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/collectedHeap.hpp"
  28 #include "jfr/jfrEvents.hpp"
  29 #include "logging/log.hpp"
  30 #include "logging/logStream.hpp"
  31 #include "memory/allocation.inline.hpp"
  32 #include "memory/padded.hpp"
  33 #include "memory/resourceArea.hpp"
  34 #include "memory/universe.hpp"
  35 #include "oops/markWord.hpp"
  36 #include "oops/oop.inline.hpp"
  37 #include "runtime/atomic.hpp"
  38 #include "runtime/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/lockStack.inline.hpp"
  45 #include "runtime/mutexLocker.hpp"
  46 #include "runtime/objectMonitor.hpp"
  47 #include "runtime/objectMonitor.inline.hpp"
  48 #include "runtime/os.inline.hpp"
  49 #include "runtime/osThread.hpp"
  50 #include "runtime/perfData.hpp"
  51 #include "runtime/safepointMechanism.inline.hpp"
  52 #include "runtime/safepointVerifiers.hpp"
  53 #include "runtime/sharedRuntime.hpp"
  54 #include "runtime/stubRoutines.hpp"
  55 #include "runtime/synchronizer.hpp"
  56 #include "runtime/threads.hpp"
  57 #include "runtime/timer.hpp"
  58 #include "runtime/trimNativeHeap.hpp"
  59 #include "runtime/vframe.hpp"
  60 #include "runtime/vmThread.hpp"
  61 #include "utilities/align.hpp"
  62 #include "utilities/dtrace.hpp"
  63 #include "utilities/events.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 = Atomic::load(&_head);
  74     m->set_next_om(head);
  75   } while (Atomic::cmpxchg(&_head, head, m) != head);
  76 
  77   size_t count = Atomic::add(&_count, 1u);
  78   if (count > max()) {
  79     Atomic::inc(&_max);
  80   }
  81 }
  82 
  83 size_t MonitorList::count() const {
  84   return Atomic::load(&_count);
  85 }
  86 
  87 size_t MonitorList::max() const {
  88   return Atomic::load(&_max);
  89 }
  90 
  91 class ObjectMonitorDeflationSafepointer : public StackObj {
  92   JavaThread* const                    _current;
  93   ObjectMonitorDeflationLogging* const _log;
  94 
  95 public:
  96   ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
  97     : _current(current), _log(log) {}
  98 
  99   void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
 100 };
 101 
 102 // Walk the in-use list and unlink deflated ObjectMonitors.
 103 // Returns the number of unlinked ObjectMonitors.
 104 size_t MonitorList::unlink_deflated(size_t deflated_count,
 105                                     GrowableArray<ObjectMonitor*>* unlinked_list,
 106                                     ObjectMonitorDeflationSafepointer* safepointer) {
 107   size_t unlinked_count = 0;
 108   ObjectMonitor* prev = nullptr;
 109   ObjectMonitor* m = Atomic::load_acquire(&_head);
 110 
 111   while (m != nullptr) {
 112     if (m->is_being_async_deflated()) {
 113       // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
 114       // modify the list once per batch. The batch starts at "m".
 115       size_t unlinked_batch = 0;
 116       ObjectMonitor* next = m;
 117       // Look for at most MonitorUnlinkBatch monitors, or the number of
 118       // deflated and not unlinked monitors, whatever comes first.
 119       assert(deflated_count >= unlinked_count, "Sanity: underflow");
 120       size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
 121       do {
 122         ObjectMonitor* next_next = next->next_om();
 123         unlinked_batch++;
 124         unlinked_list->append(next);
 125         next = next_next;
 126         if (unlinked_batch >= unlinked_batch_limit) {
 127           // Reached the max batch, so bail out of the gathering loop.
 128           break;
 129         }
 130         if (prev == nullptr && Atomic::load(&_head) != m) {
 131           // Current batch used to be at head, but it is not at head anymore.
 132           // Bail out and figure out where we currently are. This avoids long
 133           // walks searching for new prev during unlink under heavy list inserts.
 134           break;
 135         }
 136       } while (next != nullptr && next->is_being_async_deflated());
 137 
 138       // Unlink the found batch.
 139       if (prev == nullptr) {
 140         // The current batch is the first batch, so there is a chance that it starts at head.
 141         // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
 142         ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, m, next);
 143         if (prev_head != m) {
 144           // Something must have updated the head. Figure out the actual prev for this batch.
 145           for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
 146             prev = n;
 147           }
 148           assert(prev != nullptr, "Should have found the prev for the current batch");
 149           prev->set_next_om(next);
 150         }
 151       } else {
 152         // The current batch is preceded by another batch. This guarantees the current batch
 153         // does not start at head. Unlink the entire current batch without updating the head.
 154         assert(Atomic::load(&_head) != m, "Sanity");
 155         prev->set_next_om(next);
 156       }
 157 
 158       unlinked_count += unlinked_batch;
 159       if (unlinked_count >= deflated_count) {
 160         // Reached the max so bail out of the searching loop.
 161         // There should be no more deflated monitors left.
 162         break;
 163       }
 164       m = next;
 165     } else {
 166       prev = m;
 167       m = m->next_om();
 168     }
 169 
 170     // Must check for a safepoint/handshake and honor it.
 171     safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
 172   }
 173 
 174 #ifdef ASSERT
 175   // Invariant: the code above should unlink all deflated monitors.
 176   // The code that runs after this unlinking does not expect deflated monitors.
 177   // Notably, attempting to deflate the already deflated monitor would break.
 178   {
 179     ObjectMonitor* m = Atomic::load_acquire(&_head);
 180     while (m != nullptr) {
 181       assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
 182       m = m->next_om();
 183     }
 184   }
 185 #endif
 186 
 187   Atomic::sub(&_count, unlinked_count);
 188   return unlinked_count;
 189 }
 190 
 191 MonitorList::Iterator MonitorList::iterator() const {
 192   return Iterator(Atomic::load_acquire(&_head));
 193 }
 194 
 195 ObjectMonitor* MonitorList::Iterator::next() {
 196   ObjectMonitor* current = _current;
 197   _current = current->next_om();
 198   return current;
 199 }
 200 
 201 // The "core" versions of monitor enter and exit reside in this file.
 202 // The interpreter and compilers contain specialized transliterated
 203 // variants of the enter-exit fast-path operations.  See c2_MacroAssembler_x86.cpp
 204 // fast_lock(...) for instance.  If you make changes here, make sure to modify the
 205 // interpreter, and both C1 and C2 fast-path inline locking code emission.
 206 //
 207 // -----------------------------------------------------------------------------
 208 
 209 #ifdef DTRACE_ENABLED
 210 
 211 // Only bother with this argument setup if dtrace is available
 212 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
 213 
 214 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
 215   char* bytes = nullptr;                                                      \
 216   int len = 0;                                                             \
 217   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
 218   Symbol* klassname = obj->klass()->name();                                \
 219   if (klassname != nullptr) {                                                 \
 220     bytes = (char*)klassname->bytes();                                     \
 221     len = klassname->utf8_length();                                        \
 222   }
 223 
 224 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
 225   {                                                                        \
 226     if (DTraceMonitorProbes) {                                             \
 227       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 228       HOTSPOT_MONITOR_WAIT(jtid,                                           \
 229                            (uintptr_t)(monitor), bytes, len, (millis));    \
 230     }                                                                      \
 231   }
 232 
 233 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
 234 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
 235 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
 236 
 237 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
 238   {                                                                        \
 239     if (DTraceMonitorProbes) {                                             \
 240       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 241       HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */             \
 242                                     (uintptr_t)(monitor), bytes, len);     \
 243     }                                                                      \
 244   }
 245 
 246 #else //  ndef DTRACE_ENABLED
 247 
 248 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 249 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 250 
 251 #endif // ndef DTRACE_ENABLED
 252 
 253 // This exists only as a workaround of dtrace bug 6254741
 254 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
 255   DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
 256   return 0;
 257 }
 258 
 259 static constexpr size_t inflation_lock_count() {
 260   return 256;
 261 }
 262 
 263 // Static storage for an array of PlatformMutex.
 264 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
 265 
 266 static inline PlatformMutex* inflation_lock(size_t index) {
 267   return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
 268 }
 269 
 270 void ObjectSynchronizer::initialize() {
 271   for (size_t i = 0; i < inflation_lock_count(); i++) {
 272     ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
 273   }
 274   // Start the ceiling with the estimate for one thread.
 275   set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
 276 
 277   // Start the timer for deflations, so it does not trigger immediately.
 278   _last_async_deflation_time_ns = os::javaTimeNanos();
 279 }
 280 
 281 MonitorList ObjectSynchronizer::_in_use_list;
 282 // monitors_used_above_threshold() policy is as follows:
 283 //
 284 // The ratio of the current _in_use_list count to the ceiling is used
 285 // to determine if we are above MonitorUsedDeflationThreshold and need
 286 // to do an async monitor deflation cycle. The ceiling is increased by
 287 // AvgMonitorsPerThreadEstimate when a thread is added to the system
 288 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
 289 // removed from the system.
 290 //
 291 // Note: If the _in_use_list max exceeds the ceiling, then
 292 // monitors_used_above_threshold() will use the in_use_list max instead
 293 // of the thread count derived ceiling because we have used more
 294 // ObjectMonitors than the estimated average.
 295 //
 296 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
 297 // no-progress async monitor deflation cycles in a row, then the ceiling
 298 // is adjusted upwards by monitors_used_above_threshold().
 299 //
 300 // Start the ceiling with the estimate for one thread in initialize()
 301 // which is called after cmd line options are processed.
 302 static size_t _in_use_list_ceiling = 0;
 303 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
 304 bool volatile ObjectSynchronizer::_is_final_audit = false;
 305 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
 306 static uintx _no_progress_cnt = 0;
 307 static bool _no_progress_skip_increment = false;
 308 
 309 // =====================> Quick functions
 310 
 311 // The quick_* forms are special fast-path variants used to improve
 312 // performance.  In the simplest case, a "quick_*" implementation could
 313 // simply return false, in which case the caller will perform the necessary
 314 // state transitions and call the slow-path form.
 315 // The fast-path is designed to handle frequently arising cases in an efficient
 316 // manner and is just a degenerate "optimistic" variant of the slow-path.
 317 // returns true  -- to indicate the call was satisfied.
 318 // returns false -- to indicate the call needs the services of the slow-path.
 319 // A no-loitering ordinance is in effect for code in the quick_* family
 320 // operators: safepoints or indefinite blocking (blocking that might span a
 321 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
 322 // entry.
 323 //
 324 // Consider: An interesting optimization is to have the JIT recognize the
 325 // following common idiom:
 326 //   synchronized (someobj) { .... ; notify(); }
 327 // That is, we find a notify() or notifyAll() call that immediately precedes
 328 // the monitorexit operation.  In that case the JIT could fuse the operations
 329 // into a single notifyAndExit() runtime primitive.
 330 
 331 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
 332   assert(current->thread_state() == _thread_in_Java, "invariant");
 333   NoSafepointVerifier nsv;
 334   if (obj == nullptr) return false;  // slow-path for invalid obj
 335   const markWord mark = obj->mark();
 336 
 337   if (LockingMode == LM_LIGHTWEIGHT) {
 338     if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
 339       // Degenerate notify
 340       // fast-locked by caller so by definition the implied waitset is empty.
 341       return true;
 342     }
 343   } else if (LockingMode == LM_LEGACY) {
 344     if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 345       // Degenerate notify
 346       // stack-locked by caller so by definition the implied waitset is empty.
 347       return true;
 348     }
 349   }
 350 
 351   if (mark.has_monitor()) {
 352     ObjectMonitor* const mon = mark.monitor();
 353     assert(mon->object() == oop(obj), "invariant");
 354     if (mon->owner() != current) return false;  // slow-path for IMS exception
 355 
 356     if (mon->first_waiter() != nullptr) {
 357       // We have one or more waiters. Since this is an inflated monitor
 358       // that we own, we can transfer one or more threads from the waitset
 359       // to the entrylist here and now, avoiding the slow-path.
 360       if (all) {
 361         DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
 362       } else {
 363         DTRACE_MONITOR_PROBE(notify, mon, obj, current);
 364       }
 365       int free_count = 0;
 366       do {
 367         mon->INotify(current);
 368         ++free_count;
 369       } while (mon->first_waiter() != nullptr && all);
 370       OM_PERFDATA_OP(Notifications, inc(free_count));
 371     }
 372     return true;
 373   }
 374 
 375   // other IMS exception states take the slow-path
 376   return false;
 377 }
 378 
 379 
 380 // The LockNode emitted directly at the synchronization site would have
 381 // been too big if it were to have included support for the cases of inflated
 382 // recursive enter and exit, so they go here instead.
 383 // Note that we can't safely call AsyncPrintJavaStack() from within
 384 // quick_enter() as our thread state remains _in_Java.
 385 
 386 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
 387                                      BasicLock * lock) {
 388   assert(current->thread_state() == _thread_in_Java, "invariant");
 389   NoSafepointVerifier nsv;
 390   if (obj == nullptr) return false;       // Need to throw NPE
 391 
 392   if (obj->klass()->is_value_based()) {
 393     return false;
 394   }
 395 
 396   if (LockingMode == LM_LIGHTWEIGHT) {
 397     LockStack& lock_stack = current->lock_stack();
 398     if (lock_stack.is_full()) {
 399       // Always go into runtime if the lock stack is full.
 400       return false;
 401     }
 402     if (lock_stack.try_recursive_enter(obj)) {
 403       // Recursive lock successful.
 404       current->inc_held_monitor_count();
 405       return true;
 406     }
 407   }
 408 
 409   const markWord mark = obj->mark();
 410 
 411   if (mark.has_monitor()) {
 412     ObjectMonitor* const m = mark.monitor();
 413     // An async deflation or GC can race us before we manage to make
 414     // the ObjectMonitor busy by setting the owner below. If we detect
 415     // that race we just bail out to the slow-path here.
 416     if (m->object_peek() == nullptr) {
 417       return false;
 418     }
 419     JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
 420 
 421     // Lock contention and Transactional Lock Elision (TLE) diagnostics
 422     // and observability
 423     // Case: light contention possibly amenable to TLE
 424     // Case: TLE inimical operations such as nested/recursive synchronization
 425 
 426     if (owner == current) {
 427       m->_recursions++;
 428       current->inc_held_monitor_count();
 429       return true;
 430     }
 431 
 432     if (LockingMode != LM_LIGHTWEIGHT) {
 433       // This Java Monitor is inflated so obj's header will never be
 434       // displaced to this thread's BasicLock. Make the displaced header
 435       // non-null so this BasicLock is not seen as recursive nor as
 436       // being locked. We do this unconditionally so that this thread's
 437       // BasicLock cannot be mis-interpreted by any stack walkers. For
 438       // performance reasons, stack walkers generally first check for
 439       // stack-locking in the object's header, the second check is for
 440       // recursive stack-locking in the displaced header in the BasicLock,
 441       // and last are the inflated Java Monitor (ObjectMonitor) checks.
 442       lock->set_displaced_header(markWord::unused_mark());
 443     }
 444 
 445     if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) {
 446       assert(m->_recursions == 0, "invariant");
 447       current->inc_held_monitor_count();
 448       return true;
 449     }
 450   }
 451 
 452   // Note that we could inflate in quick_enter.
 453   // This is likely a useful optimization
 454   // Critically, in quick_enter() we must not:
 455   // -- block indefinitely, or
 456   // -- reach a safepoint
 457 
 458   return false;        // revert to slow-path
 459 }
 460 
 461 // Handle notifications when synchronizing on value based classes
 462 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
 463   assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
 464   frame last_frame = locking_thread->last_frame();
 465   bool bcp_was_adjusted = false;
 466   // Don't decrement bcp if it points to the frame's first instruction.  This happens when
 467   // handle_sync_on_value_based_class() is called because of a synchronized method.  There
 468   // is no actual monitorenter instruction in the byte code in this case.
 469   if (last_frame.is_interpreted_frame() &&
 470       (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
 471     // adjust bcp to point back to monitorenter so that we print the correct line numbers
 472     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
 473     bcp_was_adjusted = true;
 474   }
 475 
 476   if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
 477     ResourceMark rm;
 478     stringStream ss;
 479     locking_thread->print_active_stack_on(&ss);
 480     char* base = (char*)strstr(ss.base(), "at");
 481     char* newline = (char*)strchr(ss.base(), '\n');
 482     if (newline != nullptr) {
 483       *newline = '\0';
 484     }
 485     fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
 486   } else {
 487     assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
 488     ResourceMark rm;
 489     Log(valuebasedclasses) vblog;
 490 
 491     vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
 492     if (locking_thread->has_last_Java_frame()) {
 493       LogStream info_stream(vblog.info());
 494       locking_thread->print_active_stack_on(&info_stream);
 495     } else {
 496       vblog.info("Cannot find the last Java frame");
 497     }
 498 
 499     EventSyncOnValueBasedClass event;
 500     if (event.should_commit()) {
 501       event.set_valueBasedClass(obj->klass());
 502       event.commit();
 503     }
 504   }
 505 
 506   if (bcp_was_adjusted) {
 507     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
 508   }
 509 }
 510 
 511 static bool useHeavyMonitors() {
 512 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
 513   return LockingMode == LM_MONITOR;
 514 #else
 515   return false;
 516 #endif
 517 }
 518 
 519 // -----------------------------------------------------------------------------
 520 // Monitor Enter/Exit
 521 
 522 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
 523   // When called with locking_thread != Thread::current() some mechanism must synchronize
 524   // the locking_thread with respect to the current thread. Currently only used when
 525   // deoptimizing and re-locking locks. See Deoptimization::relock_objects
 526   assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
 527   if (!enter_fast_impl(obj, lock, locking_thread)) {
 528     // Inflated ObjectMonitor::enter_for is required
 529 
 530     // An async deflation can race after the inflate_for() call and before
 531     // enter_for() can make the ObjectMonitor busy. enter_for() returns false
 532     // if we have lost the race to async deflation and we simply try again.
 533     while (true) {
 534       ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
 535       if (monitor->enter_for(locking_thread)) {
 536         return;
 537       }
 538       assert(monitor->is_being_async_deflated(), "must be");
 539     }
 540   }
 541 }
 542 
 543 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
 544   assert(current == Thread::current(), "must be");
 545   if (!enter_fast_impl(obj, lock, current)) {
 546     // Inflated ObjectMonitor::enter is required
 547 
 548     // An async deflation can race after the inflate() call and before
 549     // enter() can make the ObjectMonitor busy. enter() returns false if
 550     // we have lost the race to async deflation and we simply try again.
 551     while (true) {
 552       ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
 553       if (monitor->enter(current)) {
 554         return;
 555       }
 556     }
 557   }
 558 }
 559 
 560 // The interpreter and compiler assembly code tries to lock using the fast path
 561 // of this algorithm. Make sure to update that code if the following function is
 562 // changed. The implementation is extremely sensitive to race condition. Be careful.
 563 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
 564 
 565   if (obj->klass()->is_value_based()) {
 566     handle_sync_on_value_based_class(obj, locking_thread);
 567   }
 568 
 569   locking_thread->inc_held_monitor_count();
 570 
 571   if (!useHeavyMonitors()) {
 572     if (LockingMode == LM_LIGHTWEIGHT) {
 573       // Fast-locking does not use the 'lock' argument.
 574       LockStack& lock_stack = locking_thread->lock_stack();
 575       if (lock_stack.is_full()) {
 576         // We unconditionally make room on the lock stack by inflating
 577         // the least recently locked object on the lock stack.
 578 
 579         // About the choice to inflate least recently locked object.
 580         // First we must chose to inflate a lock, either some lock on
 581         // the lock-stack or the lock that is currently being entered
 582         // (which may or may not be on the lock-stack).
 583         // Second the best lock to inflate is a lock which is entered
 584         // in a control flow where there are only a very few locks being
 585         // used, as the costly part of inflated locking is inflation,
 586         // not locking. But this property is entirely program dependent.
 587         // Third inflating the lock currently being entered on when it
 588         // is not present on the lock-stack will result in a still full
 589         // lock-stack. This creates a scenario where every deeper nested
 590         // monitorenter must call into the runtime.
 591         // The rational here is as follows:
 592         // Because we cannot (currently) figure out the second, and want
 593         // to avoid the third, we inflate a lock on the lock-stack.
 594         // The least recently locked lock is chosen as it is the lock
 595         // with the longest critical section.
 596 
 597         log_info(monitorinflation)("LockStack capacity exceeded, inflating.");
 598         ObjectMonitor* monitor = inflate_for(locking_thread, lock_stack.bottom(), inflate_cause_vm_internal);
 599         assert(monitor->owner() == Thread::current(), "must be owner=" PTR_FORMAT " current=" PTR_FORMAT " mark=" PTR_FORMAT,
 600                p2i(monitor->owner()), p2i(Thread::current()), monitor->object()->mark_acquire().value());
 601         assert(!lock_stack.is_full(), "must have made room here");
 602       }
 603 
 604       markWord mark = obj()->mark_acquire();
 605       while (mark.is_neutral()) {
 606         // Retry until a lock state change has been observed. cas_set_mark() may collide with non lock bits modifications.
 607         // Try to swing into 'fast-locked' state.
 608         assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
 609         const markWord locked_mark = mark.set_fast_locked();
 610         const markWord old_mark = obj()->cas_set_mark(locked_mark, mark);
 611         if (old_mark == mark) {
 612           // Successfully fast-locked, push object to lock-stack and return.
 613           lock_stack.push(obj());
 614           return true;
 615         }
 616         mark = old_mark;
 617       }
 618 
 619       if (mark.is_fast_locked() && lock_stack.try_recursive_enter(obj())) {
 620         // Recursive lock successful.
 621         return true;
 622       }
 623 
 624       // Failed to fast lock.
 625       return false;
 626     } else if (LockingMode == LM_LEGACY) {
 627       markWord mark = obj->mark();
 628       if (mark.is_neutral()) {
 629         // Anticipate successful CAS -- the ST of the displaced mark must
 630         // be visible <= the ST performed by the CAS.
 631         lock->set_displaced_header(mark);
 632         if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
 633           return true;
 634         }
 635       } else if (mark.has_locker() &&
 636                  locking_thread->is_lock_owned((address) mark.locker())) {
 637         assert(lock != mark.locker(), "must not re-lock the same lock");
 638         assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
 639         lock->set_displaced_header(markWord::from_pointer(nullptr));
 640         return true;
 641       }
 642 
 643       // The object header will never be displaced to this lock,
 644       // so it does not matter what the value is, except that it
 645       // must be non-zero to avoid looking like a re-entrant lock,
 646       // and must not look locked either.
 647       lock->set_displaced_header(markWord::unused_mark());
 648 
 649       // Failed to fast lock.
 650       return false;
 651     }
 652   } else if (VerifyHeavyMonitors) {
 653     guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
 654   }
 655 
 656   return false;
 657 }
 658 
 659 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
 660   current->dec_held_monitor_count();
 661 
 662   if (!useHeavyMonitors()) {
 663     markWord mark = object->mark();
 664     if (LockingMode == LM_LIGHTWEIGHT) {
 665       // Fast-locking does not use the 'lock' argument.
 666       LockStack& lock_stack = current->lock_stack();
 667       if (mark.is_fast_locked() && lock_stack.try_recursive_exit(object)) {
 668         // Recursively unlocked.
 669         return;
 670       }
 671 
 672       if (mark.is_fast_locked() && lock_stack.is_recursive(object)) {
 673         // This lock is recursive but is not at the top of the lock stack so we're
 674         // doing an unbalanced exit. We have to fall thru to inflation below and
 675         // let ObjectMonitor::exit() do the unlock.
 676       } else {
 677         while (mark.is_fast_locked()) {
 678           // Retry until a lock state change has been observed. cas_set_mark() may collide with non lock bits modifications.
 679           const markWord unlocked_mark = mark.set_unlocked();
 680           const markWord old_mark = object->cas_set_mark(unlocked_mark, mark);
 681           if (old_mark == mark) {
 682             size_t recursions = lock_stack.remove(object) - 1;
 683             assert(recursions == 0, "must not be recursive here");
 684             return;
 685           }
 686           mark = old_mark;
 687         }
 688       }
 689     } else if (LockingMode == LM_LEGACY) {
 690       markWord dhw = lock->displaced_header();
 691       if (dhw.value() == 0) {
 692         // If the displaced header is null, then this exit matches up with
 693         // a recursive enter. No real work to do here except for diagnostics.
 694 #ifndef PRODUCT
 695         if (mark != markWord::INFLATING()) {
 696           // Only do diagnostics if we are not racing an inflation. Simply
 697           // exiting a recursive enter of a Java Monitor that is being
 698           // inflated is safe; see the has_monitor() comment below.
 699           assert(!mark.is_neutral(), "invariant");
 700           assert(!mark.has_locker() ||
 701                  current->is_lock_owned((address)mark.locker()), "invariant");
 702           if (mark.has_monitor()) {
 703             // The BasicLock's displaced_header is marked as a recursive
 704             // enter and we have an inflated Java Monitor (ObjectMonitor).
 705             // This is a special case where the Java Monitor was inflated
 706             // after this thread entered the stack-lock recursively. When a
 707             // Java Monitor is inflated, we cannot safely walk the Java
 708             // Monitor owner's stack and update the BasicLocks because a
 709             // Java Monitor can be asynchronously inflated by a thread that
 710             // does not own the Java Monitor.
 711             ObjectMonitor* m = mark.monitor();
 712             assert(m->object()->mark() == mark, "invariant");
 713             assert(m->is_entered(current), "invariant");
 714           }
 715         }
 716 #endif
 717         return;
 718       }
 719 
 720       if (mark == markWord::from_pointer(lock)) {
 721         // If the object is stack-locked by the current thread, try to
 722         // swing the displaced header from the BasicLock back to the mark.
 723         assert(dhw.is_neutral(), "invariant");
 724         if (object->cas_set_mark(dhw, mark) == mark) {
 725           return;
 726         }
 727       }
 728     }
 729   } else if (VerifyHeavyMonitors) {
 730     guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
 731   }
 732 
 733   // We have to take the slow-path of possible inflation and then exit.
 734   // The ObjectMonitor* can't be async deflated until ownership is
 735   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
 736   ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
 737   assert(!monitor->is_owner_anonymous(), "must not be");
 738   monitor->exit(current);
 739 }
 740 
 741 // -----------------------------------------------------------------------------
 742 // JNI locks on java objects
 743 // NOTE: must use heavy weight monitor to handle jni monitor enter
 744 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
 745   if (obj->klass()->is_value_based()) {
 746     handle_sync_on_value_based_class(obj, current);
 747   }
 748 
 749   // the current locking is from JNI instead of Java code
 750   current->set_current_pending_monitor_is_from_java(false);
 751   // An async deflation can race after the inflate() call and before
 752   // enter() can make the ObjectMonitor busy. enter() returns false if
 753   // we have lost the race to async deflation and we simply try again.
 754   while (true) {
 755     ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
 756     if (monitor->enter(current)) {
 757       current->inc_held_monitor_count(1, true);
 758       break;
 759     }
 760   }
 761   current->set_current_pending_monitor_is_from_java(true);
 762 }
 763 
 764 // NOTE: must use heavy weight monitor to handle jni monitor exit
 765 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
 766   JavaThread* current = THREAD;
 767 
 768   // The ObjectMonitor* can't be async deflated until ownership is
 769   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
 770   ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
 771   // If this thread has locked the object, exit the monitor. We
 772   // intentionally do not use CHECK on check_owner because we must exit the
 773   // monitor even if an exception was already pending.
 774   if (monitor->check_owner(THREAD)) {
 775     monitor->exit(current);
 776     current->dec_held_monitor_count(1, true);
 777   }
 778 }
 779 
 780 // -----------------------------------------------------------------------------
 781 // Internal VM locks on java objects
 782 // standard constructor, allows locking failures
 783 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
 784   _thread = thread;
 785   _thread->check_for_valid_safepoint_state();
 786   _obj = obj;
 787 
 788   if (_obj() != nullptr) {
 789     ObjectSynchronizer::enter(_obj, &_lock, _thread);
 790   }
 791 }
 792 
 793 ObjectLocker::~ObjectLocker() {
 794   if (_obj() != nullptr) {
 795     ObjectSynchronizer::exit(_obj(), &_lock, _thread);
 796   }
 797 }
 798 
 799 
 800 // -----------------------------------------------------------------------------
 801 //  Wait/Notify/NotifyAll
 802 // NOTE: must use heavy weight monitor to handle wait()
 803 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 804   JavaThread* current = THREAD;
 805   if (millis < 0) {
 806     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 807   }
 808   // The ObjectMonitor* can't be async deflated because the _waiters
 809   // field is incremented before ownership is dropped and decremented
 810   // after ownership is regained.
 811   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
 812 
 813   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
 814   monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
 815 
 816   // This dummy call is in place to get around dtrace bug 6254741.  Once
 817   // that's fixed we can uncomment the following line, remove the call
 818   // and change this function back into a "void" func.
 819   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 820   int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
 821   return ret_code;
 822 }
 823 
 824 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 825   JavaThread* current = THREAD;
 826 
 827   markWord mark = obj->mark();
 828   if (LockingMode == LM_LIGHTWEIGHT) {
 829     if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
 830       // Not inflated so there can't be any waiters to notify.
 831       return;
 832     }
 833   } else if (LockingMode == LM_LEGACY) {
 834     if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 835       // Not inflated so there can't be any waiters to notify.
 836       return;
 837     }
 838   }
 839   // The ObjectMonitor* can't be async deflated until ownership is
 840   // dropped by the calling thread.
 841   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
 842   monitor->notify(CHECK);
 843 }
 844 
 845 // NOTE: see comment of notify()
 846 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 847   JavaThread* current = THREAD;
 848 
 849   markWord mark = obj->mark();
 850   if (LockingMode == LM_LIGHTWEIGHT) {
 851     if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
 852       // Not inflated so there can't be any waiters to notify.
 853       return;
 854     }
 855   } else if (LockingMode == LM_LEGACY) {
 856     if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 857       // Not inflated so there can't be any waiters to notify.
 858       return;
 859     }
 860   }
 861   // The ObjectMonitor* can't be async deflated until ownership is
 862   // dropped by the calling thread.
 863   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
 864   monitor->notifyAll(CHECK);
 865 }
 866 
 867 // -----------------------------------------------------------------------------
 868 // Hash Code handling
 869 
 870 struct SharedGlobals {
 871   char         _pad_prefix[OM_CACHE_LINE_SIZE];
 872   // This is a highly shared mostly-read variable.
 873   // To avoid false-sharing it needs to be the sole occupant of a cache line.
 874   volatile int stw_random;
 875   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 876   // Hot RW variable -- Sequester to avoid false-sharing
 877   volatile int hc_sequence;
 878   DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 879 };
 880 
 881 static SharedGlobals GVars;
 882 
 883 static markWord read_stable_mark(oop obj) {
 884   markWord mark = obj->mark_acquire();
 885   if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
 886     // New lightweight locking does not use the markWord::INFLATING() protocol.
 887     return mark;       // normal fast-path return
 888   }
 889 
 890   int its = 0;
 891   for (;;) {
 892     markWord mark = obj->mark_acquire();
 893     if (!mark.is_being_inflated()) {
 894       return mark;    // normal fast-path return
 895     }
 896 
 897     // The object is being inflated by some other thread.
 898     // The caller of read_stable_mark() must wait for inflation to complete.
 899     // Avoid live-lock.
 900 
 901     ++its;
 902     if (its > 10000 || !os::is_MP()) {
 903       if (its & 1) {
 904         os::naked_yield();
 905       } else {
 906         // Note that the following code attenuates the livelock problem but is not
 907         // a complete remedy.  A more complete solution would require that the inflating
 908         // thread hold the associated inflation lock.  The following code simply restricts
 909         // the number of spinners to at most one.  We'll have N-2 threads blocked
 910         // on the inflationlock, 1 thread holding the inflation lock and using
 911         // a yield/park strategy, and 1 thread in the midst of inflation.
 912         // A more refined approach would be to change the encoding of INFLATING
 913         // to allow encapsulation of a native thread pointer.  Threads waiting for
 914         // inflation to complete would use CAS to push themselves onto a singly linked
 915         // list rooted at the markword.  Once enqueued, they'd loop, checking a per-thread flag
 916         // and calling park().  When inflation was complete the thread that accomplished inflation
 917         // would detach the list and set the markword to inflated with a single CAS and
 918         // then for each thread on the list, set the flag and unpark() the thread.
 919 
 920         // Index into the lock array based on the current object address.
 921         static_assert(is_power_of_2(inflation_lock_count()), "must be");
 922         size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
 923         int YieldThenBlock = 0;
 924         assert(ix < inflation_lock_count(), "invariant");
 925         inflation_lock(ix)->lock();
 926         while (obj->mark_acquire() == markWord::INFLATING()) {
 927           // Beware: naked_yield() is advisory and has almost no effect on some platforms
 928           // so we periodically call current->_ParkEvent->park(1).
 929           // We use a mixed spin/yield/block mechanism.
 930           if ((YieldThenBlock++) >= 16) {
 931             Thread::current()->_ParkEvent->park(1);
 932           } else {
 933             os::naked_yield();
 934           }
 935         }
 936         inflation_lock(ix)->unlock();
 937       }
 938     } else {
 939       SpinPause();       // SMP-polite spinning
 940     }
 941   }
 942 }
 943 
 944 // hashCode() generation :
 945 //
 946 // Possibilities:
 947 // * MD5Digest of {obj,stw_random}
 948 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
 949 // * A DES- or AES-style SBox[] mechanism
 950 // * One of the Phi-based schemes, such as:
 951 //   2654435761 = 2^32 * Phi (golden ratio)
 952 //   HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
 953 // * A variation of Marsaglia's shift-xor RNG scheme.
 954 // * (obj ^ stw_random) is appealing, but can result
 955 //   in undesirable regularity in the hashCode values of adjacent objects
 956 //   (objects allocated back-to-back, in particular).  This could potentially
 957 //   result in hashtable collisions and reduced hashtable efficiency.
 958 //   There are simple ways to "diffuse" the middle address bits over the
 959 //   generated hashCode values:
 960 
 961 static inline intptr_t get_next_hash(Thread* current, oop obj) {
 962   intptr_t value = 0;
 963   if (hashCode == 0) {
 964     // This form uses global Park-Miller RNG.
 965     // On MP system we'll have lots of RW access to a global, so the
 966     // mechanism induces lots of coherency traffic.
 967     value = os::random();
 968   } else if (hashCode == 1) {
 969     // This variation has the property of being stable (idempotent)
 970     // between STW operations.  This can be useful in some of the 1-0
 971     // synchronization schemes.
 972     intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
 973     value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
 974   } else if (hashCode == 2) {
 975     value = 1;            // for sensitivity testing
 976   } else if (hashCode == 3) {
 977     value = ++GVars.hc_sequence;
 978   } else if (hashCode == 4) {
 979     value = cast_from_oop<intptr_t>(obj);
 980   } else {
 981     // Marsaglia's xor-shift scheme with thread-specific state
 982     // This is probably the best overall implementation -- we'll
 983     // likely make this the default in future releases.
 984     unsigned t = current->_hashStateX;
 985     t ^= (t << 11);
 986     current->_hashStateX = current->_hashStateY;
 987     current->_hashStateY = current->_hashStateZ;
 988     current->_hashStateZ = current->_hashStateW;
 989     unsigned v = current->_hashStateW;
 990     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
 991     current->_hashStateW = v;
 992     value = v;
 993   }
 994 
 995   value &= UseCompactObjectHeaders ? markWord::hash_mask_compact : markWord::hash_mask;
 996   if (value == 0) value = 0xBAD;
 997   assert(value != markWord::no_hash, "invariant");
 998   return value;
 999 }
1000 
1001 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
1002 
1003   while (true) {
1004     ObjectMonitor* monitor = nullptr;
1005     markWord temp, test;
1006     intptr_t hash;
1007     markWord mark = read_stable_mark(obj);
1008     if (VerifyHeavyMonitors) {
1009       assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
1010       guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1011     }
1012     if (mark.is_neutral() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1013       hash = mark.hash();
1014       if (hash != 0) {                     // if it has a hash, just return it
1015         return hash;
1016       }
1017       hash = get_next_hash(current, obj);  // get a new hash
1018       temp = mark.copy_set_hash(hash);     // merge the hash into header
1019                                            // try to install the hash
1020       test = obj->cas_set_mark(temp, mark);
1021       if (test == mark) {                  // if the hash was installed, return it
1022         return hash;
1023       }
1024       if (LockingMode == LM_LIGHTWEIGHT) {
1025         // CAS failed, retry
1026         continue;
1027       }
1028       // Failed to install the hash. It could be that another thread
1029       // installed the hash just before our attempt or inflation has
1030       // occurred or... so we fall thru to inflate the monitor for
1031       // stability and then install the hash.
1032     } else if (mark.has_monitor()) {
1033       monitor = mark.monitor();
1034       temp = monitor->header();
1035       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1036       hash = temp.hash();
1037       if (hash != 0) {
1038         // It has a hash.
1039 
1040         // Separate load of dmw/header above from the loads in
1041         // is_being_async_deflated().
1042 
1043         // dmw/header and _contentions may get written by different threads.
1044         // Make sure to observe them in the same order when having several observers.
1045         OrderAccess::loadload_for_IRIW();
1046 
1047         if (monitor->is_being_async_deflated()) {
1048           // But we can't safely use the hash if we detect that async
1049           // deflation has occurred. So we attempt to restore the
1050           // header/dmw to the object's header so that we only retry
1051           // once if the deflater thread happens to be slow.
1052           monitor->install_displaced_markword_in_object(obj);
1053           continue;
1054         }
1055         return hash;
1056       }
1057       // Fall thru so we only have one place that installs the hash in
1058       // the ObjectMonitor.
1059     } else if (LockingMode == LM_LEGACY && mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
1060       // This is a stack-lock owned by the calling thread so fetch the
1061       // displaced markWord from the BasicLock on the stack.
1062       temp = mark.displaced_mark_helper();
1063       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1064       hash = temp.hash();
1065       if (hash != 0) {                  // if it has a hash, just return it
1066         return hash;
1067       }
1068       // WARNING:
1069       // The displaced header in the BasicLock on a thread's stack
1070       // is strictly immutable. It CANNOT be changed in ANY cases.
1071       // So we have to inflate the stack-lock into an ObjectMonitor
1072       // even if the current thread owns the lock. The BasicLock on
1073       // a thread's stack can be asynchronously read by other threads
1074       // during an inflate() call so any change to that stack memory
1075       // may not propagate to other threads correctly.
1076     }
1077 
1078     // Inflate the monitor to set the hash.
1079 
1080     // An async deflation can race after the inflate() call and before we
1081     // can update the ObjectMonitor's header with the hash value below.
1082     monitor = inflate(current, obj, inflate_cause_hash_code);
1083     // Load ObjectMonitor's header/dmw field and see if it has a hash.
1084     mark = monitor->header();
1085     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1086     hash = mark.hash();
1087     if (hash == 0) {                       // if it does not have a hash
1088       hash = get_next_hash(current, obj);  // get a new hash
1089       temp = mark.copy_set_hash(hash)   ;  // merge the hash into header
1090       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1091       uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1092       test = markWord(v);
1093       if (test != mark) {
1094         // The attempt to update the ObjectMonitor's header/dmw field
1095         // did not work. This can happen if another thread managed to
1096         // merge in the hash just before our cmpxchg().
1097         // If we add any new usages of the header/dmw field, this code
1098         // will need to be updated.
1099         hash = test.hash();
1100         assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1101         assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1102       }
1103       if (monitor->is_being_async_deflated()) {
1104         // If we detect that async deflation has occurred, then we
1105         // attempt to restore the header/dmw to the object's header
1106         // so that we only retry once if the deflater thread happens
1107         // to be slow.
1108         monitor->install_displaced_markword_in_object(obj);
1109         continue;
1110       }
1111     }
1112     // We finally get the hash.
1113     return hash;
1114   }
1115 }
1116 
1117 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1118                                                    Handle h_obj) {
1119   assert(current == JavaThread::current(), "Can only be called on current thread");
1120   oop obj = h_obj();
1121 
1122   markWord mark = read_stable_mark(obj);
1123 
1124   if (LockingMode == LM_LEGACY && mark.has_locker()) {
1125     // stack-locked case, header points into owner's stack
1126     return current->is_lock_owned((address)mark.locker());
1127   }
1128 
1129   if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1130     // fast-locking case, see if lock is in current's lock stack
1131     return current->lock_stack().contains(h_obj());
1132   }
1133 
1134   if (mark.has_monitor()) {
1135     // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1136     // The first stage of async deflation does not affect any field
1137     // used by this comparison so the ObjectMonitor* is usable here.
1138     ObjectMonitor* monitor = mark.monitor();
1139     return monitor->is_entered(current) != 0;
1140   }
1141   // Unlocked case, header in place
1142   assert(mark.is_neutral(), "sanity check");
1143   return false;
1144 }
1145 
1146 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1147   oop obj = h_obj();
1148   markWord mark = read_stable_mark(obj);
1149 
1150   if (LockingMode == LM_LEGACY && mark.has_locker()) {
1151     // stack-locked so header points into owner's stack.
1152     // owning_thread_from_monitor_owner() may also return null here:
1153     return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1154   }
1155 
1156   if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1157     // fast-locked so get owner from the object.
1158     // owning_thread_from_object() may also return null here:
1159     return Threads::owning_thread_from_object(t_list, h_obj());
1160   }
1161 
1162   if (mark.has_monitor()) {
1163     // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1164     // The first stage of async deflation does not affect any field
1165     // used by this comparison so the ObjectMonitor* is usable here.
1166     ObjectMonitor* monitor = mark.monitor();
1167     assert(monitor != nullptr, "monitor should be non-null");
1168     // owning_thread_from_monitor() may also return null here:
1169     return Threads::owning_thread_from_monitor(t_list, monitor);
1170   }
1171 
1172   // Unlocked case, header in place
1173   // Cannot have assertion since this object may have been
1174   // locked by another thread when reaching here.
1175   // assert(mark.is_neutral(), "sanity check");
1176 
1177   return nullptr;
1178 }
1179 
1180 // Visitors ...
1181 
1182 // Iterate over all ObjectMonitors.
1183 template <typename Function>
1184 void ObjectSynchronizer::monitors_iterate(Function function) {
1185   MonitorList::Iterator iter = _in_use_list.iterator();
1186   while (iter.has_next()) {
1187     ObjectMonitor* monitor = iter.next();
1188     function(monitor);
1189   }
1190 }
1191 
1192 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1193 // returns true.
1194 template <typename OwnerFilter>
1195 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1196   monitors_iterate([&](ObjectMonitor* monitor) {
1197     // This function is only called at a safepoint or when the
1198     // target thread is suspended or when the target thread is
1199     // operating on itself. The current closures in use today are
1200     // only interested in an owned ObjectMonitor and ownership
1201     // cannot be dropped under the calling contexts so the
1202     // ObjectMonitor cannot be async deflated.
1203     if (monitor->has_owner() && filter(monitor->owner_raw())) {
1204       assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1205 
1206       closure->do_monitor(monitor);
1207     }
1208   });
1209 }
1210 
1211 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1212 // ObjectMonitors where owner is set to a stack-lock address in thread.
1213 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1214   auto thread_filter = [&](void* owner) { return owner == thread; };
1215   return owned_monitors_iterate_filtered(closure, thread_filter);
1216 }
1217 
1218 // Iterate ObjectMonitors owned by any thread.
1219 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1220   auto all_filter = [&](void* owner) { return true; };
1221   return owned_monitors_iterate_filtered(closure, all_filter);
1222 }
1223 
1224 static bool monitors_used_above_threshold(MonitorList* list) {
1225   if (MonitorUsedDeflationThreshold == 0) {  // disabled case is easy
1226     return false;
1227   }
1228   // Start with ceiling based on a per-thread estimate:
1229   size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1230   size_t old_ceiling = ceiling;
1231   if (ceiling < list->max()) {
1232     // The max used by the system has exceeded the ceiling so use that:
1233     ceiling = list->max();
1234   }
1235   size_t monitors_used = list->count();
1236   if (monitors_used == 0) {  // empty list is easy
1237     return false;
1238   }
1239   if (NoAsyncDeflationProgressMax != 0 &&
1240       _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1241     double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1242     size_t new_ceiling = ceiling + (size_t)((double)ceiling * remainder) + 1;
1243     ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1244     log_info(monitorinflation)("Too many deflations without progress; "
1245                                "bumping in_use_list_ceiling from " SIZE_FORMAT
1246                                " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1247     _no_progress_cnt = 0;
1248     ceiling = new_ceiling;
1249   }
1250 
1251   // Check if our monitor usage is above the threshold:
1252   size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1253   if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1254     log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
1255                                ", monitor_usage=" SIZE_FORMAT ", threshold=%d",
1256                                monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1257     return true;
1258   }
1259 
1260   return false;
1261 }
1262 
1263 size_t ObjectSynchronizer::in_use_list_ceiling() {
1264   return _in_use_list_ceiling;
1265 }
1266 
1267 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1268   Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1269 }
1270 
1271 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1272   Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1273 }
1274 
1275 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1276   _in_use_list_ceiling = new_value;
1277 }
1278 
1279 bool ObjectSynchronizer::is_async_deflation_needed() {
1280   if (is_async_deflation_requested()) {
1281     // Async deflation request.
1282     log_info(monitorinflation)("Async deflation needed: explicit request");
1283     return true;
1284   }
1285 
1286   jlong time_since_last = time_since_last_async_deflation_ms();
1287 
1288   if (AsyncDeflationInterval > 0 &&
1289       time_since_last > AsyncDeflationInterval &&
1290       monitors_used_above_threshold(&_in_use_list)) {
1291     // It's been longer than our specified deflate interval and there
1292     // are too many monitors in use. We don't deflate more frequently
1293     // than AsyncDeflationInterval (unless is_async_deflation_requested)
1294     // in order to not swamp the MonitorDeflationThread.
1295     log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1296     return true;
1297   }
1298 
1299   if (GuaranteedAsyncDeflationInterval > 0 &&
1300       time_since_last > GuaranteedAsyncDeflationInterval) {
1301     // It's been longer than our specified guaranteed deflate interval.
1302     // We need to clean up the used monitors even if the threshold is
1303     // not reached, to keep the memory utilization at bay when many threads
1304     // touched many monitors.
1305     log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) "
1306                                "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1307                                GuaranteedAsyncDeflationInterval, time_since_last);
1308 
1309     // If this deflation has no progress, then it should not affect the no-progress
1310     // tracking, otherwise threshold heuristics would think it was triggered, experienced
1311     // no progress, and needs to backoff more aggressively. In this "no progress" case,
1312     // the generic code would bump the no-progress counter, and we compensate for that
1313     // by telling it to skip the update.
1314     //
1315     // If this deflation has progress, then it should let non-progress tracking
1316     // know about this, otherwise the threshold heuristics would kick in, potentially
1317     // experience no-progress due to aggressive cleanup by this deflation, and think
1318     // it is still in no-progress stride. In this "progress" case, the generic code would
1319     // zero the counter, and we allow it to happen.
1320     _no_progress_skip_increment = true;
1321 
1322     return true;
1323   }
1324 
1325   return false;
1326 }
1327 
1328 void ObjectSynchronizer::request_deflate_idle_monitors() {
1329   MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1330   set_is_async_deflation_requested(true);
1331   ml.notify_all();
1332 }
1333 
1334 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1335   JavaThread* current = JavaThread::current();
1336   bool ret_code = false;
1337 
1338   jlong last_time = last_async_deflation_time_ns();
1339 
1340   request_deflate_idle_monitors();
1341 
1342   const int N_CHECKS = 5;
1343   for (int i = 0; i < N_CHECKS; i++) {  // sleep for at most 5 seconds
1344     if (last_async_deflation_time_ns() > last_time) {
1345       log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1346       ret_code = true;
1347       break;
1348     }
1349     {
1350       // JavaThread has to honor the blocking protocol.
1351       ThreadBlockInVM tbivm(current);
1352       os::naked_short_sleep(999);  // sleep for almost 1 second
1353     }
1354   }
1355   if (!ret_code) {
1356     log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1357   }
1358 
1359   return ret_code;
1360 }
1361 
1362 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1363   return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1364 }
1365 
1366 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1367                                        const oop obj,
1368                                        ObjectSynchronizer::InflateCause cause) {
1369   assert(event != nullptr, "invariant");
1370   event->set_monitorClass(obj->klass());
1371   event->set_address((uintptr_t)(void*)obj);
1372   event->set_cause((u1)cause);
1373   event->commit();
1374 }
1375 
1376 // Fast path code shared by multiple functions
1377 void ObjectSynchronizer::inflate_helper(oop obj) {
1378   markWord mark = obj->mark_acquire();
1379   if (mark.has_monitor()) {
1380     ObjectMonitor* monitor = mark.monitor();
1381     markWord dmw = monitor->header();
1382     assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1383     return;
1384   }
1385   (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1386 }
1387 
1388 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1389   assert(current == Thread::current(), "must be");
1390   if (LockingMode == LM_LIGHTWEIGHT && current->is_Java_thread()) {
1391     return inflate_impl(JavaThread::cast(current), obj, cause);
1392   }
1393   return inflate_impl(nullptr, obj, cause);
1394 }
1395 
1396 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1397   assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1398   return inflate_impl(thread, obj, cause);
1399 }
1400 
1401 ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* inflating_thread, oop object, const InflateCause cause) {
1402   // The JavaThread* inflating_thread parameter is only used by LM_LIGHTWEIGHT and requires
1403   // that the inflating_thread == Thread::current() or is suspended throughout the call by
1404   // some other mechanism.
1405   // Even with LM_LIGHTWEIGHT the thread might be nullptr when called from a non
1406   // JavaThread. (As may still be the case from FastHashCode). However it is only
1407   // important for the correctness of the LM_LIGHTWEIGHT algorithm that the thread
1408   // is set when called from ObjectSynchronizer::enter from the owning thread,
1409   // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
1410   EventJavaMonitorInflate event;
1411 
1412   for (;;) {
1413     const markWord mark = object->mark_acquire();
1414 
1415     // The mark can be in one of the following states:
1416     // *  inflated     - Just return if using stack-locking.
1417     //                   If using fast-locking and the ObjectMonitor owner
1418     //                   is anonymous and the inflating_thread owns the
1419     //                   object lock, then we make the inflating_thread
1420     //                   the ObjectMonitor owner and remove the lock from
1421     //                   the inflating_thread's lock stack.
1422     // *  fast-locked  - Coerce it to inflated from fast-locked.
1423     // *  stack-locked - Coerce it to inflated from stack-locked.
1424     // *  INFLATING    - Busy wait for conversion from stack-locked to
1425     //                   inflated.
1426     // *  neutral      - Aggressively inflate the object.
1427 
1428     // CASE: inflated
1429     if (mark.has_monitor()) {
1430       ObjectMonitor* inf = mark.monitor();
1431       markWord dmw = inf->header();
1432       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1433       if (LockingMode == LM_LIGHTWEIGHT && inf->is_owner_anonymous() &&
1434           inflating_thread != nullptr && inflating_thread->lock_stack().contains(object)) {
1435         inf->set_owner_from_anonymous(inflating_thread);
1436         size_t removed = inflating_thread->lock_stack().remove(object);
1437         inf->set_recursions(removed - 1);
1438       }
1439       return inf;
1440     }
1441 
1442     if (LockingMode != LM_LIGHTWEIGHT) {
1443       // New lightweight locking does not use INFLATING.
1444       // CASE: inflation in progress - inflating over a stack-lock.
1445       // Some other thread is converting from stack-locked to inflated.
1446       // Only that thread can complete inflation -- other threads must wait.
1447       // The INFLATING value is transient.
1448       // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1449       // We could always eliminate polling by parking the thread on some auxiliary list.
1450       if (mark == markWord::INFLATING()) {
1451         read_stable_mark(object);
1452         continue;
1453       }
1454     }
1455 
1456     // CASE: fast-locked
1457     // Could be fast-locked either by the inflating_thread or by some other thread.
1458     //
1459     // Note that we allocate the ObjectMonitor speculatively, _before_
1460     // attempting to set the object's mark to the new ObjectMonitor. If
1461     // the inflating_thread owns the monitor, then we set the ObjectMonitor's
1462     // owner to the inflating_thread. Otherwise, we set the ObjectMonitor's owner
1463     // to anonymous. If we lose the race to set the object's mark to the
1464     // new ObjectMonitor, then we just delete it and loop around again.
1465     //
1466     LogStreamHandle(Trace, monitorinflation) lsh;
1467     if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1468       ObjectMonitor* monitor = new ObjectMonitor(object);
1469       monitor->set_header(mark.set_unlocked());
1470       bool own = inflating_thread != nullptr && inflating_thread->lock_stack().contains(object);
1471       if (own) {
1472         // Owned by inflating_thread.
1473         monitor->set_owner_from(nullptr, inflating_thread);
1474       } else {
1475         // Owned by somebody else.
1476         monitor->set_owner_anonymous();
1477       }
1478       markWord monitor_mark = markWord::encode(monitor);
1479       markWord old_mark = object->cas_set_mark(monitor_mark, mark);
1480       if (old_mark == mark) {
1481         // Success! Return inflated monitor.
1482         if (own) {
1483           size_t removed = inflating_thread->lock_stack().remove(object);
1484           monitor->set_recursions(removed - 1);
1485         }
1486         // Once the ObjectMonitor is configured and object is associated
1487         // with the ObjectMonitor, it is safe to allow async deflation:
1488         _in_use_list.add(monitor);
1489 
1490         // Hopefully the performance counters are allocated on distinct
1491         // cache lines to avoid false sharing on MP systems ...
1492         OM_PERFDATA_OP(Inflations, inc());
1493         if (log_is_enabled(Trace, monitorinflation)) {
1494           ResourceMark rm;
1495           lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1496                        INTPTR_FORMAT ", type='%s'", p2i(object),
1497                        object->mark().value(), object->klass()->external_name());
1498         }
1499         if (event.should_commit()) {
1500           post_monitor_inflate_event(&event, object, cause);
1501         }
1502         return monitor;
1503       } else {
1504         delete monitor;
1505         continue;  // Interference -- just retry
1506       }
1507     }
1508 
1509     // CASE: stack-locked
1510     // Could be stack-locked either by current or by some other thread.
1511     //
1512     // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1513     // to install INFLATING into the mark word.  We originally installed INFLATING,
1514     // allocated the ObjectMonitor, and then finally STed the address of the
1515     // ObjectMonitor into the mark.  This was correct, but artificially lengthened
1516     // the interval in which INFLATING appeared in the mark, thus increasing
1517     // the odds of inflation contention. If we lose the race to set INFLATING,
1518     // then we just delete the ObjectMonitor and loop around again.
1519     //
1520     if (LockingMode == LM_LEGACY && mark.has_locker()) {
1521       assert(LockingMode != LM_LIGHTWEIGHT, "cannot happen with new lightweight locking");
1522       ObjectMonitor* m = new ObjectMonitor(object);
1523       // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1524       // We do this before the CAS in order to minimize the length of time
1525       // in which INFLATING appears in the mark.
1526 
1527       markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1528       if (cmp != mark) {
1529         delete m;
1530         continue;       // Interference -- just retry
1531       }
1532 
1533       // We've successfully installed INFLATING (0) into the mark-word.
1534       // This is the only case where 0 will appear in a mark-word.
1535       // Only the singular thread that successfully swings the mark-word
1536       // to 0 can perform (or more precisely, complete) inflation.
1537       //
1538       // Why do we CAS a 0 into the mark-word instead of just CASing the
1539       // mark-word from the stack-locked value directly to the new inflated state?
1540       // Consider what happens when a thread unlocks a stack-locked object.
1541       // It attempts to use CAS to swing the displaced header value from the
1542       // on-stack BasicLock back into the object header.  Recall also that the
1543       // header value (hash code, etc) can reside in (a) the object header, or
1544       // (b) a displaced header associated with the stack-lock, or (c) a displaced
1545       // header in an ObjectMonitor.  The inflate() routine must copy the header
1546       // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1547       // the while preserving the hashCode stability invariants.  If the owner
1548       // decides to release the lock while the value is 0, the unlock will fail
1549       // and control will eventually pass from slow_exit() to inflate.  The owner
1550       // will then spin, waiting for the 0 value to disappear.   Put another way,
1551       // the 0 causes the owner to stall if the owner happens to try to
1552       // drop the lock (restoring the header from the BasicLock to the object)
1553       // while inflation is in-progress.  This protocol avoids races that might
1554       // would otherwise permit hashCode values to change or "flicker" for an object.
1555       // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1556       // 0 serves as a "BUSY" inflate-in-progress indicator.
1557 
1558 
1559       // fetch the displaced mark from the owner's stack.
1560       // The owner can't die or unwind past the lock while our INFLATING
1561       // object is in the mark.  Furthermore the owner can't complete
1562       // an unlock on the object, either.
1563       markWord dmw = mark.displaced_mark_helper();
1564       // Catch if the object's header is not neutral (not locked and
1565       // not marked is what we care about here).
1566       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1567 
1568       // Setup monitor fields to proper values -- prepare the monitor
1569       m->set_header(dmw);
1570 
1571       // Optimization: if the mark.locker stack address is associated
1572       // with this thread we could simply set m->_owner = current.
1573       // Note that a thread can inflate an object
1574       // that it has stack-locked -- as might happen in wait() -- directly
1575       // with CAS.  That is, we can avoid the xchg-nullptr .... ST idiom.
1576       m->set_owner_from(nullptr, mark.locker());
1577       // TODO-FIXME: assert BasicLock->dhw != 0.
1578 
1579       // Must preserve store ordering. The monitor state must
1580       // be stable at the time of publishing the monitor address.
1581       guarantee(object->mark() == markWord::INFLATING(), "invariant");
1582       // Release semantics so that above set_object() is seen first.
1583       object->release_set_mark(markWord::encode(m));
1584 
1585       // Once ObjectMonitor is configured and the object is associated
1586       // with the ObjectMonitor, it is safe to allow async deflation:
1587       _in_use_list.add(m);
1588 
1589       // Hopefully the performance counters are allocated on distinct cache lines
1590       // to avoid false sharing on MP systems ...
1591       OM_PERFDATA_OP(Inflations, inc());
1592       if (log_is_enabled(Trace, monitorinflation)) {
1593         ResourceMark rm;
1594         lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1595                      INTPTR_FORMAT ", type='%s'", p2i(object),
1596                      object->mark().value(), object->klass()->external_name());
1597       }
1598       if (event.should_commit()) {
1599         post_monitor_inflate_event(&event, object, cause);
1600       }
1601       return m;
1602     }
1603 
1604     // CASE: neutral
1605     // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1606     // If we know we're inflating for entry it's better to inflate by swinging a
1607     // pre-locked ObjectMonitor pointer into the object header.   A successful
1608     // CAS inflates the object *and* confers ownership to the inflating thread.
1609     // In the current implementation we use a 2-step mechanism where we CAS()
1610     // to inflate and then CAS() again to try to swing _owner from null to current.
1611     // An inflateTry() method that we could call from enter() would be useful.
1612 
1613     // Catch if the object's header is not neutral (not locked and
1614     // not marked is what we care about here).
1615     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1616     ObjectMonitor* m = new ObjectMonitor(object);
1617     // prepare m for installation - set monitor to initial state
1618     m->set_header(mark);
1619 
1620     if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1621       delete m;
1622       m = nullptr;
1623       continue;
1624       // interference - the markword changed - just retry.
1625       // The state-transitions are one-way, so there's no chance of
1626       // live-lock -- "Inflated" is an absorbing state.
1627     }
1628 
1629     // Once the ObjectMonitor is configured and object is associated
1630     // with the ObjectMonitor, it is safe to allow async deflation:
1631     _in_use_list.add(m);
1632 
1633     // Hopefully the performance counters are allocated on distinct
1634     // cache lines to avoid false sharing on MP systems ...
1635     OM_PERFDATA_OP(Inflations, inc());
1636     if (log_is_enabled(Trace, monitorinflation)) {
1637       ResourceMark rm;
1638       lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1639                    INTPTR_FORMAT ", type='%s'", p2i(object),
1640                    object->mark().value(), object->klass()->external_name());
1641     }
1642     if (event.should_commit()) {
1643       post_monitor_inflate_event(&event, object, cause);
1644     }
1645     return m;
1646   }
1647 }
1648 
1649 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1650 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1651 //
1652 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1653   MonitorList::Iterator iter = _in_use_list.iterator();
1654   size_t deflated_count = 0;
1655 
1656   while (iter.has_next()) {
1657     if (deflated_count >= (size_t)MonitorDeflationMax) {
1658       break;
1659     }
1660     ObjectMonitor* mid = iter.next();
1661     if (mid->deflate_monitor()) {
1662       deflated_count++;
1663     }
1664 
1665     // Must check for a safepoint/handshake and honor it.
1666     safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1667   }
1668 
1669   return deflated_count;
1670 }
1671 
1672 class HandshakeForDeflation : public HandshakeClosure {
1673  public:
1674   HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1675 
1676   void do_thread(Thread* thread) {
1677     log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1678                                 INTPTR_FORMAT, p2i(thread));
1679   }
1680 };
1681 
1682 class VM_RendezvousGCThreads : public VM_Operation {
1683 public:
1684   bool evaluate_at_safepoint() const override { return false; }
1685   VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1686   void doit() override {
1687     Universe::heap()->safepoint_synchronize_begin();
1688     Universe::heap()->safepoint_synchronize_end();
1689   };
1690 };
1691 
1692 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1693                               ObjectMonitorDeflationSafepointer* safepointer) {
1694   NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1695   size_t deleted_count = 0;
1696   for (ObjectMonitor* monitor: *delete_list) {
1697     delete monitor;
1698     deleted_count++;
1699     // A JavaThread must check for a safepoint/handshake and honor it.
1700     safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1701   }
1702   return deleted_count;
1703 }
1704 
1705 class ObjectMonitorDeflationLogging: public StackObj {
1706   LogStreamHandle(Debug, monitorinflation) _debug;
1707   LogStreamHandle(Info, monitorinflation)  _info;
1708   LogStream*                               _stream;
1709   elapsedTimer                             _timer;
1710 
1711   size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1712   size_t count() const   { return ObjectSynchronizer::_in_use_list.count(); }
1713   size_t max() const     { return ObjectSynchronizer::_in_use_list.max(); }
1714 
1715 public:
1716   ObjectMonitorDeflationLogging()
1717     : _debug(), _info(), _stream(nullptr) {
1718     if (_debug.is_enabled()) {
1719       _stream = &_debug;
1720     } else if (_info.is_enabled()) {
1721       _stream = &_info;
1722     }
1723   }
1724 
1725   void begin() {
1726     if (_stream != nullptr) {
1727       _stream->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1728                         ceiling(), count(), max());
1729       _timer.start();
1730     }
1731   }
1732 
1733   void before_handshake(size_t unlinked_count) {
1734     if (_stream != nullptr) {
1735       _timer.stop();
1736       _stream->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1737                         ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1738                         SIZE_FORMAT ", max=" SIZE_FORMAT,
1739                         unlinked_count, ceiling(), count(), max());
1740     }
1741   }
1742 
1743   void after_handshake() {
1744     if (_stream != nullptr) {
1745       _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1746                         SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1747                         ceiling(), count(), max());
1748       _timer.start();
1749     }
1750   }
1751 
1752   void end(size_t deflated_count, size_t unlinked_count) {
1753     if (_stream != nullptr) {
1754       _timer.stop();
1755       if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1756         _stream->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1757                           deflated_count, unlinked_count, _timer.seconds());
1758       }
1759       _stream->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1760                         ceiling(), count(), max());
1761     }
1762   }
1763 
1764   void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1765     if (_stream != nullptr) {
1766       _timer.stop();
1767       _stream->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1768                         SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1769                         op_name, cnt_name, cnt, ceiling(), count(), max());
1770     }
1771   }
1772 
1773   void after_block_for_safepoint(const char* op_name) {
1774     if (_stream != nullptr) {
1775       _stream->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1776                         ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1777                         ceiling(), count(), max());
1778       _timer.start();
1779     }
1780   }
1781 };
1782 
1783 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1784   if (!SafepointMechanism::should_process(_current)) {
1785     return;
1786   }
1787 
1788   // A safepoint/handshake has started.
1789   _log->before_block_for_safepoint(op_name, count_name, counter);
1790 
1791   {
1792     // Honor block request.
1793     ThreadBlockInVM tbivm(_current);
1794   }
1795 
1796   _log->after_block_for_safepoint(op_name);
1797 }
1798 
1799 // This function is called by the MonitorDeflationThread to deflate
1800 // ObjectMonitors.
1801 size_t ObjectSynchronizer::deflate_idle_monitors() {
1802   JavaThread* current = JavaThread::current();
1803   assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1804 
1805   // The async deflation request has been processed.
1806   _last_async_deflation_time_ns = os::javaTimeNanos();
1807   set_is_async_deflation_requested(false);
1808 
1809   ObjectMonitorDeflationLogging log;
1810   ObjectMonitorDeflationSafepointer safepointer(current, &log);
1811 
1812   log.begin();
1813 
1814   // Deflate some idle ObjectMonitors.
1815   size_t deflated_count = deflate_monitor_list(&safepointer);
1816 
1817   // Unlink the deflated ObjectMonitors from the in-use list.
1818   size_t unlinked_count = 0;
1819   size_t deleted_count = 0;
1820   if (deflated_count > 0) {
1821     ResourceMark rm(current);
1822     GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1823     unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1824 
1825     log.before_handshake(unlinked_count);
1826 
1827     // A JavaThread needs to handshake in order to safely free the
1828     // ObjectMonitors that were deflated in this cycle.
1829     HandshakeForDeflation hfd_hc;
1830     Handshake::execute(&hfd_hc);
1831     // Also, we sync and desync GC threads around the handshake, so that they can
1832     // safely read the mark-word and look-through to the object-monitor, without
1833     // being afraid that the object-monitor is going away.
1834     VM_RendezvousGCThreads sync_gc;
1835     VMThread::execute(&sync_gc);
1836 
1837     log.after_handshake();
1838 
1839     // After the handshake, safely free the ObjectMonitors that were
1840     // deflated and unlinked in this cycle.
1841 
1842     // Delete the unlinked ObjectMonitors.
1843     deleted_count = delete_monitors(&delete_list, &safepointer);
1844     assert(unlinked_count == deleted_count, "must be");
1845   }
1846 
1847   log.end(deflated_count, unlinked_count);
1848 
1849   OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1850   OM_PERFDATA_OP(Deflations, inc(deflated_count));
1851 
1852   GVars.stw_random = os::random();
1853 
1854   if (deflated_count != 0) {
1855     _no_progress_cnt = 0;
1856   } else if (_no_progress_skip_increment) {
1857     _no_progress_skip_increment = false;
1858   } else {
1859     _no_progress_cnt++;
1860   }
1861 
1862   return deflated_count;
1863 }
1864 
1865 // Monitor cleanup on JavaThread::exit
1866 
1867 // Iterate through monitor cache and attempt to release thread's monitors
1868 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1869  private:
1870   JavaThread* _thread;
1871 
1872  public:
1873   ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1874   void do_monitor(ObjectMonitor* mid) {
1875     intx rec = mid->complete_exit(_thread);
1876     _thread->dec_held_monitor_count(rec + 1);
1877   }
1878 };
1879 
1880 // Release all inflated monitors owned by current thread.  Lightweight monitors are
1881 // ignored.  This is meant to be called during JNI thread detach which assumes
1882 // all remaining monitors are heavyweight.  All exceptions are swallowed.
1883 // Scanning the extant monitor list can be time consuming.
1884 // A simple optimization is to add a per-thread flag that indicates a thread
1885 // called jni_monitorenter() during its lifetime.
1886 //
1887 // Instead of NoSafepointVerifier it might be cheaper to
1888 // use an idiom of the form:
1889 //   auto int tmp = SafepointSynchronize::_safepoint_counter ;
1890 //   <code that must not run at safepoint>
1891 //   guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1892 // Since the tests are extremely cheap we could leave them enabled
1893 // for normal product builds.
1894 
1895 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1896   assert(current == JavaThread::current(), "must be current Java thread");
1897   NoSafepointVerifier nsv;
1898   ReleaseJavaMonitorsClosure rjmc(current);
1899   ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1900   assert(!current->has_pending_exception(), "Should not be possible");
1901   current->clear_pending_exception();
1902   assert(current->held_monitor_count() == 0, "Should not be possible");
1903   // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1904   current->clear_jni_monitor_count();
1905 }
1906 
1907 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1908   switch (cause) {
1909     case inflate_cause_vm_internal:    return "VM Internal";
1910     case inflate_cause_monitor_enter:  return "Monitor Enter";
1911     case inflate_cause_wait:           return "Monitor Wait";
1912     case inflate_cause_notify:         return "Monitor Notify";
1913     case inflate_cause_hash_code:      return "Monitor Hash Code";
1914     case inflate_cause_jni_enter:      return "JNI Monitor Enter";
1915     case inflate_cause_jni_exit:       return "JNI Monitor Exit";
1916     default:
1917       ShouldNotReachHere();
1918   }
1919   return "Unknown";
1920 }
1921 
1922 //------------------------------------------------------------------------------
1923 // Debugging code
1924 
1925 u_char* ObjectSynchronizer::get_gvars_addr() {
1926   return (u_char*)&GVars;
1927 }
1928 
1929 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1930   return (u_char*)&GVars.hc_sequence;
1931 }
1932 
1933 size_t ObjectSynchronizer::get_gvars_size() {
1934   return sizeof(SharedGlobals);
1935 }
1936 
1937 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1938   return (u_char*)&GVars.stw_random;
1939 }
1940 
1941 // Do the final audit and print of ObjectMonitor stats; must be done
1942 // by the VMThread at VM exit time.
1943 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1944   assert(Thread::current()->is_VM_thread(), "sanity check");
1945 
1946   if (is_final_audit()) {  // Only do the audit once.
1947     return;
1948   }
1949   set_is_final_audit();
1950   log_info(monitorinflation)("Starting the final audit.");
1951 
1952   if (log_is_enabled(Info, monitorinflation)) {
1953     // The other audit_and_print_stats() call is done at the Debug
1954     // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
1955     audit_and_print_stats(true /* on_exit */);
1956   }
1957 }
1958 
1959 // This function can be called at a safepoint or it can be called when
1960 // we are trying to exit the VM. When we are trying to exit the VM, the
1961 // list walker functions can run in parallel with the other list
1962 // operations so spin-locking is used for safety.
1963 //
1964 // Calls to this function can be added in various places as a debugging
1965 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1966 // details logged at the Info level and 'false' for the 'on_exit'
1967 // parameter to have in-use monitor details logged at the Trace level.
1968 //
1969 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1970   assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1971 
1972   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1973   LogStreamHandle(Info, monitorinflation) lsh_info;
1974   LogStreamHandle(Trace, monitorinflation) lsh_trace;
1975   LogStream* ls = nullptr;
1976   if (log_is_enabled(Trace, monitorinflation)) {
1977     ls = &lsh_trace;
1978   } else if (log_is_enabled(Debug, monitorinflation)) {
1979     ls = &lsh_debug;
1980   } else if (log_is_enabled(Info, monitorinflation)) {
1981     ls = &lsh_info;
1982   }
1983   assert(ls != nullptr, "sanity check");
1984 
1985   int error_cnt = 0;
1986 
1987   ls->print_cr("Checking in_use_list:");
1988   chk_in_use_list(ls, &error_cnt);
1989 
1990   if (error_cnt == 0) {
1991     ls->print_cr("No errors found in in_use_list checks.");
1992   } else {
1993     log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1994   }
1995 
1996   if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1997       (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1998     // When exiting this log output is at the Info level. When called
1999     // at a safepoint, this log output is at the Trace level since
2000     // there can be a lot of it.
2001     log_in_use_monitor_details(ls, !on_exit /* log_all */);
2002   }
2003 
2004   ls->flush();
2005 
2006   guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2007 }
2008 
2009 // Check the in_use_list; log the results of the checks.
2010 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
2011   size_t l_in_use_count = _in_use_list.count();
2012   size_t l_in_use_max = _in_use_list.max();
2013   out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
2014                 l_in_use_max);
2015 
2016   size_t ck_in_use_count = 0;
2017   MonitorList::Iterator iter = _in_use_list.iterator();
2018   while (iter.has_next()) {
2019     ObjectMonitor* mid = iter.next();
2020     chk_in_use_entry(mid, out, error_cnt_p);
2021     ck_in_use_count++;
2022   }
2023 
2024   if (l_in_use_count == ck_in_use_count) {
2025     out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
2026                   SIZE_FORMAT, l_in_use_count, ck_in_use_count);
2027   } else {
2028     out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
2029                   "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
2030                   ck_in_use_count);
2031   }
2032 
2033   size_t ck_in_use_max = _in_use_list.max();
2034   if (l_in_use_max == ck_in_use_max) {
2035     out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
2036                   SIZE_FORMAT, l_in_use_max, ck_in_use_max);
2037   } else {
2038     out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
2039                   "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
2040   }
2041 }
2042 
2043 // Check an in-use monitor entry; log any errors.
2044 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2045                                           int* error_cnt_p) {
2046   if (n->owner_is_DEFLATER_MARKER()) {
2047     // This could happen when monitor deflation blocks for a safepoint.
2048     return;
2049   }
2050 
2051   if (n->header().value() == 0) {
2052     out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2053                   "have non-null _header field.", p2i(n));
2054     *error_cnt_p = *error_cnt_p + 1;
2055   }
2056   const oop obj = n->object_peek();
2057   if (obj != nullptr) {
2058     const markWord mark = obj->mark();
2059     if (!mark.has_monitor()) {
2060       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2061                     "object does not think it has a monitor: obj="
2062                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2063                     p2i(obj), mark.value());
2064       *error_cnt_p = *error_cnt_p + 1;
2065     }
2066     ObjectMonitor* const obj_mon = mark.monitor();
2067     if (n != obj_mon) {
2068       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2069                     "object does not refer to the same monitor: obj="
2070                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2071                     INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2072       *error_cnt_p = *error_cnt_p + 1;
2073     }
2074   }
2075 }
2076 
2077 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2078 // flags indicate why the entry is in-use, 'object' and 'object type'
2079 // indicate the associated object and its type.
2080 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2081   if (_in_use_list.count() > 0) {
2082     stringStream ss;
2083     out->print_cr("In-use monitor info:");
2084     out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2085     out->print_cr("%18s  %s  %18s  %18s",
2086                   "monitor", "BHL", "object", "object type");
2087     out->print_cr("==================  ===  ==================  ==================");
2088 
2089     auto is_interesting = [&](ObjectMonitor* monitor) {
2090       return log_all || monitor->has_owner() || monitor->is_busy();
2091     };
2092 
2093     monitors_iterate([&](ObjectMonitor* monitor) {
2094       if (is_interesting(monitor)) {
2095         const oop obj = monitor->object_peek();
2096         const markWord mark = monitor->header();
2097         ResourceMark rm;
2098         out->print(INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT "  %s", p2i(monitor),
2099                    monitor->is_busy(), mark.hash() != 0, monitor->owner() != nullptr,
2100                    p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2101         if (monitor->is_busy()) {
2102           out->print(" (%s)", monitor->is_busy_to_string(&ss));
2103           ss.reset();
2104         }
2105         out->cr();
2106       }
2107     });
2108   }
2109 
2110   out->flush();
2111 }