src/java.base/share/classes/java/lang/ref/Reference.java

*** 1,7 ****
  /*
!  * Copyright (c) 1997, 2016, 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.  Oracle designates this
--- 1,7 ----
  /*
!  * Copyright (c) 1997, 2017, 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.  Oracle designates this
*** 138,156 ****
                  processPendingReferences();
              }
          }
      }
  
!     /* Atomically get and clear (set to null) the VM's pending list.
       */
      private static native Reference<Object> getAndClearReferencePendingList();
  
!     /* Test whether the VM's pending list contains any entries.
       */
      private static native boolean hasReferencePendingList();
  
!     /* Wait until the VM's pending list may be non-null.
       */
      private static native void waitForReferencePendingList();
  
      private static final Object processPendingLock = new Object();
      private static boolean processPendingActive = false;
--- 138,165 ----
                  processPendingReferences();
              }
          }
      }
  
!     /*
!      * system property to disable clearing before enqueuing.
!      */
!     private static final boolean disableClearBeforeEnqueue
!         = Boolean.getBoolean("jdk.ref.disableClearBeforeEnqueue");
! 
!     /*
!      * Atomically get and clear (set to null) the VM's pending list.
       */
      private static native Reference<Object> getAndClearReferencePendingList();
  
!     /*
!      * Test whether the VM's pending list contains any entries.
       */
      private static native boolean hasReferencePendingList();
  
!     /*
!      * Wait until the VM's pending list may be non-null.
       */
      private static native void waitForReferencePendingList();
  
      private static final Object processPendingLock = new Object();
      private static boolean processPendingActive = false;
*** 259,269 ****
       */
      public void clear() {
          this.referent = null;
      }
  
- 
      /* -- Queue operations -- */
  
      /**
       * Tells whether or not this reference object has been enqueued, either by
       * the program or by the garbage collector.  If this reference object was
--- 268,277 ----
*** 276,300 ****
      public boolean isEnqueued() {
          return (this.queue == ReferenceQueue.ENQUEUED);
      }
  
      /**
!      * Adds this reference object to the queue with which it is registered,
!      * if any.
       *
       * <p> This method is invoked only by Java code; when the garbage collector
       * enqueues references it does so directly, without invoking this method.
       *
       * @return   <code>true</code> if this reference object was successfully
       *           enqueued; <code>false</code> if it was already enqueued or if
       *           it was not registered with a queue when it was created
       */
      public boolean enqueue() {
          return this.queue.enqueue(this);
      }
  
- 
      /* -- Constructors -- */
  
      Reference(T referent) {
          this(referent, null);
      }
--- 284,309 ----
      public boolean isEnqueued() {
          return (this.queue == ReferenceQueue.ENQUEUED);
      }
  
      /**
!      * Clears this reference object and adds it to the queue with which
!      * it is registered, if any.
       *
       * <p> This method is invoked only by Java code; when the garbage collector
       * enqueues references it does so directly, without invoking this method.
       *
       * @return   <code>true</code> if this reference object was successfully
       *           enqueued; <code>false</code> if it was already enqueued or if
       *           it was not registered with a queue when it was created
       */
      public boolean enqueue() {
+         if (!disableClearBeforeEnqueue)
+             this.referent = null;
          return this.queue.enqueue(this);
      }
  
      /* -- Constructors -- */
  
      Reference(T referent) {
          this(referent, null);
      }
*** 417,423 ****
      public static void reachabilityFence(Object ref) {
          // Does nothing, because this method is annotated with @DontInline
          // HotSpot needs to retain the ref and not GC it before a call to this
          // method
      }
- 
  }
--- 426,431 ----