1 /*
   2  * Copyright (c) 1998, 2021, 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 "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/atomic.hpp"
  37 #include "runtime/handles.inline.hpp"
  38 #include "runtime/handshake.hpp"
  39 #include "runtime/interfaceSupport.inline.hpp"
  40 #include "runtime/mutexLocker.hpp"
  41 #include "runtime/objectMonitor.hpp"
  42 #include "runtime/objectMonitor.inline.hpp"
  43 #include "runtime/os.inline.hpp"
  44 #include "runtime/osThread.hpp"
  45 #include "runtime/perfData.hpp"
  46 #include "runtime/safepointMechanism.inline.hpp"
  47 #include "runtime/safepointVerifiers.hpp"
  48 #include "runtime/sharedRuntime.hpp"
  49 #include "runtime/stubRoutines.hpp"
  50 #include "runtime/synchronizer.hpp"
  51 #include "runtime/thread.inline.hpp"
  52 #include "runtime/timer.hpp"
  53 #include "runtime/vframe.hpp"
  54 #include "runtime/vmThread.hpp"
  55 #include "utilities/align.hpp"
  56 #include "utilities/dtrace.hpp"
  57 #include "utilities/events.hpp"
  58 #include "utilities/preserveException.hpp"
  59 
  60 class CleanupObjectMonitorsHashtable: StackObj {
  61  public:
  62   bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) {
  63     list->clear();  // clear the LinkListNodes
  64     delete list;    // then delete the LinkedList
  65     return true;
  66   }
  67 };
  68 
  69 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() {
  70   CleanupObjectMonitorsHashtable cleanup;
  71   _ptrs->unlink(&cleanup);  // cleanup the LinkedLists
  72   delete _ptrs;             // then delete the hash table
  73 }
  74 
  75 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) {
  76   ObjectMonitorsHashtable::PtrList* list = get_entry(key);
  77   if (list == nullptr) {
  78     // Create new list and add it to the hash table:
  79     list = new (ResourceObj::C_HEAP, mtThread) ObjectMonitorsHashtable::PtrList();
  80     add_entry(key, list);
  81   }
  82   list->add(om);  // Add the ObjectMonitor to the list.
  83   _om_count++;
  84 }
  85 
  86 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) {
  87   ObjectMonitorsHashtable::PtrList* list = get_entry(key);
  88   if (list == nullptr || list->find(om) == nullptr) {
  89     return false;
  90   }
  91   return true;
  92 }
  93 
  94 void MonitorList::add(ObjectMonitor* m) {
  95   ObjectMonitor* head;
  96   do {
  97     head = Atomic::load(&_head);
  98     m->set_next_om(head);
  99   } while (Atomic::cmpxchg(&_head, head, m) != head);
 100 
 101   size_t count = Atomic::add(&_count, 1u);
 102   if (count > max()) {
 103     Atomic::inc(&_max);
 104   }
 105 }
 106 
 107 size_t MonitorList::count() const {
 108   return Atomic::load(&_count);
 109 }
 110 
 111 size_t MonitorList::max() const {
 112   return Atomic::load(&_max);
 113 }
 114 
 115 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
 116 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
 117 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
 118                                     elapsedTimer* timer_p,
 119                                     GrowableArray<ObjectMonitor*>* unlinked_list) {
 120   size_t unlinked_count = 0;
 121   ObjectMonitor* prev = NULL;
 122   ObjectMonitor* head = Atomic::load_acquire(&_head);
 123   ObjectMonitor* m = head;
 124   // The in-use list head can be NULL during the final audit.
 125   while (m != NULL) {
 126     if (m->is_being_async_deflated()) {
 127       // Find next live ObjectMonitor.
 128       ObjectMonitor* next = m;
 129       do {
 130         ObjectMonitor* next_next = next->next_om();
 131         unlinked_count++;
 132         unlinked_list->append(next);
 133         next = next_next;
 134         if (unlinked_count >= (size_t)MonitorDeflationMax) {
 135           // Reached the max so bail out on the gathering loop.
 136           break;
 137         }
 138       } while (next != NULL && next->is_being_async_deflated());
 139       if (prev == NULL) {
 140         ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
 141         if (prev_head != head) {
 142           // Find new prev ObjectMonitor that just got inserted.
 143           for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
 144             prev = n;
 145           }
 146           prev->set_next_om(next);
 147         }
 148       } else {
 149         prev->set_next_om(next);
 150       }
 151       if (unlinked_count >= (size_t)MonitorDeflationMax) {
 152         // Reached the max so bail out on the searching loop.
 153         break;
 154       }
 155       m = next;
 156     } else {
 157       prev = m;
 158       m = m->next_om();
 159     }
 160 
 161     if (current->is_Java_thread()) {
 162       // A JavaThread must check for a safepoint/handshake and honor it.
 163       ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking",
 164                                             "unlinked_count", unlinked_count,
 165                                             ls, timer_p);
 166     }
 167   }
 168   Atomic::sub(&_count, unlinked_count);
 169   return unlinked_count;
 170 }
 171 
 172 MonitorList::Iterator MonitorList::iterator() const {
 173   return Iterator(Atomic::load_acquire(&_head));
 174 }
 175 
 176 ObjectMonitor* MonitorList::Iterator::next() {
 177   ObjectMonitor* current = _current;
 178   _current = current->next_om();
 179   return current;
 180 }
 181 
 182 // The "core" versions of monitor enter and exit reside in this file.
 183 // The interpreter and compilers contain specialized transliterated
 184 // variants of the enter-exit fast-path operations.  See c2_MacroAssembler_x86.cpp
 185 // fast_lock(...) for instance.  If you make changes here, make sure to modify the
 186 // interpreter, and both C1 and C2 fast-path inline locking code emission.
 187 //
 188 // -----------------------------------------------------------------------------
 189 
 190 #ifdef DTRACE_ENABLED
 191 
 192 // Only bother with this argument setup if dtrace is available
 193 // TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.
 194 
 195 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
 196   char* bytes = NULL;                                                      \
 197   int len = 0;                                                             \
 198   jlong jtid = SharedRuntime::get_java_tid(thread);                        \
 199   Symbol* klassname = obj->klass()->name();                                \
 200   if (klassname != NULL) {                                                 \
 201     bytes = (char*)klassname->bytes();                                     \
 202     len = klassname->utf8_length();                                        \
 203   }
 204 
 205 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
 206   {                                                                        \
 207     if (DTraceMonitorProbes) {                                             \
 208       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 209       HOTSPOT_MONITOR_WAIT(jtid,                                           \
 210                            (uintptr_t)(monitor), bytes, len, (millis));    \
 211     }                                                                      \
 212   }
 213 
 214 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
 215 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
 216 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
 217 
 218 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
 219   {                                                                        \
 220     if (DTraceMonitorProbes) {                                             \
 221       DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
 222       HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */             \
 223                                     (uintptr_t)(monitor), bytes, len);     \
 224     }                                                                      \
 225   }
 226 
 227 #else //  ndef DTRACE_ENABLED
 228 
 229 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
 230 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}
 231 
 232 #endif // ndef DTRACE_ENABLED
 233 
 234 // This exists only as a workaround of dtrace bug 6254741
 235 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
 236   DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
 237   return 0;
 238 }
 239 
 240 static const int NINFLATIONLOCKS = 256;
 241 static os::PlatformMutex* gInflationLocks[NINFLATIONLOCKS];
 242 
 243 void ObjectSynchronizer::initialize() {
 244   for (int i = 0; i < NINFLATIONLOCKS; i++) {
 245     gInflationLocks[i] = new os::PlatformMutex();
 246   }
 247   // Start the ceiling with the estimate for one thread.
 248   set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
 249 }
 250 
 251 MonitorList ObjectSynchronizer::_in_use_list;
 252 // monitors_used_above_threshold() policy is as follows:
 253 //
 254 // The ratio of the current _in_use_list count to the ceiling is used
 255 // to determine if we are above MonitorUsedDeflationThreshold and need
 256 // to do an async monitor deflation cycle. The ceiling is increased by
 257 // AvgMonitorsPerThreadEstimate when a thread is added to the system
 258 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
 259 // removed from the system.
 260 //
 261 // Note: If the _in_use_list max exceeds the ceiling, then
 262 // monitors_used_above_threshold() will use the in_use_list max instead
 263 // of the thread count derived ceiling because we have used more
 264 // ObjectMonitors than the estimated average.
 265 //
 266 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
 267 // no-progress async monitor deflation cycles in a row, then the ceiling
 268 // is adjusted upwards by monitors_used_above_threshold().
 269 //
 270 // Start the ceiling with the estimate for one thread in initialize()
 271 // which is called after cmd line options are processed.
 272 static size_t _in_use_list_ceiling = 0;
 273 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
 274 bool volatile ObjectSynchronizer::_is_final_audit = false;
 275 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
 276 static uintx _no_progress_cnt = 0;
 277 
 278 // =====================> Quick functions
 279 
 280 // The quick_* forms are special fast-path variants used to improve
 281 // performance.  In the simplest case, a "quick_*" implementation could
 282 // simply return false, in which case the caller will perform the necessary
 283 // state transitions and call the slow-path form.
 284 // The fast-path is designed to handle frequently arising cases in an efficient
 285 // manner and is just a degenerate "optimistic" variant of the slow-path.
 286 // returns true  -- to indicate the call was satisfied.
 287 // returns false -- to indicate the call needs the services of the slow-path.
 288 // A no-loitering ordinance is in effect for code in the quick_* family
 289 // operators: safepoints or indefinite blocking (blocking that might span a
 290 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
 291 // entry.
 292 //
 293 // Consider: An interesting optimization is to have the JIT recognize the
 294 // following common idiom:
 295 //   synchronized (someobj) { .... ; notify(); }
 296 // That is, we find a notify() or notifyAll() call that immediately precedes
 297 // the monitorexit operation.  In that case the JIT could fuse the operations
 298 // into a single notifyAndExit() runtime primitive.
 299 
 300 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
 301   assert(current->thread_state() == _thread_in_Java, "invariant");
 302   NoSafepointVerifier nsv;
 303   if (obj == NULL) return false;  // slow-path for invalid obj
 304   const markWord mark = obj->mark();
 305 
 306   if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 307     // Degenerate notify
 308     // stack-locked by caller so by definition the implied waitset is empty.
 309     return true;
 310   }
 311 
 312   if (mark.has_monitor()) {
 313     ObjectMonitor* const mon = mark.monitor();
 314     assert(mon->object() == oop(obj), "invariant");
 315     if (mon->owner() != current) return false;  // slow-path for IMS exception
 316 
 317     if (mon->first_waiter() != NULL) {
 318       // We have one or more waiters. Since this is an inflated monitor
 319       // that we own, we can transfer one or more threads from the waitset
 320       // to the entrylist here and now, avoiding the slow-path.
 321       if (all) {
 322         DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
 323       } else {
 324         DTRACE_MONITOR_PROBE(notify, mon, obj, current);
 325       }
 326       int free_count = 0;
 327       do {
 328         mon->INotify(current);
 329         ++free_count;
 330       } while (mon->first_waiter() != NULL && all);
 331       OM_PERFDATA_OP(Notifications, inc(free_count));
 332     }
 333     return true;
 334   }
 335 
 336   // other IMS exception states take the slow-path
 337   return false;
 338 }
 339 
 340 
 341 // The LockNode emitted directly at the synchronization site would have
 342 // been too big if it were to have included support for the cases of inflated
 343 // recursive enter and exit, so they go here instead.
 344 // Note that we can't safely call AsyncPrintJavaStack() from within
 345 // quick_enter() as our thread state remains _in_Java.
 346 
 347 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
 348                                      BasicLock * lock) {
 349   assert(current->thread_state() == _thread_in_Java, "invariant");
 350   NoSafepointVerifier nsv;
 351   if (obj == NULL) return false;       // Need to throw NPE
 352 
 353   if (obj->klass()->is_value_based()) {
 354     return false;
 355   }
 356 
 357   const markWord mark = obj->mark();
 358 
 359   if (mark.has_monitor()) {
 360     ObjectMonitor* const m = mark.monitor();
 361     // An async deflation or GC can race us before we manage to make
 362     // the ObjectMonitor busy by setting the owner below. If we detect
 363     // that race we just bail out to the slow-path here.
 364     if (m->object_peek() == NULL) {
 365       return false;
 366     }
 367     JavaThread* const owner = (JavaThread*) m->owner_raw();
 368 
 369     // Lock contention and Transactional Lock Elision (TLE) diagnostics
 370     // and observability
 371     // Case: light contention possibly amenable to TLE
 372     // Case: TLE inimical operations such as nested/recursive synchronization
 373 
 374     if (owner == current) {
 375       m->_recursions++;
 376       return true;
 377     }
 378 
 379     // This Java Monitor is inflated so obj's header will never be
 380     // displaced to this thread's BasicLock. Make the displaced header
 381     // non-NULL so this BasicLock is not seen as recursive nor as
 382     // being locked. We do this unconditionally so that this thread's
 383     // BasicLock cannot be mis-interpreted by any stack walkers. For
 384     // performance reasons, stack walkers generally first check for
 385     // stack-locking in the object's header, the second check is for
 386     // recursive stack-locking in the displaced header in the BasicLock,
 387     // and last are the inflated Java Monitor (ObjectMonitor) checks.
 388     lock->set_displaced_header(markWord::unused_mark());
 389 
 390     if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
 391       assert(m->_recursions == 0, "invariant");
 392       return true;
 393     }
 394   }
 395 
 396   // Note that we could inflate in quick_enter.
 397   // This is likely a useful optimization
 398   // Critically, in quick_enter() we must not:
 399   // -- block indefinitely, or
 400   // -- reach a safepoint
 401 
 402   return false;        // revert to slow-path
 403 }
 404 
 405 // Handle notifications when synchronizing on value based classes
 406 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
 407   frame last_frame = current->last_frame();
 408   bool bcp_was_adjusted = false;
 409   // Don't decrement bcp if it points to the frame's first instruction.  This happens when
 410   // handle_sync_on_value_based_class() is called because of a synchronized method.  There
 411   // is no actual monitorenter instruction in the byte code in this case.
 412   if (last_frame.is_interpreted_frame() &&
 413       (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
 414     // adjust bcp to point back to monitorenter so that we print the correct line numbers
 415     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
 416     bcp_was_adjusted = true;
 417   }
 418 
 419   if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
 420     ResourceMark rm(current);
 421     stringStream ss;
 422     current->print_stack_on(&ss);
 423     char* base = (char*)strstr(ss.base(), "at");
 424     char* newline = (char*)strchr(ss.base(), '\n');
 425     if (newline != NULL) {
 426       *newline = '\0';
 427     }
 428     fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
 429   } else {
 430     assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
 431     ResourceMark rm(current);
 432     Log(valuebasedclasses) vblog;
 433 
 434     vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
 435     if (current->has_last_Java_frame()) {
 436       LogStream info_stream(vblog.info());
 437       current->print_stack_on(&info_stream);
 438     } else {
 439       vblog.info("Cannot find the last Java frame");
 440     }
 441 
 442     EventSyncOnValueBasedClass event;
 443     if (event.should_commit()) {
 444       event.set_valueBasedClass(obj->klass());
 445       event.commit();
 446     }
 447   }
 448 
 449   if (bcp_was_adjusted) {
 450     last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
 451   }
 452 }
 453 
 454 static bool useHeavyMonitors() {
 455 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64)
 456   return UseHeavyMonitors;
 457 #else
 458   return false;
 459 #endif
 460 }
 461 
 462 // -----------------------------------------------------------------------------
 463 // Monitor Enter/Exit
 464 // The interpreter and compiler assembly code tries to lock using the fast path
 465 // of this algorithm. Make sure to update that code if the following function is
 466 // changed. The implementation is extremely sensitive to race condition. Be careful.
 467 
 468 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
 469   if (obj->klass()->is_value_based()) {
 470     handle_sync_on_value_based_class(obj, current);
 471   }
 472 
 473   if (!useHeavyMonitors()) {
 474     markWord mark = obj->mark();
 475     if (mark.is_neutral()) {
 476       // Anticipate successful CAS -- the ST of the displaced mark must
 477       // be visible <= the ST performed by the CAS.
 478       lock->set_displaced_header(mark);
 479       if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
 480         return;
 481       }
 482       // Fall through to inflate() ...
 483     } else if (mark.has_locker() &&
 484                current->is_lock_owned((address)mark.locker())) {
 485       assert(lock != mark.locker(), "must not re-lock the same lock");
 486       assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
 487       lock->set_displaced_header(markWord::from_pointer(NULL));
 488       return;
 489     }
 490 
 491     // The object header will never be displaced to this lock,
 492     // so it does not matter what the value is, except that it
 493     // must be non-zero to avoid looking like a re-entrant lock,
 494     // and must not look locked either.
 495     lock->set_displaced_header(markWord::unused_mark());
 496   } else if (VerifyHeavyMonitors) {
 497     guarantee(!obj->mark().has_locker(), "must not be stack-locked");
 498   }
 499 
 500   // An async deflation can race after the inflate() call and before
 501   // enter() can make the ObjectMonitor busy. enter() returns false if
 502   // we have lost the race to async deflation and we simply try again.
 503   while (true) {
 504     ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
 505     if (monitor->enter(current)) {
 506       return;
 507     }
 508   }
 509 }
 510 
 511 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
 512   if (!useHeavyMonitors()) {
 513     markWord mark = object->mark();
 514 
 515     markWord dhw = lock->displaced_header();
 516     if (dhw.value() == 0) {
 517       // If the displaced header is NULL, then this exit matches up with
 518       // a recursive enter. No real work to do here except for diagnostics.
 519 #ifndef PRODUCT
 520       if (mark != markWord::INFLATING()) {
 521         // Only do diagnostics if we are not racing an inflation. Simply
 522         // exiting a recursive enter of a Java Monitor that is being
 523         // inflated is safe; see the has_monitor() comment below.
 524         assert(!mark.is_neutral(), "invariant");
 525         assert(!mark.has_locker() ||
 526         current->is_lock_owned((address)mark.locker()), "invariant");
 527         if (mark.has_monitor()) {
 528           // The BasicLock's displaced_header is marked as a recursive
 529           // enter and we have an inflated Java Monitor (ObjectMonitor).
 530           // This is a special case where the Java Monitor was inflated
 531           // after this thread entered the stack-lock recursively. When a
 532           // Java Monitor is inflated, we cannot safely walk the Java
 533           // Monitor owner's stack and update the BasicLocks because a
 534           // Java Monitor can be asynchronously inflated by a thread that
 535           // does not own the Java Monitor.
 536           ObjectMonitor* m = mark.monitor();
 537           assert(m->object()->mark() == mark, "invariant");
 538           assert(m->is_entered(current), "invariant");
 539         }
 540       }
 541 #endif
 542       return;
 543     }
 544 
 545     if (mark == markWord::from_pointer(lock)) {
 546       // If the object is stack-locked by the current thread, try to
 547       // swing the displaced header from the BasicLock back to the mark.
 548       assert(dhw.is_neutral(), "invariant");
 549       if (object->cas_set_mark(dhw, mark) == mark) {
 550         return;
 551       }
 552     }
 553   } else if (VerifyHeavyMonitors) {
 554     guarantee(!object->mark().has_locker(), "must not be stack-locked");
 555   }
 556 
 557   // We have to take the slow-path of possible inflation and then exit.
 558   // The ObjectMonitor* can't be async deflated until ownership is
 559   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
 560   ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
 561   monitor->exit(current);
 562 }
 563 
 564 // -----------------------------------------------------------------------------
 565 // Class Loader  support to workaround deadlocks on the class loader lock objects
 566 // Also used by GC
 567 // complete_exit()/reenter() are used to wait on a nested lock
 568 // i.e. to give up an outer lock completely and then re-enter
 569 // Used when holding nested locks - lock acquisition order: lock1 then lock2
 570 //  1) complete_exit lock1 - saving recursion count
 571 //  2) wait on lock2
 572 //  3) when notified on lock2, unlock lock2
 573 //  4) reenter lock1 with original recursion count
 574 //  5) lock lock2
 575 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 576 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
 577   // The ObjectMonitor* can't be async deflated until ownership is
 578   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
 579   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
 580   intptr_t ret_code = monitor->complete_exit(current);
 581   return ret_code;
 582 }
 583 
 584 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
 585 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
 586   // An async deflation can race after the inflate() call and before
 587   // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
 588   // enter() returns false if we have lost the race to async deflation
 589   // and we simply try again.
 590   while (true) {
 591     ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
 592     if (monitor->reenter(recursions, current)) {
 593       return;
 594     }
 595   }
 596 }
 597 
 598 // -----------------------------------------------------------------------------
 599 // JNI locks on java objects
 600 // NOTE: must use heavy weight monitor to handle jni monitor enter
 601 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
 602   if (obj->klass()->is_value_based()) {
 603     handle_sync_on_value_based_class(obj, current);
 604   }
 605 
 606   // the current locking is from JNI instead of Java code
 607   current->set_current_pending_monitor_is_from_java(false);
 608   // An async deflation can race after the inflate() call and before
 609   // enter() can make the ObjectMonitor busy. enter() returns false if
 610   // we have lost the race to async deflation and we simply try again.
 611   while (true) {
 612     ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
 613     if (monitor->enter(current)) {
 614       break;
 615     }
 616   }
 617   current->set_current_pending_monitor_is_from_java(true);
 618 }
 619 
 620 // NOTE: must use heavy weight monitor to handle jni monitor exit
 621 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
 622   JavaThread* current = THREAD;
 623 
 624   // The ObjectMonitor* can't be async deflated until ownership is
 625   // dropped inside exit() and the ObjectMonitor* must be !is_busy().
 626   ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
 627   // If this thread has locked the object, exit the monitor. We
 628   // intentionally do not use CHECK on check_owner because we must exit the
 629   // monitor even if an exception was already pending.
 630   if (monitor->check_owner(THREAD)) {
 631     monitor->exit(current);
 632   }
 633 }
 634 
 635 // -----------------------------------------------------------------------------
 636 // Internal VM locks on java objects
 637 // standard constructor, allows locking failures
 638 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
 639   _thread = thread;
 640   _thread->check_for_valid_safepoint_state();
 641   _obj = obj;
 642 
 643   if (_obj() != NULL) {
 644     ObjectSynchronizer::enter(_obj, &_lock, _thread);
 645   }
 646 }
 647 
 648 ObjectLocker::~ObjectLocker() {
 649   if (_obj() != NULL) {
 650     ObjectSynchronizer::exit(_obj(), &_lock, _thread);
 651   }
 652 }
 653 
 654 
 655 // -----------------------------------------------------------------------------
 656 //  Wait/Notify/NotifyAll
 657 // NOTE: must use heavy weight monitor to handle wait()
 658 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
 659   JavaThread* current = THREAD;
 660   if (millis < 0) {
 661     THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
 662   }
 663   // The ObjectMonitor* can't be async deflated because the _waiters
 664   // field is incremented before ownership is dropped and decremented
 665   // after ownership is regained.
 666   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
 667 
 668   DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
 669   monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
 670 
 671   // This dummy call is in place to get around dtrace bug 6254741.  Once
 672   // that's fixed we can uncomment the following line, remove the call
 673   // and change this function back into a "void" func.
 674   // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
 675   int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
 676   return ret_code;
 677 }
 678 
 679 // No exception are possible in this case as we only use this internally when locking is
 680 // correct and we have to wait until notified - so no interrupts or timeouts.
 681 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, JavaThread* current) {
 682   // The ObjectMonitor* can't be async deflated because the _waiters
 683   // field is incremented before ownership is dropped and decremented
 684   // after ownership is regained.
 685   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
 686   monitor->wait(0 /* wait-forever */, false /* not interruptible */, current);
 687 }
 688 
 689 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
 690   JavaThread* current = THREAD;
 691 
 692   markWord mark = obj->mark();
 693   if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 694     // Not inflated so there can't be any waiters to notify.
 695     return;
 696   }
 697   // The ObjectMonitor* can't be async deflated until ownership is
 698   // dropped by the calling thread.
 699   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
 700   monitor->notify(CHECK);
 701 }
 702 
 703 // NOTE: see comment of notify()
 704 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
 705   JavaThread* current = THREAD;
 706 
 707   markWord mark = obj->mark();
 708   if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
 709     // Not inflated so there can't be any waiters to notify.
 710     return;
 711   }
 712   // The ObjectMonitor* can't be async deflated until ownership is
 713   // dropped by the calling thread.
 714   ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
 715   monitor->notifyAll(CHECK);
 716 }
 717 
 718 // -----------------------------------------------------------------------------
 719 // Hash Code handling
 720 
 721 struct SharedGlobals {
 722   char         _pad_prefix[OM_CACHE_LINE_SIZE];
 723   // This is a highly shared mostly-read variable.
 724   // To avoid false-sharing it needs to be the sole occupant of a cache line.
 725   volatile int stw_random;
 726   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 727   // Hot RW variable -- Sequester to avoid false-sharing
 728   volatile int hc_sequence;
 729   DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
 730 };
 731 
 732 static SharedGlobals GVars;
 733 
 734 static markWord read_stable_mark(oop obj) {
 735   markWord mark = obj->mark_acquire();
 736   if (!mark.is_being_inflated()) {
 737     return mark;       // normal fast-path return
 738   }
 739 
 740   int its = 0;
 741   for (;;) {
 742     markWord mark = obj->mark_acquire();
 743     if (!mark.is_being_inflated()) {
 744       return mark;    // normal fast-path return
 745     }
 746 
 747     // The object is being inflated by some other thread.
 748     // The caller of read_stable_mark() must wait for inflation to complete.
 749     // Avoid live-lock.
 750 
 751     ++its;
 752     if (its > 10000 || !os::is_MP()) {
 753       if (its & 1) {
 754         os::naked_yield();
 755       } else {
 756         // Note that the following code attenuates the livelock problem but is not
 757         // a complete remedy.  A more complete solution would require that the inflating
 758         // thread hold the associated inflation lock.  The following code simply restricts
 759         // the number of spinners to at most one.  We'll have N-2 threads blocked
 760         // on the inflationlock, 1 thread holding the inflation lock and using
 761         // a yield/park strategy, and 1 thread in the midst of inflation.
 762         // A more refined approach would be to change the encoding of INFLATING
 763         // to allow encapsulation of a native thread pointer.  Threads waiting for
 764         // inflation to complete would use CAS to push themselves onto a singly linked
 765         // list rooted at the markword.  Once enqueued, they'd loop, checking a per-thread flag
 766         // and calling park().  When inflation was complete the thread that accomplished inflation
 767         // would detach the list and set the markword to inflated with a single CAS and
 768         // then for each thread on the list, set the flag and unpark() the thread.
 769 
 770         // Index into the lock array based on the current object address.
 771         static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
 772         int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
 773         int YieldThenBlock = 0;
 774         assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
 775         gInflationLocks[ix]->lock();
 776         while (obj->mark_acquire() == markWord::INFLATING()) {
 777           // Beware: naked_yield() is advisory and has almost no effect on some platforms
 778           // so we periodically call current->_ParkEvent->park(1).
 779           // We use a mixed spin/yield/block mechanism.
 780           if ((YieldThenBlock++) >= 16) {
 781             Thread::current()->_ParkEvent->park(1);
 782           } else {
 783             os::naked_yield();
 784           }
 785         }
 786         gInflationLocks[ix]->unlock();
 787       }
 788     } else {
 789       SpinPause();       // SMP-polite spinning
 790     }
 791   }
 792 }
 793 
 794 // hashCode() generation :
 795 //
 796 // Possibilities:
 797 // * MD5Digest of {obj,stw_random}
 798 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
 799 // * A DES- or AES-style SBox[] mechanism
 800 // * One of the Phi-based schemes, such as:
 801 //   2654435761 = 2^32 * Phi (golden ratio)
 802 //   HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
 803 // * A variation of Marsaglia's shift-xor RNG scheme.
 804 // * (obj ^ stw_random) is appealing, but can result
 805 //   in undesirable regularity in the hashCode values of adjacent objects
 806 //   (objects allocated back-to-back, in particular).  This could potentially
 807 //   result in hashtable collisions and reduced hashtable efficiency.
 808 //   There are simple ways to "diffuse" the middle address bits over the
 809 //   generated hashCode values:
 810 
 811 static inline intptr_t get_next_hash(Thread* current, oop obj) {
 812   intptr_t value = 0;
 813   if (hashCode == 0) {
 814     // This form uses global Park-Miller RNG.
 815     // On MP system we'll have lots of RW access to a global, so the
 816     // mechanism induces lots of coherency traffic.
 817     value = os::random();
 818   } else if (hashCode == 1) {
 819     // This variation has the property of being stable (idempotent)
 820     // between STW operations.  This can be useful in some of the 1-0
 821     // synchronization schemes.
 822     intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
 823     value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
 824   } else if (hashCode == 2) {
 825     value = 1;            // for sensitivity testing
 826   } else if (hashCode == 3) {
 827     value = ++GVars.hc_sequence;
 828   } else if (hashCode == 4) {
 829     value = cast_from_oop<intptr_t>(obj);
 830   } else {
 831     // Marsaglia's xor-shift scheme with thread-specific state
 832     // This is probably the best overall implementation -- we'll
 833     // likely make this the default in future releases.
 834     unsigned t = current->_hashStateX;
 835     t ^= (t << 11);
 836     current->_hashStateX = current->_hashStateY;
 837     current->_hashStateY = current->_hashStateZ;
 838     current->_hashStateZ = current->_hashStateW;
 839     unsigned v = current->_hashStateW;
 840     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
 841     current->_hashStateW = v;
 842     value = v;
 843   }
 844 
 845   value &= markWord::hash_mask;
 846   if (value == 0) value = 0xBAD;
 847   assert(value != markWord::no_hash, "invariant");
 848   return value;
 849 }
 850 
 851 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
 852 
 853   while (true) {
 854     ObjectMonitor* monitor = NULL;
 855     markWord temp, test;
 856     intptr_t hash;
 857     markWord mark = read_stable_mark(obj);
 858     if (VerifyHeavyMonitors) {
 859       assert(UseHeavyMonitors, "+VerifyHeavyMonitors requires +UseHeavyMonitors");
 860       guarantee(!mark.has_locker(), "must not be stack locked");
 861     }
 862     if (mark.is_neutral()) {               // if this is a normal header
 863       hash = mark.hash();
 864       if (hash != 0) {                     // if it has a hash, just return it
 865         return hash;
 866       }
 867       hash = get_next_hash(current, obj);  // get a new hash
 868       temp = mark.copy_set_hash(hash);     // merge the hash into header
 869                                            // try to install the hash
 870       test = obj->cas_set_mark(temp, mark);
 871       if (test == mark) {                  // if the hash was installed, return it
 872         return hash;
 873       }
 874       // Failed to install the hash. It could be that another thread
 875       // installed the hash just before our attempt or inflation has
 876       // occurred or... so we fall thru to inflate the monitor for
 877       // stability and then install the hash.
 878     } else if (mark.has_monitor()) {
 879       monitor = mark.monitor();
 880       temp = monitor->header();
 881       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 882       hash = temp.hash();
 883       if (hash != 0) {
 884         // It has a hash.
 885 
 886         // Separate load of dmw/header above from the loads in
 887         // is_being_async_deflated().
 888 
 889         // dmw/header and _contentions may get written by different threads.
 890         // Make sure to observe them in the same order when having several observers.
 891         OrderAccess::loadload_for_IRIW();
 892 
 893         if (monitor->is_being_async_deflated()) {
 894           // But we can't safely use the hash if we detect that async
 895           // deflation has occurred. So we attempt to restore the
 896           // header/dmw to the object's header so that we only retry
 897           // once if the deflater thread happens to be slow.
 898           monitor->install_displaced_markword_in_object(obj);
 899           continue;
 900         }
 901         return hash;
 902       }
 903       // Fall thru so we only have one place that installs the hash in
 904       // the ObjectMonitor.
 905     } else if (current->is_lock_owned((address)mark.locker())) {
 906       // This is a stack lock owned by the calling thread so fetch the
 907       // displaced markWord from the BasicLock on the stack.
 908       temp = mark.displaced_mark_helper();
 909       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 910       hash = temp.hash();
 911       if (hash != 0) {                  // if it has a hash, just return it
 912         return hash;
 913       }
 914       // WARNING:
 915       // The displaced header in the BasicLock on a thread's stack
 916       // is strictly immutable. It CANNOT be changed in ANY cases.
 917       // So we have to inflate the stack lock into an ObjectMonitor
 918       // even if the current thread owns the lock. The BasicLock on
 919       // a thread's stack can be asynchronously read by other threads
 920       // during an inflate() call so any change to that stack memory
 921       // may not propagate to other threads correctly.
 922     }
 923 
 924     // Inflate the monitor to set the hash.
 925 
 926     // An async deflation can race after the inflate() call and before we
 927     // can update the ObjectMonitor's header with the hash value below.
 928     monitor = inflate(current, obj, inflate_cause_hash_code);
 929     // Load ObjectMonitor's header/dmw field and see if it has a hash.
 930     mark = monitor->header();
 931     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
 932     hash = mark.hash();
 933     if (hash == 0) {                       // if it does not have a hash
 934       hash = get_next_hash(current, obj);  // get a new hash
 935       temp = mark.copy_set_hash(hash)   ;  // merge the hash into header
 936       assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
 937       uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
 938       test = markWord(v);
 939       if (test != mark) {
 940         // The attempt to update the ObjectMonitor's header/dmw field
 941         // did not work. This can happen if another thread managed to
 942         // merge in the hash just before our cmpxchg().
 943         // If we add any new usages of the header/dmw field, this code
 944         // will need to be updated.
 945         hash = test.hash();
 946         assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
 947         assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
 948       }
 949       if (monitor->is_being_async_deflated()) {
 950         // If we detect that async deflation has occurred, then we
 951         // attempt to restore the header/dmw to the object's header
 952         // so that we only retry once if the deflater thread happens
 953         // to be slow.
 954         monitor->install_displaced_markword_in_object(obj);
 955         continue;
 956       }
 957     }
 958     // We finally get the hash.
 959     return hash;
 960   }
 961 }
 962 
 963 // Deprecated -- use FastHashCode() instead.
 964 
 965 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
 966   return FastHashCode(Thread::current(), obj());
 967 }
 968 
 969 
 970 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
 971                                                    Handle h_obj) {
 972   assert(current == JavaThread::current(), "Can only be called on current thread");
 973   oop obj = h_obj();
 974 
 975   markWord mark = read_stable_mark(obj);
 976 
 977   // Uncontended case, header points to stack
 978   if (mark.has_locker()) {
 979     return current->is_lock_owned((address)mark.locker());
 980   }
 981   // Contended case, header points to ObjectMonitor (tagged pointer)
 982   if (mark.has_monitor()) {
 983     // The first stage of async deflation does not affect any field
 984     // used by this comparison so the ObjectMonitor* is usable here.
 985     ObjectMonitor* monitor = mark.monitor();
 986     return monitor->is_entered(current) != 0;
 987   }
 988   // Unlocked case, header in place
 989   assert(mark.is_neutral(), "sanity check");
 990   return false;
 991 }
 992 
 993 // FIXME: jvmti should call this
 994 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
 995   oop obj = h_obj();
 996   address owner = NULL;
 997 
 998   markWord mark = read_stable_mark(obj);
 999 
1000   // Uncontended case, header points to stack
1001   if (mark.has_locker()) {
1002     owner = (address) mark.locker();
1003   }
1004 
1005   // Contended case, header points to ObjectMonitor (tagged pointer)
1006   else if (mark.has_monitor()) {
1007     // The first stage of async deflation does not affect any field
1008     // used by this comparison so the ObjectMonitor* is usable here.
1009     ObjectMonitor* monitor = mark.monitor();
1010     assert(monitor != NULL, "monitor should be non-null");
1011     owner = (address) monitor->owner();
1012   }
1013 
1014   if (owner != NULL) {
1015     // owning_thread_from_monitor_owner() may also return NULL here
1016     return Threads::owning_thread_from_monitor_owner(t_list, owner);
1017   }
1018 
1019   // Unlocked case, header in place
1020   // Cannot have assertion since this object may have been
1021   // locked by another thread when reaching here.
1022   // assert(mark.is_neutral(), "sanity check");
1023 
1024   return NULL;
1025 }
1026 
1027 // Visitors ...
1028 
1029 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1030 // ObjectMonitors where owner is set to a stack lock address in thread.
1031 //
1032 // This version of monitors_iterate() works with the in-use monitor list.
1033 //
1034 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1035   MonitorList::Iterator iter = _in_use_list.iterator();
1036   while (iter.has_next()) {
1037     ObjectMonitor* mid = iter.next();
1038     if (mid->owner() != thread) {
1039       // Not owned by the target thread and intentionally skips when owner
1040       // is set to a stack lock address in the target thread.
1041       continue;
1042     }
1043     if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1044       // Only process with closure if the object is set.
1045 
1046       // monitors_iterate() is only called at a safepoint or when the
1047       // target thread is suspended or when the target thread is
1048       // operating on itself. The current closures in use today are
1049       // only interested in an owned ObjectMonitor and ownership
1050       // cannot be dropped under the calling contexts so the
1051       // ObjectMonitor cannot be async deflated.
1052       closure->do_monitor(mid);
1053     }
1054   }
1055 }
1056 
1057 // This version of monitors_iterate() works with the specified linked list.
1058 //
1059 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure,
1060                                           ObjectMonitorsHashtable::PtrList* list,
1061                                           JavaThread* thread) {
1062   typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator;
1063   ObjectMonitorIterator iter(list->head());
1064   while (!iter.is_empty()) {
1065     ObjectMonitor* mid = *iter.next();
1066     // Owner set to a stack lock address in thread should never be seen here:
1067     assert(mid->owner() == thread, "must be");
1068     if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1069       // Only process with closure if the object is set.
1070 
1071       // monitors_iterate() is only called at a safepoint or when the
1072       // target thread is suspended or when the target thread is
1073       // operating on itself. The current closures in use today are
1074       // only interested in an owned ObjectMonitor and ownership
1075       // cannot be dropped under the calling contexts so the
1076       // ObjectMonitor cannot be async deflated.
1077       closure->do_monitor(mid);
1078     }
1079   }
1080 }
1081 
1082 static bool monitors_used_above_threshold(MonitorList* list) {
1083   if (MonitorUsedDeflationThreshold == 0) {  // disabled case is easy
1084     return false;
1085   }
1086   // Start with ceiling based on a per-thread estimate:
1087   size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1088   size_t old_ceiling = ceiling;
1089   if (ceiling < list->max()) {
1090     // The max used by the system has exceeded the ceiling so use that:
1091     ceiling = list->max();
1092   }
1093   size_t monitors_used = list->count();
1094   if (monitors_used == 0) {  // empty list is easy
1095     return false;
1096   }
1097   if (NoAsyncDeflationProgressMax != 0 &&
1098       _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1099     float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1100     size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1101     ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1102     log_info(monitorinflation)("Too many deflations without progress; "
1103                                "bumping in_use_list_ceiling from " SIZE_FORMAT
1104                                " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1105     _no_progress_cnt = 0;
1106     ceiling = new_ceiling;
1107   }
1108 
1109   // Check if our monitor usage is above the threshold:
1110   size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1111   return int(monitor_usage) > MonitorUsedDeflationThreshold;
1112 }
1113 
1114 size_t ObjectSynchronizer::in_use_list_ceiling() {
1115   return _in_use_list_ceiling;
1116 }
1117 
1118 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1119   Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1120 }
1121 
1122 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1123   Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1124 }
1125 
1126 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1127   _in_use_list_ceiling = new_value;
1128 }
1129 
1130 bool ObjectSynchronizer::is_async_deflation_needed() {
1131   if (is_async_deflation_requested()) {
1132     // Async deflation request.
1133     return true;
1134   }
1135   if (AsyncDeflationInterval > 0 &&
1136       time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1137       monitors_used_above_threshold(&_in_use_list)) {
1138     // It's been longer than our specified deflate interval and there
1139     // are too many monitors in use. We don't deflate more frequently
1140     // than AsyncDeflationInterval (unless is_async_deflation_requested)
1141     // in order to not swamp the MonitorDeflationThread.
1142     return true;
1143   }
1144   return false;
1145 }
1146 
1147 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1148   JavaThread* current = JavaThread::current();
1149   bool ret_code = false;
1150 
1151   jlong last_time = last_async_deflation_time_ns();
1152   set_is_async_deflation_requested(true);
1153   {
1154     MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1155     ml.notify_all();
1156   }
1157   const int N_CHECKS = 5;
1158   for (int i = 0; i < N_CHECKS; i++) {  // sleep for at most 5 seconds
1159     if (last_async_deflation_time_ns() > last_time) {
1160       log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1161       ret_code = true;
1162       break;
1163     }
1164     {
1165       // JavaThread has to honor the blocking protocol.
1166       ThreadBlockInVM tbivm(current);
1167       os::naked_short_sleep(999);  // sleep for almost 1 second
1168     }
1169   }
1170   if (!ret_code) {
1171     log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1172   }
1173 
1174   return ret_code;
1175 }
1176 
1177 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1178   return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1179 }
1180 
1181 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1182                                        const oop obj,
1183                                        ObjectSynchronizer::InflateCause cause) {
1184   assert(event != NULL, "invariant");
1185   assert(event->should_commit(), "invariant");
1186   event->set_monitorClass(obj->klass());
1187   event->set_address((uintptr_t)(void*)obj);
1188   event->set_cause((u1)cause);
1189   event->commit();
1190 }
1191 
1192 // Fast path code shared by multiple functions
1193 void ObjectSynchronizer::inflate_helper(oop obj) {
1194   markWord mark = obj->mark_acquire();
1195   if (mark.has_monitor()) {
1196     ObjectMonitor* monitor = mark.monitor();
1197     markWord dmw = monitor->header();
1198     assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1199     return;
1200   }
1201   (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1202 }
1203 
1204 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1205                                            const InflateCause cause) {
1206   EventJavaMonitorInflate event;
1207 
1208   for (;;) {
1209     const markWord mark = object->mark_acquire();
1210 
1211     // The mark can be in one of the following states:
1212     // *  Inflated     - just return
1213     // *  Stack-locked - coerce it to inflated
1214     // *  INFLATING    - busy wait for conversion to complete
1215     // *  Neutral      - aggressively inflate the object.
1216 
1217     // CASE: inflated
1218     if (mark.has_monitor()) {
1219       ObjectMonitor* inf = mark.monitor();
1220       markWord dmw = inf->header();
1221       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1222       return inf;
1223     }
1224 
1225     // CASE: inflation in progress - inflating over a stack-lock.
1226     // Some other thread is converting from stack-locked to inflated.
1227     // Only that thread can complete inflation -- other threads must wait.
1228     // The INFLATING value is transient.
1229     // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1230     // We could always eliminate polling by parking the thread on some auxiliary list.
1231     if (mark == markWord::INFLATING()) {
1232       read_stable_mark(object);
1233       continue;
1234     }
1235 
1236     // CASE: stack-locked
1237     // Could be stack-locked either by this thread or by some other thread.
1238     //
1239     // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1240     // to install INFLATING into the mark word.  We originally installed INFLATING,
1241     // allocated the ObjectMonitor, and then finally STed the address of the
1242     // ObjectMonitor into the mark.  This was correct, but artificially lengthened
1243     // the interval in which INFLATING appeared in the mark, thus increasing
1244     // the odds of inflation contention.
1245 
1246     LogStreamHandle(Trace, monitorinflation) lsh;
1247 
1248     if (mark.has_locker()) {
1249       ObjectMonitor* m = new ObjectMonitor(object);
1250       // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1251       // We do this before the CAS in order to minimize the length of time
1252       // in which INFLATING appears in the mark.
1253 
1254       markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1255       if (cmp != mark) {
1256         delete m;
1257         continue;       // Interference -- just retry
1258       }
1259 
1260       // We've successfully installed INFLATING (0) into the mark-word.
1261       // This is the only case where 0 will appear in a mark-word.
1262       // Only the singular thread that successfully swings the mark-word
1263       // to 0 can perform (or more precisely, complete) inflation.
1264       //
1265       // Why do we CAS a 0 into the mark-word instead of just CASing the
1266       // mark-word from the stack-locked value directly to the new inflated state?
1267       // Consider what happens when a thread unlocks a stack-locked object.
1268       // It attempts to use CAS to swing the displaced header value from the
1269       // on-stack BasicLock back into the object header.  Recall also that the
1270       // header value (hash code, etc) can reside in (a) the object header, or
1271       // (b) a displaced header associated with the stack-lock, or (c) a displaced
1272       // header in an ObjectMonitor.  The inflate() routine must copy the header
1273       // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1274       // the while preserving the hashCode stability invariants.  If the owner
1275       // decides to release the lock while the value is 0, the unlock will fail
1276       // and control will eventually pass from slow_exit() to inflate.  The owner
1277       // will then spin, waiting for the 0 value to disappear.   Put another way,
1278       // the 0 causes the owner to stall if the owner happens to try to
1279       // drop the lock (restoring the header from the BasicLock to the object)
1280       // while inflation is in-progress.  This protocol avoids races that might
1281       // would otherwise permit hashCode values to change or "flicker" for an object.
1282       // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1283       // 0 serves as a "BUSY" inflate-in-progress indicator.
1284 
1285 
1286       // fetch the displaced mark from the owner's stack.
1287       // The owner can't die or unwind past the lock while our INFLATING
1288       // object is in the mark.  Furthermore the owner can't complete
1289       // an unlock on the object, either.
1290       markWord dmw = mark.displaced_mark_helper();
1291       // Catch if the object's header is not neutral (not locked and
1292       // not marked is what we care about here).
1293       assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1294 
1295       // Setup monitor fields to proper values -- prepare the monitor
1296       m->set_header(dmw);
1297 
1298       // Optimization: if the mark.locker stack address is associated
1299       // with this thread we could simply set m->_owner = current.
1300       // Note that a thread can inflate an object
1301       // that it has stack-locked -- as might happen in wait() -- directly
1302       // with CAS.  That is, we can avoid the xchg-NULL .... ST idiom.
1303       m->set_owner_from(NULL, mark.locker());
1304       // TODO-FIXME: assert BasicLock->dhw != 0.
1305 
1306       // Must preserve store ordering. The monitor state must
1307       // be stable at the time of publishing the monitor address.
1308       guarantee(object->mark() == markWord::INFLATING(), "invariant");
1309       // Release semantics so that above set_object() is seen first.
1310       object->release_set_mark(markWord::encode(m));
1311 
1312       // Once ObjectMonitor is configured and the object is associated
1313       // with the ObjectMonitor, it is safe to allow async deflation:
1314       _in_use_list.add(m);
1315 
1316       // Hopefully the performance counters are allocated on distinct cache lines
1317       // to avoid false sharing on MP systems ...
1318       OM_PERFDATA_OP(Inflations, inc());
1319       if (log_is_enabled(Trace, monitorinflation)) {
1320         ResourceMark rm(current);
1321         lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1322                      INTPTR_FORMAT ", type='%s'", p2i(object),
1323                      object->mark().value(), object->klass()->external_name());
1324       }
1325       if (event.should_commit()) {
1326         post_monitor_inflate_event(&event, object, cause);
1327       }
1328       return m;
1329     }
1330 
1331     // CASE: neutral
1332     // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1333     // If we know we're inflating for entry it's better to inflate by swinging a
1334     // pre-locked ObjectMonitor pointer into the object header.   A successful
1335     // CAS inflates the object *and* confers ownership to the inflating thread.
1336     // In the current implementation we use a 2-step mechanism where we CAS()
1337     // to inflate and then CAS() again to try to swing _owner from NULL to current.
1338     // An inflateTry() method that we could call from enter() would be useful.
1339 
1340     // Catch if the object's header is not neutral (not locked and
1341     // not marked is what we care about here).
1342     assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1343     ObjectMonitor* m = new ObjectMonitor(object);
1344     // prepare m for installation - set monitor to initial state
1345     m->set_header(mark);
1346 
1347     if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1348       delete m;
1349       m = NULL;
1350       continue;
1351       // interference - the markword changed - just retry.
1352       // The state-transitions are one-way, so there's no chance of
1353       // live-lock -- "Inflated" is an absorbing state.
1354     }
1355 
1356     // Once the ObjectMonitor is configured and object is associated
1357     // with the ObjectMonitor, it is safe to allow async deflation:
1358     _in_use_list.add(m);
1359 
1360     // Hopefully the performance counters are allocated on distinct
1361     // cache lines to avoid false sharing on MP systems ...
1362     OM_PERFDATA_OP(Inflations, inc());
1363     if (log_is_enabled(Trace, monitorinflation)) {
1364       ResourceMark rm(current);
1365       lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1366                    INTPTR_FORMAT ", type='%s'", p2i(object),
1367                    object->mark().value(), object->klass()->external_name());
1368     }
1369     if (event.should_commit()) {
1370       post_monitor_inflate_event(&event, object, cause);
1371     }
1372     return m;
1373   }
1374 }
1375 
1376 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1377                                            const char* cnt_name, size_t cnt,
1378                                            LogStream* ls, elapsedTimer* timer_p) {
1379   if (!SafepointMechanism::should_process(current)) {
1380     return;
1381   }
1382 
1383   // A safepoint/handshake has started.
1384   if (ls != NULL) {
1385     timer_p->stop();
1386     ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1387                  SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1388                  op_name, cnt_name, cnt, in_use_list_ceiling(),
1389                  _in_use_list.count(), _in_use_list.max());
1390   }
1391 
1392   {
1393     // Honor block request.
1394     ThreadBlockInVM tbivm(current);
1395   }
1396 
1397   if (ls != NULL) {
1398     ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1399                  ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1400                  in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1401     timer_p->start();
1402   }
1403 }
1404 
1405 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1406 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1407 //
1408 // If table != nullptr, we gather owned ObjectMonitors indexed by the
1409 // owner in the table. Please note that ObjectMonitors where the owner
1410 // is set to a stack lock address are NOT associated with the JavaThread
1411 // that holds that stack lock. All of the current consumers of
1412 // ObjectMonitorsHashtable info only care about JNI locked monitors and
1413 // those do not have the owner set to a stack lock address.
1414 //
1415 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1416                                                 elapsedTimer* timer_p,
1417                                                 ObjectMonitorsHashtable* table) {
1418   MonitorList::Iterator iter = _in_use_list.iterator();
1419   size_t deflated_count = 0;
1420 
1421   while (iter.has_next()) {
1422     if (deflated_count >= (size_t)MonitorDeflationMax) {
1423       break;
1424     }
1425     ObjectMonitor* mid = iter.next();
1426     if (mid->deflate_monitor()) {
1427       deflated_count++;
1428     } else if (table != nullptr) {
1429       // The caller is interested in the owned ObjectMonitors. This does
1430       // not include when owner is set to a stack lock address in thread.
1431       // This also does not capture unowned ObjectMonitors that cannot be
1432       // deflated because of a waiter.
1433       void* key = mid->owner();
1434       // Since deflate_idle_monitors() and deflate_monitor_list() can be
1435       // called more than once, we have to make sure the entry has not
1436       // already been added.
1437       if (key != nullptr && !table->has_entry(key, mid)) {
1438         table->add_entry(key, mid);
1439       }
1440     }
1441 
1442     if (current->is_Java_thread()) {
1443       // A JavaThread must check for a safepoint/handshake and honor it.
1444       chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1445                         deflated_count, ls, timer_p);
1446     }
1447   }
1448 
1449   return deflated_count;
1450 }
1451 
1452 class HandshakeForDeflation : public HandshakeClosure {
1453  public:
1454   HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1455 
1456   void do_thread(Thread* thread) {
1457     log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1458                                 INTPTR_FORMAT, p2i(thread));
1459   }
1460 };
1461 
1462 // This function is called by the MonitorDeflationThread to deflate
1463 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1464 // and VM_ThreadDump::doit() by the VMThread.
1465 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) {
1466   Thread* current = Thread::current();
1467   if (current->is_Java_thread()) {
1468     // The async deflation request has been processed.
1469     _last_async_deflation_time_ns = os::javaTimeNanos();
1470     set_is_async_deflation_requested(false);
1471   }
1472 
1473   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1474   LogStreamHandle(Info, monitorinflation) lsh_info;
1475   LogStream* ls = NULL;
1476   if (log_is_enabled(Debug, monitorinflation)) {
1477     ls = &lsh_debug;
1478   } else if (log_is_enabled(Info, monitorinflation)) {
1479     ls = &lsh_info;
1480   }
1481 
1482   elapsedTimer timer;
1483   if (ls != NULL) {
1484     ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1485                  in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1486     timer.start();
1487   }
1488 
1489   // Deflate some idle ObjectMonitors.
1490   size_t deflated_count = deflate_monitor_list(current, ls, &timer, table);
1491   if (deflated_count > 0 || is_final_audit()) {
1492     // There are ObjectMonitors that have been deflated or this is the
1493     // final audit and all the remaining ObjectMonitors have been
1494     // deflated, BUT the MonitorDeflationThread blocked for the final
1495     // safepoint during unlinking.
1496 
1497     // Unlink deflated ObjectMonitors from the in-use list.
1498     ResourceMark rm;
1499     GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1500     size_t unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer,
1501                                                          &delete_list);
1502     if (current->is_Java_thread()) {
1503       if (ls != NULL) {
1504         timer.stop();
1505         ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1506                      ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1507                      SIZE_FORMAT ", max=" SIZE_FORMAT,
1508                      unlinked_count, in_use_list_ceiling(),
1509                      _in_use_list.count(), _in_use_list.max());
1510       }
1511 
1512       // A JavaThread needs to handshake in order to safely free the
1513       // ObjectMonitors that were deflated in this cycle.
1514       HandshakeForDeflation hfd_hc;
1515       Handshake::execute(&hfd_hc);
1516 
1517       if (ls != NULL) {
1518         ls->print_cr("after handshaking: in_use_list stats: ceiling="
1519                      SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1520                      in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1521         timer.start();
1522       }
1523     }
1524 
1525     // After the handshake, safely free the ObjectMonitors that were
1526     // deflated in this cycle.
1527     size_t deleted_count = 0;
1528     for (ObjectMonitor* monitor: delete_list) {
1529       delete monitor;
1530       deleted_count++;
1531 
1532       if (current->is_Java_thread()) {
1533         // A JavaThread must check for a safepoint/handshake and honor it.
1534         chk_for_block_req(JavaThread::cast(current), "deletion", "deleted_count",
1535                           deleted_count, ls, &timer);
1536       }
1537     }
1538   }
1539 
1540   if (ls != NULL) {
1541     timer.stop();
1542     if (deflated_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1543       ls->print_cr("deflated " SIZE_FORMAT " monitors in %3.7f secs",
1544                    deflated_count, timer.seconds());
1545     }
1546     ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1547                  in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1548     if (table != nullptr) {
1549       ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT,
1550                    table->key_count(), table->om_count());
1551     }
1552   }
1553 
1554   OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1555   OM_PERFDATA_OP(Deflations, inc(deflated_count));
1556 
1557   GVars.stw_random = os::random();
1558 
1559   if (deflated_count != 0) {
1560     _no_progress_cnt = 0;
1561   } else {
1562     _no_progress_cnt++;
1563   }
1564 
1565   return deflated_count;
1566 }
1567 
1568 // Monitor cleanup on JavaThread::exit
1569 
1570 // Iterate through monitor cache and attempt to release thread's monitors
1571 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1572  private:
1573   JavaThread* _thread;
1574 
1575  public:
1576   ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1577   void do_monitor(ObjectMonitor* mid) {
1578     (void)mid->complete_exit(_thread);
1579   }
1580 };
1581 
1582 // Release all inflated monitors owned by current thread.  Lightweight monitors are
1583 // ignored.  This is meant to be called during JNI thread detach which assumes
1584 // all remaining monitors are heavyweight.  All exceptions are swallowed.
1585 // Scanning the extant monitor list can be time consuming.
1586 // A simple optimization is to add a per-thread flag that indicates a thread
1587 // called jni_monitorenter() during its lifetime.
1588 //
1589 // Instead of NoSafepointVerifier it might be cheaper to
1590 // use an idiom of the form:
1591 //   auto int tmp = SafepointSynchronize::_safepoint_counter ;
1592 //   <code that must not run at safepoint>
1593 //   guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1594 // Since the tests are extremely cheap we could leave them enabled
1595 // for normal product builds.
1596 
1597 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1598   assert(current == JavaThread::current(), "must be current Java thread");
1599   NoSafepointVerifier nsv;
1600   ReleaseJavaMonitorsClosure rjmc(current);
1601   ObjectSynchronizer::monitors_iterate(&rjmc, current);
1602   assert(!current->has_pending_exception(), "Should not be possible");
1603   current->clear_pending_exception();
1604 }
1605 
1606 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1607   switch (cause) {
1608     case inflate_cause_vm_internal:    return "VM Internal";
1609     case inflate_cause_monitor_enter:  return "Monitor Enter";
1610     case inflate_cause_wait:           return "Monitor Wait";
1611     case inflate_cause_notify:         return "Monitor Notify";
1612     case inflate_cause_hash_code:      return "Monitor Hash Code";
1613     case inflate_cause_jni_enter:      return "JNI Monitor Enter";
1614     case inflate_cause_jni_exit:       return "JNI Monitor Exit";
1615     default:
1616       ShouldNotReachHere();
1617   }
1618   return "Unknown";
1619 }
1620 
1621 //------------------------------------------------------------------------------
1622 // Debugging code
1623 
1624 u_char* ObjectSynchronizer::get_gvars_addr() {
1625   return (u_char*)&GVars;
1626 }
1627 
1628 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1629   return (u_char*)&GVars.hc_sequence;
1630 }
1631 
1632 size_t ObjectSynchronizer::get_gvars_size() {
1633   return sizeof(SharedGlobals);
1634 }
1635 
1636 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1637   return (u_char*)&GVars.stw_random;
1638 }
1639 
1640 // Do the final audit and print of ObjectMonitor stats; must be done
1641 // by the VMThread at VM exit time.
1642 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1643   assert(Thread::current()->is_VM_thread(), "sanity check");
1644 
1645   if (is_final_audit()) {  // Only do the audit once.
1646     return;
1647   }
1648   set_is_final_audit();
1649 
1650   if (log_is_enabled(Info, monitorinflation)) {
1651     // Do a deflation in order to reduce the in-use monitor population
1652     // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1653     // which is called by ObjectSynchronizer::audit_and_print_stats().
1654     while (ObjectSynchronizer::deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) >= (size_t)MonitorDeflationMax) {
1655       ; // empty
1656     }
1657     // The other audit_and_print_stats() call is done at the Debug
1658     // level at a safepoint in ObjectSynchronizer::do_safepoint_work().
1659     ObjectSynchronizer::audit_and_print_stats(true /* on_exit */);
1660   }
1661 }
1662 
1663 // This function can be called at a safepoint or it can be called when
1664 // we are trying to exit the VM. When we are trying to exit the VM, the
1665 // list walker functions can run in parallel with the other list
1666 // operations so spin-locking is used for safety.
1667 //
1668 // Calls to this function can be added in various places as a debugging
1669 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1670 // details logged at the Info level and 'false' for the 'on_exit'
1671 // parameter to have in-use monitor details logged at the Trace level.
1672 //
1673 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1674   assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1675 
1676   LogStreamHandle(Debug, monitorinflation) lsh_debug;
1677   LogStreamHandle(Info, monitorinflation) lsh_info;
1678   LogStreamHandle(Trace, monitorinflation) lsh_trace;
1679   LogStream* ls = NULL;
1680   if (log_is_enabled(Trace, monitorinflation)) {
1681     ls = &lsh_trace;
1682   } else if (log_is_enabled(Debug, monitorinflation)) {
1683     ls = &lsh_debug;
1684   } else if (log_is_enabled(Info, monitorinflation)) {
1685     ls = &lsh_info;
1686   }
1687   assert(ls != NULL, "sanity check");
1688 
1689   int error_cnt = 0;
1690 
1691   ls->print_cr("Checking in_use_list:");
1692   chk_in_use_list(ls, &error_cnt);
1693 
1694   if (error_cnt == 0) {
1695     ls->print_cr("No errors found in in_use_list checks.");
1696   } else {
1697     log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1698   }
1699 
1700   if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1701       (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1702     // When exiting this log output is at the Info level. When called
1703     // at a safepoint, this log output is at the Trace level since
1704     // there can be a lot of it.
1705     log_in_use_monitor_details(ls);
1706   }
1707 
1708   ls->flush();
1709 
1710   guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1711 }
1712 
1713 // Check the in_use_list; log the results of the checks.
1714 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1715   size_t l_in_use_count = _in_use_list.count();
1716   size_t l_in_use_max = _in_use_list.max();
1717   out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1718                 l_in_use_max);
1719 
1720   size_t ck_in_use_count = 0;
1721   MonitorList::Iterator iter = _in_use_list.iterator();
1722   while (iter.has_next()) {
1723     ObjectMonitor* mid = iter.next();
1724     chk_in_use_entry(mid, out, error_cnt_p);
1725     ck_in_use_count++;
1726   }
1727 
1728   if (l_in_use_count == ck_in_use_count) {
1729     out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1730                   SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1731   } else {
1732     out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1733                   "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1734                   ck_in_use_count);
1735   }
1736 
1737   size_t ck_in_use_max = _in_use_list.max();
1738   if (l_in_use_max == ck_in_use_max) {
1739     out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1740                   SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1741   } else {
1742     out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1743                   "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1744   }
1745 }
1746 
1747 // Check an in-use monitor entry; log any errors.
1748 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1749                                           int* error_cnt_p) {
1750   if (n->owner_is_DEFLATER_MARKER()) {
1751     // This should not happen, but if it does, it is not fatal.
1752     out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1753                   "deflated.", p2i(n));
1754     return;
1755   }
1756   if (n->header().value() == 0) {
1757     out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1758                   "have non-NULL _header field.", p2i(n));
1759     *error_cnt_p = *error_cnt_p + 1;
1760   }
1761   const oop obj = n->object_peek();
1762   if (obj != NULL) {
1763     const markWord mark = obj->mark();
1764     if (!mark.has_monitor()) {
1765       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1766                     "object does not think it has a monitor: obj="
1767                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1768                     p2i(obj), mark.value());
1769       *error_cnt_p = *error_cnt_p + 1;
1770     }
1771     ObjectMonitor* const obj_mon = mark.monitor();
1772     if (n != obj_mon) {
1773       out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1774                     "object does not refer to the same monitor: obj="
1775                     INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1776                     INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1777       *error_cnt_p = *error_cnt_p + 1;
1778     }
1779   }
1780 }
1781 
1782 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1783 // flags indicate why the entry is in-use, 'object' and 'object type'
1784 // indicate the associated object and its type.
1785 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
1786   stringStream ss;
1787   if (_in_use_list.count() > 0) {
1788     out->print_cr("In-use monitor info:");
1789     out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1790     out->print_cr("%18s  %s  %18s  %18s",
1791                   "monitor", "BHL", "object", "object type");
1792     out->print_cr("==================  ===  ==================  ==================");
1793     MonitorList::Iterator iter = _in_use_list.iterator();
1794     while (iter.has_next()) {
1795       ObjectMonitor* mid = iter.next();
1796       const oop obj = mid->object_peek();
1797       const markWord mark = mid->header();
1798       ResourceMark rm;
1799       out->print(INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT "  %s", p2i(mid),
1800                  mid->is_busy(), mark.hash() != 0, mid->owner() != NULL,
1801                  p2i(obj), obj == NULL ? "" : obj->klass()->external_name());
1802       if (mid->is_busy()) {
1803         out->print(" (%s)", mid->is_busy_to_string(&ss));
1804         ss.reset();
1805       }
1806       out->cr();
1807     }
1808   }
1809 
1810   out->flush();
1811 }