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src/hotspot/share/runtime/objectMonitor.cpp

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rev 57232 : v2.00 -> v2.08 (CR8/v2.08/11-for-jdk14) patches combined into one; merge with jdk-14+25 snapshot; merge with jdk-14+26 snapshot.
rev 57233 : See CR8-to-CR9-changes; merge with 8230876.patch (2019.11.15); merge with jdk-14+25 snapshot; fuzzy merge with jdk-14+26 snapshot.

@@ -239,15 +239,18 @@
 
 // -----------------------------------------------------------------------------
 // Enter support
 
 void ObjectMonitor::enter(TRAPS) {
+  jint l_ref_count = ref_count();
+  ADIM_guarantee(l_ref_count > 0, "must be positive: l_ref_count=%d, ref_count=%d", l_ref_count, ref_count());
+
   // The following code is ordered to check the most common cases first
   // and to reduce RTS->RTO cache line upgrades on SPARC and IA32 processors.
   Thread * const Self = THREAD;
 
-  void * cur = Atomic::cmpxchg(&_owner, (void*)NULL, Self);
+  void* cur = try_set_owner_from(Self, NULL);
   if (cur == NULL) {
     assert(_recursions == 0, "invariant");
     return;
   }
 

@@ -258,13 +261,21 @@
   }
 
   if (Self->is_lock_owned((address)cur)) {
     assert(_recursions == 0, "internal state error");
     _recursions = 1;
-    // Commute owner from a thread-specific on-stack BasicLockObject address to
-    // a full-fledged "Thread *".
-    _owner = Self;
+    simply_set_owner_from_BasicLock(Self, cur);  // Convert from BasicLock* to Thread*.
+    return;
+  }
+
+  if (AsyncDeflateIdleMonitors &&
+      try_set_owner_from(Self, DEFLATER_MARKER) == DEFLATER_MARKER) {
+    // The deflation protocol finished the first part (setting owner),
+    // but it failed the second part (making ref_count negative) and
+    // bailed. Or the ObjectMonitor was async deflated and reused.
+    // Acquired the monitor.
+    assert(_recursions == 0, "invariant");
     return;
   }
 
   // We've encountered genuine contention.
   assert(Self->_Stalled == 0, "invariant");

@@ -291,14 +302,13 @@
   assert(Self->is_Java_thread(), "invariant");
   JavaThread * jt = (JavaThread *) Self;
   assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
   assert(jt->thread_state() != _thread_blocked, "invariant");
   assert(this->object() != NULL, "invariant");
-  assert(_contentions >= 0, "invariant");
+  assert(_contentions >= 0, "must not be negative: contentions=%d", _contentions);
 
-  // Prevent deflation at STW-time.  See deflate_idle_monitors() and is_busy().
-  // Ensure the object-monitor relationship remains stable while there's contention.
+  // Keep track of contention for JVM/TI and M&M queries.
   Atomic::inc(&_contentions);
 
   JFR_ONLY(JfrConditionalFlushWithStacktrace<EventJavaMonitorEnter> flush(jt);)
   EventJavaMonitorEnter event;
   if (event.should_commit()) {

@@ -357,11 +367,11 @@
     // states will still report that the thread is blocked trying to
     // acquire it.
   }
 
   Atomic::dec(&_contentions);
-  assert(_contentions >= 0, "invariant");
+  assert(_contentions >= 0, "must not be negative: contentions=%d", _contentions);
   Self->_Stalled = 0;
 
   // Must either set _recursions = 0 or ASSERT _recursions == 0.
   assert(_recursions == 0, "invariant");
   assert(_owner == Self, "invariant");

@@ -401,33 +411,118 @@
 // Callers must compensate as needed.
 
 int ObjectMonitor::TryLock(Thread * Self) {
   void * own = _owner;
   if (own != NULL) return 0;
-  if (Atomic::replace_if_null(&_owner, Self)) {
+  if (try_set_owner_from(Self, NULL) == NULL) {
     assert(_recursions == 0, "invariant");
     return 1;
   }
   // The lock had been free momentarily, but we lost the race to the lock.
   // Interference -- the CAS failed.
   // We can either return -1 or retry.
   // Retry doesn't make as much sense because the lock was just acquired.
   return -1;
 }
 
+// Install the displaced mark word (dmw) of a deflating ObjectMonitor
+// into the header of the object associated with the monitor. This
+// idempotent method is called by a thread that is deflating a
+// monitor and by other threads that have detected a race with the
+// deflation process.
+void ObjectMonitor::install_displaced_markword_in_object(const oop obj) {
+  // This function must only be called when (owner == DEFLATER_MARKER
+  // && ref_count <= 0), but we can't guarantee that here because
+  // those values could change when the ObjectMonitor gets moved from
+  // the global free list to a per-thread free list.
+
+  guarantee(obj != NULL, "must be non-NULL");
+  if (object() != obj) {
+    // ObjectMonitor's object ref no longer refers to the target object
+    // so the object's header has already been restored.
+    return;
+  }
+
+  markWord dmw = header();
+  if (dmw.value() == 0) {
+    // ObjectMonitor's header/dmw has been cleared so the ObjectMonitor
+    // has been deflated and taken off the global free list.
+    return;
+  }
+
+  // A non-NULL dmw has to be either neutral (not locked and not marked)
+  // or is already participating in this restoration protocol.
+  assert(dmw.is_neutral() || (dmw.is_marked() && dmw.hash() == 0),
+         "failed precondition: dmw=" INTPTR_FORMAT, dmw.value());
+
+  markWord marked_dmw = markWord::zero();
+  if (!dmw.is_marked() && dmw.hash() == 0) {
+    // This dmw has not yet started the restoration protocol so we
+    // mark a copy of the dmw to begin the protocol.
+    // Note: A dmw with a hashcode does not take this code path.
+    marked_dmw = dmw.set_marked();
+
+    // All of the callers to this function can be racing with each
+    // other trying to update the _header field.
+    dmw = (markWord) Atomic::cmpxchg(&_header, dmw, marked_dmw);
+    if (dmw.value() == 0) {
+      // ObjectMonitor's header/dmw has been cleared so the object's
+      // header has already been restored.
+      return;
+    }
+    // The _header field is now marked. The winner's 'dmw' variable
+    // contains the original, unmarked header/dmw value and any
+    // losers have a marked header/dmw value that will be cleaned
+    // up below.
+  }
+
+  if (dmw.is_marked()) {
+    // Clear the mark from the header/dmw copy in preparation for
+    // possible restoration from this thread.
+    assert(dmw.hash() == 0, "hashcode must be 0: dmw=" INTPTR_FORMAT,
+           dmw.value());
+    dmw = dmw.set_unmarked();
+  }
+  assert(dmw.is_neutral(), "must be neutral: dmw=" INTPTR_FORMAT, dmw.value());
+
+  // Install displaced mark word if the object's header still points
+  // to this ObjectMonitor. All racing callers to this function will
+  // reach this point, but only one can win.
+  obj->cas_set_mark(dmw, markWord::encode(this));
+
+  // Note: It does not matter which thread restored the header/dmw
+  // into the object's header. The thread deflating the monitor just
+  // wanted the object's header restored and it is. The threads that
+  // detected a race with the deflation process also wanted the
+  // object's header restored before they retry their operation and
+  // because it is restored they will only retry once.
+}
+
 // Convert the fields used by is_busy() to a string that can be
 // used for diagnostic output.
 const char* ObjectMonitor::is_busy_to_string(stringStream* ss) {
-  ss->print("is_busy: contentions=%d, waiters=%d, owner=" INTPTR_FORMAT
-            ", cxq=" INTPTR_FORMAT ", EntryList=" INTPTR_FORMAT, _contentions,
-            _waiters, p2i(_owner), p2i(_cxq), p2i(_EntryList));
+  ss->print("is_busy: contentions=%d, waiters=%d, ", _contentions, _waiters);
+  if (!AsyncDeflateIdleMonitors) {
+    ss->print("owner=" INTPTR_FORMAT, p2i(_owner));
+  } else if (_owner != DEFLATER_MARKER) {
+    ss->print("owner=" INTPTR_FORMAT, p2i(_owner));
+  } else {
+    // We report NULL instead of DEFLATER_MARKER here because is_busy()
+    // ignores DEFLATER_MARKER values.
+    ss->print("owner=" INTPTR_FORMAT, NULL);
+  }
+  ss->print(", cxq=" INTPTR_FORMAT ", EntryList=" INTPTR_FORMAT, p2i(_cxq),
+            p2i(_EntryList));
   return ss->base();
 }
 
 #define MAX_RECHECK_INTERVAL 1000
 
 void ObjectMonitor::EnterI(TRAPS) {
+  jint l_ref_count = ref_count();
+  ADIM_guarantee(l_ref_count > 0, "must be positive: l_ref_count=%d, ref_count=%d", l_ref_count, ref_count());
+
   Thread * const Self = THREAD;
   assert(Self->is_Java_thread(), "invariant");
   assert(((JavaThread *) Self)->thread_state() == _thread_blocked, "invariant");
 
   // Try the lock - TATAS

@@ -436,10 +531,21 @@
     assert(_owner == Self, "invariant");
     assert(_Responsible != Self, "invariant");
     return;
   }
 
+  if (AsyncDeflateIdleMonitors &&
+      try_set_owner_from(Self, DEFLATER_MARKER) == DEFLATER_MARKER) {
+    // The deflation protocol finished the first part (setting owner),
+    // but it failed the second part (making ref_count negative) and
+    // bailed. Or the ObjectMonitor was async deflated and reused.
+    // Acquired the monitor.
+    assert(_succ != Self, "invariant");
+    assert(_Responsible != Self, "invariant");
+    return;
+  }
+
   assert(InitDone, "Unexpectedly not initialized");
 
   // We try one round of spinning *before* enqueueing Self.
   //
   // If the _owner is ready but OFFPROC we could use a YieldTo()

@@ -552,10 +658,19 @@
       Self->_ParkEvent->park();
     }
 
     if (TryLock(Self) > 0) break;
 
+    if (AsyncDeflateIdleMonitors &&
+        try_set_owner_from(Self, DEFLATER_MARKER) == DEFLATER_MARKER) {
+      // The deflation protocol finished the first part (setting owner),
+      // but it failed the second part (making ref_count negative) and
+      // bailed. Or the ObjectMonitor was async deflated and reused.
+      // Acquired the monitor.
+      break;
+    }
+
     // The lock is still contested.
     // Keep a tally of the # of futile wakeups.
     // Note that the counter is not protected by a lock or updated by atomics.
     // That is by design - we trade "lossy" counters which are exposed to
     // races during updates for a lower probe effect.

@@ -656,10 +771,13 @@
 // monitor reentry in wait().
 //
 // In the future we should reconcile EnterI() and ReenterI().
 
 void ObjectMonitor::ReenterI(Thread * Self, ObjectWaiter * SelfNode) {
+  jint l_ref_count = ref_count();
+  ADIM_guarantee(l_ref_count > 0, "must be positive: l_ref_count=%d, ref_count=%d", l_ref_count, ref_count());
+
   assert(Self != NULL, "invariant");
   assert(SelfNode != NULL, "invariant");
   assert(SelfNode->_thread == Self, "invariant");
   assert(_waiters > 0, "invariant");
   assert(((oop)(object()))->mark() == markWord::encode(this), "invariant");

@@ -673,10 +791,19 @@
     assert(_owner != Self, "invariant");
 
     if (TryLock(Self) > 0) break;
     if (TrySpin(Self) > 0) break;
 
+    if (AsyncDeflateIdleMonitors &&
+        try_set_owner_from(Self, DEFLATER_MARKER) == DEFLATER_MARKER) {
+      // The deflation protocol finished the first part (setting owner),
+      // but it failed the second part (making ref_count negative) and
+      // bailed. Or the ObjectMonitor was async deflated and reused.
+      // Acquired the monitor.
+      break;
+    }
+
     // State transition wrappers around park() ...
     // ReenterI() wisely defers state transitions until
     // it's clear we must park the thread.
     {
       OSThreadContendState osts(Self->osthread());

@@ -816,12 +943,12 @@
 // inopportune) reclamation of "this".
 //
 // We'd like to assert that: (THREAD->thread_state() != _thread_blocked) ;
 // There's one exception to the claim above, however.  EnterI() can call
 // exit() to drop a lock if the acquirer has been externally suspended.
-// In that case exit() is called with _thread_state as _thread_blocked,
-// but the monitor's _contentions field is > 0, which inhibits reclamation.
+// In that case exit() is called with _thread_state == _thread_blocked,
+// but the monitor's ref_count is > 0, which inhibits reclamation.
 //
 // 1-0 exit
 // ~~~~~~~~
 // ::exit() uses a canonical 1-1 idiom with a MEMBAR although some of
 // the fast-path operators have been optimized so the common ::exit()

@@ -862,17 +989,14 @@
 // of such futile wakups is low.
 
 void ObjectMonitor::exit(bool not_suspended, TRAPS) {
   Thread * const Self = THREAD;
   if (THREAD != _owner) {
-    if (THREAD->is_lock_owned((address) _owner)) {
-      // Transmute _owner from a BasicLock pointer to a Thread address.
-      // We don't need to hold _mutex for this transition.
-      // Non-null to Non-null is safe as long as all readers can
-      // tolerate either flavor.
+    void* cur = _owner;
+    if (THREAD->is_lock_owned((address)cur)) {
       assert(_recursions == 0, "invariant");
-      _owner = THREAD;
+      simply_set_owner_from_BasicLock(Self, cur);  // Convert from BasicLock* to Thread*.
       _recursions = 0;
     } else {
       // Apparent unbalanced locking ...
       // Naively we'd like to throw IllegalMonitorStateException.
       // As a practical matter we can neither allocate nor throw an

@@ -912,14 +1036,18 @@
 #endif
 
   for (;;) {
     assert(THREAD == _owner, "invariant");
 
+    // Drop the lock.
     // release semantics: prior loads and stores from within the critical section
     // must not float (reorder) past the following store that drops the lock.
-    Atomic::release_store(&_owner, (void*)NULL);   // drop the lock
-    OrderAccess::storeload();                      // See if we need to wake a successor
+    // Uses a storeload to separate release_store(owner) from the
+    // successor check. The try_set_owner() below uses cmpxchg() so
+    // we get the fence down there.
+    release_clear_owner_with_barrier(Self, /* needs_fence */ false);
+
     if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) {
       return;
     }
     // Other threads are blocked trying to acquire the lock.
 

@@ -957,11 +1085,11 @@
     // Only the current lock owner can manipulate the EntryList or
     // drain _cxq, so we need to reacquire the lock.  If we fail
     // to reacquire the lock the responsibility for ensuring succession
     // falls to the new owner.
     //
-    if (!Atomic::replace_if_null(&_owner, THREAD)) {
+    if (try_set_owner_from(Self, NULL) != NULL) {
       return;
     }
 
     guarantee(_owner == THREAD, "invariant");
 

@@ -1089,13 +1217,13 @@
   // Hygiene -- once we've set _owner = NULL we can't safely dereference Wakee again.
   // The thread associated with Wakee may have grabbed the lock and "Wakee" may be
   // out-of-scope (non-extant).
   Wakee  = NULL;
 
-  // Drop the lock
-  Atomic::release_store(&_owner, (void*)NULL);
-  OrderAccess::fence();                               // ST _owner vs LD in unpark()
+  // Drop the lock.
+  // Uses a fence to separate release_store(owner) from the LD in unpark().
+  release_clear_owner_with_barrier(Self, /* needs_fence */ true);
 
   DTRACE_MONITOR_PROBE(contended__exit, this, object(), Self);
   Trigger->unpark();
 
   // Maintain stats and report events to JVMTI

@@ -1118,13 +1246,14 @@
   JavaThread *jt = (JavaThread *)THREAD;
 
   assert(InitDone, "Unexpectedly not initialized");
 
   if (THREAD != _owner) {
-    if (THREAD->is_lock_owned ((address)_owner)) {
+    void* cur = _owner;
+    if (THREAD->is_lock_owned((address)cur)) {
       assert(_recursions == 0, "internal state error");
-      _owner = THREAD;   // Convert from basiclock addr to Thread addr
+      simply_set_owner_from_BasicLock(Self, cur);  // Convert from BasicLock* to Thread*.
       _recursions = 0;
     }
   }
 
   guarantee(Self == _owner, "complete_exit not owner");

@@ -1141,14 +1270,14 @@
   Thread * const Self = THREAD;
   assert(Self->is_Java_thread(), "Must be Java thread!");
   JavaThread *jt = (JavaThread *)THREAD;
 
   guarantee(_owner != Self, "reenter already owner");
-  enter(THREAD);       // enter the monitor
+  enter(THREAD);
+  // Entered the monitor.
   guarantee(_recursions == 0, "reenter recursion");
   _recursions = recursions;
-  return;
 }
 
 // Checks that the current THREAD owns this monitor and causes an
 // immediate return if it doesn't. We don't use the CHECK macro
 // because we want the IMSE to be the only exception that is thrown

@@ -1168,12 +1297,13 @@
 // is not the owner, that exception will be replaced by the IMSE.
 bool ObjectMonitor::check_owner(Thread* THREAD) {
   if (_owner == THREAD) {
     return true;
   }
-  if (THREAD->is_lock_owned((address)_owner)) {
-    _owner = THREAD;  // convert from BasicLock addr to Thread addr
+  void* cur = _owner;
+  if (THREAD->is_lock_owned((address)cur)) {
+    simply_set_owner_from_BasicLock(THREAD, cur);  // Convert from BasicLock* to Thread*.
     _recursions = 0;
     return true;
   }
   THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
              "current thread is not owner", false);

@@ -1678,11 +1808,11 @@
     // the spin without prejudice or apply a "penalty" to the
     // spin count-down variable "ctr", reducing it by 100, say.
 
     Thread * ox = (Thread *) _owner;
     if (ox == NULL) {
-      ox = (Thread*)Atomic::cmpxchg(&_owner, (void*)NULL, Self);
+      ox = (Thread*)try_set_owner_from(Self, NULL);
       if (ox == NULL) {
         // The CAS succeeded -- this thread acquired ownership
         // Take care of some bookkeeping to exit spin state.
         if (_succ == Self) {
           _succ = NULL;

@@ -1942,10 +2072,135 @@
   }
 
   DEBUG_ONLY(InitDone = true;)
 }
 
+ObjectMonitorHandle::~ObjectMonitorHandle() {
+  if (_om_ptr != NULL) {
+    _om_ptr->dec_ref_count();
+    _om_ptr = NULL;
+  }
+}
+
+// Save the ObjectMonitor* associated with the specified markWord and
+// increment the ref_count. This function should only be called if
+// the caller has verified mark.has_monitor() == true. The object
+// parameter is needed to verify that ObjectMonitor* has not been
+// deflated and reused for another object.
+//
+// This function returns true if the ObjectMonitor* has been safely
+// saved. This function returns false if we have lost a race with
+// async deflation; the caller should retry as appropriate.
+//
+bool ObjectMonitorHandle::save_om_ptr(oop object, markWord mark) {
+  // is_marked() is a superset of has_monitor() so make sure we
+  // are called with the proper markWord value.
+  guarantee(mark.has_monitor() && !mark.is_marked(), "sanity check: mark="
+            INTPTR_FORMAT, mark.value());
+
+  ObjectMonitor* om_ptr = mark.monitor();
+  om_ptr->inc_ref_count();
+
+  if (AsyncDeflateIdleMonitors) {
+    // Race here if monitor is not owned! The above ref_count bump
+    // will cause subsequent async deflation to skip it. However,
+    // previous or concurrent async deflation is a race.
+    if (om_ptr->owner_is_DEFLATER_MARKER() && om_ptr->ref_count() <= 0) {
+      // Async deflation is in progress and our ref_count increment
+      // above lost the race to async deflation. 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.
+      om_ptr->install_displaced_markword_in_object(object);
+      om_ptr->dec_ref_count();
+      return false;
+    }
+    if (om_ptr->ref_count() <= 0) {
+      // Async deflation is in the process of bailing out, but has not
+      // yet restored the ref_count field so we return false to force
+      // a retry. We want a positive ref_count value for a true return.
+      om_ptr->dec_ref_count();
+      return false;
+    }
+    // The ObjectMonitor could have been deflated and reused for
+    // another object before we bumped the ref_count so make sure
+    // our object still refers to this ObjectMonitor.
+    const markWord tmp = object->mark();
+    if (!tmp.has_monitor() || tmp.monitor() != om_ptr) {
+      // Async deflation and reuse won the race so we have to retry.
+      // Skip object header restoration since that's already done.
+      om_ptr->dec_ref_count();
+      return false;
+    }
+  }
+
+  ADIM_guarantee(_om_ptr == NULL, "sanity check: _om_ptr=" INTPTR_FORMAT,
+                 p2i(_om_ptr));
+  _om_ptr = om_ptr;
+  return true;
+}
+
+// For internal use by ObjectSynchronizer::inflate().
+// This function is only used when we don't have to worry about async
+// deflation of the specified ObjectMonitor*.
+void ObjectMonitorHandle::set_om_ptr(ObjectMonitor* om_ptr) {
+  if (_om_ptr == NULL) {
+    ADIM_guarantee(om_ptr != NULL, "cannot clear an unset om_ptr");
+    om_ptr->inc_ref_count();
+    _om_ptr = om_ptr;
+  } else {
+    ADIM_guarantee(om_ptr == NULL, "can only clear a set om_ptr");
+    _om_ptr->dec_ref_count();
+    _om_ptr = NULL;
+  }
+}
+
+// Save the specified ObjectMonitor* if it is safe, i.e., not being
+// async deflated.
+//
+// This function returns true if the ObjectMonitor* has been safely
+// saved. This function returns false if the specified ObjectMonitor*
+// is NULL or if we have lost a race with async deflation; the caller
+// can retry as appropriate.
+bool ObjectMonitorHandle::set_om_ptr_if_safe(ObjectMonitor* om_ptr) {
+  if (om_ptr == NULL) {
+    return false;  // Nothing to save if input is NULL
+  }
+
+  om_ptr->inc_ref_count();
+
+  if (AsyncDeflateIdleMonitors) {
+    if (om_ptr->owner_is_DEFLATER_MARKER() && om_ptr->ref_count() <= 0) {
+      // Async deflation is in progress and our ref_count increment
+      // above lost the race to async deflation.
+      om_ptr->dec_ref_count();
+      return false;
+    }
+    if (om_ptr->ref_count() <= 0) {
+      // Async deflation is in the process of bailing out, but has not
+      // yet restored the ref_count field so we return false to force
+      // a retry. We want a positive ref_count value for a true return.
+      om_ptr->dec_ref_count();
+      return false;
+    }
+    // Unlike save_om_ptr(), we don't have context to determine if
+    // the ObjectMonitor has been deflated and reused for another
+    // object.
+  }
+
+  ADIM_guarantee(_om_ptr == NULL, "sanity check: _om_ptr=" INTPTR_FORMAT,
+                 p2i(_om_ptr));
+  _om_ptr = om_ptr;
+  return true;
+}
+
+// Unset the _om_ptr field and decrement the ref_count field.
+void ObjectMonitorHandle::unset_om_ptr() {
+  ADIM_guarantee(_om_ptr != NULL, "_om_ptr must not be NULL");
+  _om_ptr->dec_ref_count();
+  _om_ptr = NULL;
+}
+
 void ObjectMonitor::print_on(outputStream* st) const {
   // The minimal things to print for markWord printing, more can be added for debugging and logging.
   st->print("{contentions=0x%08x,waiters=0x%08x"
             ",recursions=" INTX_FORMAT ",owner=" INTPTR_FORMAT "}",
             contentions(), waiters(), recursions(),

@@ -1957,18 +2212,30 @@
 // Print the ObjectMonitor like a debugger would:
 //
 // (ObjectMonitor) 0x00007fdfb6012e40 = {
 //   _header = 0x0000000000000001
 //   _object = 0x000000070ff45fd0
-//   _next_om = 0x0000000000000000
+//   _allocation_state = Old
 //   _pad_buf0 = {
 //     [0] = '\0'
 //     ...
-//     [103] = '\0'
+//     [43] = '\0'
 //   }
 //   _owner = 0x0000000000000000
 //   _previous_owner_tid = 0
+//   _pad_buf1 = {
+//     [0] = '\0'
+//     ...
+//     [47] = '\0'
+//   }
+//   _ref_count = 1
+//   _pad_buf2 = {
+//     [0] = '\0'
+//     ...
+//     [47] = '\0'
+//   }
+//   _next_om = 0x0000000000000000
 //   _recursions = 0
 //   _EntryList = 0x0000000000000000
 //   _cxq = 0x0000000000000000
 //   _succ = 0x0000000000000000
 //   _Responsible = 0x0000000000000000

@@ -1982,18 +2249,40 @@
 //
 void ObjectMonitor::print_debug_style_on(outputStream* st) const {
   st->print_cr("(ObjectMonitor*) " INTPTR_FORMAT " = {", p2i(this));
   st->print_cr("  _header = " INTPTR_FORMAT, header().value());
   st->print_cr("  _object = " INTPTR_FORMAT, p2i(_object));
-  st->print_cr("  _next_om = " INTPTR_FORMAT, p2i(_next_om));
+  st->print("  _allocation_state = ");
+  if (is_free()) {
+    st->print("Free");
+  } else if (is_old()) {
+    st->print("Old");
+  } else if (is_new()) {
+    st->print("New");
+  } else {
+    st->print("unknown=%d", _allocation_state);
+  }
+  st->cr();
   st->print_cr("  _pad_buf0 = {");
   st->print_cr("    [0] = '\\0'");
   st->print_cr("    ...");
   st->print_cr("    [%d] = '\\0'", (int)sizeof(_pad_buf0) - 1);
   st->print_cr("  }");
   st->print_cr("  _owner = " INTPTR_FORMAT, p2i(_owner));
   st->print_cr("  _previous_owner_tid = " JLONG_FORMAT, _previous_owner_tid);
+  st->print_cr("  _pad_buf1 = {");
+  st->print_cr("    [0] = '\\0'");
+  st->print_cr("    ...");
+  st->print_cr("    [%d] = '\\0'", (int)sizeof(_pad_buf1) - 1);
+  st->print_cr("  }");
+  st->print_cr("  _ref_count = %d", ref_count());
+  st->print_cr("  _pad_buf2 = {");
+  st->print_cr("    [0] = '\\0'");
+  st->print_cr("    ...");
+  st->print_cr("    [%d] = '\\0'", (int)sizeof(_pad_buf1) - 1);
+  st->print_cr("  }");
+  st->print_cr("  _next_om = " INTPTR_FORMAT, p2i(Atomic::load(&_next_om)));
   st->print_cr("  _recursions = " INTX_FORMAT, _recursions);
   st->print_cr("  _EntryList = " INTPTR_FORMAT, p2i(_EntryList));
   st->print_cr("  _cxq = " INTPTR_FORMAT, p2i(_cxq));
   st->print_cr("  _succ = " INTPTR_FORMAT, p2i(_succ));
   st->print_cr("  _Responsible = " INTPTR_FORMAT, p2i(_Responsible));
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