1 /*
   2  * Copyright (c) 1998, 2022, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/vmSymbols.hpp"
  27 #include "jfr/jfrEvents.hpp"
  28 #include "gc/shared/suspendibleThreadSet.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/vframe.hpp"
  58 #include "runtime/vmThread.hpp"
  59 #include "utilities/align.hpp"
  60 #include "utilities/dtrace.hpp"
  61 #include "utilities/events.hpp"
  62 #include "utilities/linkedlist.hpp"
  63 #include "utilities/preserveException.hpp"
  64 
  65 class ObjectMonitorsHashtable::PtrList :
  66   public LinkedListImpl<ObjectMonitor*,
  67                         AnyObj::C_HEAP, mtThread,
  68                         AllocFailStrategy::RETURN_NULL> {};
  69 
  70 class CleanupObjectMonitorsHashtable: StackObj {
  71  public:
  72   bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) {
  73     list->clear();  // clear the LinkListNodes
  74     delete list;    // then delete the LinkedList
  75     return true;
  76   }
  77 };
  78 
  79 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() {
  80   CleanupObjectMonitorsHashtable cleanup;
  81   _ptrs->unlink(&cleanup);  // cleanup the LinkedLists
  82   delete _ptrs;             // then delete the hash table
  83 }
  84 
  85 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) {
  86   ObjectMonitorsHashtable::PtrList* list = get_entry(key);
  87   if (list == nullptr) {
  88     // Create new list and add it to the hash table:
  89     list = new (mtThread) ObjectMonitorsHashtable::PtrList;
  90     add_entry(key, list);
  91   }
  92   list->add(om);  // Add the ObjectMonitor to the list.
  93   _om_count++;
  94 }
  95 
  96 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) {
  97   ObjectMonitorsHashtable::PtrList* list = get_entry(key);
  98   if (list == nullptr || list->find(om) == nullptr) {
  99     return false;
 100   }
 101   return true;
 102 }
 103 
 104 void MonitorList::add(ObjectMonitor* m) {
 105   ObjectMonitor* head;
 106   do {
 107     head = Atomic::load(&_head);
 108     m->set_next_om(head);
 109   } while (Atomic::cmpxchg(&_head, head, m) != head);
 110 
 111   size_t count = Atomic::add(&_count, 1u);
 112   if (count > max()) {
 113     Atomic::inc(&_max);
 114   }
 115 }
 116 
 117 size_t MonitorList::count() const {
 118   return Atomic::load(&_count);
 119 }
 120 
 121 size_t MonitorList::max() const {
 122   return Atomic::load(&_max);
 123 }
 124 
 125 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
 126 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
 127 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
 128                                     elapsedTimer* timer_p,
 129                                     GrowableArray<ObjectMonitor*>* unlinked_list) {
 130   size_t unlinked_count = 0;
 131   ObjectMonitor* prev = NULL;
 132   ObjectMonitor* head = Atomic::load_acquire(&_head);
 133   ObjectMonitor* m = head;
 134   // The in-use list head can be NULL during the final audit.
 135   while (m != NULL) {
 136     if (m->is_being_async_deflated()) {
 137       // Find next live ObjectMonitor.
 138       ObjectMonitor* next = m;
 139       do {
 140         ObjectMonitor* next_next = next->next_om();
 141         unlinked_count++;
 142         unlinked_list->append(next);
 143         next = next_next;
 144         if (unlinked_count >= (size_t)MonitorDeflationMax) {
 145           // Reached the max so bail out on the gathering loop.
 146           break;
 147         }
 148       } while (next != NULL && next->is_being_async_deflated());
 149       if (prev == NULL) {
 150         ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
 151         if (prev_head != head) {
 152           // Find new prev ObjectMonitor that just got inserted.
 153           for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
 154             prev = n;
 155           }
 156           prev->set_next_om(next);
 157         }
 158       } else {
 159         prev->set_next_om(next);
 160       }
 161       if (unlinked_count >= (size_t)MonitorDeflationMax) {
 162         // Reached the max so bail out on the searching loop.
 163         break;
 164       }
 165       m = next;
 166     } else {
 167       prev = m;
 168       m = m->next_om();
 169     }
 170 
 171     if (current->is_Java_thread()) {
 172       // A JavaThread must check for a safepoint/handshake and honor it.
 173       ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking",
 174                                             "unlinked_count", unlinked_count,
 175                                             ls, timer_p);
 176     }
 177   }
 178   Atomic::sub(&_count, unlinked_count);
 179   return unlinked_count;
 180 }
 181 
 182 MonitorList::Iterator MonitorList::iterator() const {
 183   return Iterator(Atomic::load_acquire(&_head));
 184 }
 185 
 186 ObjectMonitor* MonitorList::Iterator::next() {
 187   ObjectMonitor* current = _current;
 188   _current = current->next_om();
 189   return current;
 190 }
 191 
 192 // The "core" versions of monitor enter and exit reside in this file.
 193 // The interpreter and compilers contain specialized transliterated
 194 // variants of the enter-exit fast-path operations.  See c2_MacroAssembler_x86.cpp
 195 // fast_lock(...) for instance.  If you make changes here, make sure to modify the
 196 // interpreter, and both C1 and C2 fast-path inline locking code emission.
 197 //
 198 // -----------------------------------------------------------------------------
 199 
 200 #ifdef DTRACE_ENABLED
 201 
 202 // Only bother with this argument setup if dtrace is available
 203 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
 204 
 205 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
 206   char* bytes = NULL;                                                      \
 207   int len = 0;                                                             \
 208   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
 209   Symbol* klassname = obj->klass()->name();                                \
 210   if (klassname != NULL) {                                                 \
 211     bytes = (char*)klassname->bytes();                                     \
 212     len = klassname->utf8_length();                                        \
 213   }
 214 
 215 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
 216   {                                                                        \
 217     if (DTraceMonitorProbes) {                                             \
 218       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 219       HOTSPOT_MONITOR_WAIT(jtid,                                           \
 220                            (uintptr_t)(monitor), bytes, len, (millis));    \
 221     }                                                                      \
 222   }
 223 
 224 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
 225 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
 226 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
 227 
 228 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
 229   {                                                                        \
 230     if (DTraceMonitorProbes) {                                             \
 231       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 232       HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */             \
 233                                     (uintptr_t)(monitor), bytes, len);     \
 234     }                                                                      \
 235   }
 236 
 237 #else //  ndef DTRACE_ENABLED
 238 
 239 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 240 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 241 
 242 #endif // ndef DTRACE_ENABLED
 243 
 244 // This exists only as a workaround of dtrace bug 6254741
 245 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
 246   DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
 247   return 0;
 248 }
 249 
 250 static const int NINFLATIONLOCKS = 256;
 251 static PlatformMutex* gInflationLocks[NINFLATIONLOCKS];
 252 
 253 void ObjectSynchronizer::initialize() {
 254   for (int i = 0; i < NINFLATIONLOCKS; i++) {
 255     gInflationLocks[i] = new PlatformMutex();
 256   }
 257   // Start the ceiling with the estimate for one thread.
 258   set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
 259 }
 260 
 261 MonitorList ObjectSynchronizer::_in_use_list;
 262 // monitors_used_above_threshold() policy is as follows:
 263 //
 264 // The ratio of the current _in_use_list count to the ceiling is used
 265 // to determine if we are above MonitorUsedDeflationThreshold and need
 266 // to do an async monitor deflation cycle. The ceiling is increased by
 267 // AvgMonitorsPerThreadEstimate when a thread is added to the system
 268 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
 269 // removed from the system.
 270 //
 271 // Note: If the _in_use_list max exceeds the ceiling, then
 272 // monitors_used_above_threshold() will use the in_use_list max instead
 273 // of the thread count derived ceiling because we have used more
 274 // ObjectMonitors than the estimated average.
 275 //
 276 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
 277 // no-progress async monitor deflation cycles in a row, then the ceiling
 278 // is adjusted upwards by monitors_used_above_threshold().
 279 //
 280 // Start the ceiling with the estimate for one thread in initialize()
 281 // which is called after cmd line options are processed.
 282 static size_t _in_use_list_ceiling = 0;
 283 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
 284 bool volatile ObjectSynchronizer::_is_final_audit = false;
 285 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
 286 static uintx _no_progress_cnt = 0;
 287 
 288 // =====================> Quick functions
 289 
 290 // The quick_* forms are special fast-path variants used to improve
 291 // performance.  In the simplest case, a "quick_*" implementation could
 292 // simply return false, in which case the caller will perform the necessary
 293 // state transitions and call the slow-path form.
 294 // The fast-path is designed to handle frequently arising cases in an efficient
 295 // manner and is just a degenerate "optimistic" variant of the slow-path.
 296 // returns true  -- to indicate the call was satisfied.
 297 // returns false -- to indicate the call needs the services of the slow-path.
 298 // A no-loitering ordinance is in effect for code in the quick_* family
 299 // operators: safepoints or indefinite blocking (blocking that might span a
 300 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
 301 // entry.
 302 //
 303 // Consider: An interesting optimization is to have the JIT recognize the
 304 // following common idiom:
 305 //   synchronized (someobj) { .... ; notify(); }
 306 // That is, we find a notify() or notifyAll() call that immediately precedes
 307 // the monitorexit operation.  In that case the JIT could fuse the operations
 308 // into a single notifyAndExit() runtime primitive.
 309 
 310 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
 311   assert(current->thread_state() == _thread_in_Java, "invariant");
 312   NoSafepointVerifier nsv;
 313   if (obj == NULL) return false;  // slow-path for invalid obj
 314   const markWord mark = obj->mark();
 315 
 316   if ((mark.is_fast_locked() && current->lock_stack().contains(oop(obj))) ||
 317       (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) {
 318     // Degenerate notify
 319     // stack-locked by caller so by definition the implied waitset is empty.
 320     return true;
 321   }
 322 
 323   if (mark.has_monitor()) {
 324     ObjectMonitor* const mon = mark.monitor();
 325     assert(mon->object() == oop(obj), "invariant");
 326     if (mon->owner() != current) return false;  // slow-path for IMS exception
 327 
 328     if (mon->first_waiter() != NULL) {
 329       // We have one or more waiters. Since this is an inflated monitor
 330       // that we own, we can transfer one or more threads from the waitset
 331       // to the entrylist here and now, avoiding the slow-path.
 332       if (all) {
 333         DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
 334       } else {
 335         DTRACE_MONITOR_PROBE(notify, mon, obj, current);
 336       }
 337       int free_count = 0;
 338       do {
 339         mon->INotify(current);
 340         ++free_count;
 341       } while (mon->first_waiter() != NULL && all);
 342       OM_PERFDATA_OP(Notifications, inc(free_count));
 343     }
 344     return true;
 345   }
 346 
 347   // other IMS exception states take the slow-path
 348   return false;
 349 }
 350 
 351 
 352 // The LockNode emitted directly at the synchronization site would have
 353 // been too big if it were to have included support for the cases of inflated
 354 // recursive enter and exit, so they go here instead.
 355 // Note that we can't safely call AsyncPrintJavaStack() from within
 356 // quick_enter() as our thread state remains _in_Java.
 357 
 358 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
 359                                      BasicLock * lock) {
 360   assert(current->thread_state() == _thread_in_Java, "invariant");
 361   NoSafepointVerifier nsv;
 362   if (obj == NULL) return false;       // Need to throw NPE
 363 
 364   if (obj->klass()->is_value_based()) {
 365     return false;
 366   }
 367 
 368   const markWord mark = obj->mark();
 369 
 370   if (mark.has_monitor()) {
 371     ObjectMonitor* const m = mark.monitor();
 372     // An async deflation or GC can race us before we manage to make
 373     // the ObjectMonitor busy by setting the owner below. If we detect
 374     // that race we just bail out to the slow-path here.
 375     if (m->object_peek() == NULL) {
 376       return false;
 377     }
 378     JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
 379 
 380     // Lock contention and Transactional Lock Elision (TLE) diagnostics
 381     // and observability
 382     // Case: light contention possibly amenable to TLE
 383     // Case: TLE inimical operations such as nested/recursive synchronization
 384 
 385     if (owner == current) {
 386       m->_recursions++;
 387       current->inc_held_monitor_count();
 388       return true;
 389     }
 390 
 391     // This Java Monitor is inflated so obj's header will never be
 392     // displaced to this thread's BasicLock. Make the displaced header
 393     // non-NULL so this BasicLock is not seen as recursive nor as
 394     // being locked. We do this unconditionally so that this thread's
 395     // BasicLock cannot be mis-interpreted by any stack walkers. For
 396     // performance reasons, stack walkers generally first check for
 397     // stack-locking in the object's header, the second check is for
 398     // recursive stack-locking in the displaced header in the BasicLock,
 399     // and last are the inflated Java Monitor (ObjectMonitor) checks.
 400     if (!UseFastLocking) {
 401       lock->set_displaced_header(markWord::unused_mark());
 402     }
 403 
 404     if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
 405       assert(m->_recursions == 0, "invariant");
 406       current->inc_held_monitor_count();
 407       return true;
 408     }
 409   }
 410 
 411   // Note that we could inflate in quick_enter.
 412   // This is likely a useful optimization
 413   // Critically, in quick_enter() we must not:
 414   // -- block indefinitely, or
 415   // -- reach a safepoint
 416 
 417   return false;        // revert to slow-path
 418 }
 419 
 420 // Handle notifications when synchronizing on value based classes
 421 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
 422   frame last_frame = current->last_frame();
 423   bool bcp_was_adjusted = false;
 424   // Don't decrement bcp if it points to the frame's first instruction.  This happens when
 425   // handle_sync_on_value_based_class() is called because of a synchronized method.  There
 426   // is no actual monitorenter instruction in the byte code in this case.
 427   if (last_frame.is_interpreted_frame() &&
 428       (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
 429     // adjust bcp to point back to monitorenter so that we print the correct line numbers
 430     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
 431     bcp_was_adjusted = true;
 432   }
 433 
 434   if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
 435     ResourceMark rm(current);
 436     stringStream ss;
 437     current->print_active_stack_on(&ss);
 438     char* base = (char*)strstr(ss.base(), "at");
 439     char* newline = (char*)strchr(ss.base(), '\n');
 440     if (newline != NULL) {
 441       *newline = '\0';
 442     }
 443     fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
 444   } else {
 445     assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
 446     ResourceMark rm(current);
 447     Log(valuebasedclasses) vblog;
 448 
 449     vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
 450     if (current->has_last_Java_frame()) {
 451       LogStream info_stream(vblog.info());
 452       current->print_active_stack_on(&info_stream);
 453     } else {
 454       vblog.info("Cannot find the last Java frame");
 455     }
 456 
 457     EventSyncOnValueBasedClass event;
 458     if (event.should_commit()) {
 459       event.set_valueBasedClass(obj->klass());
 460       event.commit();
 461     }
 462   }
 463 
 464   if (bcp_was_adjusted) {
 465     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
 466   }
 467 }
 468 
 469 static bool useHeavyMonitors() {
 470 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64)
 471   return UseHeavyMonitors;
 472 #else
 473   return false;
 474 #endif
 475 }
 476 
 477 // -----------------------------------------------------------------------------
 478 // Monitor Enter/Exit
 479 // The interpreter and compiler assembly code tries to lock using the fast path
 480 // of this algorithm. Make sure to update that code if the following function is
 481 // changed. The implementation is extremely sensitive to race condition. Be careful.
 482 
 483 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
 484   if (obj->klass()->is_value_based()) {
 485     handle_sync_on_value_based_class(obj, current);
 486   }
 487 
 488   current->inc_held_monitor_count();
 489 
 490   if (!useHeavyMonitors()) {
 491     if (UseFastLocking) {
 492       LockStack& lock_stack = current->lock_stack();
 493 
 494       markWord header = obj()->mark_acquire();
 495       while (true) {
 496         if (header.is_neutral()) {
 497           assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
 498           // Try to swing into 'fast-locked' state without inflating.
 499           markWord locked_header = header.set_fast_locked();
 500           markWord witness = obj()->cas_set_mark(locked_header, header);
 501           if (witness == header) {
 502             // Successfully fast-locked, push object to lock-stack and return.
 503             lock_stack.push(obj());
 504             return;
 505           }
 506           // Otherwise retry.
 507           header = witness;
 508         } else {
 509           // Fall-through to inflate-enter.
 510           break;
 511         }
 512       }
 513     } else {
 514       markWord mark = obj->mark();
 515       if (mark.is_neutral()) {
 516         // Anticipate successful CAS -- the ST of the displaced mark must
 517         // be visible <= the ST performed by the CAS.
 518         lock->set_displaced_header(mark);
 519         if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
 520           return;
 521         }
 522         // Fall through to inflate() ...
 523       } else if (mark.has_locker() &&
 524                  current->is_lock_owned((address) mark.locker())) {
 525         assert(lock != mark.locker(), "must not re-lock the same lock");
 526         assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
 527         lock->set_displaced_header(markWord::from_pointer(NULL));
 528         return;
 529       }
 530 
 531       // The object header will never be displaced to this lock,
 532       // so it does not matter what the value is, except that it
 533       // must be non-zero to avoid looking like a re-entrant lock,
 534       // and must not look locked either.
 535       lock->set_displaced_header(markWord::unused_mark());
 536     }
 537   } else if (VerifyHeavyMonitors) {
 538     guarantee(!obj->mark().has_locker() && !obj->mark().is_fast_locked(), "must not be stack-locked");
 539   }
 540 
 541   // An async deflation can race after the inflate() call and before
 542   // enter() can make the ObjectMonitor busy. enter() returns false if
 543   // we have lost the race to async deflation and we simply try again.
 544   while (true) {
 545     ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
 546     if (monitor->enter(current)) {
 547       return;
 548     }
 549   }
 550 }
 551 
 552 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
 553   current->dec_held_monitor_count();
 554 
 555   if (!useHeavyMonitors()) {
 556     markWord mark = object->mark();
 557     if (UseFastLocking) {
 558       if (mark.is_fast_locked()) {
 559         markWord unlocked_header = mark.set_unlocked();
 560         markWord witness = object->cas_set_mark(unlocked_header, mark);
 561         if (witness != mark) {
 562           // Another thread beat us, it can only have installed an anonymously locked monitor at this point.
 563           // Fetch that monitor, set owner correctly to this thread, and exit it (allowing waiting threads to enter).
 564           assert(witness.has_monitor(), "must have monitor");
 565           ObjectMonitor* monitor = witness.monitor();
 566           assert(monitor->is_owner_anonymous(), "must be anonymous owner");
 567           monitor->set_owner_from_anonymous(current);
 568           monitor->exit(current);
 569         }
 570         LockStack& lock_stack = current->lock_stack();
 571         lock_stack.remove(object);
 572         return;
 573       }
 574     } else {
 575       markWord dhw = lock->displaced_header();
 576       if (dhw.value() == 0) {
 577         // If the displaced header is NULL, then this exit matches up with
 578         // a recursive enter. No real work to do here except for diagnostics.
 579 #ifndef PRODUCT
 580         if (mark != markWord::INFLATING()) {
 581           // Only do diagnostics if we are not racing an inflation. Simply
 582           // exiting a recursive enter of a Java Monitor that is being
 583           // inflated is safe; see the has_monitor() comment below.
 584           assert(!mark.is_neutral(), "invariant");
 585           assert(!mark.has_locker() ||
 586                  current->is_lock_owned((address)mark.locker()), "invariant");
 587           if (mark.has_monitor()) {
 588             // The BasicLock's displaced_header is marked as a recursive
 589             // enter and we have an inflated Java Monitor (ObjectMonitor).
 590             // This is a special case where the Java Monitor was inflated
 591             // after this thread entered the stack-lock recursively. When a
 592             // Java Monitor is inflated, we cannot safely walk the Java
 593             // Monitor owner's stack and update the BasicLocks because a
 594             // Java Monitor can be asynchronously inflated by a thread that
 595             // does not own the Java Monitor.
 596             ObjectMonitor* m = mark.monitor();
 597             assert(m->object()->mark() == mark, "invariant");
 598             assert(m->is_entered(current), "invariant");
 599           }
 600         }
 601 #endif
 602         return;
 603       }
 604 
 605       if (mark == markWord::from_pointer(lock)) {
 606         // If the object is stack-locked by the current thread, try to
 607         // swing the displaced header from the BasicLock back to the mark.
 608         assert(dhw.is_neutral(), "invariant");
 609         if (object->cas_set_mark(dhw, mark) == mark) {
 610           return;
 611         }
 612       }
 613     }
 614   } else if (VerifyHeavyMonitors) {
 615     guarantee(!object->mark().has_locker(), "must not be stack-locked");
 616   }
 617 
 618   // We have to take the slow-path of possible inflation and then exit.
 619   // The ObjectMonitor* can't be async deflated until ownership is
 620   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
 621   ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
 622   if (UseFastLocking && monitor->is_owner_anonymous()) {
 623     // It must be us. Pop lock object from lock stack.
 624     LockStack& lock_stack = current->lock_stack();
 625     oop popped = lock_stack.pop();
 626     assert(popped == object, "must be owned by this thread");
 627     monitor->set_owner_from_anonymous(current);
 628   }
 629   monitor->exit(current);
 630 }
 631 
 632 // -----------------------------------------------------------------------------
 633 // Class Loader  support to workaround deadlocks on the class loader lock objects
 634 // Also used by GC
 635 // complete_exit()/reenter() are used to wait on a nested lock
 636 // i.e. to give up an outer lock completely and then re-enter
 637 // Used when holding nested locks - lock acquisition order: lock1 then lock2
 638 //  1) complete_exit lock1 - saving recursion count
 639 //  2) wait on lock2
 640 //  3) when notified on lock2, unlock lock2
 641 //  4) reenter lock1 with original recursion count
 642 //  5) lock lock2
 643 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 644 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
 645   // The ObjectMonitor* can't be async deflated until ownership is
 646   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
 647   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
 648   intx recur_count = monitor->complete_exit(current);
 649   current->dec_held_monitor_count(recur_count + 1);
 650   return recur_count;
 651 }
 652 
 653 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 654 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
 655   // An async deflation can race after the inflate() call and before
 656   // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
 657   // enter() returns false if we have lost the race to async deflation
 658   // and we simply try again.
 659   while (true) {
 660     ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
 661     if (monitor->reenter(recursions, current)) {
 662       current->inc_held_monitor_count(recursions + 1);
 663       return;
 664     }
 665   }
 666 }
 667 
 668 // -----------------------------------------------------------------------------
 669 // JNI locks on java objects
 670 // NOTE: must use heavy weight monitor to handle jni monitor enter
 671 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
 672   if (obj->klass()->is_value_based()) {
 673     handle_sync_on_value_based_class(obj, current);
 674   }
 675 
 676   // the current locking is from JNI instead of Java code
 677   current->set_current_pending_monitor_is_from_java(false);
 678   // An async deflation can race after the inflate() call and before
 679   // enter() can make the ObjectMonitor busy. enter() returns false if
 680   // we have lost the race to async deflation and we simply try again.
 681   while (true) {
 682     ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
 683     if (monitor->enter(current)) {
 684       current->inc_held_monitor_count(1, true);
 685       break;
 686     }
 687   }
 688   current->set_current_pending_monitor_is_from_java(true);
 689 }
 690 
 691 // NOTE: must use heavy weight monitor to handle jni monitor exit
 692 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
 693   JavaThread* current = THREAD;
 694 
 695   // The ObjectMonitor* can't be async deflated until ownership is
 696   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
 697   ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
 698   // If this thread has locked the object, exit the monitor. We
 699   // intentionally do not use CHECK on check_owner because we must exit the
 700   // monitor even if an exception was already pending.
 701   if (monitor->check_owner(THREAD)) {
 702     monitor->exit(current);
 703     current->dec_held_monitor_count(1, true);
 704   }
 705 }
 706 
 707 // -----------------------------------------------------------------------------
 708 // Internal VM locks on java objects
 709 // standard constructor, allows locking failures
 710 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
 711   _thread = thread;
 712   _thread->check_for_valid_safepoint_state();
 713   _obj = obj;
 714 
 715   if (_obj() != NULL) {
 716     ObjectSynchronizer::enter(_obj, &_lock, _thread);
 717   }
 718 }
 719 
 720 ObjectLocker::~ObjectLocker() {
 721   if (_obj() != NULL) {
 722     ObjectSynchronizer::exit(_obj(), &_lock, _thread);
 723   }
 724 }
 725 
 726 
 727 // -----------------------------------------------------------------------------
 728 //  Wait/Notify/NotifyAll
 729 // NOTE: must use heavy weight monitor to handle wait()
 730 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 731   JavaThread* current = THREAD;
 732   if (millis < 0) {
 733     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 734   }
 735   // The ObjectMonitor* can't be async deflated because the _waiters
 736   // field is incremented before ownership is dropped and decremented
 737   // after ownership is regained.
 738   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
 739 
 740   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
 741   monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
 742 
 743   // This dummy call is in place to get around dtrace bug 6254741.  Once
 744   // that's fixed we can uncomment the following line, remove the call
 745   // and change this function back into a "void" func.
 746   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 747   int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
 748   return ret_code;
 749 }
 750 
 751 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 752   JavaThread* current = THREAD;
 753 
 754   markWord mark = obj->mark();
 755   if ((mark.is_fast_locked() && current->lock_stack().contains(obj())) ||
 756       (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) {
 757     // Not inflated so there can't be any waiters to notify.
 758     return;
 759   }
 760   // The ObjectMonitor* can't be async deflated until ownership is
 761   // dropped by the calling thread.
 762   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
 763   monitor->notify(CHECK);
 764 }
 765 
 766 // NOTE: see comment of notify()
 767 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 768   JavaThread* current = THREAD;
 769 
 770   markWord mark = obj->mark();
 771   if ((mark.is_fast_locked() && current->lock_stack().contains(obj())) ||
 772       (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) {
 773     // Not inflated so there can't be any waiters to notify.
 774     return;
 775   }
 776   // The ObjectMonitor* can't be async deflated until ownership is
 777   // dropped by the calling thread.
 778   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
 779   monitor->notifyAll(CHECK);
 780 }
 781 
 782 // -----------------------------------------------------------------------------
 783 // Hash Code handling
 784 
 785 struct SharedGlobals {
 786   char         _pad_prefix[OM_CACHE_LINE_SIZE];
 787   // This is a highly shared mostly-read variable.
 788   // To avoid false-sharing it needs to be the sole occupant of a cache line.
 789   volatile int stw_random;
 790   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 791   // Hot RW variable -- Sequester to avoid false-sharing
 792   volatile int hc_sequence;
 793   DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 794 };
 795 
 796 static SharedGlobals GVars;
 797 
 798 static markWord read_stable_mark(oop obj) {
 799   markWord mark = obj->mark_acquire();
 800   if (!mark.is_being_inflated() || UseFastLocking) {
 801     return mark;       // normal fast-path return
 802   }
 803 
 804   int its = 0;
 805   for (;;) {
 806     markWord mark = obj->mark_acquire();
 807     if (!mark.is_being_inflated()) {
 808       return mark;    // normal fast-path return
 809     }
 810 
 811     // The object is being inflated by some other thread.
 812     // The caller of read_stable_mark() must wait for inflation to complete.
 813     // Avoid live-lock.
 814 
 815     ++its;
 816     if (its > 10000 || !os::is_MP()) {
 817       if (its & 1) {
 818         os::naked_yield();
 819       } else {
 820         // Note that the following code attenuates the livelock problem but is not
 821         // a complete remedy.  A more complete solution would require that the inflating
 822         // thread hold the associated inflation lock.  The following code simply restricts
 823         // the number of spinners to at most one.  We'll have N-2 threads blocked
 824         // on the inflationlock, 1 thread holding the inflation lock and using
 825         // a yield/park strategy, and 1 thread in the midst of inflation.
 826         // A more refined approach would be to change the encoding of INFLATING
 827         // to allow encapsulation of a native thread pointer.  Threads waiting for
 828         // inflation to complete would use CAS to push themselves onto a singly linked
 829         // list rooted at the markword.  Once enqueued, they'd loop, checking a per-thread flag
 830         // and calling park().  When inflation was complete the thread that accomplished inflation
 831         // would detach the list and set the markword to inflated with a single CAS and
 832         // then for each thread on the list, set the flag and unpark() the thread.
 833 
 834         // Index into the lock array based on the current object address.
 835         static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
 836         int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
 837         int YieldThenBlock = 0;
 838         assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
 839         gInflationLocks[ix]->lock();
 840         while (obj->mark_acquire() == markWord::INFLATING()) {
 841           // Beware: naked_yield() is advisory and has almost no effect on some platforms
 842           // so we periodically call current->_ParkEvent->park(1).
 843           // We use a mixed spin/yield/block mechanism.
 844           if ((YieldThenBlock++) >= 16) {
 845             Thread::current()->_ParkEvent->park(1);
 846           } else {
 847             os::naked_yield();
 848           }
 849         }
 850         gInflationLocks[ix]->unlock();
 851       }
 852     } else {
 853       SpinPause();       // SMP-polite spinning
 854     }
 855   }
 856 }
 857 
 858 // hashCode() generation :
 859 //
 860 // Possibilities:
 861 // * MD5Digest of {obj,stw_random}
 862 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
 863 // * A DES- or AES-style SBox[] mechanism
 864 // * One of the Phi-based schemes, such as:
 865 //   2654435761 = 2^32 * Phi (golden ratio)
 866 //   HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
 867 // * A variation of Marsaglia's shift-xor RNG scheme.
 868 // * (obj ^ stw_random) is appealing, but can result
 869 //   in undesirable regularity in the hashCode values of adjacent objects
 870 //   (objects allocated back-to-back, in particular).  This could potentially
 871 //   result in hashtable collisions and reduced hashtable efficiency.
 872 //   There are simple ways to "diffuse" the middle address bits over the
 873 //   generated hashCode values:
 874 
 875 static inline intptr_t get_next_hash(Thread* current, oop obj) {
 876   intptr_t value = 0;
 877   if (hashCode == 0) {
 878     // This form uses global Park-Miller RNG.
 879     // On MP system we'll have lots of RW access to a global, so the
 880     // mechanism induces lots of coherency traffic.
 881     value = os::random();
 882   } else if (hashCode == 1) {
 883     // This variation has the property of being stable (idempotent)
 884     // between STW operations.  This can be useful in some of the 1-0
 885     // synchronization schemes.
 886     intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
 887     value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
 888   } else if (hashCode == 2) {
 889     value = 1;            // for sensitivity testing
 890   } else if (hashCode == 3) {
 891     value = ++GVars.hc_sequence;
 892   } else if (hashCode == 4) {
 893     value = cast_from_oop<intptr_t>(obj);
 894   } else {
 895     // Marsaglia's xor-shift scheme with thread-specific state
 896     // This is probably the best overall implementation -- we'll
 897     // likely make this the default in future releases.
 898     unsigned t = current->_hashStateX;
 899     t ^= (t << 11);
 900     current->_hashStateX = current->_hashStateY;
 901     current->_hashStateY = current->_hashStateZ;
 902     current->_hashStateZ = current->_hashStateW;
 903     unsigned v = current->_hashStateW;
 904     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
 905     current->_hashStateW = v;
 906     value = v;
 907   }
 908 
 909   value &= markWord::hash_mask;
 910   if (value == 0) value = 0xBAD;
 911   assert(value != markWord::no_hash, "invariant");
 912   return value;
 913 }
 914 
 915 static bool is_lock_owned(Thread* thread, oop obj) {
 916   assert(UseFastLocking, "only call this with fast-locking enabled");
 917   return thread->is_Java_thread() ? reinterpret_cast<JavaThread*>(thread)->lock_stack().contains(obj) : false;
 918 }
 919 
 920 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
 921 
 922   while (true) {
 923     ObjectMonitor* monitor = NULL;
 924     markWord temp, test;
 925     intptr_t hash;
 926     markWord mark = read_stable_mark(obj);
 927     if (VerifyHeavyMonitors) {
 928       assert(UseHeavyMonitors, "+VerifyHeavyMonitors requires +UseHeavyMonitors");
 929       guarantee(!mark.has_locker(), "must not be stack locked");
 930     }
 931     if (mark.is_neutral()) {               // if this is a normal header
 932       hash = mark.hash();
 933       if (hash != 0) {                     // if it has a hash, just return it
 934         return hash;
 935       }
 936       hash = get_next_hash(current, obj);  // get a new hash
 937       temp = mark.copy_set_hash(hash);     // merge the hash into header
 938                                            // try to install the hash
 939       test = obj->cas_set_mark(temp, mark);
 940       if (test == mark) {                  // if the hash was installed, return it
 941         return hash;
 942       }
 943       // Failed to install the hash. It could be that another thread
 944       // installed the hash just before our attempt or inflation has
 945       // occurred or... so we fall thru to inflate the monitor for
 946       // stability and then install the hash.
 947     } else if (mark.has_monitor()) {
 948       monitor = mark.monitor();
 949       temp = monitor->header();
 950       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 951       hash = temp.hash();
 952       if (hash != 0) {
 953         // It has a hash.
 954 
 955         // Separate load of dmw/header above from the loads in
 956         // is_being_async_deflated().
 957 
 958         // dmw/header and _contentions may get written by different threads.
 959         // Make sure to observe them in the same order when having several observers.
 960         OrderAccess::loadload_for_IRIW();
 961 
 962         if (monitor->is_being_async_deflated()) {
 963           // But we can't safely use the hash if we detect that async
 964           // deflation has occurred. So we attempt to restore the
 965           // header/dmw to the object's header so that we only retry
 966           // once if the deflater thread happens to be slow.
 967           monitor->install_displaced_markword_in_object(obj);
 968           continue;
 969         }
 970         return hash;
 971       }
 972       // Fall thru so we only have one place that installs the hash in
 973       // the ObjectMonitor.
 974     } else if (mark.is_fast_locked() && is_lock_owned(current, obj)) {
 975       // This is a fast lock owned by the calling thread so use the
 976       // markWord from the object.
 977       hash = mark.hash();
 978       if (hash != 0) {                  // if it has a hash, just return it
 979         return hash;
 980       }
 981     } else if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 982       // This is a stack lock owned by the calling thread so fetch the
 983       // displaced markWord from the BasicLock on the stack.
 984       temp = mark.displaced_mark_helper();
 985       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 986       hash = temp.hash();
 987       if (hash != 0) {                  // if it has a hash, just return it
 988         return hash;
 989       }
 990       // WARNING:
 991       // The displaced header in the BasicLock on a thread's stack
 992       // is strictly immutable. It CANNOT be changed in ANY cases.
 993       // So we have to inflate the stack lock into an ObjectMonitor
 994       // even if the current thread owns the lock. The BasicLock on
 995       // a thread's stack can be asynchronously read by other threads
 996       // during an inflate() call so any change to that stack memory
 997       // may not propagate to other threads correctly.
 998     }
 999 
1000     // Inflate the monitor to set the hash.
1001 
1002     // An async deflation can race after the inflate() call and before we
1003     // can update the ObjectMonitor's header with the hash value below.
1004     monitor = inflate(current, obj, inflate_cause_hash_code);
1005     // Load ObjectMonitor's header/dmw field and see if it has a hash.
1006     mark = monitor->header();
1007     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1008     hash = mark.hash();
1009     if (hash == 0) {                       // if it does not have a hash
1010       hash = get_next_hash(current, obj);  // get a new hash
1011       temp = mark.copy_set_hash(hash)   ;  // merge the hash into header
1012       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1013       uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1014       test = markWord(v);
1015       if (test != mark) {
1016         // The attempt to update the ObjectMonitor's header/dmw field
1017         // did not work. This can happen if another thread managed to
1018         // merge in the hash just before our cmpxchg().
1019         // If we add any new usages of the header/dmw field, this code
1020         // will need to be updated.
1021         hash = test.hash();
1022         assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1023         assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1024       }
1025       if (monitor->is_being_async_deflated()) {
1026         // If we detect that async deflation has occurred, then we
1027         // attempt to restore the header/dmw to the object's header
1028         // so that we only retry once if the deflater thread happens
1029         // to be slow.
1030         monitor->install_displaced_markword_in_object(obj);
1031         continue;
1032       }
1033     }
1034     // We finally get the hash.
1035     return hash;
1036   }
1037 }
1038 
1039 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1040                                                    Handle h_obj) {
1041   assert(current == JavaThread::current(), "Can only be called on current thread");
1042   oop obj = h_obj();
1043 
1044   markWord mark = read_stable_mark(obj);
1045 
1046   // Uncontended case, header points to stack
1047   if (mark.has_locker()) {
1048     return current->is_lock_owned((address)mark.locker());
1049   }
1050 
1051   // Fast-locking case.
1052   if (mark.is_fast_locked()) {
1053     return current->lock_stack().contains(h_obj());
1054   }
1055 
1056   // Contended case, header points to ObjectMonitor (tagged pointer)
1057   if (mark.has_monitor()) {
1058     // The first stage of async deflation does not affect any field
1059     // used by this comparison so the ObjectMonitor* is usable here.
1060     ObjectMonitor* monitor = mark.monitor();
1061     return monitor->is_entered(current) != 0;
1062   }
1063   // Unlocked case, header in place
1064   assert(mark.is_neutral(), "sanity check");
1065   return false;
1066 }
1067 
1068 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1069   oop obj = h_obj();
1070   markWord mark = read_stable_mark(obj);
1071 
1072   // Uncontended case, header points to stack
1073   if (mark.has_locker()) {
1074     return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1075   }
1076 
1077   if (mark.is_fast_locked()) {
1078     return Threads::owning_thread_from_object(t_list, h_obj());
1079   }
1080 
1081   // Contended case, header points to ObjectMonitor (tagged pointer)
1082   if (mark.has_monitor()) {
1083     // The first stage of async deflation does not affect any field
1084     // used by this comparison so the ObjectMonitor* is usable here.
1085     ObjectMonitor* monitor = mark.monitor();
1086     assert(monitor != NULL, "monitor should be non-null");
1087     return Threads::owning_thread_from_monitor(t_list, monitor);
1088   }
1089 
1090   return NULL;
1091 }
1092 
1093 // Visitors ...
1094 
1095 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1096 // ObjectMonitors where owner is set to a stack lock address in thread.
1097 //
1098 // This version of monitors_iterate() works with the in-use monitor list.
1099 //
1100 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1101   MonitorList::Iterator iter = _in_use_list.iterator();
1102   while (iter.has_next()) {
1103     ObjectMonitor* mid = iter.next();
1104     if (mid->owner() != thread) {
1105       // Not owned by the target thread and intentionally skips when owner
1106       // is set to a stack lock address in the target thread.
1107       continue;
1108     }
1109     if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1110       // Only process with closure if the object is set.
1111 
1112       // monitors_iterate() is only called at a safepoint or when the
1113       // target thread is suspended or when the target thread is
1114       // operating on itself. The current closures in use today are
1115       // only interested in an owned ObjectMonitor and ownership
1116       // cannot be dropped under the calling contexts so the
1117       // ObjectMonitor cannot be async deflated.
1118       closure->do_monitor(mid);
1119     }
1120   }
1121 }
1122 
1123 // This version of monitors_iterate() works with the specified linked list.
1124 //
1125 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure,
1126                                           ObjectMonitorsHashtable::PtrList* list,
1127                                           JavaThread* thread) {
1128   typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator;
1129   ObjectMonitorIterator iter(list->head());
1130   while (!iter.is_empty()) {
1131     ObjectMonitor* mid = *iter.next();
1132     // Owner set to a stack lock address in thread should never be seen here:
1133     assert(mid->owner() == thread, "must be");
1134     if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1135       // Only process with closure if the object is set.
1136 
1137       // monitors_iterate() is only called at a safepoint or when the
1138       // target thread is suspended or when the target thread is
1139       // operating on itself. The current closures in use today are
1140       // only interested in an owned ObjectMonitor and ownership
1141       // cannot be dropped under the calling contexts so the
1142       // ObjectMonitor cannot be async deflated.
1143       closure->do_monitor(mid);
1144     }
1145   }
1146 }
1147 
1148 static bool monitors_used_above_threshold(MonitorList* list) {
1149   if (MonitorUsedDeflationThreshold == 0) {  // disabled case is easy
1150     return false;
1151   }
1152   // Start with ceiling based on a per-thread estimate:
1153   size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1154   size_t old_ceiling = ceiling;
1155   if (ceiling < list->max()) {
1156     // The max used by the system has exceeded the ceiling so use that:
1157     ceiling = list->max();
1158   }
1159   size_t monitors_used = list->count();
1160   if (monitors_used == 0) {  // empty list is easy
1161     return false;
1162   }
1163   if (NoAsyncDeflationProgressMax != 0 &&
1164       _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1165     float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1166     size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1167     ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1168     log_info(monitorinflation)("Too many deflations without progress; "
1169                                "bumping in_use_list_ceiling from " SIZE_FORMAT
1170                                " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1171     _no_progress_cnt = 0;
1172     ceiling = new_ceiling;
1173   }
1174 
1175   // Check if our monitor usage is above the threshold:
1176   size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1177   return int(monitor_usage) > MonitorUsedDeflationThreshold;
1178 }
1179 
1180 size_t ObjectSynchronizer::in_use_list_ceiling() {
1181   return _in_use_list_ceiling;
1182 }
1183 
1184 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1185   Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1186 }
1187 
1188 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1189   Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1190 }
1191 
1192 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1193   _in_use_list_ceiling = new_value;
1194 }
1195 
1196 bool ObjectSynchronizer::is_async_deflation_needed() {
1197   if (is_async_deflation_requested()) {
1198     // Async deflation request.
1199     return true;
1200   }
1201   if (AsyncDeflationInterval > 0 &&
1202       time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1203       monitors_used_above_threshold(&_in_use_list)) {
1204     // It's been longer than our specified deflate interval and there
1205     // are too many monitors in use. We don't deflate more frequently
1206     // than AsyncDeflationInterval (unless is_async_deflation_requested)
1207     // in order to not swamp the MonitorDeflationThread.
1208     return true;
1209   }
1210   return false;
1211 }
1212 
1213 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1214   JavaThread* current = JavaThread::current();
1215   bool ret_code = false;
1216 
1217   jlong last_time = last_async_deflation_time_ns();
1218   set_is_async_deflation_requested(true);
1219   {
1220     MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1221     ml.notify_all();
1222   }
1223   const int N_CHECKS = 5;
1224   for (int i = 0; i < N_CHECKS; i++) {  // sleep for at most 5 seconds
1225     if (last_async_deflation_time_ns() > last_time) {
1226       log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1227       ret_code = true;
1228       break;
1229     }
1230     {
1231       // JavaThread has to honor the blocking protocol.
1232       ThreadBlockInVM tbivm(current);
1233       os::naked_short_sleep(999);  // sleep for almost 1 second
1234     }
1235   }
1236   if (!ret_code) {
1237     log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1238   }
1239 
1240   return ret_code;
1241 }
1242 
1243 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1244   return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1245 }
1246 
1247 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1248                                        const oop obj,
1249                                        ObjectSynchronizer::InflateCause cause) {
1250   assert(event != NULL, "invariant");
1251   event->set_monitorClass(obj->klass());
1252   event->set_address((uintptr_t)(void*)obj);
1253   event->set_cause((u1)cause);
1254   event->commit();
1255 }
1256 
1257 // Fast path code shared by multiple functions
1258 void ObjectSynchronizer::inflate_helper(oop obj) {
1259   markWord mark = obj->mark_acquire();
1260   if (mark.has_monitor()) {
1261     ObjectMonitor* monitor = mark.monitor();
1262     markWord dmw = monitor->header();
1263     assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1264     return;
1265   }
1266   (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1267 }
1268 
1269 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1270                                            const InflateCause cause) {
1271   EventJavaMonitorInflate event;
1272 
1273   for (;;) {
1274     const markWord mark = object->mark_acquire();
1275 
1276     // The mark can be in one of the following states:
1277     // *  Inflated     - just return
1278     // *  Stack-locked - coerce it to inflated
1279     // *  INFLATING    - busy wait for conversion to complete
1280     // *  Neutral      - aggressively inflate the object.
1281 
1282     // CASE: inflated
1283     if (mark.has_monitor()) {
1284       ObjectMonitor* inf = mark.monitor();
1285       markWord dmw = inf->header();
1286       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1287       if (UseFastLocking && inf->is_owner_anonymous() && is_lock_owned(current, object)) {
1288         inf->set_owner_from_anonymous(current);
1289         assert(current->is_Java_thread(), "must be Java thread");
1290         reinterpret_cast<JavaThread*>(current)->lock_stack().remove(object);
1291       }
1292       return inf;
1293     }
1294 
1295     // CASE: inflation in progress - inflating over a stack-lock.
1296     // Some other thread is converting from stack-locked to inflated.
1297     // Only that thread can complete inflation -- other threads must wait.
1298     // The INFLATING value is transient.
1299     // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1300     // We could always eliminate polling by parking the thread on some auxiliary list.
1301     // NOTE: We need to check UseFastLocking here, because with fast-locking, the header
1302     // may legitimately be zero: cleared lock-bits and all upper header bits zero.
1303     // With fast-locking, the INFLATING protocol is not used.
1304     if (mark == markWord::INFLATING() && !UseFastLocking) {
1305       read_stable_mark(object);
1306       continue;
1307     }
1308 
1309     // CASE: stack-locked
1310     // Could be stack-locked either by this thread or by some other thread.
1311     //
1312     // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1313     // to install INFLATING into the mark word.  We originally installed INFLATING,
1314     // allocated the ObjectMonitor, and then finally STed the address of the
1315     // ObjectMonitor into the mark.  This was correct, but artificially lengthened
1316     // the interval in which INFLATING appeared in the mark, thus increasing
1317     // the odds of inflation contention.
1318 
1319     LogStreamHandle(Trace, monitorinflation) lsh;
1320     if (mark.is_fast_locked()) {
1321       assert(UseFastLocking, "can only happen with fast-locking");
1322       ObjectMonitor* monitor = new ObjectMonitor(object);
1323       monitor->set_header(mark.set_unlocked());
1324       bool own = is_lock_owned(current, object);
1325       if (own) {
1326         // Owned by us.
1327         monitor->set_owner_from(NULL, current);
1328       } else {
1329         // Owned by somebody else.
1330         monitor->set_owner_anonymous();
1331       }
1332       markWord monitor_mark = markWord::encode(monitor);
1333       markWord witness = object->cas_set_mark(monitor_mark, mark);
1334       if (witness == mark) {
1335         // Success! Return inflated monitor.
1336         if (own) {
1337           assert(current->is_Java_thread(), "must be: checked in is_lock_owned()");
1338           reinterpret_cast<JavaThread*>(current)->lock_stack().remove(object);
1339         }
1340         // Once the ObjectMonitor is configured and object is associated
1341         // with the ObjectMonitor, it is safe to allow async deflation:
1342         _in_use_list.add(monitor);
1343 
1344         // Hopefully the performance counters are allocated on distinct
1345         // cache lines to avoid false sharing on MP systems ...
1346         OM_PERFDATA_OP(Inflations, inc());
1347         if (log_is_enabled(Trace, monitorinflation)) {
1348           ResourceMark rm(current);
1349           lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1350                        INTPTR_FORMAT ", type='%s'", p2i(object),
1351                        object->mark().value(), object->klass()->external_name());
1352         }
1353         if (event.should_commit()) {
1354           post_monitor_inflate_event(&event, object, cause);
1355         }
1356         return monitor;
1357       } else {
1358         delete monitor;
1359         continue;
1360       }
1361     }
1362 
1363     if (mark.has_locker()) {
1364       assert(!UseFastLocking, "can not happen with fast-locking");
1365       ObjectMonitor* m = new ObjectMonitor(object);
1366       // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1367       // We do this before the CAS in order to minimize the length of time
1368       // in which INFLATING appears in the mark.
1369 
1370       markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1371       if (cmp != mark) {
1372         delete m;
1373         continue;       // Interference -- just retry
1374       }
1375 
1376       // We've successfully installed INFLATING (0) into the mark-word.
1377       // This is the only case where 0 will appear in a mark-word.
1378       // Only the singular thread that successfully swings the mark-word
1379       // to 0 can perform (or more precisely, complete) inflation.
1380       //
1381       // Why do we CAS a 0 into the mark-word instead of just CASing the
1382       // mark-word from the stack-locked value directly to the new inflated state?
1383       // Consider what happens when a thread unlocks a stack-locked object.
1384       // It attempts to use CAS to swing the displaced header value from the
1385       // on-stack BasicLock back into the object header.  Recall also that the
1386       // header value (hash code, etc) can reside in (a) the object header, or
1387       // (b) a displaced header associated with the stack-lock, or (c) a displaced
1388       // header in an ObjectMonitor.  The inflate() routine must copy the header
1389       // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1390       // the while preserving the hashCode stability invariants.  If the owner
1391       // decides to release the lock while the value is 0, the unlock will fail
1392       // and control will eventually pass from slow_exit() to inflate.  The owner
1393       // will then spin, waiting for the 0 value to disappear.   Put another way,
1394       // the 0 causes the owner to stall if the owner happens to try to
1395       // drop the lock (restoring the header from the BasicLock to the object)
1396       // while inflation is in-progress.  This protocol avoids races that might
1397       // would otherwise permit hashCode values to change or "flicker" for an object.
1398       // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1399       // 0 serves as a "BUSY" inflate-in-progress indicator.
1400 
1401 
1402       // fetch the displaced mark from the owner's stack.
1403       // The owner can't die or unwind past the lock while our INFLATING
1404       // object is in the mark.  Furthermore the owner can't complete
1405       // an unlock on the object, either.
1406       markWord dmw = mark.displaced_mark_helper();
1407       // Catch if the object's header is not neutral (not locked and
1408       // not marked is what we care about here).
1409       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1410 
1411       // Setup monitor fields to proper values -- prepare the monitor
1412       m->set_header(dmw);
1413 
1414       // Optimization: if the mark.locker stack address is associated
1415       // with this thread we could simply set m->_owner = current.
1416       // Note that a thread can inflate an object
1417       // that it has stack-locked -- as might happen in wait() -- directly
1418       // with CAS.  That is, we can avoid the xchg-NULL .... ST idiom.
1419       m->set_owner_from(NULL, mark.locker());
1420       // TODO-FIXME: assert BasicLock->dhw != 0.
1421 
1422       // Must preserve store ordering. The monitor state must
1423       // be stable at the time of publishing the monitor address.
1424       guarantee(object->mark() == markWord::INFLATING(), "invariant");
1425       // Release semantics so that above set_object() is seen first.
1426       object->release_set_mark(markWord::encode(m));
1427 
1428       // Once ObjectMonitor is configured and the object is associated
1429       // with the ObjectMonitor, it is safe to allow async deflation:
1430       _in_use_list.add(m);
1431 
1432       // Hopefully the performance counters are allocated on distinct cache lines
1433       // to avoid false sharing on MP systems ...
1434       OM_PERFDATA_OP(Inflations, inc());
1435       if (log_is_enabled(Trace, monitorinflation)) {
1436         ResourceMark rm(current);
1437         lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1438                      INTPTR_FORMAT ", type='%s'", p2i(object),
1439                      object->mark().value(), object->klass()->external_name());
1440       }
1441       if (event.should_commit()) {
1442         post_monitor_inflate_event(&event, object, cause);
1443       }
1444       return m;
1445     }
1446 
1447     // CASE: neutral
1448     // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1449     // If we know we're inflating for entry it's better to inflate by swinging a
1450     // pre-locked ObjectMonitor pointer into the object header.   A successful
1451     // CAS inflates the object *and* confers ownership to the inflating thread.
1452     // In the current implementation we use a 2-step mechanism where we CAS()
1453     // to inflate and then CAS() again to try to swing _owner from NULL to current.
1454     // An inflateTry() method that we could call from enter() would be useful.
1455 
1456     // Catch if the object's header is not neutral (not locked and
1457     // not marked is what we care about here).
1458     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1459     ObjectMonitor* m = new ObjectMonitor(object);
1460     // prepare m for installation - set monitor to initial state
1461     m->set_header(mark);
1462 
1463     if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1464       delete m;
1465       m = NULL;
1466       continue;
1467       // interference - the markword changed - just retry.
1468       // The state-transitions are one-way, so there's no chance of
1469       // live-lock -- "Inflated" is an absorbing state.
1470     }
1471 
1472     // Once the ObjectMonitor is configured and object is associated
1473     // with the ObjectMonitor, it is safe to allow async deflation:
1474     _in_use_list.add(m);
1475 
1476     // Hopefully the performance counters are allocated on distinct
1477     // cache lines to avoid false sharing on MP systems ...
1478     OM_PERFDATA_OP(Inflations, inc());
1479     if (log_is_enabled(Trace, monitorinflation)) {
1480       ResourceMark rm(current);
1481       lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1482                    INTPTR_FORMAT ", type='%s'", p2i(object),
1483                    object->mark().value(), object->klass()->external_name());
1484     }
1485     if (event.should_commit()) {
1486       post_monitor_inflate_event(&event, object, cause);
1487     }
1488     return m;
1489   }
1490 }
1491 
1492 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1493                                            const char* cnt_name, size_t cnt,
1494                                            LogStream* ls, elapsedTimer* timer_p) {
1495   if (!SafepointMechanism::should_process(current)) {
1496     return;
1497   }
1498 
1499   // A safepoint/handshake has started.
1500   if (ls != NULL) {
1501     timer_p->stop();
1502     ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1503                  SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1504                  op_name, cnt_name, cnt, in_use_list_ceiling(),
1505                  _in_use_list.count(), _in_use_list.max());
1506   }
1507 
1508   {
1509     // Honor block request.
1510     ThreadBlockInVM tbivm(current);
1511   }
1512 
1513   if (ls != NULL) {
1514     ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1515                  ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1516                  in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1517     timer_p->start();
1518   }
1519 }
1520 
1521 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1522 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1523 //
1524 // If table != nullptr, we gather owned ObjectMonitors indexed by the
1525 // owner in the table. Please note that ObjectMonitors where the owner
1526 // is set to a stack lock address are NOT associated with the JavaThread
1527 // that holds that stack lock. All of the current consumers of
1528 // ObjectMonitorsHashtable info only care about JNI locked monitors and
1529 // those do not have the owner set to a stack lock address.
1530 //
1531 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1532                                                 elapsedTimer* timer_p,
1533                                                 ObjectMonitorsHashtable* table) {
1534   MonitorList::Iterator iter = _in_use_list.iterator();
1535   size_t deflated_count = 0;
1536 
1537   while (iter.has_next()) {
1538     if (deflated_count >= (size_t)MonitorDeflationMax) {
1539       break;
1540     }
1541     ObjectMonitor* mid = iter.next();
1542     if (mid->deflate_monitor()) {
1543       deflated_count++;
1544     } else if (table != nullptr) {
1545       // The caller is interested in the owned ObjectMonitors. This does
1546       // not include when owner is set to a stack lock address in thread.
1547       // This also does not capture unowned ObjectMonitors that cannot be
1548       // deflated because of a waiter.
1549       void* key = mid->owner();
1550       // Since deflate_idle_monitors() and deflate_monitor_list() can be
1551       // called more than once, we have to make sure the entry has not
1552       // already been added.
1553       if (key != nullptr && !table->has_entry(key, mid)) {
1554         table->add_entry(key, mid);
1555       }
1556     }
1557 
1558     if (current->is_Java_thread()) {
1559       // A JavaThread must check for a safepoint/handshake and honor it.
1560       chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1561                         deflated_count, ls, timer_p);
1562     }
1563   }
1564 
1565   return deflated_count;
1566 }
1567 
1568 class HandshakeForDeflation : public HandshakeClosure {
1569  public:
1570   HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1571 
1572   void do_thread(Thread* thread) {
1573     log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1574                                 INTPTR_FORMAT, p2i(thread));
1575   }
1576 };
1577 
1578 class VM_RendezvousGCThreads : public VM_Operation {
1579 public:
1580   bool evaluate_at_safepoint() const override { return false; }
1581   VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1582   void doit() override {
1583     SuspendibleThreadSet::synchronize();
1584     SuspendibleThreadSet::desynchronize();
1585   };
1586 };
1587 
1588 // This function is called by the MonitorDeflationThread to deflate
1589 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1590 // and VM_ThreadDump::doit() by the VMThread.
1591 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) {
1592   Thread* current = Thread::current();
1593   if (current->is_Java_thread()) {
1594     // The async deflation request has been processed.
1595     _last_async_deflation_time_ns = os::javaTimeNanos();
1596     set_is_async_deflation_requested(false);
1597   }
1598 
1599   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1600   LogStreamHandle(Info, monitorinflation) lsh_info;
1601   LogStream* ls = NULL;
1602   if (log_is_enabled(Debug, monitorinflation)) {
1603     ls = &lsh_debug;
1604   } else if (log_is_enabled(Info, monitorinflation)) {
1605     ls = &lsh_info;
1606   }
1607 
1608   elapsedTimer timer;
1609   if (ls != NULL) {
1610     ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1611                  in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1612     timer.start();
1613   }
1614 
1615   // Deflate some idle ObjectMonitors.
1616   size_t deflated_count = deflate_monitor_list(current, ls, &timer, table);
1617   size_t unlinked_count = 0;
1618   size_t deleted_count = 0;
1619   if (deflated_count > 0 || is_final_audit()) {
1620     // There are ObjectMonitors that have been deflated or this is the
1621     // final audit and all the remaining ObjectMonitors have been
1622     // deflated, BUT the MonitorDeflationThread blocked for the final
1623     // safepoint during unlinking.
1624 
1625     // Unlink deflated ObjectMonitors from the in-use list.
1626     ResourceMark rm;
1627     GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1628     unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, &delete_list);
1629     if (current->is_Java_thread()) {
1630       if (ls != NULL) {
1631         timer.stop();
1632         ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1633                      ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1634                      SIZE_FORMAT ", max=" SIZE_FORMAT,
1635                      unlinked_count, in_use_list_ceiling(),
1636                      _in_use_list.count(), _in_use_list.max());
1637       }
1638 
1639       // A JavaThread needs to handshake in order to safely free the
1640       // ObjectMonitors that were deflated in this cycle.
1641       // Also, we sync and desync GC threads around the handshake, so that they can
1642       // safely read the mark-word and look-through to the object-monitor, without
1643       // being afraid that the object-monitor is going away.
1644       HandshakeForDeflation hfd_hc;
1645       Handshake::execute(&hfd_hc);
1646       VM_RendezvousGCThreads sync_gc;
1647       VMThread::execute(&sync_gc);
1648 
1649       if (ls != NULL) {
1650         ls->print_cr("after handshaking: in_use_list stats: ceiling="
1651                      SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1652                      in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1653         timer.start();
1654       }
1655     }
1656 
1657     // After the handshake, safely free the ObjectMonitors that were
1658     // deflated in this cycle.
1659     for (ObjectMonitor* monitor: delete_list) {
1660       delete monitor;
1661       deleted_count++;
1662 
1663       if (current->is_Java_thread()) {
1664         // A JavaThread must check for a safepoint/handshake and honor it.
1665         chk_for_block_req(JavaThread::cast(current), "deletion", "deleted_count",
1666                           deleted_count, ls, &timer);
1667       }
1668     }
1669     assert(unlinked_count == deleted_count, "must be");
1670   }
1671 
1672   if (ls != NULL) {
1673     timer.stop();
1674     if (deflated_count != 0 || unlinked_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1675       ls->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1676                    deflated_count, unlinked_count, timer.seconds());
1677     }
1678     ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1679                  in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1680     if (table != nullptr) {
1681       ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT,
1682                    table->key_count(), table->om_count());
1683     }
1684   }
1685 
1686   OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1687   OM_PERFDATA_OP(Deflations, inc(deflated_count));
1688 
1689   GVars.stw_random = os::random();
1690 
1691   if (deflated_count != 0) {
1692     _no_progress_cnt = 0;
1693   } else {
1694     _no_progress_cnt++;
1695   }
1696 
1697   return deflated_count;
1698 }
1699 
1700 // Monitor cleanup on JavaThread::exit
1701 
1702 // Iterate through monitor cache and attempt to release thread's monitors
1703 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1704  private:
1705   JavaThread* _thread;
1706 
1707  public:
1708   ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1709   void do_monitor(ObjectMonitor* mid) {
1710     intx rec = mid->complete_exit(_thread);
1711     _thread->dec_held_monitor_count(rec + 1);
1712   }
1713 };
1714 
1715 // Release all inflated monitors owned by current thread.  Lightweight monitors are
1716 // ignored.  This is meant to be called during JNI thread detach which assumes
1717 // all remaining monitors are heavyweight.  All exceptions are swallowed.
1718 // Scanning the extant monitor list can be time consuming.
1719 // A simple optimization is to add a per-thread flag that indicates a thread
1720 // called jni_monitorenter() during its lifetime.
1721 //
1722 // Instead of NoSafepointVerifier it might be cheaper to
1723 // use an idiom of the form:
1724 //   auto int tmp = SafepointSynchronize::_safepoint_counter ;
1725 //   <code that must not run at safepoint>
1726 //   guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1727 // Since the tests are extremely cheap we could leave them enabled
1728 // for normal product builds.
1729 
1730 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1731   assert(current == JavaThread::current(), "must be current Java thread");
1732   NoSafepointVerifier nsv;
1733   ReleaseJavaMonitorsClosure rjmc(current);
1734   ObjectSynchronizer::monitors_iterate(&rjmc, current);
1735   assert(!current->has_pending_exception(), "Should not be possible");
1736   current->clear_pending_exception();
1737   assert(current->held_monitor_count() == 0, "Should not be possible");
1738   // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1739   current->clear_jni_monitor_count();
1740 }
1741 
1742 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1743   switch (cause) {
1744     case inflate_cause_vm_internal:    return "VM Internal";
1745     case inflate_cause_monitor_enter:  return "Monitor Enter";
1746     case inflate_cause_wait:           return "Monitor Wait";
1747     case inflate_cause_notify:         return "Monitor Notify";
1748     case inflate_cause_hash_code:      return "Monitor Hash Code";
1749     case inflate_cause_jni_enter:      return "JNI Monitor Enter";
1750     case inflate_cause_jni_exit:       return "JNI Monitor Exit";
1751     default:
1752       ShouldNotReachHere();
1753   }
1754   return "Unknown";
1755 }
1756 
1757 //------------------------------------------------------------------------------
1758 // Debugging code
1759 
1760 u_char* ObjectSynchronizer::get_gvars_addr() {
1761   return (u_char*)&GVars;
1762 }
1763 
1764 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1765   return (u_char*)&GVars.hc_sequence;
1766 }
1767 
1768 size_t ObjectSynchronizer::get_gvars_size() {
1769   return sizeof(SharedGlobals);
1770 }
1771 
1772 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1773   return (u_char*)&GVars.stw_random;
1774 }
1775 
1776 // Do the final audit and print of ObjectMonitor stats; must be done
1777 // by the VMThread at VM exit time.
1778 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1779   assert(Thread::current()->is_VM_thread(), "sanity check");
1780 
1781   if (is_final_audit()) {  // Only do the audit once.
1782     return;
1783   }
1784   set_is_final_audit();
1785   log_info(monitorinflation)("Starting the final audit.");
1786 
1787   if (log_is_enabled(Info, monitorinflation)) {
1788     // Do deflations in order to reduce the in-use monitor population
1789     // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1790     // which is called by ObjectSynchronizer::audit_and_print_stats().
1791     while (deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) > 0) {
1792       ; // empty
1793     }
1794     // The other audit_and_print_stats() call is done at the Debug
1795     // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
1796     audit_and_print_stats(true /* on_exit */);
1797   }
1798 }
1799 
1800 // This function can be called at a safepoint or it can be called when
1801 // we are trying to exit the VM. When we are trying to exit the VM, the
1802 // list walker functions can run in parallel with the other list
1803 // operations so spin-locking is used for safety.
1804 //
1805 // Calls to this function can be added in various places as a debugging
1806 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1807 // details logged at the Info level and 'false' for the 'on_exit'
1808 // parameter to have in-use monitor details logged at the Trace level.
1809 //
1810 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1811   assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1812 
1813   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1814   LogStreamHandle(Info, monitorinflation) lsh_info;
1815   LogStreamHandle(Trace, monitorinflation) lsh_trace;
1816   LogStream* ls = NULL;
1817   if (log_is_enabled(Trace, monitorinflation)) {
1818     ls = &lsh_trace;
1819   } else if (log_is_enabled(Debug, monitorinflation)) {
1820     ls = &lsh_debug;
1821   } else if (log_is_enabled(Info, monitorinflation)) {
1822     ls = &lsh_info;
1823   }
1824   assert(ls != NULL, "sanity check");
1825 
1826   int error_cnt = 0;
1827 
1828   ls->print_cr("Checking in_use_list:");
1829   chk_in_use_list(ls, &error_cnt);
1830 
1831   if (error_cnt == 0) {
1832     ls->print_cr("No errors found in in_use_list checks.");
1833   } else {
1834     log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1835   }
1836 
1837   if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1838       (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1839     // When exiting this log output is at the Info level. When called
1840     // at a safepoint, this log output is at the Trace level since
1841     // there can be a lot of it.
1842     log_in_use_monitor_details(ls);
1843   }
1844 
1845   ls->flush();
1846 
1847   guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1848 }
1849 
1850 // Check the in_use_list; log the results of the checks.
1851 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1852   size_t l_in_use_count = _in_use_list.count();
1853   size_t l_in_use_max = _in_use_list.max();
1854   out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1855                 l_in_use_max);
1856 
1857   size_t ck_in_use_count = 0;
1858   MonitorList::Iterator iter = _in_use_list.iterator();
1859   while (iter.has_next()) {
1860     ObjectMonitor* mid = iter.next();
1861     chk_in_use_entry(mid, out, error_cnt_p);
1862     ck_in_use_count++;
1863   }
1864 
1865   if (l_in_use_count == ck_in_use_count) {
1866     out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1867                   SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1868   } else {
1869     out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1870                   "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1871                   ck_in_use_count);
1872   }
1873 
1874   size_t ck_in_use_max = _in_use_list.max();
1875   if (l_in_use_max == ck_in_use_max) {
1876     out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1877                   SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1878   } else {
1879     out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1880                   "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1881   }
1882 }
1883 
1884 // Check an in-use monitor entry; log any errors.
1885 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1886                                           int* error_cnt_p) {
1887   if (n->owner_is_DEFLATER_MARKER()) {
1888     // This should not happen, but if it does, it is not fatal.
1889     out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1890                   "deflated.", p2i(n));
1891     return;
1892   }
1893   if (n->header().value() == 0) {
1894     out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1895                   "have non-NULL _header field.", p2i(n));
1896     *error_cnt_p = *error_cnt_p + 1;
1897   }
1898   const oop obj = n->object_peek();
1899   if (obj != NULL) {
1900     const markWord mark = obj->mark();
1901     if (!mark.has_monitor()) {
1902       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1903                     "object does not think it has a monitor: obj="
1904                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1905                     p2i(obj), mark.value());
1906       *error_cnt_p = *error_cnt_p + 1;
1907     }
1908     ObjectMonitor* const obj_mon = mark.monitor();
1909     if (n != obj_mon) {
1910       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1911                     "object does not refer to the same monitor: obj="
1912                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1913                     INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1914       *error_cnt_p = *error_cnt_p + 1;
1915     }
1916   }
1917 }
1918 
1919 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1920 // flags indicate why the entry is in-use, 'object' and 'object type'
1921 // indicate the associated object and its type.
1922 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
1923   stringStream ss;
1924   if (_in_use_list.count() > 0) {
1925     out->print_cr("In-use monitor info:");
1926     out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1927     out->print_cr("%18s  %s  %18s  %18s",
1928                   "monitor", "BHL", "object", "object type");
1929     out->print_cr("==================  ===  ==================  ==================");
1930     MonitorList::Iterator iter = _in_use_list.iterator();
1931     while (iter.has_next()) {
1932       ObjectMonitor* mid = iter.next();
1933       const oop obj = mid->object_peek();
1934       const markWord mark = mid->header();
1935       ResourceMark rm;
1936       out->print(INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT "  %s", p2i(mid),
1937                  mid->is_busy(), mark.hash() != 0, mid->owner() != NULL,
1938                  p2i(obj), obj == NULL ? "" : obj->klass()->external_name());
1939       if (mid->is_busy()) {
1940         out->print(" (%s)", mid->is_busy_to_string(&ss));
1941         ss.reset();
1942       }
1943       out->cr();
1944     }
1945   }
1946 
1947   out->flush();
1948 }