavaThread::current();
1018   bool ret_code = false;
1019 
1020   jlong last_time = last_async_deflation_time_ns();
1021 
1022   request_deflate_idle_monitors();
1023 
1024   const int N_CHECKS = 5;
1025   for (int i = 0; i < N_CHECKS; i++) {  // sleep for at most 5 seconds
1026     if (last_async_deflation_time_ns() > last_time) {
1027       log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1028       ret_code = true;
1029       break;
1030     }
1031     {
1032       // JavaThread has to honor the blocking protocol.
1033       ThreadBlockInVM tbivm(current);
1034       os::naked_short_sleep(999);  // sleep for almost 1 second
1035     }
1036   }
1037   if (!ret_code) {
1038     log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1039   }
1040 
1041   return ret_code;
1042 }
1043 
1044 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1045   return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1046 }
1047 
1048 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1049 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1050 //
1051 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1052   MonitorList::Iterator iter = _in_use_list.iterator();
1053   size_t deflated_count = 0;
1054   Thread* current = Thread::current();
1055 
1056   while (iter.has_next()) {
1057     if (deflated_count >= (size_t)MonitorDeflationMax) {
1058       break;
1059     }
1060     ObjectMonitor* mid = iter.next();
1061     if (mid->deflate_monitor(current)) {
1062       deflated_count++;
1063     }
1064 
1065     // Must check for a safepoint/handshake and honor it.
1066     safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1067   }
1068 
1069   return deflated_count;
1070 }
1071 
1072 class DeflationHandshakeClosure : public HandshakeClosure {
1073  public:
1074   DeflationHandshakeClosure() : HandshakeClosure("DeflationHandshakeClosure") {}
1075 
1076   void do_thread(Thread* thread) {
1077     log_trace(monitorinflation)("DeflationHandshakeClosure::do_thread: thread="
1078                                 INTPTR_FORMAT, p2i(thread));
1079     if (thread->is_Java_thread()) {
1080       // Clear OM cache
1081       JavaThread* jt = JavaThread::cast(thread);
1082       jt->om_clear_monitor_cache();
1083     }
1084   }
1085 };
1086 
1087 class VM_RendezvousGCThreads : public VM_Operation {
1088 public:
1089   bool evaluate_at_safepoint() const override { return false; }
1090   VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1091   void doit() override {
1092     Universe::heap()->safepoint_synchronize_begin();
1093     Universe::heap()->safepoint_synchronize_end();
1094   };
1095 };
1096 
1097 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1098                               ObjectMonitorDeflationSafepointer* safepointer) {
1099   NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1100   size_t deleted_count = 0;
1101   for (ObjectMonitor* monitor: *delete_list) {
1102     delete monitor;
1103     deleted_count++;
1104     // A JavaThread must check for a safepoint/handshake and honor it.
1105     safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1106   }
1107   return deleted_count;
1108 }
1109 
1110 class ObjectMonitorDeflationLogging: public StackObj {
1111   LogStreamHandle(Debug, monitorinflation) _debug;
1112   LogStreamHandle(Info, monitorinflation)  _info;
1113   LogStream*                               _stream;
1114   elapsedTimer                             _timer;
1115 
1116   size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1117   size_t count() const   { return ObjectSynchronizer::in_use_list_count(); }
1118   size_t max() const     { return ObjectSynchronizer::in_use_list_max(); }
1119 
1120 public:
1121   ObjectMonitorDeflationLogging()
1122     : _debug(), _info(), _stream(nullptr) {
1123     if (_debug.is_enabled()) {
1124       _stream = &_debug;
1125     } else if (_info.is_enabled()) {
1126       _stream = &_info;
1127     }
1128   }
1129 
1130   void begin() {
1131     if (_stream != nullptr) {
1132       _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1133                         ceiling(), count(), max());
1134       _timer.start();
1135     }
1136   }
1137 
1138   void before_handshake(size_t unlinked_count) {
1139     if (_stream != nullptr) {
1140       _timer.stop();
1141       _stream->print_cr("before handshaking: unlinked_count=%zu"
1142                         ", in_use_list stats: ceiling=%zu, count="
1143                         "%zu, max=%zu",
1144                         unlinked_count, ceiling(), count(), max());
1145     }
1146   }
1147 
1148   void after_handshake() {
1149     if (_stream != nullptr) {
1150       _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1151                         "%zu, count=%zu, max=%zu",
1152                         ceiling(), count(), max());
1153       _timer.start();
1154     }
1155   }
1156 
1157   void end(size_t deflated_count, size_t unlinked_count) {
1158     if (_stream != nullptr) {
1159       _timer.stop();
1160       if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1161         _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1162                           deflated_count, unlinked_count, _timer.seconds());
1163       }
1164       _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1165                         ceiling(), count(), max());
1166     }
1167   }
1168 
1169   void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1170     if (_stream != nullptr) {
1171       _timer.stop();
1172       _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1173                         "%zu, count=%zu, max=%zu",
1174                         op_name, cnt_name, cnt, ceiling(), count(), max());
1175     }
1176   }
1177 
1178   void after_block_for_safepoint(const char* op_name) {
1179     if (_stream != nullptr) {
1180       _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1181                         ", count=%zu, max=%zu", op_name,
1182                         ceiling(), count(), max());
1183       _timer.start();
1184     }
1185   }
1186 };
1187 
1188 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1189   if (!SafepointMechanism::should_process(_current)) {
1190     return;
1191   }
1192 
1193   // A safepoint/handshake has started.
1194   _log->before_block_for_safepoint(op_name, count_name, counter);
1195 
1196   {
1197     // Honor block request.
1198     ThreadBlockInVM tbivm(_current);
1199   }
1200 
1201   _log->after_block_for_safepoint(op_name);
1202 }
1203 
1204 // This function is called by the MonitorDeflationThread to deflate
1205 // ObjectMonitors.
1206 size_t ObjectSynchronizer::deflate_idle_monitors() {
1207   JavaThread* current = JavaThread::current();
1208   assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1209 
1210   // The async deflation request has been processed.
1211   _last_async_deflation_time_ns = os::javaTimeNanos();
1212   set_is_async_deflation_requested(false);
1213 
1214   ObjectMonitorDeflationLogging log;
1215   ObjectMonitorDeflationSafepointer safepointer(current, &log);
1216 
1217   log.begin();
1218 
1219   // Deflate some idle ObjectMonitors.
1220   size_t deflated_count = deflate_monitor_list(&safepointer);
1221 
1222   // Unlink the deflated ObjectMonitors from the in-use list.
1223   size_t unlinked_count = 0;
1224   size_t deleted_count = 0;
1225   if (deflated_count > 0) {
1226     ResourceMark rm(current);
1227     GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1228     unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1229 
1230 #ifdef ASSERT
1231     if (UseObjectMonitorTable) {
1232       for (ObjectMonitor* monitor : delete_list) {
1233         assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1234       }
1235     }
1236 #endif
1237 
1238     log.before_handshake(unlinked_count);
1239 
1240     // A JavaThread needs to handshake in order to safely free the
1241     // ObjectMonitors that were deflated in this cycle.
1242     DeflationHandshakeClosure dhc;
1243     Handshake::execute(&dhc);
1244     // Also, we sync and desync GC threads around the handshake, so that they can
1245     // safely read the mark-word and look-through to the object-monitor, without
1246     // being afraid that the object-monitor is going away.
1247     VM_RendezvousGCThreads sync_gc;
1248     VMThread::execute(&sync_gc);
1249 
1250     log.after_handshake();
1251 
1252     // After the handshake, safely free the ObjectMonitors that were
1253     // deflated and unlinked in this cycle.
1254 
1255     // Delete the unlinked ObjectMonitors.
1256     deleted_count = delete_monitors(&delete_list, &safepointer);
1257     assert(unlinked_count == deleted_count, "must be");
1258   }
1259 
1260   log.end(deflated_count, unlinked_count);
1261 
1262   GVars.stw_random = os::random();
1263 
1264   if (deflated_count != 0) {
1265     _no_progress_cnt = 0;
1266   } else if (_no_progress_skip_increment) {
1267     _no_progress_skip_increment = false;
1268   } else {
1269     _no_progress_cnt++;
1270   }
1271 
1272   return deflated_count;
1273 }
1274 
1275 // Monitor cleanup on JavaThread::exit
1276 
1277 // Iterate through monitor cache and attempt to release thread's monitors
1278 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1279  private:
1280   JavaThread* _thread;
1281 
1282  public:
1283   ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1284   void do_monitor(ObjectMonitor* mid) {
1285     mid->complete_exit(_thread);
1286   }
1287 };
1288 
1289 // Release all inflated monitors owned by current thread.  Lightweight monitors are
1290 // ignored.  This is meant to be called during JNI thread detach which assumes
1291 // all remaining monitors are heavyweight.  All exceptions are swallowed.
1292 // Scanning the extant monitor list can be time consuming.
1293 // A simple optimization is to add a per-thread flag that indicates a thread
1294 // called jni_monitorenter() during its lifetime.
1295 //
1296 // Instead of NoSafepointVerifier it might be cheaper to
1297 // use an idiom of the form:
1298 //   auto int tmp = SafepointSynchronize::_safepoint_counter ;
1299 //   <code that must not run at safepoint>
1300 //   guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1301 // Since the tests are extremely cheap we could leave them enabled
1302 // for normal product builds.
1303 
1304 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1305   assert(current == JavaThread::current(), "must be current Java thread");
1306   NoSafepointVerifier nsv;
1307   ReleaseJavaMonitorsClosure rjmc(current);
1308   ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1309   assert(!current->has_pending_exception(), "Should not be possible");
1310   current->clear_pending_exception();
1311 }
1312 
1313 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1314   switch (cause) {
1315     case inflate_cause_vm_internal:    return "VM Internal";
1316     case inflate_cause_monitor_enter:  return "Monitor Enter";
1317     case inflate_cause_wait:           return "Monitor Wait";
1318     case inflate_cause_notify:         return "Monitor Notify";
1319     case inflate_cause_jni_enter:      return "JNI Monitor Enter";
1320     case inflate_cause_jni_exit:       return "JNI Monitor Exit";
1321     default:
1322       ShouldNotReachHere();
1323   }
1324   return "Unknown";
1325 }
1326 
1327 //------------------------------------------------------------------------------
1328 // Debugging code
1329 
1330 u_char* ObjectSynchronizer::get_gvars_addr() {
1331   return (u_char*)&GVars;
1332 }
1333 
1334 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1335   return (u_char*)&GVars.hc_sequence;
1336 }
1337 
1338 size_t ObjectSynchronizer::get_gvars_size() {
1339   return sizeof(SharedGlobals);
1340 }
1341 
1342 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1343   return (u_char*)&GVars.stw_random;
1344 }
1345 
1346 // Do the final audit and print of ObjectMonitor stats; must be done
1347 // by the VMThread at VM exit time.
1348 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1349   assert(Thread::current()->is_VM_thread(), "sanity check");
1350 
1351   if (is_final_audit()) {  // Only do the audit once.
1352     return;
1353   }
1354   set_is_final_audit();
1355   log_info(monitorinflation)("Starting the final audit.");
1356 
1357   if (log_is_enabled(Info, monitorinflation)) {
1358     LogStreamHandle(Info, monitorinflation) ls;
1359     audit_and_print_stats(&ls, true /* on_exit */);
1360   }
1361 }
1362 
1363 // This function can be called by the MonitorDeflationThread or it can be called when
1364 // we are trying to exit the VM. The list walker functions can run in parallel with
1365 // the other list operations.
1366 // Calls to this function can be added in various places as a debugging
1367 // aid.
1368 //
1369 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1370   int error_cnt = 0;
1371 
1372   ls->print_cr("Checking in_use_list:");
1373   chk_in_use_list(ls, &error_cnt);
1374 
1375   if (error_cnt == 0) {
1376     ls->print_cr("No errors found in in_use_list checks.");
1377   } else {
1378     log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1379   }
1380 
1381   // When exiting, only log the interesting entries at the Info level.
1382   // When called at intervals by the MonitorDeflationThread, log output
1383   // at the Trace level since there can be a lot of it.
1384   if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1385     LogStreamHandle(Trace, monitorinflation) ls_tr;
1386     log_in_use_monitor_details(&ls_tr, true /* log_all */);
1387   } else if (on_exit) {
1388     log_in_use_monitor_details(ls, false /* log_all */);
1389   }
1390 
1391   ls->flush();
1392 
1393   guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1394 }
1395 
1396 // Check the in_use_list; log the results of the checks.
1397 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1398   size_t l_in_use_count = _in_use_list.count();
1399   size_t l_in_use_max = _in_use_list.max();
1400   out->print_cr("count=%zu, max=%zu", l_in_use_count,
1401                 l_in_use_max);
1402 
1403   size_t ck_in_use_count = 0;
1404   MonitorList::Iterator iter = _in_use_list.iterator();
1405   while (iter.has_next()) {
1406     ObjectMonitor* mid = iter.next();
1407     chk_in_use_entry(mid, out, error_cnt_p);
1408     ck_in_use_count++;
1409   }
1410 
1411   if (l_in_use_count == ck_in_use_count) {
1412     out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
1413                   l_in_use_count, ck_in_use_count);
1414   } else {
1415     out->print_cr("WARNING: in_use_count=%zu is not equal to "
1416                   "ck_in_use_count=%zu", l_in_use_count,
1417                   ck_in_use_count);
1418   }
1419 
1420   size_t ck_in_use_max = _in_use_list.max();
1421   if (l_in_use_max == ck_in_use_max) {
1422     out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
1423                   l_in_use_max, ck_in_use_max);
1424   } else {
1425     out->print_cr("WARNING: in_use_max=%zu is not equal to "
1426                   "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
1427   }
1428 }
1429 
1430 // Check an in-use monitor entry; log any errors.
1431 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1432                                           int* error_cnt_p) {
1433   if (n->owner_is_DEFLATER_MARKER()) {
1434     // This could happen when monitor deflation blocks for a safepoint.
1435     return;
1436   }
1437 
1438 
1439   if (n->metadata() == 0) {
1440     out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1441                   "have non-null _metadata (header/hash) field.", p2i(n));
1442     *error_cnt_p = *error_cnt_p + 1;
1443   }
1444 
1445   const oop obj = n->object_peek();
1446   if (obj == nullptr) {
1447     return;
1448   }
1449 
1450   const markWord mark = obj->mark();
1451   if (!mark.has_monitor()) {
1452     out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1453                   "object does not think it has a monitor: obj="
1454                   INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1455                   p2i(obj), mark.value());
1456     *error_cnt_p = *error_cnt_p + 1;
1457     return;
1458   }
1459 
1460   ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
1461   if (n != obj_mon) {
1462     out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1463                   "object does not refer to the same monitor: obj="
1464                   INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1465                   INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1466     *error_cnt_p = *error_cnt_p + 1;
1467   }
1468 }
1469 
1470 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1471 // flags indicate why the entry is in-use, 'object' and 'object type'
1472 // indicate the associated object and its type.
1473 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
1474   if (_in_use_list.count() > 0) {
1475     stringStream ss;
1476     out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
1477     out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1478     out->print_cr("%18s  %s  %18s  %18s",
1479                   "monitor", "BHL", "object", "object type");
1480     out->print_cr("==================  ===  ==================  ==================");
1481 
1482     auto is_interesting = [&](ObjectMonitor* monitor) {
1483       return log_all || monitor->has_owner() || monitor->is_busy();
1484     };
1485 
1486     monitors_iterate([&](ObjectMonitor* monitor) {
1487       if (is_interesting(monitor)) {
1488         const oop obj = monitor->object_peek();
1489         const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
1490         ResourceMark rm;
1491         out->print(INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT "  %s", p2i(monitor),
1492                    monitor->is_busy(), hash != 0, monitor->has_owner(),
1493                    p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
1494         if (monitor->is_busy()) {
1495           out->print(" (%s)", monitor->is_busy_to_string(&ss));
1496           ss.reset();
1497         }
1498         out->cr();
1499       }
1500     });
1501   }
1502 
1503   out->flush();
1504 }