src/hotspot/share/runtime/objectMonitor.hpp

@@ -1,7 +1,7 @@
  /*
-  * Copyright (c) 1998, 2022, Oracle and/or its affiliates. All rights reserved.
+  * Copyright (c) 1998, 2024, 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.

@@ -143,12 +143,26 @@
    // have busy multi-threaded access. _header and _object are set at initial
    // inflation. The _object does not change, so it is a good choice to share
    // its cache line with _header.
    DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) +
                          sizeof(WeakHandle));
-   // Used by async deflation as a marker in the _owner field:
-   #define DEFLATER_MARKER reinterpret_cast<void*>(-1)
+   // Used by async deflation as a marker in the _owner field.
+   // Note that the choice of the two markers is peculiar:
+   // - They need to represent values that cannot be pointers. In particular,
+   //   we achieve this by using the lowest two bits.
+   // - ANONYMOUS_OWNER should be a small value, it is used in generated code
+   //   and small values encode much better.
+   // - We test for anonymous owner by testing for the lowest bit, therefore
+   //   DEFLATER_MARKER must *not* have that bit set.
+   #define DEFLATER_MARKER reinterpret_cast<void*>(2)
+ public:
+   // NOTE: Typed as uintptr_t so that we can pick it up in SA, via vmStructs.
+   static const uintptr_t ANONYMOUS_OWNER = 1;
+ 
+ private:
+   static void* anon_owner_ptr() { return reinterpret_cast<void*>(ANONYMOUS_OWNER); }
+ 
    void* volatile _owner;            // pointer to owning thread OR BasicLock
    volatile jlong _previous_owner_tid;  // thread id of the previous owner of the monitor
    // Separate _owner and _next_om on different cache lines since
    // both can have busy multi-threaded access. _previous_owner_tid is only
    // changed by ObjectMonitor::exit() so it is a good choice to share the

@@ -242,12 +256,13 @@
      }
      return ret_code != 0;
    }
    const char* is_busy_to_string(stringStream* ss);
  
-   intptr_t  is_entered(JavaThread* current) const;
+   bool is_entered(JavaThread* current) const;
  
+   bool      has_owner() const;
    void*     owner() const;  // Returns NULL if DEFLATER_MARKER is observed.
    void*     owner_raw() const;
    // Returns true if owner field == DEFLATER_MARKER and false otherwise.
    bool      owner_is_DEFLATER_MARKER() const;
    // Returns true if 'this' is being async deflated and false otherwise.

@@ -261,10 +276,22 @@
    // Try to set _owner field to new_value if the current value matches
    // old_value, using Atomic::cmpxchg(). Otherwise, does not change the
    // _owner field. Returns the prior value of the _owner field.
    void*     try_set_owner_from(void* old_value, void* new_value);
  
+   void set_owner_anonymous() {
+     set_owner_from(NULL, anon_owner_ptr());
+   }
+ 
+   bool is_owner_anonymous() const {
+     return owner_raw() == anon_owner_ptr();
+   }
+ 
+   void set_owner_from_anonymous(Thread* owner) {
+     set_owner_from(anon_owner_ptr(), owner);
+   }
+ 
    // Simply get _next_om field.
    ObjectMonitor* next_om() const;
    // Get _next_om field with acquire semantics.
    ObjectMonitor* next_om_acquire() const;
    // Simply set _next_om field to new_value.

@@ -279,10 +306,11 @@
    jint      waiters() const;
  
    jint      contentions() const;
    void      add_to_contentions(jint value);
    intx      recursions() const                                         { return _recursions; }
+   void      set_recursions(size_t recursions);
  
    // JVM/TI GetObjectMonitorUsage() needs this:
    ObjectWaiter* first_waiter()                                         { return _WaitSet; }
    ObjectWaiter* next_waiter(ObjectWaiter* o)                           { return o->_next; }
    JavaThread* thread_of_waiter(ObjectWaiter* o)                        { return o->_thread; }

@@ -313,10 +341,11 @@
     public:
      ClearSuccOnSuspend(ObjectMonitor* om) : _om(om)  {}
      void operator()(JavaThread* current);
    };
   public:
+   bool      enter_for(JavaThread* locking_thread);
    bool      enter(JavaThread* current);
    void      exit(JavaThread* current, bool not_suspended = true);
    void      wait(jlong millis, bool interruptible, TRAPS);
    void      notify(TRAPS);
    void      notifyAll(TRAPS);

@@ -329,10 +358,12 @@
  
    // Use the following at your own risk
    intx      complete_exit(JavaThread* current);
    bool      reenter(intx recursions, JavaThread* current);
  
+   static void maybe_deflate_dead(oop* p);
+ 
   private:
    void      AddWaiter(ObjectWaiter* waiter);
    void      INotify(JavaThread* current);
    ObjectWaiter* DequeueWaiter();
    void      DequeueSpecificWaiter(ObjectWaiter* waiter);