1 /*
   2  * Copyright (c) 1998, 2025, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "classfile/vmSymbols.hpp"
  26 #include "gc/shared/collectedHeap.hpp"
  27 #include "jfr/jfrEvents.hpp"
  28 #include "logging/log.hpp"
  29 #include "logging/logStream.hpp"
  30 #include "memory/allocation.inline.hpp"
  31 #include "memory/padded.hpp"
  32 #include "memory/resourceArea.hpp"
  33 #include "memory/universe.hpp"
  34 #include "oops/markWord.hpp"
  35 #include "oops/oop.inline.hpp"
  36 #include "runtime/atomicAccess.hpp"
  37 #include "runtime/basicLock.inline.hpp"
  38 #include "runtime/frame.inline.hpp"
  39 #include "runtime/globals.hpp"
  40 #include "runtime/handles.inline.hpp"
  41 #include "runtime/handshake.hpp"
  42 #include "runtime/interfaceSupport.inline.hpp"
  43 #include "runtime/javaThread.hpp"
  44 #include "runtime/lightweightSynchronizer.hpp"
  45 #include "runtime/lockStack.inline.hpp"
  46 #include "runtime/mutexLocker.hpp"
  47 #include "runtime/objectMonitor.inline.hpp"
  48 #include "runtime/os.inline.hpp"
  49 #include "runtime/osThread.hpp"
  50 #include "runtime/safepointMechanism.inline.hpp"
  51 #include "runtime/safepointVerifiers.hpp"
  52 #include "runtime/sharedRuntime.hpp"
  53 #include "runtime/stubRoutines.hpp"
  54 #include "runtime/synchronizer.inline.hpp"
  55 #include "runtime/threads.hpp"
  56 #include "runtime/timer.hpp"
  57 #include "runtime/trimNativeHeap.hpp"
  58 #include "runtime/vframe.hpp"
  59 #include "runtime/vmThread.hpp"
  60 #include "utilities/align.hpp"
  61 #include "utilities/dtrace.hpp"
  62 #include "utilities/events.hpp"
  63 #include "utilities/globalCounter.inline.hpp"
  64 #include "utilities/globalDefinitions.hpp"
  65 #include "utilities/linkedlist.hpp"
  66 #include "utilities/preserveException.hpp"
  67 
  68 class ObjectMonitorDeflationLogging;
  69 
  70 void MonitorList::add(ObjectMonitor* m) {
  71   ObjectMonitor* head;
  72   do {
  73     head = AtomicAccess::load(&_head);
  74     m->set_next_om(head);
  75   } while (AtomicAccess::cmpxchg(&_head, head, m) != head);
  76 
  77   size_t count = AtomicAccess::add(&_count, 1u, memory_order_relaxed);
  78   size_t old_max;
  79   do {
  80     old_max = AtomicAccess::load(&_max);
  81     if (count <= old_max) {
  82       break;
  83     }
  84   } while (AtomicAccess::cmpxchg(&_max, old_max, count, memory_order_relaxed) != old_max);
  85 }
  86 
  87 size_t MonitorList::count() const {
  88   return AtomicAccess::load(&_count);
  89 }
  90 
  91 size_t MonitorList::max() const {
  92   return AtomicAccess::load(&_max);
  93 }
  94 
  95 class ObjectMonitorDeflationSafepointer : public StackObj {
  96   JavaThread* const                    _current;
  97   ObjectMonitorDeflationLogging* const _log;
  98 
  99 public:
 100   ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
 101     : _current(current), _log(log) {}
 102 
 103   void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
 104 };
 105 
 106 // Walk the in-use list and unlink deflated ObjectMonitors.
 107 // Returns the number of unlinked ObjectMonitors.
 108 size_t MonitorList::unlink_deflated(size_t deflated_count,
 109                                     GrowableArray<ObjectMonitor*>* unlinked_list,
 110                                     ObjectMonitorDeflationSafepointer* safepointer) {
 111   size_t unlinked_count = 0;
 112   ObjectMonitor* prev = nullptr;
 113   ObjectMonitor* m = AtomicAccess::load_acquire(&_head);
 114 
 115   while (m != nullptr) {
 116     if (m->is_being_async_deflated()) {
 117       // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
 118       // modify the list once per batch. The batch starts at "m".
 119       size_t unlinked_batch = 0;
 120       ObjectMonitor* next = m;
 121       // Look for at most MonitorUnlinkBatch monitors, or the number of
 122       // deflated and not unlinked monitors, whatever comes first.
 123       assert(deflated_count >= unlinked_count, "Sanity: underflow");
 124       size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
 125       do {
 126         ObjectMonitor* next_next = next->next_om();
 127         unlinked_batch++;
 128         unlinked_list->append(next);
 129         next = next_next;
 130         if (unlinked_batch >= unlinked_batch_limit) {
 131           // Reached the max batch, so bail out of the gathering loop.
 132           break;
 133         }
 134         if (prev == nullptr && AtomicAccess::load(&_head) != m) {
 135           // Current batch used to be at head, but it is not at head anymore.
 136           // Bail out and figure out where we currently are. This avoids long
 137           // walks searching for new prev during unlink under heavy list inserts.
 138           break;
 139         }
 140       } while (next != nullptr && next->is_being_async_deflated());
 141 
 142       // Unlink the found batch.
 143       if (prev == nullptr) {
 144         // The current batch is the first batch, so there is a chance that it starts at head.
 145         // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
 146         ObjectMonitor* prev_head = AtomicAccess::cmpxchg(&_head, m, next);
 147         if (prev_head != m) {
 148           // Something must have updated the head. Figure out the actual prev for this batch.
 149           for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
 150             prev = n;
 151           }
 152           assert(prev != nullptr, "Should have found the prev for the current batch");
 153           prev->set_next_om(next);
 154         }
 155       } else {
 156         // The current batch is preceded by another batch. This guarantees the current batch
 157         // does not start at head. Unlink the entire current batch without updating the head.
 158         assert(AtomicAccess::load(&_head) != m, "Sanity");
 159         prev->set_next_om(next);
 160       }
 161 
 162       unlinked_count += unlinked_batch;
 163       if (unlinked_count >= deflated_count) {
 164         // Reached the max so bail out of the searching loop.
 165         // There should be no more deflated monitors left.
 166         break;
 167       }
 168       m = next;
 169     } else {
 170       prev = m;
 171       m = m->next_om();
 172     }
 173 
 174     // Must check for a safepoint/handshake and honor it.
 175     safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
 176   }
 177 
 178 #ifdef ASSERT
 179   // Invariant: the code above should unlink all deflated monitors.
 180   // The code that runs after this unlinking does not expect deflated monitors.
 181   // Notably, attempting to deflate the already deflated monitor would break.
 182   {
 183     ObjectMonitor* m = AtomicAccess::load_acquire(&_head);
 184     while (m != nullptr) {
 185       assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
 186       m = m->next_om();
 187     }
 188   }
 189 #endif
 190 
 191   AtomicAccess::sub(&_count, unlinked_count);
 192   return unlinked_count;
 193 }
 194 
 195 MonitorList::Iterator MonitorList::iterator() const {
 196   return Iterator(AtomicAccess::load_acquire(&_head));
 197 }
 198 
 199 ObjectMonitor* MonitorList::Iterator::next() {
 200   ObjectMonitor* current = _current;
 201   _current = current->next_om();
 202   return current;
 203 }
 204 
 205 // The "core" versions of monitor enter and exit reside in this file.
 206 // The interpreter and compilers contain specialized transliterated
 207 // variants of the enter-exit fast-path operations.  See c2_MacroAssembler_x86.cpp
 208 // fast_lock(...) for instance.  If you make changes here, make sure to modify the
 209 // interpreter, and both C1 and C2 fast-path inline locking code emission.
 210 //
 211 // -----------------------------------------------------------------------------
 212 
 213 #ifdef DTRACE_ENABLED
 214 
 215 // Only bother with this argument setup if dtrace is available
 216 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
 217 
 218 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
 219   char* bytes = nullptr;                                                      \
 220   int len = 0;                                                             \
 221   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
 222   Symbol* klassname = obj->klass()->name();                                \
 223   if (klassname != nullptr) {                                                 \
 224     bytes = (char*)klassname->bytes();                                     \
 225     len = klassname->utf8_length();                                        \
 226   }
 227 
 228 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
 229   {                                                                        \
 230     if (DTraceMonitorProbes) {                                             \
 231       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 232       HOTSPOT_MONITOR_WAIT(jtid,                                           \
 233                            (uintptr_t)(monitor), bytes, len, (millis));    \
 234     }                                                                      \
 235   }
 236 
 237 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
 238 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
 239 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
 240 
 241 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
 242   {                                                                        \
 243     if (DTraceMonitorProbes) {                                             \
 244       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 245       HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */             \
 246                                     (uintptr_t)(monitor), bytes, len);     \
 247     }                                                                      \
 248   }
 249 
 250 #else //  ndef DTRACE_ENABLED
 251 
 252 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 253 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 254 
 255 #endif // ndef DTRACE_ENABLED
 256 
 257 // This exists only as a workaround of dtrace bug 6254741
 258 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
 259   DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
 260   return 0;
 261 }
 262 
 263 static constexpr size_t inflation_lock_count() {
 264   return 256;
 265 }
 266 
 267 // Static storage for an array of PlatformMutex.
 268 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
 269 
 270 static inline PlatformMutex* inflation_lock(size_t index) {
 271   return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
 272 }
 273 
 274 void ObjectSynchronizer::initialize() {
 275   for (size_t i = 0; i < inflation_lock_count(); i++) {
 276     ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
 277   }
 278   // Start the ceiling with the estimate for one thread.
 279   set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
 280 
 281   // Start the timer for deflations, so it does not trigger immediately.
 282   _last_async_deflation_time_ns = os::javaTimeNanos();
 283 
 284   LightweightSynchronizer::initialize();
 285 }
 286 
 287 MonitorList ObjectSynchronizer::_in_use_list;
 288 // monitors_used_above_threshold() policy is as follows:
 289 //
 290 // The ratio of the current _in_use_list count to the ceiling is used
 291 // to determine if we are above MonitorUsedDeflationThreshold and need
 292 // to do an async monitor deflation cycle. The ceiling is increased by
 293 // AvgMonitorsPerThreadEstimate when a thread is added to the system
 294 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
 295 // removed from the system.
 296 //
 297 // Note: If the _in_use_list max exceeds the ceiling, then
 298 // monitors_used_above_threshold() will use the in_use_list max instead
 299 // of the thread count derived ceiling because we have used more
 300 // ObjectMonitors than the estimated average.
 301 //
 302 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
 303 // no-progress async monitor deflation cycles in a row, then the ceiling
 304 // is adjusted upwards by monitors_used_above_threshold().
 305 //
 306 // Start the ceiling with the estimate for one thread in initialize()
 307 // which is called after cmd line options are processed.
 308 static size_t _in_use_list_ceiling = 0;
 309 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
 310 bool volatile ObjectSynchronizer::_is_final_audit = false;
 311 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
 312 static uintx _no_progress_cnt = 0;
 313 static bool _no_progress_skip_increment = false;
 314 
 315 // =====================> Quick functions
 316 
 317 // The quick_* forms are special fast-path variants used to improve
 318 // performance.  In the simplest case, a "quick_*" implementation could
 319 // simply return false, in which case the caller will perform the necessary
 320 // state transitions and call the slow-path form.
 321 // The fast-path is designed to handle frequently arising cases in an efficient
 322 // manner and is just a degenerate "optimistic" variant of the slow-path.
 323 // returns true  -- to indicate the call was satisfied.
 324 // returns false -- to indicate the call needs the services of the slow-path.
 325 // A no-loitering ordinance is in effect for code in the quick_* family
 326 // operators: safepoints or indefinite blocking (blocking that might span a
 327 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
 328 // entry.
 329 //
 330 // Consider: An interesting optimization is to have the JIT recognize the
 331 // following common idiom:
 332 //   synchronized (someobj) { .... ; notify(); }
 333 // That is, we find a notify() or notifyAll() call that immediately precedes
 334 // the monitorexit operation.  In that case the JIT could fuse the operations
 335 // into a single notifyAndExit() runtime primitive.
 336 
 337 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
 338   assert(current->thread_state() == _thread_in_Java, "invariant");
 339   NoSafepointVerifier nsv;
 340   if (obj == nullptr) return false;  // slow-path for invalid obj
 341   const markWord mark = obj->mark();
 342 
 343   if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
 344     // Degenerate notify
 345     // fast-locked by caller so by definition the implied waitset is empty.
 346     return true;
 347   }
 348 
 349   if (mark.has_monitor()) {
 350     ObjectMonitor* const mon = read_monitor(current, obj, mark);
 351     if (mon == nullptr) {
 352       // Racing with inflation/deflation go slow path
 353       return false;
 354     }
 355     assert(mon->object() == oop(obj), "invariant");
 356     if (!mon->has_owner(current)) return false;  // slow-path for IMS exception
 357 
 358     if (mon->first_waiter() != nullptr) {
 359       // We have one or more waiters. Since this is an inflated monitor
 360       // that we own, we quickly notify them here and now, avoiding the slow-path.
 361       if (all) {
 362         mon->quick_notifyAll(current);
 363       } else {
 364         mon->quick_notify(current);
 365       }
 366     }
 367     return true;
 368   }
 369 
 370   // other IMS exception states take the slow-path
 371   return false;
 372 }
 373 
 374 // Handle notifications when synchronizing on value based classes
 375 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
 376   assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
 377   frame last_frame = locking_thread->last_frame();
 378   bool bcp_was_adjusted = false;
 379   // Don't decrement bcp if it points to the frame's first instruction.  This happens when
 380   // handle_sync_on_value_based_class() is called because of a synchronized method.  There
 381   // is no actual monitorenter instruction in the byte code in this case.
 382   if (last_frame.is_interpreted_frame() &&
 383       (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
 384     // adjust bcp to point back to monitorenter so that we print the correct line numbers
 385     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
 386     bcp_was_adjusted = true;
 387   }
 388 
 389   if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
 390     ResourceMark rm;
 391     stringStream ss;
 392     locking_thread->print_active_stack_on(&ss);
 393     char* base = (char*)strstr(ss.base(), "at");
 394     char* newline = (char*)strchr(ss.base(), '\n');
 395     if (newline != nullptr) {
 396       *newline = '\0';
 397     }
 398     fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
 399   } else {
 400     assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
 401     ResourceMark rm;
 402     Log(valuebasedclasses) vblog;
 403 
 404     vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
 405     if (locking_thread->has_last_Java_frame()) {
 406       LogStream info_stream(vblog.info());
 407       locking_thread->print_active_stack_on(&info_stream);
 408     } else {
 409       vblog.info("Cannot find the last Java frame");
 410     }
 411 
 412     EventSyncOnValueBasedClass event;
 413     if (event.should_commit()) {
 414       event.set_valueBasedClass(obj->klass());
 415       event.commit();
 416     }
 417   }
 418 
 419   if (bcp_was_adjusted) {
 420     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
 421   }
 422 }
 423 
 424 // -----------------------------------------------------------------------------
 425 // Monitor Enter/Exit
 426 
 427 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
 428   // When called with locking_thread != Thread::current() some mechanism must synchronize
 429   // the locking_thread with respect to the current thread. Currently only used when
 430   // deoptimizing and re-locking locks. See Deoptimization::relock_objects
 431   assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
 432   return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
 433 }
 434 
 435 // -----------------------------------------------------------------------------
 436 // JNI locks on java objects
 437 // NOTE: must use heavy weight monitor to handle jni monitor enter
 438 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
 439   // Top native frames in the stack will not be seen if we attempt
 440   // preemption, since we start walking from the last Java anchor.
 441   NoPreemptMark npm(current);
 442 
 443   if (obj->klass()->is_value_based()) {
 444     handle_sync_on_value_based_class(obj, current);
 445   }
 446 
 447   // the current locking is from JNI instead of Java code
 448   current->set_current_pending_monitor_is_from_java(false);
 449   // An async deflation can race after the inflate() call and before
 450   // enter() can make the ObjectMonitor busy. enter() returns false if
 451   // we have lost the race to async deflation and we simply try again.
 452   while (true) {
 453     BasicLock lock;
 454     if (LightweightSynchronizer::inflate_and_enter(obj(), &lock, inflate_cause_jni_enter, current, current) != nullptr) {
 455       current->inc_held_monitor_count(1, true);
 456       break;
 457     }
 458   }
 459   current->set_current_pending_monitor_is_from_java(true);
 460 }
 461 
 462 // NOTE: must use heavy weight monitor to handle jni monitor exit
 463 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
 464   JavaThread* current = THREAD;
 465 
 466   ObjectMonitor* monitor;
 467   monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
 468   // If this thread has locked the object, exit the monitor. We
 469   // intentionally do not use CHECK on check_owner because we must exit the
 470   // monitor even if an exception was already pending.
 471   if (monitor->check_owner(THREAD)) {
 472     monitor->exit(current);
 473     current->dec_held_monitor_count(1, true);
 474   }
 475 }
 476 
 477 // -----------------------------------------------------------------------------
 478 // Internal VM locks on java objects
 479 // standard constructor, allows locking failures
 480 ObjectLocker::ObjectLocker(Handle obj, TRAPS) : _thread(THREAD), _obj(obj),
 481   _npm(_thread, _thread->at_preemptable_init() /* ignore_mark */), _skip_exit(false) {
 482   assert(!_thread->preempting(), "");
 483 
 484   _thread->check_for_valid_safepoint_state();
 485 
 486   if (_obj() != nullptr) {
 487     ObjectSynchronizer::enter(_obj, &_lock, _thread);
 488 
 489     if (_thread->preempting()) {
 490       // If preemption was cancelled we acquired the monitor after freezing
 491       // the frames. Redoing the vm call laterĀ in thaw will require us to
 492       // release it since the call should look like the original one. We
 493       // do it in ~ObjectLocker to reduce the window of time we hold the
 494       // monitor since we can't do anything useful with it now, and would
 495       // otherwise just force other vthreads to preempt in case they try
 496       // to acquire this monitor.
 497       _skip_exit = !_thread->preemption_cancelled();
 498       _thread->set_pending_preempted_exception();
 499     }
 500   }
 501 }
 502 
 503 ObjectLocker::~ObjectLocker() {
 504   if (_obj() != nullptr && !_skip_exit) {
 505     ObjectSynchronizer::exit(_obj(), &_lock, _thread);
 506   }
 507 }
 508 
 509 void ObjectLocker::wait_uninterruptibly(TRAPS) {
 510   ObjectSynchronizer::waitUninterruptibly(_obj, 0, _thread);
 511   if (_thread->preempting()) {
 512     _skip_exit = true;
 513     _thread->set_pending_preempted_exception();
 514   }
 515 }
 516 
 517 // -----------------------------------------------------------------------------
 518 //  Wait/Notify/NotifyAll
 519 // NOTE: must use heavy weight monitor to handle wait()
 520 
 521 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 522   JavaThread* current = THREAD;
 523   if (millis < 0) {
 524     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 525   }
 526 
 527   ObjectMonitor* monitor;
 528   monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
 529 
 530   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
 531   monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
 532 
 533   // This dummy call is in place to get around dtrace bug 6254741.  Once
 534   // that's fixed we can uncomment the following line, remove the call
 535   // and change this function back into a "void" func.
 536   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 537   int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
 538   return ret_code;
 539 }
 540 
 541 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
 542   assert(millis >= 0, "timeout value is negative");
 543 
 544   ObjectMonitor* monitor;
 545   monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
 546   monitor->wait(millis, false, THREAD);
 547 }
 548 
 549 
 550 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 551   JavaThread* current = THREAD;
 552 
 553   markWord mark = obj->mark();
 554   if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
 555     // Not inflated so there can't be any waiters to notify.
 556     return;
 557   }
 558   ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
 559   monitor->notify(CHECK);
 560 }
 561 
 562 // NOTE: see comment of notify()
 563 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 564   JavaThread* current = THREAD;
 565 
 566   markWord mark = obj->mark();
 567   if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
 568     // Not inflated so there can't be any waiters to notify.
 569     return;
 570   }
 571 
 572   ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
 573   monitor->notifyAll(CHECK);
 574 }
 575 
 576 // -----------------------------------------------------------------------------
 577 // Hash Code handling
 578 
 579 struct SharedGlobals {
 580   char         _pad_prefix[OM_CACHE_LINE_SIZE];
 581   // This is a highly shared mostly-read variable.
 582   // To avoid false-sharing it needs to be the sole occupant of a cache line.
 583   volatile int stw_random;
 584   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 585   // Hot RW variable -- Sequester to avoid false-sharing
 586   volatile int hc_sequence;
 587   DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 588 };
 589 
 590 static SharedGlobals GVars;
 591 
 592 // hashCode() generation :
 593 //
 594 // Possibilities:
 595 // * MD5Digest of {obj,stw_random}
 596 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
 597 // * A DES- or AES-style SBox[] mechanism
 598 // * One of the Phi-based schemes, such as:
 599 //   2654435761 = 2^32 * Phi (golden ratio)
 600 //   HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
 601 // * A variation of Marsaglia's shift-xor RNG scheme.
 602 // * (obj ^ stw_random) is appealing, but can result
 603 //   in undesirable regularity in the hashCode values of adjacent objects
 604 //   (objects allocated back-to-back, in particular).  This could potentially
 605 //   result in hashtable collisions and reduced hashtable efficiency.
 606 //   There are simple ways to "diffuse" the middle address bits over the
 607 //   generated hashCode values:
 608 
 609 static intptr_t get_next_hash(Thread* current, oop obj) {
 610   intptr_t value = 0;
 611   if (hashCode == 0) {
 612     // This form uses global Park-Miller RNG.
 613     // On MP system we'll have lots of RW access to a global, so the
 614     // mechanism induces lots of coherency traffic.
 615     value = os::random();
 616   } else if (hashCode == 1) {
 617     // This variation has the property of being stable (idempotent)
 618     // between STW operations.  This can be useful in some of the 1-0
 619     // synchronization schemes.
 620     intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
 621     value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
 622   } else if (hashCode == 2) {
 623     value = 1;            // for sensitivity testing
 624   } else if (hashCode == 3) {
 625     value = ++GVars.hc_sequence;
 626   } else if (hashCode == 4) {
 627     value = cast_from_oop<intptr_t>(obj);
 628   } else {
 629     // Marsaglia's xor-shift scheme with thread-specific state
 630     // This is probably the best overall implementation -- we'll
 631     // likely make this the default in future releases.
 632     unsigned t = current->_hashStateX;
 633     t ^= (t << 11);
 634     current->_hashStateX = current->_hashStateY;
 635     current->_hashStateY = current->_hashStateZ;
 636     current->_hashStateZ = current->_hashStateW;
 637     unsigned v = current->_hashStateW;
 638     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
 639     current->_hashStateW = v;
 640     value = v;
 641   }
 642 
 643   value &= markWord::hash_mask;
 644   if (value == 0) value = 0xBAD;
 645   assert(value != markWord::no_hash, "invariant");
 646   return value;
 647 }
 648 
 649 static intptr_t install_hash_code(Thread* current, oop obj) {
 650   assert(UseObjectMonitorTable, "must be");
 651 
 652   markWord mark = obj->mark_acquire();
 653   for (;;) {
 654     intptr_t hash = mark.hash();
 655     if (hash != 0) {
 656       return hash;
 657     }
 658 
 659     hash = get_next_hash(current, obj);
 660     const markWord old_mark = mark;
 661     const markWord new_mark = old_mark.copy_set_hash(hash);
 662 
 663     mark = obj->cas_set_mark(new_mark, old_mark);
 664     if (old_mark == mark) {
 665       return hash;
 666     }
 667   }
 668 }
 669 
 670 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
 671   if (UseObjectMonitorTable) {
 672     // Since the monitor isn't in the object header, the hash can simply be
 673     // installed in the object header.
 674     return install_hash_code(current, obj);
 675   }
 676 
 677   while (true) {
 678     ObjectMonitor* monitor = nullptr;
 679     markWord temp, test;
 680     intptr_t hash;
 681     markWord mark = obj->mark_acquire();
 682     if (mark.is_unlocked() || mark.is_fast_locked()) {
 683       hash = mark.hash();
 684       if (hash != 0) {                     // if it has a hash, just return it
 685         return hash;
 686       }
 687       hash = get_next_hash(current, obj);  // get a new hash
 688       temp = mark.copy_set_hash(hash);     // merge the hash into header
 689                                            // try to install the hash
 690       test = obj->cas_set_mark(temp, mark);
 691       if (test == mark) {                  // if the hash was installed, return it
 692         return hash;
 693       }
 694       // CAS failed, retry
 695       continue;
 696 
 697       // Failed to install the hash. It could be that another thread
 698       // installed the hash just before our attempt or inflation has
 699       // occurred or... so we fall thru to inflate the monitor for
 700       // stability and then install the hash.
 701     } else if (mark.has_monitor()) {
 702       monitor = mark.monitor();
 703       temp = monitor->header();
 704       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 705       hash = temp.hash();
 706       if (hash != 0) {
 707         // It has a hash.
 708 
 709         // Separate load of dmw/header above from the loads in
 710         // is_being_async_deflated().
 711 
 712         // dmw/header and _contentions may get written by different threads.
 713         // Make sure to observe them in the same order when having several observers.
 714         OrderAccess::loadload_for_IRIW();
 715 
 716         if (monitor->is_being_async_deflated()) {
 717           // But we can't safely use the hash if we detect that async
 718           // deflation has occurred. So we attempt to restore the
 719           // header/dmw to the object's header so that we only retry
 720           // once if the deflater thread happens to be slow.
 721           monitor->install_displaced_markword_in_object(obj);
 722           continue;
 723         }
 724         return hash;
 725       }
 726       // Fall thru so we only have one place that installs the hash in
 727       // the ObjectMonitor.
 728     }
 729 
 730     // NOTE: an async deflation can race after we get the monitor and
 731     // before we can update the ObjectMonitor's header with the hash
 732     // value below.
 733     assert(mark.has_monitor(), "must be");
 734     monitor = mark.monitor();
 735 
 736     // Load ObjectMonitor's header/dmw field and see if it has a hash.
 737     mark = monitor->header();
 738     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
 739     hash = mark.hash();
 740     if (hash == 0) {                       // if it does not have a hash
 741       hash = get_next_hash(current, obj);  // get a new hash
 742       temp = mark.copy_set_hash(hash)   ;  // merge the hash into header
 743       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 744       uintptr_t v = AtomicAccess::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
 745       test = markWord(v);
 746       if (test != mark) {
 747         // The attempt to update the ObjectMonitor's header/dmw field
 748         // did not work. This can happen if another thread managed to
 749         // merge in the hash just before our cmpxchg().
 750         // If we add any new usages of the header/dmw field, this code
 751         // will need to be updated.
 752         hash = test.hash();
 753         assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
 754         assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
 755       }
 756       if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
 757         // If we detect that async deflation has occurred, then we
 758         // attempt to restore the header/dmw to the object's header
 759         // so that we only retry once if the deflater thread happens
 760         // to be slow.
 761         monitor->install_displaced_markword_in_object(obj);
 762         continue;
 763       }
 764     }
 765     // We finally get the hash.
 766     return hash;
 767   }
 768 }
 769 
 770 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
 771                                                    Handle h_obj) {
 772   assert(current == JavaThread::current(), "Can only be called on current thread");
 773   oop obj = h_obj();
 774 
 775   markWord mark = obj->mark_acquire();
 776 
 777   if (mark.is_fast_locked()) {
 778     // fast-locking case, see if lock is in current's lock stack
 779     return current->lock_stack().contains(h_obj());
 780   }
 781 
 782   while (mark.has_monitor()) {
 783     ObjectMonitor* monitor = read_monitor(current, obj, mark);
 784     if (monitor != nullptr) {
 785       return monitor->is_entered(current) != 0;
 786     }
 787     // Racing with inflation/deflation, retry
 788     mark = obj->mark_acquire();
 789 
 790     if (mark.is_fast_locked()) {
 791       // Some other thread fast_locked, current could not have held the lock
 792       return false;
 793     }
 794   }
 795 
 796   // Unlocked case, header in place
 797   assert(mark.is_unlocked(), "sanity check");
 798   return false;
 799 }
 800 
 801 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
 802   oop obj = h_obj();
 803   markWord mark = obj->mark_acquire();
 804 
 805   if (mark.is_fast_locked()) {
 806     // fast-locked so get owner from the object.
 807     // owning_thread_from_object() may also return null here:
 808     return Threads::owning_thread_from_object(t_list, h_obj());
 809   }
 810 
 811   while (mark.has_monitor()) {
 812     ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
 813     if (monitor != nullptr) {
 814       return Threads::owning_thread_from_monitor(t_list, monitor);
 815     }
 816     // Racing with inflation/deflation, retry
 817     mark = obj->mark_acquire();
 818 
 819     if (mark.is_fast_locked()) {
 820       // Some other thread fast_locked
 821       return Threads::owning_thread_from_object(t_list, h_obj());
 822     }
 823   }
 824 
 825   // Unlocked case, header in place
 826   // Cannot have assertion since this object may have been
 827   // locked by another thread when reaching here.
 828   // assert(mark.is_unlocked(), "sanity check");
 829 
 830   return nullptr;
 831 }
 832 
 833 // Visitors ...
 834 
 835 // Iterate over all ObjectMonitors.
 836 template <typename Function>
 837 void ObjectSynchronizer::monitors_iterate(Function function) {
 838   MonitorList::Iterator iter = _in_use_list.iterator();
 839   while (iter.has_next()) {
 840     ObjectMonitor* monitor = iter.next();
 841     function(monitor);
 842   }
 843 }
 844 
 845 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
 846 // returns true.
 847 template <typename OwnerFilter>
 848 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
 849   monitors_iterate([&](ObjectMonitor* monitor) {
 850     // This function is only called at a safepoint or when the
 851     // target thread is suspended or when the target thread is
 852     // operating on itself. The current closures in use today are
 853     // only interested in an owned ObjectMonitor and ownership
 854     // cannot be dropped under the calling contexts so the
 855     // ObjectMonitor cannot be async deflated.
 856     if (monitor->has_owner() && filter(monitor)) {
 857       assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
 858 
 859       closure->do_monitor(monitor);
 860     }
 861   });
 862 }
 863 
 864 // Iterate ObjectMonitors where the owner == thread; this does NOT include
 865 // ObjectMonitors where owner is set to a stack-lock address in thread.
 866 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
 867   int64_t key = ObjectMonitor::owner_id_from(thread);
 868   auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
 869   return owned_monitors_iterate_filtered(closure, thread_filter);
 870 }
 871 
 872 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
 873   int64_t key = ObjectMonitor::owner_id_from(vthread);
 874   auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
 875   return owned_monitors_iterate_filtered(closure, thread_filter);
 876 }
 877 
 878 // Iterate ObjectMonitors owned by any thread.
 879 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
 880   auto all_filter = [&](ObjectMonitor* monitor) { return true; };
 881   return owned_monitors_iterate_filtered(closure, all_filter);
 882 }
 883 
 884 static bool monitors_used_above_threshold(MonitorList* list) {
 885   if (MonitorUsedDeflationThreshold == 0) {  // disabled case is easy
 886     return false;
 887   }
 888   size_t monitors_used = list->count();
 889   if (monitors_used == 0) {  // empty list is easy
 890     return false;
 891   }
 892   size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
 893   // Make sure that we use a ceiling value that is not lower than
 894   // previous, not lower than the recorded max used by the system, and
 895   // not lower than the current number of monitors in use (which can
 896   // race ahead of max). The result is guaranteed > 0.
 897   size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
 898 
 899   // Check if our monitor usage is above the threshold:
 900   size_t monitor_usage = (monitors_used * 100LL) / ceiling;
 901   if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
 902     // Deflate monitors if over the threshold percentage, unless no
 903     // progress on previous deflations.
 904     bool is_above_threshold = true;
 905 
 906     // Check if it's time to adjust the in_use_list_ceiling up, due
 907     // to too many async deflation attempts without any progress.
 908     if (NoAsyncDeflationProgressMax != 0 &&
 909         _no_progress_cnt >= NoAsyncDeflationProgressMax) {
 910       double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
 911       size_t delta = (size_t)(ceiling * remainder) + 1;
 912       size_t new_ceiling = (ceiling > SIZE_MAX - delta)
 913         ? SIZE_MAX         // Overflow, let's clamp new_ceiling.
 914         : ceiling + delta;
 915 
 916       ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
 917       log_info(monitorinflation)("Too many deflations without progress; "
 918                                  "bumping in_use_list_ceiling from %zu"
 919                                  " to %zu", old_ceiling, new_ceiling);
 920       _no_progress_cnt = 0;
 921       ceiling = new_ceiling;
 922 
 923       // Check if our monitor usage is still above the threshold:
 924       monitor_usage = (monitors_used * 100LL) / ceiling;
 925       is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
 926     }
 927     log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
 928                                ", monitor_usage=%zu, threshold=%d",
 929                                monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
 930     return is_above_threshold;
 931   }
 932 
 933   return false;
 934 }
 935 
 936 size_t ObjectSynchronizer::in_use_list_count() {
 937   return _in_use_list.count();
 938 }
 939 
 940 size_t ObjectSynchronizer::in_use_list_max() {
 941   return _in_use_list.max();
 942 }
 943 
 944 size_t ObjectSynchronizer::in_use_list_ceiling() {
 945   return _in_use_list_ceiling;
 946 }
 947 
 948 void ObjectSynchronizer::dec_in_use_list_ceiling() {
 949   AtomicAccess::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
 950 }
 951 
 952 void ObjectSynchronizer::inc_in_use_list_ceiling() {
 953   AtomicAccess::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
 954 }
 955 
 956 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
 957   _in_use_list_ceiling = new_value;
 958 }
 959 
 960 bool ObjectSynchronizer::is_async_deflation_needed() {
 961   if (is_async_deflation_requested()) {
 962     // Async deflation request.
 963     log_info(monitorinflation)("Async deflation needed: explicit request");
 964     return true;
 965   }
 966 
 967   jlong time_since_last = time_since_last_async_deflation_ms();
 968 
 969   if (AsyncDeflationInterval > 0 &&
 970       time_since_last > AsyncDeflationInterval &&
 971       monitors_used_above_threshold(&_in_use_list)) {
 972     // It's been longer than our specified deflate interval and there
 973     // are too many monitors in use. We don't deflate more frequently
 974     // than AsyncDeflationInterval (unless is_async_deflation_requested)
 975     // in order to not swamp the MonitorDeflationThread.
 976     log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
 977     return true;
 978   }
 979 
 980   if (GuaranteedAsyncDeflationInterval > 0 &&
 981       time_since_last > GuaranteedAsyncDeflationInterval) {
 982     // It's been longer than our specified guaranteed deflate interval.
 983     // We need to clean up the used monitors even if the threshold is
 984     // not reached, to keep the memory utilization at bay when many threads
 985     // touched many monitors.
 986     log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
 987                                "is greater than time since last deflation (" JLONG_FORMAT " ms)",
 988                                GuaranteedAsyncDeflationInterval, time_since_last);
 989 
 990     // If this deflation has no progress, then it should not affect the no-progress
 991     // tracking, otherwise threshold heuristics would think it was triggered, experienced
 992     // no progress, and needs to backoff more aggressively. In this "no progress" case,
 993     // the generic code would bump the no-progress counter, and we compensate for that
 994     // by telling it to skip the update.
 995     //
 996     // If this deflation has progress, then it should let non-progress tracking
 997     // know about this, otherwise the threshold heuristics would kick in, potentially
 998     // experience no-progress due to aggressive cleanup by this deflation, and think
 999     // it is still in no-progress stride. In this "progress" case, the generic code would
1000     // zero the counter, and we allow it to happen.
1001     _no_progress_skip_increment = true;
1002 
1003     return true;
1004   }
1005 
1006   return false;
1007 }
1008 
1009 void ObjectSynchronizer::request_deflate_idle_monitors() {
1010   MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1011   set_is_async_deflation_requested(true);
1012   ml.notify_all();
1013 }
1014 
1015 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1016   JavaThread* current = JavaThread::current();
1017   bool ret_code = false;
1018 
1019   jlong last_time = last_async_deflation_time_ns();
1020 
1021   request_deflate_idle_monitors();
1022 
1023   const int N_CHECKS = 5;
1024   for (int i = 0; i < N_CHECKS; i++) {  // sleep for at most 5 seconds
1025     if (last_async_deflation_time_ns() > last_time) {
1026       log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1027       ret_code = true;
1028       break;
1029     }
1030     {
1031       // JavaThread has to honor the blocking protocol.
1032       ThreadBlockInVM tbivm(current);
1033       os::naked_short_sleep(999);  // sleep for almost 1 second
1034     }
1035   }
1036   if (!ret_code) {
1037     log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1038   }
1039 
1040   return ret_code;
1041 }
1042 
1043 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1044   return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1045 }
1046 
1047 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1048 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1049 //
1050 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1051   MonitorList::Iterator iter = _in_use_list.iterator();
1052   size_t deflated_count = 0;
1053   Thread* current = Thread::current();
1054 
1055   while (iter.has_next()) {
1056     if (deflated_count >= (size_t)MonitorDeflationMax) {
1057       break;
1058     }
1059     ObjectMonitor* mid = iter.next();
1060     if (mid->deflate_monitor(current)) {
1061       deflated_count++;
1062     }
1063 
1064     // Must check for a safepoint/handshake and honor it.
1065     safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1066   }
1067 
1068   return deflated_count;
1069 }
1070 
1071 class DeflationHandshakeClosure : public HandshakeClosure {
1072  public:
1073   DeflationHandshakeClosure() : HandshakeClosure("DeflationHandshakeClosure") {}
1074 
1075   void do_thread(Thread* thread) {
1076     log_trace(monitorinflation)("DeflationHandshakeClosure::do_thread: thread="
1077                                 INTPTR_FORMAT, p2i(thread));
1078     if (thread->is_Java_thread()) {
1079       // Clear OM cache
1080       JavaThread* jt = JavaThread::cast(thread);
1081       jt->om_clear_monitor_cache();
1082     }
1083   }
1084 };
1085 
1086 class VM_RendezvousGCThreads : public VM_Operation {
1087 public:
1088   bool evaluate_at_safepoint() const override { return false; }
1089   VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1090   void doit() override {
1091     Universe::heap()->safepoint_synchronize_begin();
1092     Universe::heap()->safepoint_synchronize_end();
1093   };
1094 };
1095 
1096 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1097                               ObjectMonitorDeflationSafepointer* safepointer) {
1098   NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1099   size_t deleted_count = 0;
1100   for (ObjectMonitor* monitor: *delete_list) {
1101     delete monitor;
1102     deleted_count++;
1103     // A JavaThread must check for a safepoint/handshake and honor it.
1104     safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1105   }
1106   return deleted_count;
1107 }
1108 
1109 class ObjectMonitorDeflationLogging: public StackObj {
1110   LogStreamHandle(Debug, monitorinflation) _debug;
1111   LogStreamHandle(Info, monitorinflation)  _info;
1112   LogStream*                               _stream;
1113   elapsedTimer                             _timer;
1114 
1115   size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1116   size_t count() const   { return ObjectSynchronizer::in_use_list_count(); }
1117   size_t max() const     { return ObjectSynchronizer::in_use_list_max(); }
1118 
1119 public:
1120   ObjectMonitorDeflationLogging()
1121     : _debug(), _info(), _stream(nullptr) {
1122     if (_debug.is_enabled()) {
1123       _stream = &_debug;
1124     } else if (_info.is_enabled()) {
1125       _stream = &_info;
1126     }
1127   }
1128 
1129   void begin() {
1130     if (_stream != nullptr) {
1131       _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1132                         ceiling(), count(), max());
1133       _timer.start();
1134     }
1135   }
1136 
1137   void before_handshake(size_t unlinked_count) {
1138     if (_stream != nullptr) {
1139       _timer.stop();
1140       _stream->print_cr("before handshaking: unlinked_count=%zu"
1141                         ", in_use_list stats: ceiling=%zu, count="
1142                         "%zu, max=%zu",
1143                         unlinked_count, ceiling(), count(), max());
1144     }
1145   }
1146 
1147   void after_handshake() {
1148     if (_stream != nullptr) {
1149       _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1150                         "%zu, count=%zu, max=%zu",
1151                         ceiling(), count(), max());
1152       _timer.start();
1153     }
1154   }
1155 
1156   void end(size_t deflated_count, size_t unlinked_count) {
1157     if (_stream != nullptr) {
1158       _timer.stop();
1159       if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1160         _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1161                           deflated_count, unlinked_count, _timer.seconds());
1162       }
1163       _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1164                         ceiling(), count(), max());
1165     }
1166   }
1167 
1168   void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1169     if (_stream != nullptr) {
1170       _timer.stop();
1171       _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1172                         "%zu, count=%zu, max=%zu",
1173                         op_name, cnt_name, cnt, ceiling(), count(), max());
1174     }
1175   }
1176 
1177   void after_block_for_safepoint(const char* op_name) {
1178     if (_stream != nullptr) {
1179       _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1180                         ", count=%zu, max=%zu", op_name,
1181                         ceiling(), count(), max());
1182       _timer.start();
1183     }
1184   }
1185 };
1186 
1187 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1188   if (!SafepointMechanism::should_process(_current)) {
1189     return;
1190   }
1191 
1192   // A safepoint/handshake has started.
1193   _log->before_block_for_safepoint(op_name, count_name, counter);
1194 
1195   {
1196     // Honor block request.
1197     ThreadBlockInVM tbivm(_current);
1198   }
1199 
1200   _log->after_block_for_safepoint(op_name);
1201 }
1202 
1203 // This function is called by the MonitorDeflationThread to deflate
1204 // ObjectMonitors.
1205 size_t ObjectSynchronizer::deflate_idle_monitors() {
1206   JavaThread* current = JavaThread::current();
1207   assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1208 
1209   // The async deflation request has been processed.
1210   _last_async_deflation_time_ns = os::javaTimeNanos();
1211   set_is_async_deflation_requested(false);
1212 
1213   ObjectMonitorDeflationLogging log;
1214   ObjectMonitorDeflationSafepointer safepointer(current, &log);
1215 
1216   log.begin();
1217 
1218   // Deflate some idle ObjectMonitors.
1219   size_t deflated_count = deflate_monitor_list(&safepointer);
1220 
1221   // Unlink the deflated ObjectMonitors from the in-use list.
1222   size_t unlinked_count = 0;
1223   size_t deleted_count = 0;
1224   if (deflated_count > 0) {
1225     ResourceMark rm(current);
1226     GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1227     unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1228 
1229 #ifdef ASSERT
1230     if (UseObjectMonitorTable) {
1231       for (ObjectMonitor* monitor : delete_list) {
1232         assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1233       }
1234     }
1235 #endif
1236 
1237     log.before_handshake(unlinked_count);
1238 
1239     // A JavaThread needs to handshake in order to safely free the
1240     // ObjectMonitors that were deflated in this cycle.
1241     DeflationHandshakeClosure dhc;
1242     Handshake::execute(&dhc);
1243     // Also, we sync and desync GC threads around the handshake, so that they can
1244     // safely read the mark-word and look-through to the object-monitor, without
1245     // being afraid that the object-monitor is going away.
1246     VM_RendezvousGCThreads sync_gc;
1247     VMThread::execute(&sync_gc);
1248 
1249     log.after_handshake();
1250 
1251     // After the handshake, safely free the ObjectMonitors that were
1252     // deflated and unlinked in this cycle.
1253 
1254     // Delete the unlinked ObjectMonitors.
1255     deleted_count = delete_monitors(&delete_list, &safepointer);
1256     assert(unlinked_count == deleted_count, "must be");
1257   }
1258 
1259   log.end(deflated_count, unlinked_count);
1260 
1261   GVars.stw_random = os::random();
1262 
1263   if (deflated_count != 0) {
1264     _no_progress_cnt = 0;
1265   } else if (_no_progress_skip_increment) {
1266     _no_progress_skip_increment = false;
1267   } else {
1268     _no_progress_cnt++;
1269   }
1270 
1271   return deflated_count;
1272 }
1273 
1274 // Monitor cleanup on JavaThread::exit
1275 
1276 // Iterate through monitor cache and attempt to release thread's monitors
1277 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1278  private:
1279   JavaThread* _thread;
1280 
1281  public:
1282   ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1283   void do_monitor(ObjectMonitor* mid) {
1284     intx rec = mid->complete_exit(_thread);
1285     _thread->dec_held_monitor_count(rec + 1);
1286   }
1287 };
1288 
1289 // Release all inflated monitors owned by current thread.  Lightweight monitors are
1290 // ignored.  This is meant to be called during JNI thread detach which assumes
1291 // all remaining monitors are heavyweight.  All exceptions are swallowed.
1292 // Scanning the extant monitor list can be time consuming.
1293 // A simple optimization is to add a per-thread flag that indicates a thread
1294 // called jni_monitorenter() during its lifetime.
1295 //
1296 // Instead of NoSafepointVerifier it might be cheaper to
1297 // use an idiom of the form:
1298 //   auto int tmp = SafepointSynchronize::_safepoint_counter ;
1299 //   <code that must not run at safepoint>
1300 //   guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1301 // Since the tests are extremely cheap we could leave them enabled
1302 // for normal product builds.
1303 
1304 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1305   assert(current == JavaThread::current(), "must be current Java thread");
1306   NoSafepointVerifier nsv;
1307   ReleaseJavaMonitorsClosure rjmc(current);
1308   ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1309   assert(!current->has_pending_exception(), "Should not be possible");
1310   current->clear_pending_exception();
1311   assert(current->held_monitor_count() == 0, "Should not be possible");
1312   // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1313   current->clear_jni_monitor_count();
1314 }
1315 
1316 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1317   switch (cause) {
1318     case inflate_cause_vm_internal:    return "VM Internal";
1319     case inflate_cause_monitor_enter:  return "Monitor Enter";
1320     case inflate_cause_wait:           return "Monitor Wait";
1321     case inflate_cause_notify:         return "Monitor Notify";
1322     case inflate_cause_jni_enter:      return "JNI Monitor Enter";
1323     case inflate_cause_jni_exit:       return "JNI Monitor Exit";
1324     default:
1325       ShouldNotReachHere();
1326   }
1327   return "Unknown";
1328 }
1329 
1330 //------------------------------------------------------------------------------
1331 // Debugging code
1332 
1333 u_char* ObjectSynchronizer::get_gvars_addr() {
1334   return (u_char*)&GVars;
1335 }
1336 
1337 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1338   return (u_char*)&GVars.hc_sequence;
1339 }
1340 
1341 size_t ObjectSynchronizer::get_gvars_size() {
1342   return sizeof(SharedGlobals);
1343 }
1344 
1345 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1346   return (u_char*)&GVars.stw_random;
1347 }
1348 
1349 // Do the final audit and print of ObjectMonitor stats; must be done
1350 // by the VMThread at VM exit time.
1351 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1352   assert(Thread::current()->is_VM_thread(), "sanity check");
1353 
1354   if (is_final_audit()) {  // Only do the audit once.
1355     return;
1356   }
1357   set_is_final_audit();
1358   log_info(monitorinflation)("Starting the final audit.");
1359 
1360   if (log_is_enabled(Info, monitorinflation)) {
1361     LogStreamHandle(Info, monitorinflation) ls;
1362     audit_and_print_stats(&ls, true /* on_exit */);
1363   }
1364 }
1365 
1366 // This function can be called by the MonitorDeflationThread or it can be called when
1367 // we are trying to exit the VM. The list walker functions can run in parallel with
1368 // the other list operations.
1369 // Calls to this function can be added in various places as a debugging
1370 // aid.
1371 //
1372 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1373   int error_cnt = 0;
1374 
1375   ls->print_cr("Checking in_use_list:");
1376   chk_in_use_list(ls, &error_cnt);
1377 
1378   if (error_cnt == 0) {
1379     ls->print_cr("No errors found in in_use_list checks.");
1380   } else {
1381     log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1382   }
1383 
1384   // When exiting, only log the interesting entries at the Info level.
1385   // When called at intervals by the MonitorDeflationThread, log output
1386   // at the Trace level since there can be a lot of it.
1387   if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1388     LogStreamHandle(Trace, monitorinflation) ls_tr;
1389     log_in_use_monitor_details(&ls_tr, true /* log_all */);
1390   } else if (on_exit) {
1391     log_in_use_monitor_details(ls, false /* log_all */);
1392   }
1393 
1394   ls->flush();
1395 
1396   guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1397 }
1398 
1399 // Check the in_use_list; log the results of the checks.
1400 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1401   size_t l_in_use_count = _in_use_list.count();
1402   size_t l_in_use_max = _in_use_list.max();
1403   out->print_cr("count=%zu, max=%zu", l_in_use_count,
1404                 l_in_use_max);
1405 
1406   size_t ck_in_use_count = 0;
1407   MonitorList::Iterator iter = _in_use_list.iterator();
1408   while (iter.has_next()) {
1409     ObjectMonitor* mid = iter.next();
1410     chk_in_use_entry(mid, out, error_cnt_p);
1411     ck_in_use_count++;
1412   }
1413 
1414   if (l_in_use_count == ck_in_use_count) {
1415     out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
1416                   l_in_use_count, ck_in_use_count);
1417   } else {
1418     out->print_cr("WARNING: in_use_count=%zu is not equal to "
1419                   "ck_in_use_count=%zu", l_in_use_count,
1420                   ck_in_use_count);
1421   }
1422 
1423   size_t ck_in_use_max = _in_use_list.max();
1424   if (l_in_use_max == ck_in_use_max) {
1425     out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
1426                   l_in_use_max, ck_in_use_max);
1427   } else {
1428     out->print_cr("WARNING: in_use_max=%zu is not equal to "
1429                   "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
1430   }
1431 }
1432 
1433 // Check an in-use monitor entry; log any errors.
1434 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1435                                           int* error_cnt_p) {
1436   if (n->owner_is_DEFLATER_MARKER()) {
1437     // This could happen when monitor deflation blocks for a safepoint.
1438     return;
1439   }
1440 
1441 
1442   if (n->metadata() == 0) {
1443     out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1444                   "have non-null _metadata (header/hash) field.", p2i(n));
1445     *error_cnt_p = *error_cnt_p + 1;
1446   }
1447 
1448   const oop obj = n->object_peek();
1449   if (obj == nullptr) {
1450     return;
1451   }
1452 
1453   const markWord mark = obj->mark();
1454   if (!mark.has_monitor()) {
1455     out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1456                   "object does not think it has a monitor: obj="
1457                   INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1458                   p2i(obj), mark.value());
1459     *error_cnt_p = *error_cnt_p + 1;
1460     return;
1461   }
1462 
1463   ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
1464   if (n != obj_mon) {
1465     out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1466                   "object does not refer to the same monitor: obj="
1467                   INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1468                   INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1469     *error_cnt_p = *error_cnt_p + 1;
1470   }
1471 }
1472 
1473 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1474 // flags indicate why the entry is in-use, 'object' and 'object type'
1475 // indicate the associated object and its type.
1476 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
1477   if (_in_use_list.count() > 0) {
1478     stringStream ss;
1479     out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
1480     out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1481     out->print_cr("%18s  %s  %18s  %18s",
1482                   "monitor", "BHL", "object", "object type");
1483     out->print_cr("==================  ===  ==================  ==================");
1484 
1485     auto is_interesting = [&](ObjectMonitor* monitor) {
1486       return log_all || monitor->has_owner() || monitor->is_busy();
1487     };
1488 
1489     monitors_iterate([&](ObjectMonitor* monitor) {
1490       if (is_interesting(monitor)) {
1491         const oop obj = monitor->object_peek();
1492         const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
1493         ResourceMark rm;
1494         out->print(INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT "  %s", p2i(monitor),
1495                    monitor->is_busy(), hash != 0, monitor->has_owner(),
1496                    p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
1497         if (monitor->is_busy()) {
1498           out->print(" (%s)", monitor->is_busy_to_string(&ss));
1499           ss.reset();
1500         }
1501         out->cr();
1502       }
1503     });
1504   }
1505 
1506   out->flush();
1507 }