share/runtime/synchronizer.cpp

/*
 * Copyright (c) 1998, 2021, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include "precompiled.hpp"
#include "classfile/vmSymbols.hpp"
#include "jfr/jfrEvents.hpp"
#include "logging/log.hpp"
#include "logging/logStream.hpp"
#include "memory/allocation.inline.hpp"
#include "memory/padded.hpp"
#include "memory/resourceArea.hpp"
#include "memory/universe.hpp"
#include "oops/markWord.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/biasedLocking.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/handshake.hpp"
#include "runtime/interfaceSupport.inline.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/objectMonitor.hpp"
#include "runtime/objectMonitor.inline.hpp"
#include "runtime/os.inline.hpp"
#include "runtime/osThread.hpp"
#include "runtime/perfData.hpp"
#include "runtime/safepointMechanism.inline.hpp"
#include "runtime/safepointVerifiers.hpp"
#include "runtime/sharedRuntime.hpp"
#include "runtime/stubRoutines.hpp"
#include "runtime/synchronizer.hpp"
#include "runtime/thread.inline.hpp"
#include "runtime/timer.hpp"
#include "runtime/vframe.hpp"
#include "runtime/vmThread.hpp"
#include "utilities/align.hpp"
#include "utilities/dtrace.hpp"
#include "utilities/events.hpp"
#include "utilities/preserveException.hpp"

void MonitorList::add(ObjectMonitor* m) {
  ObjectMonitor* head;
  do {
    head = Atomic::load(&_head);
    m->set_next_om(head);
  } while (Atomic::cmpxchg(&_head, head, m) != head);

  size_t count = Atomic::add(&_count, 1u);
  if (count > max()) {
    Atomic::inc(&_max);
  }
}

size_t MonitorList::count() const {
  return Atomic::load(&_count);
}

size_t MonitorList::max() const {
  return Atomic::load(&_max);
}

// Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
// ObjectMonitors. Returns the number of unlinked ObjectMonitors.
size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
                                    elapsedTimer* timer_p,
                                    GrowableArray<ObjectMonitor*>* unlinked_list) {
  size_t unlinked_count = 0;
  ObjectMonitor* prev = NULL;
  ObjectMonitor* head = Atomic::load_acquire(&_head);
  ObjectMonitor* m = head;
  // The in-use list head can be NULL during the final audit.
  while (m != NULL) {
    if (m->is_being_async_deflated()) {
      // Find next live ObjectMonitor.
      ObjectMonitor* next = m;
      do {
        ObjectMonitor* next_next = next->next_om();
        unlinked_count++;
        unlinked_list->append(next);
        next = next_next;
        if (unlinked_count >= (size_t)MonitorDeflationMax) {
          // Reached the max so bail out on the gathering loop.
          break;
        }
      } while (next != NULL && next->is_being_async_deflated());
      if (prev == NULL) {
        ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
        if (prev_head != head) {
          // Find new prev ObjectMonitor that just got inserted.
          for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
            prev = n;
          }
          prev->set_next_om(next);
        }
      } else {
        prev->set_next_om(next);
      }
      if (unlinked_count >= (size_t)MonitorDeflationMax) {
        // Reached the max so bail out on the searching loop.
        break;
      }
      m = next;
    } else {
      prev = m;
      m = m->next_om();
    }

    if (current->is_Java_thread()) {
      // A JavaThread must check for a safepoint/handshake and honor it.
      ObjectSynchronizer::chk_for_block_req(current->as_Java_thread(), "unlinking",
                                            "unlinked_count", unlinked_count,
                                            ls, timer_p);
    }
  }
  Atomic::sub(&_count, unlinked_count);
  return unlinked_count;
}

MonitorList::Iterator MonitorList::iterator() const {
  return Iterator(Atomic::load_acquire(&_head));
}

ObjectMonitor* MonitorList::Iterator::next() {
  ObjectMonitor* current = _current;
  _current = current->next_om();
  return current;
}

// The "core" versions of monitor enter and exit reside in this file.
// The interpreter and compilers contain specialized transliterated
// variants of the enter-exit fast-path operations.  See c2_MacroAssembler_x86.cpp
// fast_lock(...) for instance.  If you make changes here, make sure to modify the
// interpreter, and both C1 and C2 fast-path inline locking code emission.
//
// -----------------------------------------------------------------------------

#ifdef DTRACE_ENABLED

// Only bother with this argument setup if dtrace is available
// TODO-FIXME: probes should not fire when caller is _blocked.  assert() accordingly.

#define DTRACE_MONITOR_PROBE_COMMON(obj, thread)                           \
  char* bytes = NULL;                                                      \
  int len = 0;                                                             \
  jlong jtid = SharedRuntime::get_java_tid(thread);                        \
  Symbol* klassname = obj->klass()->name();                                \
  if (klassname != NULL) {                                                 \
    bytes = (char*)klassname->bytes();                                     \
    len = klassname->utf8_length();                                        \
  }

#define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis)            \
  {                                                                        \
    if (DTraceMonitorProbes) {                                             \
      DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
      HOTSPOT_MONITOR_WAIT(jtid,                                           \
                           (uintptr_t)(monitor), bytes, len, (millis));    \
    }                                                                      \
  }

#define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
#define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
#define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED

#define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread)                  \
  {                                                                        \
    if (DTraceMonitorProbes) {                                             \
      DTRACE_MONITOR_PROBE_COMMON(obj, thread);                            \
      HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */             \
                                    (uintptr_t)(monitor), bytes, len);     \
    }                                                                      \
  }

#else //  ndef DTRACE_ENABLED

#define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon)    {;}
#define DTRACE_MONITOR_PROBE(probe, obj, thread, mon)          {;}

#endif // ndef DTRACE_ENABLED

// This exists only as a workaround of dtrace bug 6254741
int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
  DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
  return 0;
}

static const int NINFLATIONLOCKS = 256;
static os::PlatformMutex* gInflationLocks[NINFLATIONLOCKS];

void ObjectSynchronizer::initialize() {
  for (int i = 0; i < NINFLATIONLOCKS; i++) {
    gInflationLocks[i] = new os::PlatformMutex();
  }
  // Start the ceiling with the estimate for one thread.
  set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
}

MonitorList ObjectSynchronizer::_in_use_list;
// monitors_used_above_threshold() policy is as follows:
//
// The ratio of the current _in_use_list count to the ceiling is used
// to determine if we are above MonitorUsedDeflationThreshold and need
// to do an async monitor deflation cycle. The ceiling is increased by
// AvgMonitorsPerThreadEstimate when a thread is added to the system
// and is decreased by AvgMonitorsPerThreadEstimate when a thread is
// removed from the system.
//
// Note: If the _in_use_list max exceeds the ceiling, then
// monitors_used_above_threshold() will use the in_use_list max instead
// of the thread count derived ceiling because we have used more
// ObjectMonitors than the estimated average.
//
// Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
// no-progress async monitor deflation cycles in a row, then the ceiling
// is adjusted upwards by monitors_used_above_threshold().
//
// Start the ceiling with the estimate for one thread in initialize()
// which is called after cmd line options are processed.
static size_t _in_use_list_ceiling = 0;
bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
bool volatile ObjectSynchronizer::_is_final_audit = false;
jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
static uintx _no_progress_cnt = 0;

// =====================> Quick functions

// The quick_* forms are special fast-path variants used to improve
// performance.  In the simplest case, a "quick_*" implementation could
// simply return false, in which case the caller will perform the necessary
// state transitions and call the slow-path form.
// The fast-path is designed to handle frequently arising cases in an efficient
// manner and is just a degenerate "optimistic" variant of the slow-path.
// returns true  -- to indicate the call was satisfied.
// returns false -- to indicate the call needs the services of the slow-path.
// A no-loitering ordinance is in effect for code in the quick_* family
// operators: safepoints or indefinite blocking (blocking that might span a
// safepoint) are forbidden. Generally the thread_state() is _in_Java upon
// entry.
//
// Consider: An interesting optimization is to have the JIT recognize the
// following common idiom:
//   synchronized (someobj) { .... ; notify(); }
// That is, we find a notify() or notifyAll() call that immediately precedes
// the monitorexit operation.  In that case the JIT could fuse the operations
// into a single notifyAndExit() runtime primitive.

bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
  assert(current->thread_state() == _thread_in_Java, "invariant");
  NoSafepointVerifier nsv;
  if (obj == NULL) return false;  // slow-path for invalid obj
  const markWord mark = obj->mark();

  if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
    // Degenerate notify
    // stack-locked by caller so by definition the implied waitset is empty.
    return true;
  }

  if (mark.has_monitor()) {
    ObjectMonitor* const mon = mark.monitor();
    assert(mon->object() == oop(obj), "invariant");
    if (mon->owner() != current) return false;  // slow-path for IMS exception

    if (mon->first_waiter() != NULL) {
      // We have one or more waiters. Since this is an inflated monitor
      // that we own, we can transfer one or more threads from the waitset
      // to the entrylist here and now, avoiding the slow-path.
      if (all) {
        DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
      } else {
        DTRACE_MONITOR_PROBE(notify, mon, obj, current);
      }
      int free_count = 0;
      do {
        mon->INotify(current);
        ++free_count;
      } while (mon->first_waiter() != NULL && all);
      OM_PERFDATA_OP(Notifications, inc(free_count));
    }
    return true;
  }

  // biased locking and any other IMS exception states take the slow-path
  return false;
}


// The LockNode emitted directly at the synchronization site would have
// been too big if it were to have included support for the cases of inflated
// recursive enter and exit, so they go here instead.
// Note that we can't safely call AsyncPrintJavaStack() from within
// quick_enter() as our thread state remains _in_Java.

bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
                                     BasicLock * lock) {
  assert(current->thread_state() == _thread_in_Java, "invariant");
  NoSafepointVerifier nsv;
  if (obj == NULL) return false;       // Need to throw NPE

  if (obj->klass()->is_value_based()) {
    return false;
  }

  const markWord mark = obj->mark();

  if (mark.has_monitor()) {
    ObjectMonitor* const m = mark.monitor();
    // An async deflation or GC can race us before we manage to make
    // the ObjectMonitor busy by setting the owner below. If we detect
    // that race we just bail out to the slow-path here.
    if (m->object_peek() == NULL) {
      return false;
    }
    JavaThread* const owner = (JavaThread*) m->owner_raw();

    // Lock contention and Transactional Lock Elision (TLE) diagnostics
    // and observability
    // Case: light contention possibly amenable to TLE
    // Case: TLE inimical operations such as nested/recursive synchronization

    if (owner == current) {
      m->_recursions++;
      return true;
    }

    // This Java Monitor is inflated so obj's header will never be
    // displaced to this thread's BasicLock. Make the displaced header
    // non-NULL so this BasicLock is not seen as recursive nor as
    // being locked. We do this unconditionally so that this thread's
    // BasicLock cannot be mis-interpreted by any stack walkers. For
    // performance reasons, stack walkers generally first check for
    // Biased Locking in the object's header, the second check is for
    // stack-locking in the object's header, the third check is for
    // recursive stack-locking in the displaced header in the BasicLock,
    // and last are the inflated Java Monitor (ObjectMonitor) checks.
    lock->set_displaced_header(markWord::unused_mark());

    if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
      assert(m->_recursions == 0, "invariant");
      return true;
    }
  }

  // Note that we could inflate in quick_enter.
  // This is likely a useful optimization
  // Critically, in quick_enter() we must not:
  // -- perform bias revocation, or
  // -- block indefinitely, or
  // -- reach a safepoint

  return false;        // revert to slow-path
}

// Handle notifications when synchronizing on value based classes
void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
  frame last_frame = current->last_frame();
  bool bcp_was_adjusted = false;
  // Don't decrement bcp if it points to the frame's first instruction.  This happens when
  // handle_sync_on_value_based_class() is called because of a synchronized method.  There
  // is no actual monitorenter instruction in the byte code in this case.
  if (last_frame.is_interpreted_frame() &&
      (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
    // adjust bcp to point back to monitorenter so that we print the correct line numbers
    last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
    bcp_was_adjusted = true;
  }

  if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
    ResourceMark rm(current);
    stringStream ss;
    current->print_stack_on(&ss);
    char* base = (char*)strstr(ss.base(), "at");
    char* newline = (char*)strchr(ss.base(), '\n');
    if (newline != NULL) {
      *newline = '\0';
    }
    fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
  } else {
    assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
    ResourceMark rm(current);
    Log(valuebasedclasses) vblog;

    vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
    if (current->has_last_Java_frame()) {
      LogStream info_stream(vblog.info());
      current->print_stack_on(&info_stream);
    } else {
      vblog.info("Cannot find the last Java frame");
    }

    EventSyncOnValueBasedClass event;
    if (event.should_commit()) {
      event.set_valueBasedClass(obj->klass());
      event.commit();
    }
  }

  if (bcp_was_adjusted) {
    last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
  }
}

// -----------------------------------------------------------------------------
// Monitor Enter/Exit
// The interpreter and compiler assembly code tries to lock using the fast path
// of this algorithm. Make sure to update that code if the following function is
// changed. The implementation is extremely sensitive to race condition. Be careful.

void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
  if (obj->klass()->is_value_based()) {
    handle_sync_on_value_based_class(obj, current);
  }

  if (UseBiasedLocking) {
    BiasedLocking::revoke(current, obj);
  }

  markWord mark = obj->mark();
  assert(!mark.has_bias_pattern(), "should not see bias pattern here");

  if (mark.is_neutral()) {
    // Anticipate successful CAS -- the ST of the displaced mark must
    // be visible <= the ST performed by the CAS.
    lock->set_displaced_header(mark);
    if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
      return;
    }
    // Fall through to inflate() ...
  } else if (mark.has_locker() &&
             current->is_lock_owned((address)mark.locker())) {
    assert(lock != mark.locker(), "must not re-lock the same lock");
    assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
    lock->set_displaced_header(markWord::from_pointer(NULL));
    return;
  }

  // The object header will never be displaced to this lock,
  // so it does not matter what the value is, except that it
  // must be non-zero to avoid looking like a re-entrant lock,
  // and must not look locked either.
  lock->set_displaced_header(markWord::unused_mark());
  // An async deflation can race after the inflate() call and before
  // enter() can make the ObjectMonitor busy. enter() returns false if
  // we have lost the race to async deflation and we simply try again.
  while (true) {
    ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
    if (monitor->enter(current)) {
      return;
    }
  }
}

void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
  markWord mark = object->mark();
  // We cannot check for Biased Locking if we are racing an inflation.
  assert(mark == markWord::INFLATING() ||
         !mark.has_bias_pattern(), "should not see bias pattern here");

  markWord dhw = lock->displaced_header();
  if (dhw.value() == 0) {
    // If the displaced header is NULL, then this exit matches up with
    // a recursive enter. No real work to do here except for diagnostics.
#ifndef PRODUCT
    if (mark != markWord::INFLATING()) {
      // Only do diagnostics if we are not racing an inflation. Simply
      // exiting a recursive enter of a Java Monitor that is being
      // inflated is safe; see the has_monitor() comment below.
      assert(!mark.is_neutral(), "invariant");
      assert(!mark.has_locker() ||
             current->is_lock_owned((address)mark.locker()), "invariant");
      if (mark.has_monitor()) {
        // The BasicLock's displaced_header is marked as a recursive
        // enter and we have an inflated Java Monitor (ObjectMonitor).
        // This is a special case where the Java Monitor was inflated
        // after this thread entered the stack-lock recursively. When a
        // Java Monitor is inflated, we cannot safely walk the Java
        // Monitor owner's stack and update the BasicLocks because a
        // Java Monitor can be asynchronously inflated by a thread that
        // does not own the Java Monitor.
        ObjectMonitor* m = mark.monitor();
        assert(m->object()->mark() == mark, "invariant");
        assert(m->is_entered(current), "invariant");
      }
    }
#endif
    return;
  }

  if (mark == markWord::from_pointer(lock)) {
    // If the object is stack-locked by the current thread, try to
    // swing the displaced header from the BasicLock back to the mark.
    assert(dhw.is_neutral(), "invariant");
    if (object->cas_set_mark(dhw, mark) == mark) {
      return;
    }
  }

  // We have to take the slow-path of possible inflation and then exit.
  // The ObjectMonitor* can't be async deflated until ownership is
  // dropped inside exit() and the ObjectMonitor* must be !is_busy().
  ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
  monitor->exit(current);
}

// -----------------------------------------------------------------------------
// Class Loader  support to workaround deadlocks on the class loader lock objects
// Also used by GC
// complete_exit()/reenter() are used to wait on a nested lock
// i.e. to give up an outer lock completely and then re-enter
// Used when holding nested locks - lock acquisition order: lock1 then lock2
//  1) complete_exit lock1 - saving recursion count
//  2) wait on lock2
//  3) when notified on lock2, unlock lock2
//  4) reenter lock1 with original recursion count
//  5) lock lock2
// NOTE: must use heavy weight monitor to handle complete_exit/reenter()
intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
  if (UseBiasedLocking) {
    BiasedLocking::revoke(current, obj);
    assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
  }

  // The ObjectMonitor* can't be async deflated until ownership is
  // dropped inside exit() and the ObjectMonitor* must be !is_busy().
  ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
  intptr_t ret_code = monitor->complete_exit(current);
  return ret_code;
}

// NOTE: must use heavy weight monitor to handle complete_exit/reenter()
void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
  if (UseBiasedLocking) {
    BiasedLocking::revoke(current, obj);
    assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
  }

  // An async deflation can race after the inflate() call and before
  // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
  // enter() returns false if we have lost the race to async deflation
  // and we simply try again.
  while (true) {
    ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
    if (monitor->reenter(recursions, current)) {
      return;
    }
  }
}

// -----------------------------------------------------------------------------
// JNI locks on java objects
// NOTE: must use heavy weight monitor to handle jni monitor enter
void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
  if (obj->klass()->is_value_based()) {
    handle_sync_on_value_based_class(obj, current);
  }

  // the current locking is from JNI instead of Java code
  if (UseBiasedLocking) {
    BiasedLocking::revoke(current, obj);
    assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
  }
  current->set_current_pending_monitor_is_from_java(false);
  // An async deflation can race after the inflate() call and before
  // enter() can make the ObjectMonitor busy. enter() returns false if
  // we have lost the race to async deflation and we simply try again.
  while (true) {
    ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
    if (monitor->enter(current)) {
      break;
    }
  }
  current->set_current_pending_monitor_is_from_java(true);
}

// NOTE: must use heavy weight monitor to handle jni monitor exit
void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
  JavaThread* current = THREAD;
  if (UseBiasedLocking) {
    Handle h_obj(current, obj);
    BiasedLocking::revoke(current, h_obj);
    obj = h_obj();
  }
  assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");

  // The ObjectMonitor* can't be async deflated until ownership is
  // dropped inside exit() and the ObjectMonitor* must be !is_busy().
  ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
  // If this thread has locked the object, exit the monitor. We
  // intentionally do not use CHECK on check_owner because we must exit the
  // monitor even if an exception was already pending.
  if (monitor->check_owner(THREAD)) {
    monitor->exit(current);
  }
}

// -----------------------------------------------------------------------------
// Internal VM locks on java objects
// standard constructor, allows locking failures
ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
  _thread = thread;
  _thread->check_for_valid_safepoint_state();
  _obj = obj;

  if (_obj() != NULL) {
    ObjectSynchronizer::enter(_obj, &_lock, _thread);
  }
}

ObjectLocker::~ObjectLocker() {
  if (_obj() != NULL) {
    ObjectSynchronizer::exit(_obj(), &_lock, _thread);
  }
}


// -----------------------------------------------------------------------------
//  Wait/Notify/NotifyAll
// NOTE: must use heavy weight monitor to handle wait()
int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
  JavaThread* current = THREAD;
  if (UseBiasedLocking) {
    BiasedLocking::revoke(current, obj);
    assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
  }
  if (millis < 0) {
    THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
  }
  // The ObjectMonitor* can't be async deflated because the _waiters
  // field is incremented before ownership is dropped and decremented
  // after ownership is regained.
  ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);

  DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
  monitor->wait(millis, true, THREAD); // Not CHECK as we need following code

  // This dummy call is in place to get around dtrace bug 6254741.  Once
  // that's fixed we can uncomment the following line, remove the call
  // and change this function back into a "void" func.
  // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
  int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
  return ret_code;
}

// No exception are possible in this case as we only use this internally when locking is
// correct and we have to wait until notified - so no interrupts or timeouts.
void ObjectSynchronizer::wait_uninterruptibly(Handle obj, JavaThread* current) {
  if (UseBiasedLocking) {
    BiasedLocking::revoke(current, obj);
    assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
  }
  // The ObjectMonitor* can't be async deflated because the _waiters
  // field is incremented before ownership is dropped and decremented
  // after ownership is regained.
  ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
  monitor->wait(0 /* wait-forever */, false /* not interruptible */, current);
}

void ObjectSynchronizer::notify(Handle obj, TRAPS) {
  JavaThread* current = THREAD;
  if (UseBiasedLocking) {
    BiasedLocking::revoke(current, obj);
    assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
  }

  markWord mark = obj->mark();
  if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
    // Not inflated so there can't be any waiters to notify.
    return;
  }
  // The ObjectMonitor* can't be async deflated until ownership is
  // dropped by the calling thread.
  ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
  monitor->notify(CHECK);
}

// NOTE: see comment of notify()
void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
  JavaThread* current = THREAD;
  if (UseBiasedLocking) {
    BiasedLocking::revoke(current, obj);
    assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
  }

  markWord mark = obj->mark();
  if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
    // Not inflated so there can't be any waiters to notify.
    return;
  }
  // The ObjectMonitor* can't be async deflated until ownership is
  // dropped by the calling thread.
  ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
  monitor->notifyAll(CHECK);
}

// -----------------------------------------------------------------------------
// Hash Code handling

struct SharedGlobals {
  char         _pad_prefix[OM_CACHE_LINE_SIZE];
  // This is a highly shared mostly-read variable.
  // To avoid false-sharing it needs to be the sole occupant of a cache line.
  volatile int stw_random;
  DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
  // Hot RW variable -- Sequester to avoid false-sharing
  volatile int hc_sequence;
  DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
};

static SharedGlobals GVars;

static markWord read_stable_mark(oop obj) {
  markWord mark = obj->mark();
  if (!mark.is_being_inflated()) {
    return mark;       // normal fast-path return
  }

  int its = 0;
  for (;;) {
    markWord mark = obj->mark();
    if (!mark.is_being_inflated()) {
      return mark;    // normal fast-path return
    }

    // The object is being inflated by some other thread.
    // The caller of read_stable_mark() must wait for inflation to complete.
    // Avoid live-lock.

    ++its;
    if (its > 10000 || !os::is_MP()) {
      if (its & 1) {
        os::naked_yield();
      } else {
        // Note that the following code attenuates the livelock problem but is not
        // a complete remedy.  A more complete solution would require that the inflating
        // thread hold the associated inflation lock.  The following code simply restricts
        // the number of spinners to at most one.  We'll have N-2 threads blocked
        // on the inflationlock, 1 thread holding the inflation lock and using
        // a yield/park strategy, and 1 thread in the midst of inflation.
        // A more refined approach would be to change the encoding of INFLATING
        // to allow encapsulation of a native thread pointer.  Threads waiting for
        // inflation to complete would use CAS to push themselves onto a singly linked
        // list rooted at the markword.  Once enqueued, they'd loop, checking a per-thread flag
        // and calling park().  When inflation was complete the thread that accomplished inflation
        // would detach the list and set the markword to inflated with a single CAS and
        // then for each thread on the list, set the flag and unpark() the thread.

        // Index into the lock array based on the current object address.
        static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
        int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
        int YieldThenBlock = 0;
        assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
        gInflationLocks[ix]->lock();
        while (obj->mark() == markWord::INFLATING()) {
          // Beware: naked_yield() is advisory and has almost no effect on some platforms
          // so we periodically call current->_ParkEvent->park(1).
          // We use a mixed spin/yield/block mechanism.
          if ((YieldThenBlock++) >= 16) {
            Thread::current()->_ParkEvent->park(1);
          } else {
            os::naked_yield();
          }
        }
        gInflationLocks[ix]->unlock();
      }
    } else {
      SpinPause();       // SMP-polite spinning
    }
  }
}

// hashCode() generation :
//
// Possibilities:
// * MD5Digest of {obj,stw_random}
// * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
// * A DES- or AES-style SBox[] mechanism
// * One of the Phi-based schemes, such as:
//   2654435761 = 2^32 * Phi (golden ratio)
//   HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
// * A variation of Marsaglia's shift-xor RNG scheme.
// * (obj ^ stw_random) is appealing, but can result
//   in undesirable regularity in the hashCode values of adjacent objects
//   (objects allocated back-to-back, in particular).  This could potentially
//   result in hashtable collisions and reduced hashtable efficiency.
//   There are simple ways to "diffuse" the middle address bits over the
//   generated hashCode values:

static inline intptr_t get_next_hash(Thread* current, oop obj) {
  intptr_t value = 0;
  if (hashCode == 0) {
    // This form uses global Park-Miller RNG.
    // On MP system we'll have lots of RW access to a global, so the
    // mechanism induces lots of coherency traffic.
    value = os::random();
  } else if (hashCode == 1) {
    // This variation has the property of being stable (idempotent)
    // between STW operations.  This can be useful in some of the 1-0
    // synchronization schemes.
    intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
    value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
  } else if (hashCode == 2) {
    value = 1;            // for sensitivity testing
  } else if (hashCode == 3) {
    value = ++GVars.hc_sequence;
  } else if (hashCode == 4) {
    value = cast_from_oop<intptr_t>(obj);
  } else {
    // Marsaglia's xor-shift scheme with thread-specific state
    // This is probably the best overall implementation -- we'll
    // likely make this the default in future releases.
    unsigned t = current->_hashStateX;
    t ^= (t << 11);
    current->_hashStateX = current->_hashStateY;
    current->_hashStateY = current->_hashStateZ;
    current->_hashStateZ = current->_hashStateW;
    unsigned v = current->_hashStateW;
    v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
    current->_hashStateW = v;
    value = v;
  }

  value &= markWord::hash_mask;
  if (value == 0) value = 0xBAD;
  assert(value != markWord::no_hash, "invariant");
  return value;
}

intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
  if (UseBiasedLocking) {
    // NOTE: many places throughout the JVM do not expect a safepoint
    // to be taken here. However, we only ever bias Java instances and all
    // of the call sites of identity_hash that might revoke biases have
    // been checked to make sure they can handle a safepoint. The
    // added check of the bias pattern is to avoid useless calls to
    // thread-local storage.
    if (obj->mark().has_bias_pattern()) {
      // Handle for oop obj in case of STW safepoint
      Handle hobj(current, obj);
      if (SafepointSynchronize::is_at_safepoint()) {
        BiasedLocking::revoke_at_safepoint(hobj);
      } else {
        BiasedLocking::revoke(current->as_Java_thread(), hobj);
      }
      obj = hobj();
      assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
    }
  }

  while (true) {
    ObjectMonitor* monitor = NULL;
    markWord temp, test;
    intptr_t hash;
    markWord mark = read_stable_mark(obj);

    // object should remain ineligible for biased locking
    assert(!mark.has_bias_pattern(), "invariant");

    if (mark.is_neutral()) {               // if this is a normal header
      hash = mark.hash();
      if (hash != 0) {                     // if it has a hash, just return it
        return hash;
      }
      hash = get_next_hash(current, obj);  // get a new hash
      temp = mark.copy_set_hash(hash);     // merge the hash into header
                                           // try to install the hash
      test = obj->cas_set_mark(temp, mark);
      if (test == mark) {                  // if the hash was installed, return it
        return hash;
      }
      // Failed to install the hash. It could be that another thread
      // installed the hash just before our attempt or inflation has
      // occurred or... so we fall thru to inflate the monitor for
      // stability and then install the hash.
    } else if (mark.has_monitor()) {
      monitor = mark.monitor();
      temp = monitor->header();
      assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
      hash = temp.hash();
      if (hash != 0) {
        // It has a hash.

        // Separate load of dmw/header above from the loads in
        // is_being_async_deflated().

        // dmw/header and _contentions may get written by different threads.
        // Make sure to observe them in the same order when having several observers.
        OrderAccess::loadload_for_IRIW();

        if (monitor->is_being_async_deflated()) {
          // But we can't safely use the hash if we detect that async
          // deflation has occurred. So we attempt to restore the
          // header/dmw to the object's header so that we only retry
          // once if the deflater thread happens to be slow.
          monitor->install_displaced_markword_in_object(obj);
          continue;
        }
        return hash;
      }
      // Fall thru so we only have one place that installs the hash in
      // the ObjectMonitor.
    } else if (current->is_lock_owned((address)mark.locker())) {
      // This is a stack lock owned by the calling thread so fetch the
      // displaced markWord from the BasicLock on the stack.
      temp = mark.displaced_mark_helper();
      assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
      hash = temp.hash();
      if (hash != 0) {                  // if it has a hash, just return it
        return hash;
      }
      // WARNING:
      // The displaced header in the BasicLock on a thread's stack
      // is strictly immutable. It CANNOT be changed in ANY cases.
      // So we have to inflate the stack lock into an ObjectMonitor
      // even if the current thread owns the lock. The BasicLock on
      // a thread's stack can be asynchronously read by other threads
      // during an inflate() call so any change to that stack memory
      // may not propagate to other threads correctly.
    }

    // Inflate the monitor to set the hash.

    // An async deflation can race after the inflate() call and before we
    // can update the ObjectMonitor's header with the hash value below.
    monitor = inflate(current, obj, inflate_cause_hash_code);
    // Load ObjectMonitor's header/dmw field and see if it has a hash.
    mark = monitor->header();
    assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
    hash = mark.hash();
    if (hash == 0) {                       // if it does not have a hash
      hash = get_next_hash(current, obj);  // get a new hash
      temp = mark.copy_set_hash(hash)   ;  // merge the hash into header
      assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
      uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
      test = markWord(v);
      if (test != mark) {
        // The attempt to update the ObjectMonitor's header/dmw field
        // did not work. This can happen if another thread managed to
        // merge in the hash just before our cmpxchg().
        // If we add any new usages of the header/dmw field, this code
        // will need to be updated.
        hash = test.hash();
        assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
        assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
      }
      if (monitor->is_being_async_deflated()) {
        // If we detect that async deflation has occurred, then we
        // attempt to restore the header/dmw to the object's header
        // so that we only retry once if the deflater thread happens
        // to be slow.
        monitor->install_displaced_markword_in_object(obj);
        continue;
      }
    }
    // We finally get the hash.
    return hash;
  }
}

// Deprecated -- use FastHashCode() instead.

intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
  return FastHashCode(Thread::current(), obj());
}


bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
                                                   Handle h_obj) {
  if (UseBiasedLocking) {
    BiasedLocking::revoke(current, h_obj);
    assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
  }

  assert(current == JavaThread::current(), "Can only be called on current thread");
  oop obj = h_obj();

  markWord mark = read_stable_mark(obj);

  // Uncontended case, header points to stack
  if (mark.has_locker()) {
    return current->is_lock_owned((address)mark.locker());
  }
  // Contended case, header points to ObjectMonitor (tagged pointer)
  if (mark.has_monitor()) {
    // The first stage of async deflation does not affect any field
    // used by this comparison so the ObjectMonitor* is usable here.
    ObjectMonitor* monitor = mark.monitor();
    return monitor->is_entered(current) != 0;
  }
  // Unlocked case, header in place
  assert(mark.is_neutral(), "sanity check");
  return false;
}

// FIXME: jvmti should call this
JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
  if (UseBiasedLocking) {
    if (SafepointSynchronize::is_at_safepoint()) {
      BiasedLocking::revoke_at_safepoint(h_obj);
    } else {
      BiasedLocking::revoke(JavaThread::current(), h_obj);
    }
    assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
  }

  oop obj = h_obj();
  address owner = NULL;

  markWord mark = read_stable_mark(obj);

  // Uncontended case, header points to stack
  if (mark.has_locker()) {
    owner = (address) mark.locker();
  }

  // Contended case, header points to ObjectMonitor (tagged pointer)
  else if (mark.has_monitor()) {
    // The first stage of async deflation does not affect any field
    // used by this comparison so the ObjectMonitor* is usable here.
    ObjectMonitor* monitor = mark.monitor();
    assert(monitor != NULL, "monitor should be non-null");
    owner = (address) monitor->owner();
  }

  if (owner != NULL) {
    // owning_thread_from_monitor_owner() may also return NULL here
    return Threads::owning_thread_from_monitor_owner(t_list, owner);
  }

  // Unlocked case, header in place
  // Cannot have assertion since this object may have been
  // locked by another thread when reaching here.
  // assert(mark.is_neutral(), "sanity check");

  return NULL;
}

// Visitors ...

void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
  MonitorList::Iterator iter = _in_use_list.iterator();
  while (iter.has_next()) {
    ObjectMonitor* mid = iter.next();
    if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
      // Only process with closure if the object is set.

      // monitors_iterate() is only called at a safepoint or when the
      // target thread is suspended or when the target thread is
      // operating on itself. The current closures in use today are
      // only interested in an owned ObjectMonitor and ownership
      // cannot be dropped under the calling contexts so the
      // ObjectMonitor cannot be async deflated.
      closure->do_monitor(mid);
    }
  }
}

static bool monitors_used_above_threshold(MonitorList* list) {
  if (MonitorUsedDeflationThreshold == 0) {  // disabled case is easy
    return false;
  }
  // Start with ceiling based on a per-thread estimate:
  size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
  size_t old_ceiling = ceiling;
  if (ceiling < list->max()) {
    // The max used by the system has exceeded the ceiling so use that:
    ceiling = list->max();
  }
  size_t monitors_used = list->count();
  if (monitors_used == 0) {  // empty list is easy
    return false;
  }
  if (NoAsyncDeflationProgressMax != 0 &&
      _no_progress_cnt >= NoAsyncDeflationProgressMax) {
    float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
    size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
    ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
    log_info(monitorinflation)("Too many deflations without progress; "
                               "bumping in_use_list_ceiling from " SIZE_FORMAT
                               " to " SIZE_FORMAT, old_ceiling, new_ceiling);
    _no_progress_cnt = 0;
    ceiling = new_ceiling;
  }

  // Check if our monitor usage is above the threshold:
  size_t monitor_usage = (monitors_used * 100LL) / ceiling;
  return int(monitor_usage) > MonitorUsedDeflationThreshold;
}

size_t ObjectSynchronizer::in_use_list_ceiling() {
  return _in_use_list_ceiling;
}

void ObjectSynchronizer::dec_in_use_list_ceiling() {
  Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
}

void ObjectSynchronizer::inc_in_use_list_ceiling() {
  Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
}

void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
  _in_use_list_ceiling = new_value;
}

bool ObjectSynchronizer::is_async_deflation_needed() {
  if (is_async_deflation_requested()) {
    // Async deflation request.
    return true;
  }
  if (AsyncDeflationInterval > 0 &&
      time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
      monitors_used_above_threshold(&_in_use_list)) {
    // It's been longer than our specified deflate interval and there
    // are too many monitors in use. We don't deflate more frequently
    // than AsyncDeflationInterval (unless is_async_deflation_requested)
    // in order to not swamp the MonitorDeflationThread.
    return true;
  }
  return false;
}

bool ObjectSynchronizer::request_deflate_idle_monitors() {
  JavaThread* current = JavaThread::current();
  bool ret_code = false;

  jlong last_time = last_async_deflation_time_ns();
  set_is_async_deflation_requested(true);
  {
    MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
    ml.notify_all();
  }
  const int N_CHECKS = 5;
  for (int i = 0; i < N_CHECKS; i++) {  // sleep for at most 5 seconds
    if (last_async_deflation_time_ns() > last_time) {
      log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
      ret_code = true;
      break;
    }
    {
      // JavaThread has to honor the blocking protocol.
      ThreadBlockInVM tbivm(current);
      os::naked_short_sleep(999);  // sleep for almost 1 second
    }
  }
  if (!ret_code) {
    log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
  }

  return ret_code;
}

jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
  return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
}

static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
                                       const oop obj,
                                       ObjectSynchronizer::InflateCause cause) {
  assert(event != NULL, "invariant");
  assert(event->should_commit(), "invariant");
  event->set_monitorClass(obj->klass());
  event->set_address((uintptr_t)(void*)obj);
  event->set_cause((u1)cause);
  event->commit();
}

// Fast path code shared by multiple functions
void ObjectSynchronizer::inflate_helper(oop obj) {
  markWord mark = obj->mark();
  if (mark.has_monitor()) {
    ObjectMonitor* monitor = mark.monitor();
    markWord dmw = monitor->header();
    assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
    return;
  }
  (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
}

ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
                                           const InflateCause cause) {
  EventJavaMonitorInflate event;

  for (;;) {
    const markWord mark = object->mark();
    assert(!mark.has_bias_pattern(), "invariant");

    // The mark can be in one of the following states:
    // *  Inflated     - just return
    // *  Stack-locked - coerce it to inflated
    // *  INFLATING    - busy wait for conversion to complete
    // *  Neutral      - aggressively inflate the object.
    // *  BIASED       - Illegal.  We should never see this

    // CASE: inflated
    if (mark.has_monitor()) {
      ObjectMonitor* inf = mark.monitor();
      markWord dmw = inf->header();
      assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
      return inf;
    }

    // CASE: inflation in progress - inflating over a stack-lock.
    // Some other thread is converting from stack-locked to inflated.
    // Only that thread can complete inflation -- other threads must wait.
    // The INFLATING value is transient.
    // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
    // We could always eliminate polling by parking the thread on some auxiliary list.
    if (mark == markWord::INFLATING()) {
      read_stable_mark(object);
      continue;
    }

    // CASE: stack-locked
    // Could be stack-locked either by this thread or by some other thread.
    //
    // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
    // to install INFLATING into the mark word.  We originally installed INFLATING,
    // allocated the ObjectMonitor, and then finally STed the address of the
    // ObjectMonitor into the mark.  This was correct, but artificially lengthened
    // the interval in which INFLATING appeared in the mark, thus increasing
    // the odds of inflation contention.

    LogStreamHandle(Trace, monitorinflation) lsh;

    if (mark.has_locker()) {
      ObjectMonitor* m = new ObjectMonitor(object);
      // Optimistically prepare the ObjectMonitor - anticipate successful CAS
      // We do this before the CAS in order to minimize the length of time
      // in which INFLATING appears in the mark.

      markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
      if (cmp != mark) {
        delete m;
        continue;       // Interference -- just retry
      }

      // We've successfully installed INFLATING (0) into the mark-word.
      // This is the only case where 0 will appear in a mark-word.
      // Only the singular thread that successfully swings the mark-word
      // to 0 can perform (or more precisely, complete) inflation.
      //
      // Why do we CAS a 0 into the mark-word instead of just CASing the
      // mark-word from the stack-locked value directly to the new inflated state?
      // Consider what happens when a thread unlocks a stack-locked object.
      // It attempts to use CAS to swing the displaced header value from the
      // on-stack BasicLock back into the object header.  Recall also that the
      // header value (hash code, etc) can reside in (a) the object header, or
      // (b) a displaced header associated with the stack-lock, or (c) a displaced
      // header in an ObjectMonitor.  The inflate() routine must copy the header
      // value from the BasicLock on the owner's stack to the ObjectMonitor, all
      // the while preserving the hashCode stability invariants.  If the owner
      // decides to release the lock while the value is 0, the unlock will fail
      // and control will eventually pass from slow_exit() to inflate.  The owner
      // will then spin, waiting for the 0 value to disappear.   Put another way,
      // the 0 causes the owner to stall if the owner happens to try to
      // drop the lock (restoring the header from the BasicLock to the object)
      // while inflation is in-progress.  This protocol avoids races that might
      // would otherwise permit hashCode values to change or "flicker" for an object.
      // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
      // 0 serves as a "BUSY" inflate-in-progress indicator.


      // fetch the displaced mark from the owner's stack.
      // The owner can't die or unwind past the lock while our INFLATING
      // object is in the mark.  Furthermore the owner can't complete
      // an unlock on the object, either.
      markWord dmw = mark.displaced_mark_helper();
      // Catch if the object's header is not neutral (not locked and
      // not marked is what we care about here).
      assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());

      // Setup monitor fields to proper values -- prepare the monitor
      m->set_header(dmw);

      // Optimization: if the mark.locker stack address is associated
      // with this thread we could simply set m->_owner = current.
      // Note that a thread can inflate an object
      // that it has stack-locked -- as might happen in wait() -- directly
      // with CAS.  That is, we can avoid the xchg-NULL .... ST idiom.
      m->set_owner_from(NULL, mark.locker());
      // TODO-FIXME: assert BasicLock->dhw != 0.

      // Must preserve store ordering. The monitor state must
      // be stable at the time of publishing the monitor address.
      guarantee(object->mark() == markWord::INFLATING(), "invariant");
      // Release semantics so that above set_object() is seen first.
      object->release_set_mark(markWord::encode(m));

      // Once ObjectMonitor is configured and the object is associated
      // with the ObjectMonitor, it is safe to allow async deflation:
      _in_use_list.add(m);

      // Hopefully the performance counters are allocated on distinct cache lines
      // to avoid false sharing on MP systems ...
      OM_PERFDATA_OP(Inflations, inc());
      if (log_is_enabled(Trace, monitorinflation)) {
        ResourceMark rm(current);
        lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
                     INTPTR_FORMAT ", type='%s'", p2i(object),
                     object->mark().value(), object->klass()->external_name());
      }
      if (event.should_commit()) {
        post_monitor_inflate_event(&event, object, cause);
      }
      return m;
    }

    // CASE: neutral
    // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
    // If we know we're inflating for entry it's better to inflate by swinging a
    // pre-locked ObjectMonitor pointer into the object header.   A successful
    // CAS inflates the object *and* confers ownership to the inflating thread.
    // In the current implementation we use a 2-step mechanism where we CAS()
    // to inflate and then CAS() again to try to swing _owner from NULL to current.
    // An inflateTry() method that we could call from enter() would be useful.

    // Catch if the object's header is not neutral (not locked and
    // not marked is what we care about here).
    assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
    ObjectMonitor* m = new ObjectMonitor(object);
    // prepare m for installation - set monitor to initial state
    m->set_header(mark);

    if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
      delete m;
      m = NULL;
      continue;
      // interference - the markword changed - just retry.
      // The state-transitions are one-way, so there's no chance of
      // live-lock -- "Inflated" is an absorbing state.
    }

    // Once the ObjectMonitor is configured and object is associated
    // with the ObjectMonitor, it is safe to allow async deflation:
    _in_use_list.add(m);

    // Hopefully the performance counters are allocated on distinct
    // cache lines to avoid false sharing on MP systems ...
    OM_PERFDATA_OP(Inflations, inc());
    if (log_is_enabled(Trace, monitorinflation)) {
      ResourceMark rm(current);
      lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
                   INTPTR_FORMAT ", type='%s'", p2i(object),
                   object->mark().value(), object->klass()->external_name());
    }
    if (event.should_commit()) {
      post_monitor_inflate_event(&event, object, cause);
    }
    return m;
  }
}

void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
                                           const char* cnt_name, size_t cnt,
                                           LogStream* ls, elapsedTimer* timer_p) {
  if (!SafepointMechanism::should_process(current)) {
    return;
  }

  // A safepoint/handshake has started.
  if (ls != NULL) {
    timer_p->stop();
    ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
                 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
                 op_name, cnt_name, cnt, in_use_list_ceiling(),
                 _in_use_list.count(), _in_use_list.max());
  }

  {
    // Honor block request.
    ThreadBlockInVM tbivm(current);
  }

  if (ls != NULL) {
    ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
                 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
                 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
    timer_p->start();
  }
}

// Walk the in-use list and deflate (at most MonitorDeflationMax) idle
// ObjectMonitors. Returns the number of deflated ObjectMonitors.
size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
                                                elapsedTimer* timer_p) {
  MonitorList::Iterator iter = _in_use_list.iterator();
  size_t deflated_count = 0;

  while (iter.has_next()) {
    if (deflated_count >= (size_t)MonitorDeflationMax) {
      break;
    }
    ObjectMonitor* mid = iter.next();
    if (mid->deflate_monitor()) {
      deflated_count++;
    }

    if (current->is_Java_thread()) {
      // A JavaThread must check for a safepoint/handshake and honor it.
      chk_for_block_req(current->as_Java_thread(), "deflation", "deflated_count",
                        deflated_count, ls, timer_p);
    }
  }

  return deflated_count;
}

class HandshakeForDeflation : public HandshakeClosure {
 public:
  HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}

  void do_thread(Thread* thread) {
    log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
                                INTPTR_FORMAT, p2i(thread));
  }
};

// This function is called by the MonitorDeflationThread to deflate
// ObjectMonitors. It is also called via do_final_audit_and_print_stats()
// by the VMThread.
size_t ObjectSynchronizer::deflate_idle_monitors() {
  Thread* current = Thread::current();
  if (current->is_Java_thread()) {
    // The async deflation request has been processed.
    _last_async_deflation_time_ns = os::javaTimeNanos();
    set_is_async_deflation_requested(false);
  }

  LogStreamHandle(Debug, monitorinflation) lsh_debug;
  LogStreamHandle(Info, monitorinflation) lsh_info;
  LogStream* ls = NULL;
  if (log_is_enabled(Debug, monitorinflation)) {
    ls = &lsh_debug;
  } else if (log_is_enabled(Info, monitorinflation)) {
    ls = &lsh_info;
  }

  elapsedTimer timer;
  if (ls != NULL) {
    ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
                 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
    timer.start();
  }

  // Deflate some idle ObjectMonitors.
  size_t deflated_count = deflate_monitor_list(current, ls, &timer);
  if (deflated_count > 0 || is_final_audit()) {
    // There are ObjectMonitors that have been deflated or this is the
    // final audit and all the remaining ObjectMonitors have been
    // deflated, BUT the MonitorDeflationThread blocked for the final
    // safepoint during unlinking.

    // Unlink deflated ObjectMonitors from the in-use list.
    ResourceMark rm;
    GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
    size_t unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer,
                                                         &delete_list);
    if (current->is_Java_thread()) {
      if (ls != NULL) {
        timer.stop();
        ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
                     ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
                     SIZE_FORMAT ", max=" SIZE_FORMAT,
                     unlinked_count, in_use_list_ceiling(),
                     _in_use_list.count(), _in_use_list.max());
      }

      // A JavaThread needs to handshake in order to safely free the
      // ObjectMonitors that were deflated in this cycle.
      HandshakeForDeflation hfd_hc;
      Handshake::execute(&hfd_hc);

      if (ls != NULL) {
        ls->print_cr("after handshaking: in_use_list stats: ceiling="
                     SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
                     in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
        timer.start();
      }
    }

    // After the handshake, safely free the ObjectMonitors that were
    // deflated in this cycle.
    size_t deleted_count = 0;
    for (ObjectMonitor* monitor: delete_list) {
      delete monitor;
      deleted_count++;

      if (current->is_Java_thread()) {
        // A JavaThread must check for a safepoint/handshake and honor it.
        chk_for_block_req(current->as_Java_thread(), "deletion", "deleted_count",
                          deleted_count, ls, &timer);
      }
    }
  }

  if (ls != NULL) {
    timer.stop();
    if (deflated_count != 0 || log_is_enabled(Debug, monitorinflation)) {
      ls->print_cr("deflated " SIZE_FORMAT " monitors in %3.7f secs",
                   deflated_count, timer.seconds());
    }
    ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
                 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
  }

  OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
  OM_PERFDATA_OP(Deflations, inc(deflated_count));

  GVars.stw_random = os::random();

  if (deflated_count != 0) {
    _no_progress_cnt = 0;
  } else {
    _no_progress_cnt++;
  }

  return deflated_count;
}

// Monitor cleanup on JavaThread::exit

// Iterate through monitor cache and attempt to release thread's monitors
class ReleaseJavaMonitorsClosure: public MonitorClosure {
 private:
  JavaThread* _thread;

 public:
  ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
  void do_monitor(ObjectMonitor* mid) {
    if (mid->owner() == _thread) {
      (void)mid->complete_exit(_thread);
    }
  }
};

// Release all inflated monitors owned by current thread.  Lightweight monitors are
// ignored.  This is meant to be called during JNI thread detach which assumes
// all remaining monitors are heavyweight.  All exceptions are swallowed.
// Scanning the extant monitor list can be time consuming.
// A simple optimization is to add a per-thread flag that indicates a thread
// called jni_monitorenter() during its lifetime.
//
// Instead of NoSafepointVerifier it might be cheaper to
// use an idiom of the form:
//   auto int tmp = SafepointSynchronize::_safepoint_counter ;
//   <code that must not run at safepoint>
//   guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
// Since the tests are extremely cheap we could leave them enabled
// for normal product builds.

void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
  assert(current == JavaThread::current(), "must be current Java thread");
  NoSafepointVerifier nsv;
  ReleaseJavaMonitorsClosure rjmc(current);
  ObjectSynchronizer::monitors_iterate(&rjmc);
  assert(!current->has_pending_exception(), "Should not be possible");
  current->clear_pending_exception();
}

const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
  switch (cause) {
    case inflate_cause_vm_internal:    return "VM Internal";
    case inflate_cause_monitor_enter:  return "Monitor Enter";
    case inflate_cause_wait:           return "Monitor Wait";
    case inflate_cause_notify:         return "Monitor Notify";
    case inflate_cause_hash_code:      return "Monitor Hash Code";
    case inflate_cause_jni_enter:      return "JNI Monitor Enter";
    case inflate_cause_jni_exit:       return "JNI Monitor Exit";
    default:
      ShouldNotReachHere();
  }
  return "Unknown";
}

//------------------------------------------------------------------------------
// Debugging code

u_char* ObjectSynchronizer::get_gvars_addr() {
  return (u_char*)&GVars;
}

u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
  return (u_char*)&GVars.hc_sequence;
}

size_t ObjectSynchronizer::get_gvars_size() {
  return sizeof(SharedGlobals);
}

u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
  return (u_char*)&GVars.stw_random;
}

// Do the final audit and print of ObjectMonitor stats; must be done
// by the VMThread at VM exit time.
void ObjectSynchronizer::do_final_audit_and_print_stats() {
  assert(Thread::current()->is_VM_thread(), "sanity check");

  if (is_final_audit()) {  // Only do the audit once.
    return;
  }
  set_is_final_audit();

  if (log_is_enabled(Info, monitorinflation)) {
    // Do a deflation in order to reduce the in-use monitor population
    // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
    // which is called by ObjectSynchronizer::audit_and_print_stats().
    while (ObjectSynchronizer::deflate_idle_monitors() != 0) {
      ; // empty
    }
    // The other audit_and_print_stats() call is done at the Debug
    // level at a safepoint in ObjectSynchronizer::do_safepoint_work().
    ObjectSynchronizer::audit_and_print_stats(true /* on_exit */);
  }
}

// This function can be called at a safepoint or it can be called when
// we are trying to exit the VM. When we are trying to exit the VM, the
// list walker functions can run in parallel with the other list
// operations so spin-locking is used for safety.
//
// Calls to this function can be added in various places as a debugging
// aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
// details logged at the Info level and 'false' for the 'on_exit'
// parameter to have in-use monitor details logged at the Trace level.
//
void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
  assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");

  LogStreamHandle(Debug, monitorinflation) lsh_debug;
  LogStreamHandle(Info, monitorinflation) lsh_info;
  LogStreamHandle(Trace, monitorinflation) lsh_trace;
  LogStream* ls = NULL;
  if (log_is_enabled(Trace, monitorinflation)) {
    ls = &lsh_trace;
  } else if (log_is_enabled(Debug, monitorinflation)) {
    ls = &lsh_debug;
  } else if (log_is_enabled(Info, monitorinflation)) {
    ls = &lsh_info;
  }
  assert(ls != NULL, "sanity check");

  int error_cnt = 0;

  ls->print_cr("Checking in_use_list:");
  chk_in_use_list(ls, &error_cnt);

  if (error_cnt == 0) {
    ls->print_cr("No errors found in in_use_list checks.");
  } else {
    log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
  }

  if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
      (!on_exit && log_is_enabled(Trace, monitorinflation))) {
    // When exiting this log output is at the Info level. When called
    // at a safepoint, this log output is at the Trace level since
    // there can be a lot of it.
    log_in_use_monitor_details(ls);
  }

  ls->flush();

  guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
}

// Check the in_use_list; log the results of the checks.
void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
  size_t l_in_use_count = _in_use_list.count();
  size_t l_in_use_max = _in_use_list.max();
  out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
                l_in_use_max);

  size_t ck_in_use_count = 0;
  MonitorList::Iterator iter = _in_use_list.iterator();
  while (iter.has_next()) {
    ObjectMonitor* mid = iter.next();
    chk_in_use_entry(mid, out, error_cnt_p);
    ck_in_use_count++;
  }

  if (l_in_use_count == ck_in_use_count) {
    out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
                  SIZE_FORMAT, l_in_use_count, ck_in_use_count);
  } else {
    out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
                  "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
                  ck_in_use_count);
  }

  size_t ck_in_use_max = _in_use_list.max();
  if (l_in_use_max == ck_in_use_max) {
    out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
                  SIZE_FORMAT, l_in_use_max, ck_in_use_max);
  } else {
    out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
                  "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
  }
}

// Check an in-use monitor entry; log any errors.
void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
                                          int* error_cnt_p) {
  if (n->owner_is_DEFLATER_MARKER()) {
    // This should not happen, but if it does, it is not fatal.
    out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
                  "deflated.", p2i(n));
    return;
  }
  if (n->header().value() == 0) {
    out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
                  "have non-NULL _header field.", p2i(n));
    *error_cnt_p = *error_cnt_p + 1;
  }
  const oop obj = n->object_peek();
  if (obj != NULL) {
    const markWord mark = obj->mark();
    if (!mark.has_monitor()) {
      out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
                    "object does not think it has a monitor: obj="
                    INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
                    p2i(obj), mark.value());
      *error_cnt_p = *error_cnt_p + 1;
    }
    ObjectMonitor* const obj_mon = mark.monitor();
    if (n != obj_mon) {
      out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
                    "object does not refer to the same monitor: obj="
                    INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
                    INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
      *error_cnt_p = *error_cnt_p + 1;
    }
  }
}

// Log details about ObjectMonitors on the in_use_list. The 'BHL'
// flags indicate why the entry is in-use, 'object' and 'object type'
// indicate the associated object and its type.
void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
  stringStream ss;
  if (_in_use_list.count() > 0) {
    out->print_cr("In-use monitor info:");
    out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
    out->print_cr("%18s  %s  %18s  %18s",
                  "monitor", "BHL", "object", "object type");
    out->print_cr("==================  ===  ==================  ==================");
    MonitorList::Iterator iter = _in_use_list.iterator();
    while (iter.has_next()) {
      ObjectMonitor* mid = iter.next();
      const oop obj = mid->object_peek();
      const markWord mark = mid->header();
      ResourceMark rm;
      out->print(INTPTR_FORMAT "  %d%d%d  " INTPTR_FORMAT "  %s", p2i(mid),
                 mid->is_busy(), mark.hash() != 0, mid->owner() != NULL,
                 p2i(obj), obj == NULL ? "" : obj->klass()->external_name());
      if (mid->is_busy()) {
        out->print(" (%s)", mid->is_busy_to_string(&ss));
        ss.reset();
      }
      out->cr();
    }
  }

  out->flush();
}