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

@@ -87,11 +87,11 @@
      * field is also used for linking Reference objects in the pending list.
      */
 
     private T referent;         /* Treated specially by GC */
 
-    ReferenceQueue<? super T> queue;
+    volatile ReferenceQueue<? super T> queue;
 
     /* When active:   NULL
      *     pending:   this
      *    Enqueued:   next reference in queue (or this if last)
      *    Inactive:   this

@@ -223,13 +223,11 @@
      *
      * @return   <code>true</code> if and only if this reference object has
      *           been enqueued
      */
     public boolean isEnqueued() {
-        synchronized (this) {
-            return (this.next != null && this.queue == ReferenceQueue.ENQUEUED);
-        }
+        return (this.queue == ReferenceQueue.ENQUEUED);
     }
 
     /**
      * Adds this reference object to the queue with which it is registered,
      * if any.