1 /*
   2  * Copyright (c) 1998, 2023, 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/handles.inline.hpp"
  40 #include "runtime/handshake.hpp"
  41 #include "runtime/interfaceSupport.inline.hpp"
  42 #include "runtime/javaThread.hpp"
  43 #include "runtime/lockStack.inline.hpp"
  44 #include "runtime/mutexLocker.hpp"
  45 #include "runtime/objectMonitor.hpp"
  46 #include "runtime/objectMonitor.inline.hpp"
  47 #include "runtime/os.inline.hpp"
  48 #include "runtime/osThread.hpp"
  49 #include "runtime/perfData.hpp"
  50 #include "runtime/safepointMechanism.inline.hpp"
  51 #include "runtime/safepointVerifiers.hpp"
  52 #include "runtime/sharedRuntime.hpp"
  53 #include "runtime/stubRoutines.hpp"
  54 #include "runtime/synchronizer.hpp"
  55 #include "runtime/threads.hpp"
  56 #include "runtime/timer.hpp"
  57 #include "runtime/trimNativeHeap.hpp"
  58 #include "runtime/vframe.hpp"
  59 #include "runtime/vmThread.hpp"
  60 #include "utilities/align.hpp"
  61 #include "utilities/dtrace.hpp"
  62 #include "utilities/events.hpp"
  63 #include "utilities/linkedlist.hpp"
  64 #include "utilities/preserveException.hpp"
  65 
  66 void MonitorList::add(ObjectMonitor* m) {
  67   ObjectMonitor* head;
  68   do {
  69     head = Atomic::load(&_head);
  70     m->set_next_om(head);
  71   } while (Atomic::cmpxchg(&_head, head, m) != head);
  72 
  73   size_t count = Atomic::add(&_count, 1u);
  74   if (count > max()) {
  75     Atomic::inc(&_max);
  76   }
  77 }
  78 
  79 size_t MonitorList::count() const {
  80   return Atomic::load(&_count);
  81 }
  82 
  83 size_t MonitorList::max() const {
  84   return Atomic::load(&_max);
  85 }
  86 
  87 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
  88 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
  89 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
  90                                     elapsedTimer* timer_p,
  91                                     GrowableArray<ObjectMonitor*>* unlinked_list) {
  92   size_t unlinked_count = 0;
  93   ObjectMonitor* prev = nullptr;
  94   ObjectMonitor* head = Atomic::load_acquire(&_head);
  95   ObjectMonitor* m = head;
  96   // The in-use list head can be null during the final audit.
  97   while (m != nullptr) {
  98     if (m->is_being_async_deflated()) {
  99       // Find next live ObjectMonitor.
 100       ObjectMonitor* next = m;
 101       do {
 102         ObjectMonitor* next_next = next->next_om();
 103         unlinked_count++;
 104         unlinked_list->append(next);
 105         next = next_next;
 106         if (unlinked_count >= (size_t)MonitorDeflationMax) {
 107           // Reached the max so bail out on the gathering loop.
 108           break;
 109         }
 110       } while (next != nullptr && next->is_being_async_deflated());
 111       if (prev == nullptr) {
 112         ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
 113         if (prev_head != head) {
 114           // Find new prev ObjectMonitor that just got inserted.
 115           for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
 116             prev = n;
 117           }
 118           prev->set_next_om(next);
 119         }
 120       } else {
 121         prev->set_next_om(next);
 122       }
 123       if (unlinked_count >= (size_t)MonitorDeflationMax) {
 124         // Reached the max so bail out on the searching loop.
 125         break;
 126       }
 127       m = next;
 128     } else {
 129       prev = m;
 130       m = m->next_om();
 131     }
 132 
 133     if (current->is_Java_thread()) {
 134       // A JavaThread must check for a safepoint/handshake and honor it.
 135       ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking",
 136                                             "unlinked_count", unlinked_count,
 137                                             ls, timer_p);
 138     }
 139   }
 140   Atomic::sub(&_count, unlinked_count);
 141   return unlinked_count;
 142 }
 143 
 144 MonitorList::Iterator MonitorList::iterator() const {
 145   return Iterator(Atomic::load_acquire(&_head));
 146 }
 147 
 148 ObjectMonitor* MonitorList::Iterator::next() {
 149   ObjectMonitor* current = _current;
 150   _current = current->next_om();
 151   return current;
 152 }
 153 
 154 // The "core" versions of monitor enter and exit reside in this file.
 155 // The interpreter and compilers contain specialized transliterated
 156 // variants of the enter-exit fast-path operations.  See c2_MacroAssembler_x86.cpp
 157 // fast_lock(...) for instance.  If you make changes here, make sure to modify the
 158 // interpreter, and both C1 and C2 fast-path inline locking code emission.
 159 //
 160 // -----------------------------------------------------------------------------
 161 
 162 #ifdef DTRACE_ENABLED
 163 
 164 // Only bother with this argument setup if dtrace is available
 165 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
 166 
 167 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
 168   char* bytes = nullptr;                                                      \
 169   int len = 0;                                                             \
 170   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
 171   Symbol* klassname = obj->klass()->name();                                \
 172   if (klassname != nullptr) {                                                 \
 173     bytes = (char*)klassname->bytes();                                     \
 174     len = klassname->utf8_length();                                        \
 175   }
 176 
 177 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
 178   {                                                                        \
 179     if (DTraceMonitorProbes) {                                             \
 180       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 181       HOTSPOT_MONITOR_WAIT(jtid,                                           \
 182                            (uintptr_t)(monitor), bytes, len, (millis));    \
 183     }                                                                      \
 184   }
 185 
 186 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
 187 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
 188 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
 189 
 190 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
 191   {                                                                        \
 192     if (DTraceMonitorProbes) {                                             \
 193       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 194       HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */             \
 195                                     (uintptr_t)(monitor), bytes, len);     \
 196     }                                                                      \
 197   }
 198 
 199 #else //  ndef DTRACE_ENABLED
 200 
 201 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 202 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 203 
 204 #endif // ndef DTRACE_ENABLED
 205 
 206 // This exists only as a workaround of dtrace bug 6254741
 207 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
 208   DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
 209   return 0;
 210 }
 211 
 212 static constexpr size_t inflation_lock_count() {
 213   return 256;
 214 }
 215 
 216 // Static storage for an array of PlatformMutex.
 217 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
 218 
 219 static inline PlatformMutex* inflation_lock(size_t index) {
 220   return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
 221 }
 222 
 223 void ObjectSynchronizer::initialize() {
 224   for (size_t i = 0; i < inflation_lock_count(); i++) {
 225     ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
 226   }
 227   // Start the ceiling with the estimate for one thread.
 228   set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
 229 
 230   // Start the timer for deflations, so it does not trigger immediately.
 231   _last_async_deflation_time_ns = os::javaTimeNanos();
 232 }
 233 
 234 MonitorList ObjectSynchronizer::_in_use_list;
 235 // monitors_used_above_threshold() policy is as follows:
 236 //
 237 // The ratio of the current _in_use_list count to the ceiling is used
 238 // to determine if we are above MonitorUsedDeflationThreshold and need
 239 // to do an async monitor deflation cycle. The ceiling is increased by
 240 // AvgMonitorsPerThreadEstimate when a thread is added to the system
 241 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
 242 // removed from the system.
 243 //
 244 // Note: If the _in_use_list max exceeds the ceiling, then
 245 // monitors_used_above_threshold() will use the in_use_list max instead
 246 // of the thread count derived ceiling because we have used more
 247 // ObjectMonitors than the estimated average.
 248 //
 249 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
 250 // no-progress async monitor deflation cycles in a row, then the ceiling
 251 // is adjusted upwards by monitors_used_above_threshold().
 252 //
 253 // Start the ceiling with the estimate for one thread in initialize()
 254 // which is called after cmd line options are processed.
 255 static size_t _in_use_list_ceiling = 0;
 256 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
 257 bool volatile ObjectSynchronizer::_is_final_audit = false;
 258 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
 259 static uintx _no_progress_cnt = 0;
 260 static bool _no_progress_skip_increment = false;
 261 
 262 // =====================> Quick functions
 263 
 264 // The quick_* forms are special fast-path variants used to improve
 265 // performance.  In the simplest case, a "quick_*" implementation could
 266 // simply return false, in which case the caller will perform the necessary
 267 // state transitions and call the slow-path form.
 268 // The fast-path is designed to handle frequently arising cases in an efficient
 269 // manner and is just a degenerate "optimistic" variant of the slow-path.
 270 // returns true  -- to indicate the call was satisfied.
 271 // returns false -- to indicate the call needs the services of the slow-path.
 272 // A no-loitering ordinance is in effect for code in the quick_* family
 273 // operators: safepoints or indefinite blocking (blocking that might span a
 274 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
 275 // entry.
 276 //
 277 // Consider: An interesting optimization is to have the JIT recognize the
 278 // following common idiom:
 279 //   synchronized (someobj) { .... ; notify(); }
 280 // That is, we find a notify() or notifyAll() call that immediately precedes
 281 // the monitorexit operation.  In that case the JIT could fuse the operations
 282 // into a single notifyAndExit() runtime primitive.
 283 
 284 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
 285   assert(current->thread_state() == _thread_in_Java, "invariant");
 286   NoSafepointVerifier nsv;
 287   if (obj == nullptr) return false;  // slow-path for invalid obj
 288   const markWord mark = obj->mark();
 289 
 290   if (LockingMode == LM_LIGHTWEIGHT) {
 291     if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
 292       // Degenerate notify
 293       // fast-locked by caller so by definition the implied waitset is empty.
 294       return true;
 295     }
 296   } else if (LockingMode == LM_LEGACY) {
 297     if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 298       // Degenerate notify
 299       // stack-locked by caller so by definition the implied waitset is empty.
 300       return true;
 301     }
 302   }
 303 
 304   if (mark.has_monitor()) {
 305     ObjectMonitor* const mon = mark.monitor();
 306     assert(mon->object() == oop(obj), "invariant");
 307     if (mon->owner() != current) return false;  // slow-path for IMS exception
 308 
 309     if (mon->first_waiter() != nullptr) {
 310       // We have one or more waiters. Since this is an inflated monitor
 311       // that we own, we can transfer one or more threads from the waitset
 312       // to the entrylist here and now, avoiding the slow-path.
 313       if (all) {
 314         DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
 315       } else {
 316         DTRACE_MONITOR_PROBE(notify, mon, obj, current);
 317       }
 318       int free_count = 0;
 319       do {
 320         mon->INotify(current);
 321         ++free_count;
 322       } while (mon->first_waiter() != nullptr && all);
 323       OM_PERFDATA_OP(Notifications, inc(free_count));
 324     }
 325     return true;
 326   }
 327 
 328   // other IMS exception states take the slow-path
 329   return false;
 330 }
 331 
 332 
 333 // The LockNode emitted directly at the synchronization site would have
 334 // been too big if it were to have included support for the cases of inflated
 335 // recursive enter and exit, so they go here instead.
 336 // Note that we can't safely call AsyncPrintJavaStack() from within
 337 // quick_enter() as our thread state remains _in_Java.
 338 
 339 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
 340                                      BasicLock * lock) {
 341   assert(current->thread_state() == _thread_in_Java, "invariant");
 342   NoSafepointVerifier nsv;
 343   if (obj == nullptr) return false;       // Need to throw NPE
 344 
 345   if (obj->klass()->is_value_based()) {
 346     return false;
 347   }
 348 
 349   const markWord mark = obj->mark();
 350 
 351   if (mark.has_monitor()) {
 352     ObjectMonitor* const m = mark.monitor();
 353     // An async deflation or GC can race us before we manage to make
 354     // the ObjectMonitor busy by setting the owner below. If we detect
 355     // that race we just bail out to the slow-path here.
 356     if (m->object_peek() == nullptr) {
 357       return false;
 358     }
 359     JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
 360 
 361     // Lock contention and Transactional Lock Elision (TLE) diagnostics
 362     // and observability
 363     // Case: light contention possibly amenable to TLE
 364     // Case: TLE inimical operations such as nested/recursive synchronization
 365 
 366     if (owner == current) {
 367       m->_recursions++;
 368       current->inc_held_monitor_count();
 369       return true;
 370     }
 371 
 372     if (LockingMode != LM_LIGHTWEIGHT) {
 373       // This Java Monitor is inflated so obj's header will never be
 374       // displaced to this thread's BasicLock. Make the displaced header
 375       // non-null so this BasicLock is not seen as recursive nor as
 376       // being locked. We do this unconditionally so that this thread's
 377       // BasicLock cannot be mis-interpreted by any stack walkers. For
 378       // performance reasons, stack walkers generally first check for
 379       // stack-locking in the object's header, the second check is for
 380       // recursive stack-locking in the displaced header in the BasicLock,
 381       // and last are the inflated Java Monitor (ObjectMonitor) checks.
 382       lock->set_displaced_header(markWord::unused_mark());
 383     }
 384 
 385     if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) {
 386       assert(m->_recursions == 0, "invariant");
 387       current->inc_held_monitor_count();
 388       return true;
 389     }
 390   }
 391 
 392   // Note that we could inflate in quick_enter.
 393   // This is likely a useful optimization
 394   // Critically, in quick_enter() we must not:
 395   // -- block indefinitely, or
 396   // -- reach a safepoint
 397 
 398   return false;        // revert to slow-path
 399 }
 400 
 401 // Handle notifications when synchronizing on value based classes
 402 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
 403   frame last_frame = current->last_frame();
 404   bool bcp_was_adjusted = false;
 405   // Don't decrement bcp if it points to the frame's first instruction.  This happens when
 406   // handle_sync_on_value_based_class() is called because of a synchronized method.  There
 407   // is no actual monitorenter instruction in the byte code in this case.
 408   if (last_frame.is_interpreted_frame() &&
 409       (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
 410     // adjust bcp to point back to monitorenter so that we print the correct line numbers
 411     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
 412     bcp_was_adjusted = true;
 413   }
 414 
 415   if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
 416     ResourceMark rm(current);
 417     stringStream ss;
 418     current->print_active_stack_on(&ss);
 419     char* base = (char*)strstr(ss.base(), "at");
 420     char* newline = (char*)strchr(ss.base(), '\n');
 421     if (newline != nullptr) {
 422       *newline = '\0';
 423     }
 424     fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
 425   } else {
 426     assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
 427     ResourceMark rm(current);
 428     Log(valuebasedclasses) vblog;
 429 
 430     vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
 431     if (current->has_last_Java_frame()) {
 432       LogStream info_stream(vblog.info());
 433       current->print_active_stack_on(&info_stream);
 434     } else {
 435       vblog.info("Cannot find the last Java frame");
 436     }
 437 
 438     EventSyncOnValueBasedClass event;
 439     if (event.should_commit()) {
 440       event.set_valueBasedClass(obj->klass());
 441       event.commit();
 442     }
 443   }
 444 
 445   if (bcp_was_adjusted) {
 446     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
 447   }
 448 }
 449 
 450 static bool useHeavyMonitors() {
 451 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
 452   return LockingMode == LM_MONITOR;
 453 #else
 454   return false;
 455 #endif
 456 }
 457 
 458 // -----------------------------------------------------------------------------
 459 // Monitor Enter/Exit
 460 // The interpreter and compiler assembly code tries to lock using the fast path
 461 // of this algorithm. Make sure to update that code if the following function is
 462 // changed. The implementation is extremely sensitive to race condition. Be careful.
 463 
 464 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
 465   if (obj->klass()->is_value_based()) {
 466     handle_sync_on_value_based_class(obj, current);
 467   }
 468 
 469   current->inc_held_monitor_count();
 470 
 471   if (!useHeavyMonitors()) {
 472     if (LockingMode == LM_LIGHTWEIGHT) {
 473       // Fast-locking does not use the 'lock' argument.
 474       LockStack& lock_stack = current->lock_stack();
 475       if (lock_stack.can_push()) {
 476         markWord mark = obj()->mark_acquire();
 477         if (mark.is_neutral()) {
 478           assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
 479           // Try to swing into 'fast-locked' state.
 480           markWord locked_mark = mark.set_fast_locked();
 481           markWord old_mark = obj()->cas_set_mark(locked_mark, mark);
 482           if (old_mark == mark) {
 483             // Successfully fast-locked, push object to lock-stack and return.
 484             lock_stack.push(obj());
 485             return;
 486           }
 487         }
 488       }
 489       // All other paths fall-through to inflate-enter.
 490     } else if (LockingMode == LM_LEGACY) {
 491       markWord mark = obj->mark();
 492       if (mark.is_neutral()) {
 493         // Anticipate successful CAS -- the ST of the displaced mark must
 494         // be visible <= the ST performed by the CAS.
 495         lock->set_displaced_header(mark);
 496         if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
 497           return;
 498         }
 499         // Fall through to inflate() ...
 500       } else if (mark.has_locker() &&
 501                  current->is_lock_owned((address) mark.locker())) {
 502         assert(lock != mark.locker(), "must not re-lock the same lock");
 503         assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
 504         lock->set_displaced_header(markWord::from_pointer(nullptr));
 505         return;
 506       }
 507 
 508       // The object header will never be displaced to this lock,
 509       // so it does not matter what the value is, except that it
 510       // must be non-zero to avoid looking like a re-entrant lock,
 511       // and must not look locked either.
 512       lock->set_displaced_header(markWord::unused_mark());
 513     }
 514   } else if (VerifyHeavyMonitors) {
 515     guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
 516   }
 517 
 518   // An async deflation can race after the inflate() call and before
 519   // enter() can make the ObjectMonitor busy. enter() returns false if
 520   // we have lost the race to async deflation and we simply try again.
 521   while (true) {
 522     ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
 523     if (monitor->enter(current)) {
 524       return;
 525     }
 526   }
 527 }
 528 
 529 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
 530   current->dec_held_monitor_count();
 531 
 532   if (!useHeavyMonitors()) {
 533     markWord mark = object->mark();
 534     if (LockingMode == LM_LIGHTWEIGHT) {
 535       // Fast-locking does not use the 'lock' argument.
 536       if (mark.is_fast_locked()) {
 537         markWord unlocked_mark = mark.set_unlocked();
 538         markWord old_mark = object->cas_set_mark(unlocked_mark, mark);
 539         if (old_mark != mark) {
 540           // Another thread won the CAS, it must have inflated the monitor.
 541           // It can only have installed an anonymously locked monitor at this point.
 542           // Fetch that monitor, set owner correctly to this thread, and
 543           // exit it (allowing waiting threads to enter).
 544           assert(old_mark.has_monitor(), "must have monitor");
 545           ObjectMonitor* monitor = old_mark.monitor();
 546           assert(monitor->is_owner_anonymous(), "must be anonymous owner");
 547           monitor->set_owner_from_anonymous(current);
 548           monitor->exit(current);
 549         }
 550         LockStack& lock_stack = current->lock_stack();
 551         lock_stack.remove(object);
 552         return;
 553       }
 554     } else if (LockingMode == LM_LEGACY) {
 555       markWord dhw = lock->displaced_header();
 556       if (dhw.value() == 0) {
 557         // If the displaced header is null, then this exit matches up with
 558         // a recursive enter. No real work to do here except for diagnostics.
 559 #ifndef PRODUCT
 560         if (mark != markWord::INFLATING()) {
 561           // Only do diagnostics if we are not racing an inflation. Simply
 562           // exiting a recursive enter of a Java Monitor that is being
 563           // inflated is safe; see the has_monitor() comment below.
 564           assert(!mark.is_neutral(), "invariant");
 565           assert(!mark.has_locker() ||
 566                  current->is_lock_owned((address)mark.locker()), "invariant");
 567           if (mark.has_monitor()) {
 568             // The BasicLock's displaced_header is marked as a recursive
 569             // enter and we have an inflated Java Monitor (ObjectMonitor).
 570             // This is a special case where the Java Monitor was inflated
 571             // after this thread entered the stack-lock recursively. When a
 572             // Java Monitor is inflated, we cannot safely walk the Java
 573             // Monitor owner's stack and update the BasicLocks because a
 574             // Java Monitor can be asynchronously inflated by a thread that
 575             // does not own the Java Monitor.
 576             ObjectMonitor* m = mark.monitor();
 577             assert(m->object()->mark() == mark, "invariant");
 578             assert(m->is_entered(current), "invariant");
 579           }
 580         }
 581 #endif
 582         return;
 583       }
 584 
 585       if (mark == markWord::from_pointer(lock)) {
 586         // If the object is stack-locked by the current thread, try to
 587         // swing the displaced header from the BasicLock back to the mark.
 588         assert(dhw.is_neutral(), "invariant");
 589         if (object->cas_set_mark(dhw, mark) == mark) {
 590           return;
 591         }
 592       }
 593     }
 594   } else if (VerifyHeavyMonitors) {
 595     guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
 596   }
 597 
 598   // We have to take the slow-path of possible inflation and then exit.
 599   // The ObjectMonitor* can't be async deflated until ownership is
 600   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
 601   ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
 602   if (LockingMode == LM_LIGHTWEIGHT && monitor->is_owner_anonymous()) {
 603     // It must be owned by us. Pop lock object from lock stack.
 604     LockStack& lock_stack = current->lock_stack();
 605     oop popped = lock_stack.pop();
 606     assert(popped == object, "must be owned by this thread");
 607     monitor->set_owner_from_anonymous(current);
 608   }
 609   monitor->exit(current);
 610 }
 611 
 612 // -----------------------------------------------------------------------------
 613 // JNI locks on java objects
 614 // NOTE: must use heavy weight monitor to handle jni monitor enter
 615 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
 616   if (obj->klass()->is_value_based()) {
 617     handle_sync_on_value_based_class(obj, current);
 618   }
 619 
 620   // the current locking is from JNI instead of Java code
 621   current->set_current_pending_monitor_is_from_java(false);
 622   // An async deflation can race after the inflate() call and before
 623   // enter() can make the ObjectMonitor busy. enter() returns false if
 624   // we have lost the race to async deflation and we simply try again.
 625   while (true) {
 626     ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
 627     if (monitor->enter(current)) {
 628       current->inc_held_monitor_count(1, true);
 629       break;
 630     }
 631   }
 632   current->set_current_pending_monitor_is_from_java(true);
 633 }
 634 
 635 // NOTE: must use heavy weight monitor to handle jni monitor exit
 636 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
 637   JavaThread* current = THREAD;
 638 
 639   // The ObjectMonitor* can't be async deflated until ownership is
 640   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
 641   ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
 642   // If this thread has locked the object, exit the monitor. We
 643   // intentionally do not use CHECK on check_owner because we must exit the
 644   // monitor even if an exception was already pending.
 645   if (monitor->check_owner(THREAD)) {
 646     monitor->exit(current);
 647     current->dec_held_monitor_count(1, true);
 648   }
 649 }
 650 
 651 // -----------------------------------------------------------------------------
 652 // Internal VM locks on java objects
 653 // standard constructor, allows locking failures
 654 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
 655   _thread = thread;
 656   _thread->check_for_valid_safepoint_state();
 657   _obj = obj;
 658 
 659   if (_obj() != nullptr) {
 660     ObjectSynchronizer::enter(_obj, &_lock, _thread);
 661   }
 662 }
 663 
 664 ObjectLocker::~ObjectLocker() {
 665   if (_obj() != nullptr) {
 666     ObjectSynchronizer::exit(_obj(), &_lock, _thread);
 667   }
 668 }
 669 
 670 
 671 // -----------------------------------------------------------------------------
 672 //  Wait/Notify/NotifyAll
 673 // NOTE: must use heavy weight monitor to handle wait()
 674 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 675   JavaThread* current = THREAD;
 676   if (millis < 0) {
 677     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 678   }
 679   // The ObjectMonitor* can't be async deflated because the _waiters
 680   // field is incremented before ownership is dropped and decremented
 681   // after ownership is regained.
 682   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
 683 
 684   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
 685   monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
 686 
 687   // This dummy call is in place to get around dtrace bug 6254741.  Once
 688   // that's fixed we can uncomment the following line, remove the call
 689   // and change this function back into a "void" func.
 690   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 691   int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
 692   return ret_code;
 693 }
 694 
 695 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 696   JavaThread* current = THREAD;
 697 
 698   markWord mark = obj->mark();
 699   if (LockingMode == LM_LIGHTWEIGHT) {
 700     if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
 701       // Not inflated so there can't be any waiters to notify.
 702       return;
 703     }
 704   } else if (LockingMode == LM_LEGACY) {
 705     if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 706       // Not inflated so there can't be any waiters to notify.
 707       return;
 708     }
 709   }
 710   // The ObjectMonitor* can't be async deflated until ownership is
 711   // dropped by the calling thread.
 712   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
 713   monitor->notify(CHECK);
 714 }
 715 
 716 // NOTE: see comment of notify()
 717 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 718   JavaThread* current = THREAD;
 719 
 720   markWord mark = obj->mark();
 721   if (LockingMode == LM_LIGHTWEIGHT) {
 722     if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
 723       // Not inflated so there can't be any waiters to notify.
 724       return;
 725     }
 726   } else if (LockingMode == LM_LEGACY) {
 727     if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 728       // Not inflated so there can't be any waiters to notify.
 729       return;
 730     }
 731   }
 732   // The ObjectMonitor* can't be async deflated until ownership is
 733   // dropped by the calling thread.
 734   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
 735   monitor->notifyAll(CHECK);
 736 }
 737 
 738 // -----------------------------------------------------------------------------
 739 // Hash Code handling
 740 
 741 struct SharedGlobals {
 742   char         _pad_prefix[OM_CACHE_LINE_SIZE];
 743   // This is a highly shared mostly-read variable.
 744   // To avoid false-sharing it needs to be the sole occupant of a cache line.
 745   volatile int stw_random;
 746   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 747   // Hot RW variable -- Sequester to avoid false-sharing
 748   volatile int hc_sequence;
 749   DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 750 };
 751 
 752 static SharedGlobals GVars;
 753 
 754 static markWord read_stable_mark(oop obj) {
 755   markWord mark = obj->mark_acquire();
 756   if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
 757     // New lightweight locking does not use the markWord::INFLATING() protocol.
 758     return mark;       // normal fast-path return
 759   }
 760 
 761   int its = 0;
 762   for (;;) {
 763     markWord mark = obj->mark_acquire();
 764     if (!mark.is_being_inflated()) {
 765       return mark;    // normal fast-path return
 766     }
 767 
 768     // The object is being inflated by some other thread.
 769     // The caller of read_stable_mark() must wait for inflation to complete.
 770     // Avoid live-lock.
 771 
 772     ++its;
 773     if (its > 10000 || !os::is_MP()) {
 774       if (its & 1) {
 775         os::naked_yield();
 776       } else {
 777         // Note that the following code attenuates the livelock problem but is not
 778         // a complete remedy.  A more complete solution would require that the inflating
 779         // thread hold the associated inflation lock.  The following code simply restricts
 780         // the number of spinners to at most one.  We'll have N-2 threads blocked
 781         // on the inflationlock, 1 thread holding the inflation lock and using
 782         // a yield/park strategy, and 1 thread in the midst of inflation.
 783         // A more refined approach would be to change the encoding of INFLATING
 784         // to allow encapsulation of a native thread pointer.  Threads waiting for
 785         // inflation to complete would use CAS to push themselves onto a singly linked
 786         // list rooted at the markword.  Once enqueued, they'd loop, checking a per-thread flag
 787         // and calling park().  When inflation was complete the thread that accomplished inflation
 788         // would detach the list and set the markword to inflated with a single CAS and
 789         // then for each thread on the list, set the flag and unpark() the thread.
 790 
 791         // Index into the lock array based on the current object address.
 792         static_assert(is_power_of_2(inflation_lock_count()), "must be");
 793         size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
 794         int YieldThenBlock = 0;
 795         assert(ix < inflation_lock_count(), "invariant");
 796         inflation_lock(ix)->lock();
 797         while (obj->mark_acquire() == markWord::INFLATING()) {
 798           // Beware: naked_yield() is advisory and has almost no effect on some platforms
 799           // so we periodically call current->_ParkEvent->park(1).
 800           // We use a mixed spin/yield/block mechanism.
 801           if ((YieldThenBlock++) >= 16) {
 802             Thread::current()->_ParkEvent->park(1);
 803           } else {
 804             os::naked_yield();
 805           }
 806         }
 807         inflation_lock(ix)->unlock();
 808       }
 809     } else {
 810       SpinPause();       // SMP-polite spinning
 811     }
 812   }
 813 }
 814 
 815 // hashCode() generation :
 816 //
 817 // Possibilities:
 818 // * MD5Digest of {obj,stw_random}
 819 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
 820 // * A DES- or AES-style SBox[] mechanism
 821 // * One of the Phi-based schemes, such as:
 822 //   2654435761 = 2^32 * Phi (golden ratio)
 823 //   HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
 824 // * A variation of Marsaglia's shift-xor RNG scheme.
 825 // * (obj ^ stw_random) is appealing, but can result
 826 //   in undesirable regularity in the hashCode values of adjacent objects
 827 //   (objects allocated back-to-back, in particular).  This could potentially
 828 //   result in hashtable collisions and reduced hashtable efficiency.
 829 //   There are simple ways to "diffuse" the middle address bits over the
 830 //   generated hashCode values:
 831 
 832 static inline intptr_t get_next_hash(Thread* current, oop obj) {
 833   intptr_t value = 0;
 834   if (hashCode == 0) {
 835     // This form uses global Park-Miller RNG.
 836     // On MP system we'll have lots of RW access to a global, so the
 837     // mechanism induces lots of coherency traffic.
 838     value = os::random();
 839   } else if (hashCode == 1) {
 840     // This variation has the property of being stable (idempotent)
 841     // between STW operations.  This can be useful in some of the 1-0
 842     // synchronization schemes.
 843     intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
 844     value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
 845   } else if (hashCode == 2) {
 846     value = 1;            // for sensitivity testing
 847   } else if (hashCode == 3) {
 848     value = ++GVars.hc_sequence;
 849   } else if (hashCode == 4) {
 850     value = cast_from_oop<intptr_t>(obj);
 851   } else {
 852     // Marsaglia's xor-shift scheme with thread-specific state
 853     // This is probably the best overall implementation -- we'll
 854     // likely make this the default in future releases.
 855     unsigned t = current->_hashStateX;
 856     t ^= (t << 11);
 857     current->_hashStateX = current->_hashStateY;
 858     current->_hashStateY = current->_hashStateZ;
 859     current->_hashStateZ = current->_hashStateW;
 860     unsigned v = current->_hashStateW;
 861     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
 862     current->_hashStateW = v;
 863     value = v;
 864   }
 865 
 866   value &= markWord::hash_mask;
 867   if (value == 0) value = 0xBAD;
 868   assert(value != markWord::no_hash, "invariant");
 869   return value;
 870 }
 871 
 872 // Can be called from non JavaThreads (e.g., VMThread) for FastHashCode
 873 // calculations as part of JVM/TI tagging.
 874 static bool is_lock_owned(Thread* thread, oop obj) {
 875   assert(LockingMode == LM_LIGHTWEIGHT, "only call this with new lightweight locking enabled");
 876   return thread->is_Java_thread() ? JavaThread::cast(thread)->lock_stack().contains(obj) : false;
 877 }
 878 
 879 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
 880 
 881   while (true) {
 882     ObjectMonitor* monitor = nullptr;
 883     markWord temp, test;
 884     intptr_t hash;
 885     markWord mark = read_stable_mark(obj);
 886     if (VerifyHeavyMonitors) {
 887       assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
 888       guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
 889     }
 890     if (mark.is_neutral()) {               // if this is a normal header
 891       hash = mark.hash();
 892       if (hash != 0) {                     // if it has a hash, just return it
 893         return hash;
 894       }
 895       hash = get_next_hash(current, obj);  // get a new hash
 896       temp = mark.copy_set_hash(hash);     // merge the hash into header
 897                                            // try to install the hash
 898       test = obj->cas_set_mark(temp, mark);
 899       if (test == mark) {                  // if the hash was installed, return it
 900         return hash;
 901       }
 902       // Failed to install the hash. It could be that another thread
 903       // installed the hash just before our attempt or inflation has
 904       // occurred or... so we fall thru to inflate the monitor for
 905       // stability and then install the hash.
 906     } else if (mark.has_monitor()) {
 907       monitor = mark.monitor();
 908       temp = monitor->header();
 909       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 910       hash = temp.hash();
 911       if (hash != 0) {
 912         // It has a hash.
 913 
 914         // Separate load of dmw/header above from the loads in
 915         // is_being_async_deflated().
 916 
 917         // dmw/header and _contentions may get written by different threads.
 918         // Make sure to observe them in the same order when having several observers.
 919         OrderAccess::loadload_for_IRIW();
 920 
 921         if (monitor->is_being_async_deflated()) {
 922           // But we can't safely use the hash if we detect that async
 923           // deflation has occurred. So we attempt to restore the
 924           // header/dmw to the object's header so that we only retry
 925           // once if the deflater thread happens to be slow.
 926           monitor->install_displaced_markword_in_object(obj);
 927           continue;
 928         }
 929         return hash;
 930       }
 931       // Fall thru so we only have one place that installs the hash in
 932       // the ObjectMonitor.
 933     } else if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked() && is_lock_owned(current, obj)) {
 934       // This is a fast-lock owned by the calling thread so use the
 935       // markWord from the object.
 936       hash = mark.hash();
 937       if (hash != 0) {                  // if it has a hash, just return it
 938         return hash;
 939       }
 940     } else if (LockingMode == LM_LEGACY && mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 941       // This is a stack-lock owned by the calling thread so fetch the
 942       // displaced markWord from the BasicLock on the stack.
 943       temp = mark.displaced_mark_helper();
 944       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 945       hash = temp.hash();
 946       if (hash != 0) {                  // if it has a hash, just return it
 947         return hash;
 948       }
 949       // WARNING:
 950       // The displaced header in the BasicLock on a thread's stack
 951       // is strictly immutable. It CANNOT be changed in ANY cases.
 952       // So we have to inflate the stack-lock into an ObjectMonitor
 953       // even if the current thread owns the lock. The BasicLock on
 954       // a thread's stack can be asynchronously read by other threads
 955       // during an inflate() call so any change to that stack memory
 956       // may not propagate to other threads correctly.
 957     }
 958 
 959     // Inflate the monitor to set the hash.
 960 
 961     // An async deflation can race after the inflate() call and before we
 962     // can update the ObjectMonitor's header with the hash value below.
 963     monitor = inflate(current, obj, inflate_cause_hash_code);
 964     // Load ObjectMonitor's header/dmw field and see if it has a hash.
 965     mark = monitor->header();
 966     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
 967     hash = mark.hash();
 968     if (hash == 0) {                       // if it does not have a hash
 969       hash = get_next_hash(current, obj);  // get a new hash
 970       temp = mark.copy_set_hash(hash)   ;  // merge the hash into header
 971       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 972       uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
 973       test = markWord(v);
 974       if (test != mark) {
 975         // The attempt to update the ObjectMonitor's header/dmw field
 976         // did not work. This can happen if another thread managed to
 977         // merge in the hash just before our cmpxchg().
 978         // If we add any new usages of the header/dmw field, this code
 979         // will need to be updated.
 980         hash = test.hash();
 981         assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
 982         assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
 983       }
 984       if (monitor->is_being_async_deflated()) {
 985         // If we detect that async deflation has occurred, then we
 986         // attempt to restore the header/dmw to the object's header
 987         // so that we only retry once if the deflater thread happens
 988         // to be slow.
 989         monitor->install_displaced_markword_in_object(obj);
 990         continue;
 991       }
 992     }
 993     // We finally get the hash.
 994     return hash;
 995   }
 996 }
 997 
 998 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
 999                                                    Handle h_obj) {
1000   assert(current == JavaThread::current(), "Can only be called on current thread");
1001   oop obj = h_obj();
1002 
1003   markWord mark = read_stable_mark(obj);
1004 
1005   if (LockingMode == LM_LEGACY && mark.has_locker()) {
1006     // stack-locked case, header points into owner's stack
1007     return current->is_lock_owned((address)mark.locker());
1008   }
1009 
1010   if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1011     // fast-locking case, see if lock is in current's lock stack
1012     return current->lock_stack().contains(h_obj());
1013   }
1014 
1015   if (mark.has_monitor()) {
1016     // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1017     // The first stage of async deflation does not affect any field
1018     // used by this comparison so the ObjectMonitor* is usable here.
1019     ObjectMonitor* monitor = mark.monitor();
1020     return monitor->is_entered(current) != 0;
1021   }
1022   // Unlocked case, header in place
1023   assert(mark.is_neutral(), "sanity check");
1024   return false;
1025 }
1026 
1027 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1028   oop obj = h_obj();
1029   markWord mark = read_stable_mark(obj);
1030 
1031   if (LockingMode == LM_LEGACY && mark.has_locker()) {
1032     // stack-locked so header points into owner's stack.
1033     // owning_thread_from_monitor_owner() may also return null here:
1034     return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1035   }
1036 
1037   if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1038     // fast-locked so get owner from the object.
1039     // owning_thread_from_object() may also return null here:
1040     return Threads::owning_thread_from_object(t_list, h_obj());
1041   }
1042 
1043   if (mark.has_monitor()) {
1044     // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1045     // The first stage of async deflation does not affect any field
1046     // used by this comparison so the ObjectMonitor* is usable here.
1047     ObjectMonitor* monitor = mark.monitor();
1048     assert(monitor != nullptr, "monitor should be non-null");
1049     // owning_thread_from_monitor() may also return null here:
1050     return Threads::owning_thread_from_monitor(t_list, monitor);
1051   }
1052 
1053   // Unlocked case, header in place
1054   // Cannot have assertion since this object may have been
1055   // locked by another thread when reaching here.
1056   // assert(mark.is_neutral(), "sanity check");
1057 
1058   return nullptr;
1059 }
1060 
1061 // Visitors ...
1062 
1063 // Iterate over all ObjectMonitors.
1064 template <typename Function>
1065 void ObjectSynchronizer::monitors_iterate(Function function) {
1066   MonitorList::Iterator iter = _in_use_list.iterator();
1067   while (iter.has_next()) {
1068     ObjectMonitor* monitor = iter.next();
1069     function(monitor);
1070   }
1071 }
1072 
1073 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1074 // returns true.
1075 template <typename OwnerFilter>
1076 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1077   monitors_iterate([&](ObjectMonitor* monitor) {
1078     // This function is only called at a safepoint or when the
1079     // target thread is suspended or when the target thread is
1080     // operating on itself. The current closures in use today are
1081     // only interested in an owned ObjectMonitor and ownership
1082     // cannot be dropped under the calling contexts so the
1083     // ObjectMonitor cannot be async deflated.
1084     if (monitor->has_owner() && filter(monitor->owner_raw())) {
1085       assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1086       assert(monitor->object_peek() != nullptr, "Owned monitors should not have a dead object");
1087 
1088       closure->do_monitor(monitor);
1089     }
1090   });
1091 }
1092 
1093 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1094 // ObjectMonitors where owner is set to a stack-lock address in thread.
1095 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1096   auto thread_filter = [&](void* owner) { return owner == thread; };
1097   return owned_monitors_iterate_filtered(closure, thread_filter);
1098 }
1099 
1100 // Iterate ObjectMonitors owned by any thread.
1101 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1102   auto all_filter = [&](void* owner) { return true; };
1103   return owned_monitors_iterate_filtered(closure, all_filter);
1104 }
1105 
1106 static bool monitors_used_above_threshold(MonitorList* list) {
1107   if (MonitorUsedDeflationThreshold == 0) {  // disabled case is easy
1108     return false;
1109   }
1110   // Start with ceiling based on a per-thread estimate:
1111   size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1112   size_t old_ceiling = ceiling;
1113   if (ceiling < list->max()) {
1114     // The max used by the system has exceeded the ceiling so use that:
1115     ceiling = list->max();
1116   }
1117   size_t monitors_used = list->count();
1118   if (monitors_used == 0) {  // empty list is easy
1119     return false;
1120   }
1121   if (NoAsyncDeflationProgressMax != 0 &&
1122       _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1123     double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1124     size_t new_ceiling = ceiling + (size_t)((double)ceiling * remainder) + 1;
1125     ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1126     log_info(monitorinflation)("Too many deflations without progress; "
1127                                "bumping in_use_list_ceiling from " SIZE_FORMAT
1128                                " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1129     _no_progress_cnt = 0;
1130     ceiling = new_ceiling;
1131   }
1132 
1133   // Check if our monitor usage is above the threshold:
1134   size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1135   if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1136     log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
1137                                ", monitor_usage=" SIZE_FORMAT ", threshold=%d",
1138                                monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1139     return true;
1140   }
1141 
1142   return false;
1143 }
1144 
1145 size_t ObjectSynchronizer::in_use_list_ceiling() {
1146   return _in_use_list_ceiling;
1147 }
1148 
1149 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1150   Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1151 }
1152 
1153 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1154   Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1155 }
1156 
1157 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1158   _in_use_list_ceiling = new_value;
1159 }
1160 
1161 bool ObjectSynchronizer::is_async_deflation_needed() {
1162   if (is_async_deflation_requested()) {
1163     // Async deflation request.
1164     log_info(monitorinflation)("Async deflation needed: explicit request");
1165     return true;
1166   }
1167 
1168   jlong time_since_last = time_since_last_async_deflation_ms();
1169 
1170   if (AsyncDeflationInterval > 0 &&
1171       time_since_last > AsyncDeflationInterval &&
1172       monitors_used_above_threshold(&_in_use_list)) {
1173     // It's been longer than our specified deflate interval and there
1174     // are too many monitors in use. We don't deflate more frequently
1175     // than AsyncDeflationInterval (unless is_async_deflation_requested)
1176     // in order to not swamp the MonitorDeflationThread.
1177     log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1178     return true;
1179   }
1180 
1181   if (GuaranteedAsyncDeflationInterval > 0 &&
1182       time_since_last > GuaranteedAsyncDeflationInterval) {
1183     // It's been longer than our specified guaranteed deflate interval.
1184     // We need to clean up the used monitors even if the threshold is
1185     // not reached, to keep the memory utilization at bay when many threads
1186     // touched many monitors.
1187     log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) "
1188                                "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1189                                GuaranteedAsyncDeflationInterval, time_since_last);
1190 
1191     // If this deflation has no progress, then it should not affect the no-progress
1192     // tracking, otherwise threshold heuristics would think it was triggered, experienced
1193     // no progress, and needs to backoff more aggressively. In this "no progress" case,
1194     // the generic code would bump the no-progress counter, and we compensate for that
1195     // by telling it to skip the update.
1196     //
1197     // If this deflation has progress, then it should let non-progress tracking
1198     // know about this, otherwise the threshold heuristics would kick in, potentially
1199     // experience no-progress due to aggressive cleanup by this deflation, and think
1200     // it is still in no-progress stride. In this "progress" case, the generic code would
1201     // zero the counter, and we allow it to happen.
1202     _no_progress_skip_increment = true;
1203 
1204     return true;
1205   }
1206 
1207   return false;
1208 }
1209 
1210 void ObjectSynchronizer::request_deflate_idle_monitors() {
1211   MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1212   set_is_async_deflation_requested(true);
1213   ml.notify_all();
1214 }
1215 
1216 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1217   JavaThread* current = JavaThread::current();
1218   bool ret_code = false;
1219 
1220   jlong last_time = last_async_deflation_time_ns();
1221 
1222   request_deflate_idle_monitors();
1223 
1224   const int N_CHECKS = 5;
1225   for (int i = 0; i < N_CHECKS; i++) {  // sleep for at most 5 seconds
1226     if (last_async_deflation_time_ns() > last_time) {
1227       log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1228       ret_code = true;
1229       break;
1230     }
1231     {
1232       // JavaThread has to honor the blocking protocol.
1233       ThreadBlockInVM tbivm(current);
1234       os::naked_short_sleep(999);  // sleep for almost 1 second
1235     }
1236   }
1237   if (!ret_code) {
1238     log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1239   }
1240 
1241   return ret_code;
1242 }
1243 
1244 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1245   return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1246 }
1247 
1248 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1249                                        const oop obj,
1250                                        ObjectSynchronizer::InflateCause cause) {
1251   assert(event != nullptr, "invariant");
1252   event->set_monitorClass(obj->klass());
1253   event->set_address((uintptr_t)(void*)obj);
1254   event->set_cause((u1)cause);
1255   event->commit();
1256 }
1257 
1258 // Fast path code shared by multiple functions
1259 void ObjectSynchronizer::inflate_helper(oop obj) {
1260   markWord mark = obj->mark_acquire();
1261   if (mark.has_monitor()) {
1262     ObjectMonitor* monitor = mark.monitor();
1263     markWord dmw = monitor->header();
1264     assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1265     return;
1266   }
1267   (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1268 }
1269 
1270 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1271                                            const InflateCause cause) {
1272   EventJavaMonitorInflate event;
1273 
1274   for (;;) {
1275     const markWord mark = object->mark_acquire();
1276 
1277     // The mark can be in one of the following states:
1278     // *  inflated     - Just return if using stack-locking.
1279     //                   If using fast-locking and the ObjectMonitor owner
1280     //                   is anonymous and the current thread owns the
1281     //                   object lock, then we make the current thread the
1282     //                   ObjectMonitor owner and remove the lock from the
1283     //                   current thread's lock stack.
1284     // *  fast-locked  - Coerce it to inflated from fast-locked.
1285     // *  stack-locked - Coerce it to inflated from stack-locked.
1286     // *  INFLATING    - Busy wait for conversion from stack-locked to
1287     //                   inflated.
1288     // *  neutral      - Aggressively inflate the object.
1289 
1290     // CASE: inflated
1291     if (mark.has_monitor()) {
1292       ObjectMonitor* inf = mark.monitor();
1293       markWord dmw = inf->header();
1294       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1295       if (LockingMode == LM_LIGHTWEIGHT && inf->is_owner_anonymous() && is_lock_owned(current, object)) {
1296         inf->set_owner_from_anonymous(current);
1297         JavaThread::cast(current)->lock_stack().remove(object);
1298       }
1299       return inf;
1300     }
1301 
1302     if (LockingMode != LM_LIGHTWEIGHT) {
1303       // New lightweight locking does not use INFLATING.
1304       // CASE: inflation in progress - inflating over a stack-lock.
1305       // Some other thread is converting from stack-locked to inflated.
1306       // Only that thread can complete inflation -- other threads must wait.
1307       // The INFLATING value is transient.
1308       // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1309       // We could always eliminate polling by parking the thread on some auxiliary list.
1310       if (mark == markWord::INFLATING()) {
1311         read_stable_mark(object);
1312         continue;
1313       }
1314     }
1315 
1316     // CASE: fast-locked
1317     // Could be fast-locked either by current or by some other thread.
1318     //
1319     // Note that we allocate the ObjectMonitor speculatively, _before_
1320     // attempting to set the object's mark to the new ObjectMonitor. If
1321     // this thread owns the monitor, then we set the ObjectMonitor's
1322     // owner to this thread. Otherwise, we set the ObjectMonitor's owner
1323     // to anonymous. If we lose the race to set the object's mark to the
1324     // new ObjectMonitor, then we just delete it and loop around again.
1325     //
1326     LogStreamHandle(Trace, monitorinflation) lsh;
1327     if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1328       ObjectMonitor* monitor = new ObjectMonitor(object);
1329       monitor->set_header(mark.set_unlocked());
1330       bool own = is_lock_owned(current, object);
1331       if (own) {
1332         // Owned by us.
1333         monitor->set_owner_from(nullptr, current);
1334       } else {
1335         // Owned by somebody else.
1336         monitor->set_owner_anonymous();
1337       }
1338       markWord monitor_mark = markWord::encode(monitor);
1339       markWord old_mark = object->cas_set_mark(monitor_mark, mark);
1340       if (old_mark == mark) {
1341         // Success! Return inflated monitor.
1342         if (own) {
1343           JavaThread::cast(current)->lock_stack().remove(object);
1344         }
1345         // Once the ObjectMonitor is configured and object is associated
1346         // with the ObjectMonitor, it is safe to allow async deflation:
1347         _in_use_list.add(monitor);
1348 
1349         // Hopefully the performance counters are allocated on distinct
1350         // cache lines to avoid false sharing on MP systems ...
1351         OM_PERFDATA_OP(Inflations, inc());
1352         if (log_is_enabled(Trace, monitorinflation)) {
1353           ResourceMark rm(current);
1354           lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1355                        INTPTR_FORMAT ", type='%s'", p2i(object),
1356                        object->mark().value(), object->klass()->external_name());
1357         }
1358         if (event.should_commit()) {
1359           post_monitor_inflate_event(&event, object, cause);
1360         }
1361         return monitor;
1362       } else {
1363         delete monitor;
1364         continue;  // Interference -- just retry
1365       }
1366     }
1367 
1368     // CASE: stack-locked
1369     // Could be stack-locked either by current or by some other thread.
1370     //
1371     // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1372     // to install INFLATING into the mark word.  We originally installed INFLATING,
1373     // allocated the ObjectMonitor, and then finally STed the address of the
1374     // ObjectMonitor into the mark.  This was correct, but artificially lengthened
1375     // the interval in which INFLATING appeared in the mark, thus increasing
1376     // the odds of inflation contention. If we lose the race to set INFLATING,
1377     // then we just delete the ObjectMonitor and loop around again.
1378     //
1379     if (LockingMode == LM_LEGACY && mark.has_locker()) {
1380       assert(LockingMode != LM_LIGHTWEIGHT, "cannot happen with new lightweight locking");
1381       ObjectMonitor* m = new ObjectMonitor(object);
1382       // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1383       // We do this before the CAS in order to minimize the length of time
1384       // in which INFLATING appears in the mark.
1385 
1386       markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1387       if (cmp != mark) {
1388         delete m;
1389         continue;       // Interference -- just retry
1390       }
1391 
1392       // We've successfully installed INFLATING (0) into the mark-word.
1393       // This is the only case where 0 will appear in a mark-word.
1394       // Only the singular thread that successfully swings the mark-word
1395       // to 0 can perform (or more precisely, complete) inflation.
1396       //
1397       // Why do we CAS a 0 into the mark-word instead of just CASing the
1398       // mark-word from the stack-locked value directly to the new inflated state?
1399       // Consider what happens when a thread unlocks a stack-locked object.
1400       // It attempts to use CAS to swing the displaced header value from the
1401       // on-stack BasicLock back into the object header.  Recall also that the
1402       // header value (hash code, etc) can reside in (a) the object header, or
1403       // (b) a displaced header associated with the stack-lock, or (c) a displaced
1404       // header in an ObjectMonitor.  The inflate() routine must copy the header
1405       // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1406       // the while preserving the hashCode stability invariants.  If the owner
1407       // decides to release the lock while the value is 0, the unlock will fail
1408       // and control will eventually pass from slow_exit() to inflate.  The owner
1409       // will then spin, waiting for the 0 value to disappear.   Put another way,
1410       // the 0 causes the owner to stall if the owner happens to try to
1411       // drop the lock (restoring the header from the BasicLock to the object)
1412       // while inflation is in-progress.  This protocol avoids races that might
1413       // would otherwise permit hashCode values to change or "flicker" for an object.
1414       // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1415       // 0 serves as a "BUSY" inflate-in-progress indicator.
1416 
1417 
1418       // fetch the displaced mark from the owner's stack.
1419       // The owner can't die or unwind past the lock while our INFLATING
1420       // object is in the mark.  Furthermore the owner can't complete
1421       // an unlock on the object, either.
1422       markWord dmw = mark.displaced_mark_helper();
1423       // Catch if the object's header is not neutral (not locked and
1424       // not marked is what we care about here).
1425       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1426 
1427       // Setup monitor fields to proper values -- prepare the monitor
1428       m->set_header(dmw);
1429 
1430       // Optimization: if the mark.locker stack address is associated
1431       // with this thread we could simply set m->_owner = current.
1432       // Note that a thread can inflate an object
1433       // that it has stack-locked -- as might happen in wait() -- directly
1434       // with CAS.  That is, we can avoid the xchg-nullptr .... ST idiom.
1435       m->set_owner_from(nullptr, mark.locker());
1436       // TODO-FIXME: assert BasicLock->dhw != 0.
1437 
1438       // Must preserve store ordering. The monitor state must
1439       // be stable at the time of publishing the monitor address.
1440       guarantee(object->mark() == markWord::INFLATING(), "invariant");
1441       // Release semantics so that above set_object() is seen first.
1442       object->release_set_mark(markWord::encode(m));
1443 
1444       // Once ObjectMonitor is configured and the object is associated
1445       // with the ObjectMonitor, it is safe to allow async deflation:
1446       _in_use_list.add(m);
1447 
1448       // Hopefully the performance counters are allocated on distinct cache lines
1449       // to avoid false sharing on MP systems ...
1450       OM_PERFDATA_OP(Inflations, inc());
1451       if (log_is_enabled(Trace, monitorinflation)) {
1452         ResourceMark rm(current);
1453         lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1454                      INTPTR_FORMAT ", type='%s'", p2i(object),
1455                      object->mark().value(), object->klass()->external_name());
1456       }
1457       if (event.should_commit()) {
1458         post_monitor_inflate_event(&event, object, cause);
1459       }
1460       return m;
1461     }
1462 
1463     // CASE: neutral
1464     // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1465     // If we know we're inflating for entry it's better to inflate by swinging a
1466     // pre-locked ObjectMonitor pointer into the object header.   A successful
1467     // CAS inflates the object *and* confers ownership to the inflating thread.
1468     // In the current implementation we use a 2-step mechanism where we CAS()
1469     // to inflate and then CAS() again to try to swing _owner from null to current.
1470     // An inflateTry() method that we could call from enter() would be useful.
1471 
1472     // Catch if the object's header is not neutral (not locked and
1473     // not marked is what we care about here).
1474     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1475     ObjectMonitor* m = new ObjectMonitor(object);
1476     // prepare m for installation - set monitor to initial state
1477     m->set_header(mark);
1478 
1479     if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1480       delete m;
1481       m = nullptr;
1482       continue;
1483       // interference - the markword changed - just retry.
1484       // The state-transitions are one-way, so there's no chance of
1485       // live-lock -- "Inflated" is an absorbing state.
1486     }
1487 
1488     // Once the ObjectMonitor is configured and object is associated
1489     // with the ObjectMonitor, it is safe to allow async deflation:
1490     _in_use_list.add(m);
1491 
1492     // Hopefully the performance counters are allocated on distinct
1493     // cache lines to avoid false sharing on MP systems ...
1494     OM_PERFDATA_OP(Inflations, inc());
1495     if (log_is_enabled(Trace, monitorinflation)) {
1496       ResourceMark rm(current);
1497       lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1498                    INTPTR_FORMAT ", type='%s'", p2i(object),
1499                    object->mark().value(), object->klass()->external_name());
1500     }
1501     if (event.should_commit()) {
1502       post_monitor_inflate_event(&event, object, cause);
1503     }
1504     return m;
1505   }
1506 }
1507 
1508 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1509                                            const char* cnt_name, size_t cnt,
1510                                            LogStream* ls, elapsedTimer* timer_p) {
1511   if (!SafepointMechanism::should_process(current)) {
1512     return;
1513   }
1514 
1515   // A safepoint/handshake has started.
1516   if (ls != nullptr) {
1517     timer_p->stop();
1518     ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1519                  SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1520                  op_name, cnt_name, cnt, in_use_list_ceiling(),
1521                  _in_use_list.count(), _in_use_list.max());
1522   }
1523 
1524   {
1525     // Honor block request.
1526     ThreadBlockInVM tbivm(current);
1527   }
1528 
1529   if (ls != nullptr) {
1530     ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1531                  ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1532                  in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1533     timer_p->start();
1534   }
1535 }
1536 
1537 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1538 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1539 //
1540 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1541                                                 elapsedTimer* timer_p) {
1542   MonitorList::Iterator iter = _in_use_list.iterator();
1543   size_t deflated_count = 0;
1544 
1545   while (iter.has_next()) {
1546     if (deflated_count >= (size_t)MonitorDeflationMax) {
1547       break;
1548     }
1549     ObjectMonitor* mid = iter.next();
1550     if (mid->deflate_monitor()) {
1551       deflated_count++;
1552     }
1553 
1554     if (current->is_Java_thread()) {
1555       // A JavaThread must check for a safepoint/handshake and honor it.
1556       chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1557                         deflated_count, ls, timer_p);
1558     }
1559   }
1560 
1561   return deflated_count;
1562 }
1563 
1564 class HandshakeForDeflation : public HandshakeClosure {
1565  public:
1566   HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1567 
1568   void do_thread(Thread* thread) {
1569     log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1570                                 INTPTR_FORMAT, p2i(thread));
1571   }
1572 };
1573 
1574 class VM_RendezvousGCThreads : public VM_Operation {
1575 public:
1576   bool evaluate_at_safepoint() const override { return false; }
1577   VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1578   void doit() override {
1579     Universe::heap()->safepoint_synchronize_begin();
1580     Universe::heap()->safepoint_synchronize_end();
1581   };
1582 };
1583 
1584 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list) {
1585   NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1586   size_t count = 0;
1587   for (ObjectMonitor* monitor: *delete_list) {
1588     delete monitor;
1589     count++;
1590   }
1591   return count;
1592 }
1593 
1594 // This function is called by the MonitorDeflationThread to deflate
1595 // ObjectMonitors.
1596 size_t ObjectSynchronizer::deflate_idle_monitors() {
1597   Thread* current = Thread::current();
1598   if (current->is_Java_thread()) {
1599     // The async deflation request has been processed.
1600     _last_async_deflation_time_ns = os::javaTimeNanos();
1601     set_is_async_deflation_requested(false);
1602   }
1603 
1604   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1605   LogStreamHandle(Info, monitorinflation) lsh_info;
1606   LogStream* ls = nullptr;
1607   if (log_is_enabled(Debug, monitorinflation)) {
1608     ls = &lsh_debug;
1609   } else if (log_is_enabled(Info, monitorinflation)) {
1610     ls = &lsh_info;
1611   }
1612 
1613   elapsedTimer timer;
1614   if (ls != nullptr) {
1615     ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1616                  in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1617     timer.start();
1618   }
1619 
1620   // Deflate some idle ObjectMonitors.
1621   size_t deflated_count = deflate_monitor_list(current, ls, &timer);
1622   size_t unlinked_count = 0;
1623   size_t deleted_count = 0;
1624   if (deflated_count > 0) {
1625     // There are ObjectMonitors that have been deflated.
1626 
1627     // Unlink deflated ObjectMonitors from the in-use list.
1628     ResourceMark rm;
1629     GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1630     unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, &delete_list);
1631     if (current->is_monitor_deflation_thread()) {
1632       if (ls != nullptr) {
1633         timer.stop();
1634         ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1635                      ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1636                      SIZE_FORMAT ", max=" SIZE_FORMAT,
1637                      unlinked_count, in_use_list_ceiling(),
1638                      _in_use_list.count(), _in_use_list.max());
1639       }
1640 
1641       // A JavaThread needs to handshake in order to safely free the
1642       // ObjectMonitors that were deflated in this cycle.
1643       HandshakeForDeflation hfd_hc;
1644       Handshake::execute(&hfd_hc);
1645       // Also, we sync and desync GC threads around the handshake, so that they can
1646       // safely read the mark-word and look-through to the object-monitor, without
1647       // being afraid that the object-monitor is going away.
1648       VM_RendezvousGCThreads sync_gc;
1649       VMThread::execute(&sync_gc);
1650 
1651       if (ls != nullptr) {
1652         ls->print_cr("after handshaking: in_use_list stats: ceiling="
1653                      SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1654                      in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1655         timer.start();
1656       }
1657     } else {
1658       // This is not a monitor deflation thread.
1659       // No handshake or rendezvous is needed when we are already at safepoint.
1660       assert_at_safepoint();
1661     }
1662 
1663     // After the handshake, safely free the ObjectMonitors that were
1664     // deflated and unlinked in this cycle.
1665     if (current->is_Java_thread()) {
1666       if (ls != NULL) {
1667         timer.stop();
1668         ls->print_cr("before setting blocked: unlinked_count=" SIZE_FORMAT
1669                      ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1670                      SIZE_FORMAT ", max=" SIZE_FORMAT,
1671                      unlinked_count, in_use_list_ceiling(),
1672                      _in_use_list.count(), _in_use_list.max());
1673       }
1674       // Mark the calling JavaThread blocked (safepoint safe) while we free
1675       // the ObjectMonitors so we don't delay safepoints whilst doing that.
1676       ThreadBlockInVM tbivm(JavaThread::cast(current));
1677       if (ls != NULL) {
1678         ls->print_cr("after setting blocked: in_use_list stats: ceiling="
1679                      SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1680                      in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1681         timer.start();
1682       }
1683       deleted_count = delete_monitors(&delete_list);
1684       // ThreadBlockInVM is destroyed here
1685     } else {
1686       // A non-JavaThread can just free the ObjectMonitors:
1687       deleted_count = delete_monitors(&delete_list);
1688     }
1689     assert(unlinked_count == deleted_count, "must be");
1690   }
1691 
1692   if (ls != nullptr) {
1693     timer.stop();
1694     if (deflated_count != 0 || unlinked_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1695       ls->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1696                    deflated_count, unlinked_count, timer.seconds());
1697     }
1698     ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1699                  in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1700   }
1701 
1702   OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1703   OM_PERFDATA_OP(Deflations, inc(deflated_count));
1704 
1705   GVars.stw_random = os::random();
1706 
1707   if (deflated_count != 0) {
1708     _no_progress_cnt = 0;
1709   } else if (_no_progress_skip_increment) {
1710     _no_progress_skip_increment = false;
1711   } else {
1712     _no_progress_cnt++;
1713   }
1714 
1715   return deflated_count;
1716 }
1717 
1718 // Monitor cleanup on JavaThread::exit
1719 
1720 // Iterate through monitor cache and attempt to release thread's monitors
1721 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1722  private:
1723   JavaThread* _thread;
1724 
1725  public:
1726   ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1727   void do_monitor(ObjectMonitor* mid) {
1728     intx rec = mid->complete_exit(_thread);
1729     _thread->dec_held_monitor_count(rec + 1);
1730   }
1731 };
1732 
1733 // Release all inflated monitors owned by current thread.  Lightweight monitors are
1734 // ignored.  This is meant to be called during JNI thread detach which assumes
1735 // all remaining monitors are heavyweight.  All exceptions are swallowed.
1736 // Scanning the extant monitor list can be time consuming.
1737 // A simple optimization is to add a per-thread flag that indicates a thread
1738 // called jni_monitorenter() during its lifetime.
1739 //
1740 // Instead of NoSafepointVerifier it might be cheaper to
1741 // use an idiom of the form:
1742 //   auto int tmp = SafepointSynchronize::_safepoint_counter ;
1743 //   <code that must not run at safepoint>
1744 //   guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1745 // Since the tests are extremely cheap we could leave them enabled
1746 // for normal product builds.
1747 
1748 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1749   assert(current == JavaThread::current(), "must be current Java thread");
1750   NoSafepointVerifier nsv;
1751   ReleaseJavaMonitorsClosure rjmc(current);
1752   ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1753   assert(!current->has_pending_exception(), "Should not be possible");
1754   current->clear_pending_exception();
1755   assert(current->held_monitor_count() == 0, "Should not be possible");
1756   // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1757   current->clear_jni_monitor_count();
1758 }
1759 
1760 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1761   switch (cause) {
1762     case inflate_cause_vm_internal:    return "VM Internal";
1763     case inflate_cause_monitor_enter:  return "Monitor Enter";
1764     case inflate_cause_wait:           return "Monitor Wait";
1765     case inflate_cause_notify:         return "Monitor Notify";
1766     case inflate_cause_hash_code:      return "Monitor Hash Code";
1767     case inflate_cause_jni_enter:      return "JNI Monitor Enter";
1768     case inflate_cause_jni_exit:       return "JNI Monitor Exit";
1769     default:
1770       ShouldNotReachHere();
1771   }
1772   return "Unknown";
1773 }
1774 
1775 //------------------------------------------------------------------------------
1776 // Debugging code
1777 
1778 u_char* ObjectSynchronizer::get_gvars_addr() {
1779   return (u_char*)&GVars;
1780 }
1781 
1782 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1783   return (u_char*)&GVars.hc_sequence;
1784 }
1785 
1786 size_t ObjectSynchronizer::get_gvars_size() {
1787   return sizeof(SharedGlobals);
1788 }
1789 
1790 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1791   return (u_char*)&GVars.stw_random;
1792 }
1793 
1794 // Do the final audit and print of ObjectMonitor stats; must be done
1795 // by the VMThread at VM exit time.
1796 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1797   assert(Thread::current()->is_VM_thread(), "sanity check");
1798 
1799   if (is_final_audit()) {  // Only do the audit once.
1800     return;
1801   }
1802   set_is_final_audit();
1803   log_info(monitorinflation)("Starting the final audit.");
1804 
1805   if (log_is_enabled(Info, monitorinflation)) {
1806     // The other audit_and_print_stats() call is done at the Debug
1807     // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
1808     audit_and_print_stats(true /* on_exit */);
1809   }
1810 }
1811 
1812 // This function can be called at a safepoint or it can be called when
1813 // we are trying to exit the VM. When we are trying to exit the VM, the
1814 // list walker functions can run in parallel with the other list
1815 // operations so spin-locking is used for safety.
1816 //
1817 // Calls to this function can be added in various places as a debugging
1818 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1819 // details logged at the Info level and 'false' for the 'on_exit'
1820 // parameter to have in-use monitor details logged at the Trace level.
1821 //
1822 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1823   assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1824 
1825   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1826   LogStreamHandle(Info, monitorinflation) lsh_info;
1827   LogStreamHandle(Trace, monitorinflation) lsh_trace;
1828   LogStream* ls = nullptr;
1829   if (log_is_enabled(Trace, monitorinflation)) {
1830     ls = &lsh_trace;
1831   } else if (log_is_enabled(Debug, monitorinflation)) {
1832     ls = &lsh_debug;
1833   } else if (log_is_enabled(Info, monitorinflation)) {
1834     ls = &lsh_info;
1835   }
1836   assert(ls != nullptr, "sanity check");
1837 
1838   int error_cnt = 0;
1839 
1840   ls->print_cr("Checking in_use_list:");
1841   chk_in_use_list(ls, &error_cnt);
1842 
1843   if (error_cnt == 0) {
1844     ls->print_cr("No errors found in in_use_list checks.");
1845   } else {
1846     log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1847   }
1848 
1849   if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1850       (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1851     // When exiting this log output is at the Info level. When called
1852     // at a safepoint, this log output is at the Trace level since
1853     // there can be a lot of it.
1854     log_in_use_monitor_details(ls, !on_exit /* log_all */);
1855   }
1856 
1857   ls->flush();
1858 
1859   guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1860 }
1861 
1862 // Check the in_use_list; log the results of the checks.
1863 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1864   size_t l_in_use_count = _in_use_list.count();
1865   size_t l_in_use_max = _in_use_list.max();
1866   out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1867                 l_in_use_max);
1868 
1869   size_t ck_in_use_count = 0;
1870   MonitorList::Iterator iter = _in_use_list.iterator();
1871   while (iter.has_next()) {
1872     ObjectMonitor* mid = iter.next();
1873     chk_in_use_entry(mid, out, error_cnt_p);
1874     ck_in_use_count++;
1875   }
1876 
1877   if (l_in_use_count == ck_in_use_count) {
1878     out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1879                   SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1880   } else {
1881     out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1882                   "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1883                   ck_in_use_count);
1884   }
1885 
1886   size_t ck_in_use_max = _in_use_list.max();
1887   if (l_in_use_max == ck_in_use_max) {
1888     out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1889                   SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1890   } else {
1891     out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1892                   "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1893   }
1894 }
1895 
1896 // Check an in-use monitor entry; log any errors.
1897 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1898                                           int* error_cnt_p) {
1899   if (n->owner_is_DEFLATER_MARKER()) {
1900     // This should not happen, but if it does, it is not fatal.
1901     out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1902                   "deflated.", p2i(n));
1903     return;
1904   }
1905   if (n->header().value() == 0) {
1906     out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1907                   "have non-null _header field.", p2i(n));
1908     *error_cnt_p = *error_cnt_p + 1;
1909   }
1910   const oop obj = n->object_peek();
1911   if (obj != nullptr) {
1912     const markWord mark = obj->mark();
1913     if (!mark.has_monitor()) {
1914       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1915                     "object does not think it has a monitor: obj="
1916                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1917                     p2i(obj), mark.value());
1918       *error_cnt_p = *error_cnt_p + 1;
1919     }
1920     ObjectMonitor* const obj_mon = mark.monitor();
1921     if (n != obj_mon) {
1922       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1923                     "object does not refer to the same monitor: obj="
1924                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1925                     INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1926       *error_cnt_p = *error_cnt_p + 1;
1927     }
1928   }
1929 }
1930 
1931 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1932 // flags indicate why the entry is in-use, 'object' and 'object type'
1933 // indicate the associated object and its type.
1934 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
1935   if (_in_use_list.count() > 0) {
1936     stringStream ss;
1937     out->print_cr("In-use monitor info:");
1938     out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1939     out->print_cr("%18s  %s  %18s  %18s",
1940                   "monitor", "BHL", "object", "object type");
1941     out->print_cr("==================  ===  ==================  ==================");
1942 
1943     auto is_interesting = [&](ObjectMonitor* monitor) {
1944       return log_all || monitor->has_owner() || monitor->is_busy();
1945     };
1946 
1947     monitors_iterate([&](ObjectMonitor* monitor) {
1948       if (is_interesting(monitor)) {
1949         const oop obj = monitor->object_peek();
1950         const markWord mark = monitor->header();
1951         ResourceMark rm;
1952         out->print(INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT "  %s", p2i(monitor),
1953                    monitor->is_busy(), mark.hash() != 0, monitor->owner() != nullptr,
1954                    p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
1955         if (monitor->is_busy()) {
1956           out->print(" (%s)", monitor->is_busy_to_string(&ss));
1957           ss.reset();
1958         }
1959         out->cr();
1960       }
1961     });
1962   }
1963 
1964   out->flush();
1965 }