--- old/src/hotspot/share/runtime/objectMonitor.hpp	2019-08-28 15:00:51.210963961 -0400
+++ new/src/hotspot/share/runtime/objectMonitor.hpp	2019-08-28 15:00:51.046963967 -0400
@@ -137,6 +137,7 @@
   };
 
  private:
+  friend class ObjectMonitorHandle;
   friend class ObjectSynchronizer;
   friend class ObjectWaiter;
   friend class VMStructs;
@@ -158,6 +159,8 @@
   DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE,
                         sizeof(volatile markWord) + sizeof(void* volatile) +
                         sizeof(ObjectMonitor *));
+  // Used by async deflation as a marker in the _owner field:
+  #define DEFLATER_MARKER reinterpret_cast<void*>(-1)
  protected:                         // protected for JvmtiRawMonitor
   void* volatile _owner;            // pointer to owning thread OR BasicLock
  private:
@@ -177,12 +180,21 @@
 
   volatile jint  _contentions;      // Number of active contentions in enter(). It is used by is_busy()
                                     // along with other fields to determine if an ObjectMonitor can be
-                                    // deflated. See ObjectSynchronizer::deflate_monitor().
+                                    // deflated. See ObjectSynchronizer::deflate_monitor() and
+                                    // ObjectSynchronizer::deflate_monitor_using_JT().
  protected:
   ObjectWaiter* volatile _WaitSet;  // LL of threads wait()ing on the monitor
   volatile jint  _waiters;          // number of waiting threads
  private:
   volatile int _WaitSetLock;        // protects Wait Queue - simple spinlock
+  volatile jint _ref_count;         // ref count for ObjectMonitor* and used by the async deflation
+                                    // protocol. See ObjectSynchronizer::deflate_monitor_using_JT().
+  typedef enum {
+    Free = 0,  // Free must be 0 for monitor to be free after memset(..,0,..).
+    New,
+    Old
+  } AllocationState;
+  AllocationState _allocation_state;
 
  public:
   static void Initialize();
@@ -244,13 +256,27 @@
 
   intptr_t is_busy() const {
     // TODO-FIXME: assert _owner == null implies _recursions = 0
-    return _contentions|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList);
+    // We do not include _ref_count in the is_busy() check because
+    // _ref_count is for indicating that the ObjectMonitor* is in
+    // use which is orthogonal to whether the ObjectMonitor itself
+    // is in use for a locking operation.
+    intptr_t ret_code = _contentions | _waiters | intptr_t(_cxq) | intptr_t(_EntryList);
+    if (!AsyncDeflateIdleMonitors) {
+      ret_code |= intptr_t(_owner);
+    } else {
+      if (_owner != DEFLATER_MARKER) {
+        ret_code |= intptr_t(_owner);
+      }
+    }
+    return ret_code;
   }
   const char* is_busy_to_string(stringStream* ss);
 
   intptr_t  is_entered(Thread* current) const;
 
-  void*     owner() const;
+  void*     owner() const;  // Returns NULL if DEFLATER_MARKER is observed.
+  // Returns true if owner field == DEFLATER_MARKER and false otherwise.
+  bool      owner_is_DEFLATER_MARKER();
   void      set_owner(void* owner);
 
   jint      waiters() const;
@@ -295,11 +321,21 @@
   void*     object() const;
   void*     object_addr();
   void      set_object(void* obj);
+  void      set_allocation_state(AllocationState s);
+  AllocationState allocation_state() const;
+  bool      is_free() const;
+  bool      is_active() const;
+  bool      is_old() const;
+  bool      is_new() const;
+  void      dec_ref_count();
+  void      inc_ref_count();
+  jint      ref_count() const;
 
   // Returns true if the specified thread owns the ObjectMonitor. Otherwise
   // returns false and throws IllegalMonitorStateException (IMSE).
   bool      check_owner(Thread* THREAD);
   void      clear();
+  void      clear_using_JT();
 
   void      enter(TRAPS);
   void      exit(bool not_suspended, TRAPS);
@@ -323,10 +359,42 @@
   void      ReenterI(Thread* self, ObjectWaiter* self_node);
   void      UnlinkAfterAcquire(Thread* self, ObjectWaiter* self_node);
   int       TryLock(Thread* self);
-  int       NotRunnable(Thread* self, Thread * Owner);
+  int       NotRunnable(Thread* self, Thread* Owner);
   int       TrySpin(Thread* self);
   void      ExitEpilog(Thread* self, ObjectWaiter* Wakee);
   bool      ExitSuspendEquivalent(JavaThread* self);
+  void      install_displaced_markword_in_object(const oop obj);
 };
 
+// A helper object for managing an ObjectMonitor*'s ref_count. There
+// are special safety considerations when async deflation is used.
+class ObjectMonitorHandle : public StackObj {
+ private:
+  ObjectMonitor* _om_ptr;
+ public:
+  ObjectMonitorHandle() { _om_ptr = NULL; }
+  ~ObjectMonitorHandle();
+
+  ObjectMonitor* om_ptr() const { return _om_ptr; }
+  // Save the ObjectMonitor* associated with the specified markWord and
+  // increment the ref_count.
+  bool save_om_ptr(oop object, markWord mark);
+
+  // For internal used by ObjectSynchronizer::monitors_iterate().
+  ObjectMonitorHandle(ObjectMonitor* _om_ptr);
+  // For internal use by ObjectSynchronizer::inflate().
+  void set_om_ptr(ObjectMonitor* om_ptr);
+};
+
+// Macro to use guarantee() for more strict AsyncDeflateIdleMonitors
+// checks and assert() otherwise.
+#define ADIM_guarantee(p, ...)       \
+  do {                               \
+    if (AsyncDeflateIdleMonitors) {  \
+      guarantee(p, __VA_ARGS__);     \
+    } else {                         \
+      assert(p, __VA_ARGS__);        \
+    }                                \
+  } while (0)
+
 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP