--- old/src/hotspot/share/runtime/objectMonitor.cpp	2019-07-11 14:36:29.000000000 -0400
+++ new/src/hotspot/share/runtime/objectMonitor.cpp	2019-07-11 14:36:28.000000000 -0400
@@ -239,7 +239,7 @@
 // Enter support
 
 void ObjectMonitor::enter(TRAPS) {
-  ADIM_guarantee(_ref_count > 0, "must be positive: ref_count=%d", _ref_count);
+  ADIM_guarantee(ref_count() > 0, "must be positive: ref_count=%d", 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.
@@ -266,6 +266,16 @@
     return;
   }
 
+  if (AsyncDeflateIdleMonitors &&
+      Atomic::cmpxchg(Self, &_owner, 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");
   Self->_Stalled = intptr_t(this);
@@ -437,8 +447,8 @@
 
   markOop dmw = header();
   if (dmw == NULL) {
-    // ObjectMonitor's header/dmw has been cleared by the deflating
-    // thread so the object's header has already been restored.
+    // ObjectMonitor's header/dmw has been cleared so the object's
+    // header has already been restored.
     return;
   }
 
@@ -458,8 +468,8 @@
     // other trying to update the _header field.
     dmw = (markOop) Atomic::cmpxchg(marked_dmw, &_header, dmw);
     if (dmw == NULL) {
-      // ObjectMonitor's header/dmw has been cleared by the deflating
-      // thread so the object's header has already been restored.
+      // 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
@@ -499,16 +509,23 @@
 // 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 {
+    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) {
-  ADIM_guarantee(_ref_count > 0, "must be positive: ref_count=%d", _ref_count);
+  ADIM_guarantee(ref_count() > 0, "must be positive: ref_count=%d", ref_count());
 
   Thread * const Self = THREAD;
   assert(Self->is_Java_thread(), "invariant");
@@ -522,15 +539,15 @@
     return;
   }
 
-  if (_owner == DEFLATER_MARKER) {
-    // The deflation protocol finished the first part (setting owner), but
-    // it failed the second part (making ref_count negative) and bailed.
-    if (Atomic::cmpxchg(Self, &_owner, DEFLATER_MARKER) == DEFLATER_MARKER) {
-      // Acquired the monitor.
-      assert(_succ != Self, "invariant");
-      assert(_Responsible != Self, "invariant");
-      return;
-    }
+  if (AsyncDeflateIdleMonitors &&
+      Atomic::cmpxchg(Self, &_owner, 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");
@@ -649,13 +666,13 @@
 
     if (TryLock(Self) > 0) break;
 
-    if (_owner == DEFLATER_MARKER) {
-      // The deflation protocol finished the first part (setting owner), but
-      // it failed the second part (making ref_count negative) and bailed.
-      if (Atomic::cmpxchg(Self, &_owner, DEFLATER_MARKER) == DEFLATER_MARKER) {
-        // Acquired the monitor.
-        break;
-      }
+    if (AsyncDeflateIdleMonitors &&
+        Atomic::cmpxchg(Self, &_owner, 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.
@@ -762,7 +779,7 @@
 // In the future we should reconcile EnterI() and ReenterI().
 
 void ObjectMonitor::ReenterI(Thread * Self, ObjectWaiter * SelfNode) {
-  ADIM_guarantee(_ref_count > 0, "must be positive: ref_count=%d", _ref_count);
+  ADIM_guarantee(ref_count() > 0, "must be positive: ref_count=%d", ref_count());
 
   assert(Self != NULL, "invariant");
   assert(SelfNode != NULL, "invariant");
@@ -781,13 +798,13 @@
     if (TryLock(Self) > 0) break;
     if (TrySpin(Self) > 0) break;
 
-    if (_owner == DEFLATER_MARKER) {
-      // The deflation protocol finished the first part (setting owner), but
-      // it failed the second part (making ref_count negative) and bailed.
-      if (Atomic::cmpxchg(Self, &_owner, DEFLATER_MARKER) == DEFLATER_MARKER) {
-        // Acquired the monitor.
-        break;
-      }
+    if (AsyncDeflateIdleMonitors &&
+        Atomic::cmpxchg(Self, &_owner, 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() ...
@@ -2083,7 +2100,7 @@
     // 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 == DEFLATER_MARKER && om_ptr->ref_count() <= 0) {
+    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