2006-08-24 Jeroen Frijters <jeroen@frijters.net>

        * java/lang/ref/Reference.java
        (queue, nextOnQueue): Made volatile.
        (enqueue): Made thread safe.
        * java/lang/ref/ReferenceQueue.java
        (lock): New field.
        (poll): Removed synchronized.
        (enqueue): Changed to synchronize on lock object, to update Reference
        state and return success status.
        (dequeue, remove): Synchronize on lock object.

2 files changed, 42 insertions, 24 deletions

diff --git a/java/lang/ref/Reference.java b/java/lang/ref/Reference.java
index 4b6a3adbc..7ea9bdd5a 100644
--- a/java/lang/ref/Reference.java
+++ b/java/lang/ref/Reference.java
@@ -1,5 +1,5 @@
 /* java.lang.ref.Reference
-   Copyright (C) 1999, 2002, 2003 Free Software Foundation, Inc.
+   Copyright (C) 1999, 2002, 2003, 2006 Free Software Foundation, Inc.
 
 This file is part of GNU Classpath.
 
@@ -82,7 +82,7 @@ public abstract class Reference
    * The queue this reference is registered on. This is null, if this
    * wasn't registered to any queue or reference was already enqueued.
    */
-  ReferenceQueue queue;
+  volatile ReferenceQueue queue;
 
   /**
    * Link to the next entry on the queue.  If this is null, this
@@ -91,7 +91,7 @@ public abstract class Reference
    * (not to null, that value is used to mark a not enqueued
    * reference).  
    */
-  Reference nextOnQueue;
+  volatile Reference nextOnQueue;
 
   /**
    * This lock should be taken by the garbage collector, before
@@ -166,11 +166,10 @@ public abstract class Reference
    */
   public boolean enqueue() 
   {
-    if (queue != null && nextOnQueue == null)
+    ReferenceQueue q = queue;
+    if (q != null)
       {
-	queue.enqueue(this);
-	queue = null;
-	return true;
+	return q.enqueue(this);
       }
     return false;
   }
diff --git a/java/lang/ref/ReferenceQueue.java b/java/lang/ref/ReferenceQueue.java
index f4729f282..59e00c858 100644
--- a/java/lang/ref/ReferenceQueue.java
+++ b/java/lang/ref/ReferenceQueue.java
@@ -1,5 +1,5 @@
 /* java.lang.ref.ReferenceQueue
-   Copyright (C) 1999 Free Software Foundation, Inc.
+   Copyright (C) 1999, 2006 Free Software Foundation, Inc.
 
 This file is part of GNU Classpath.
 
@@ -63,6 +63,12 @@ public class ReferenceQueue
   private Reference first;
 
   /**
+   * This is the lock that protects our linked list and is used to signal
+   * a thread waiting in remove().
+   */
+  private final Object lock = new Object();
+
+  /**
    * Creates a new empty reference queue.
    */
   public ReferenceQueue()
@@ -76,7 +82,7 @@ public class ReferenceQueue
    * @return a reference on the queue, if there is one,
    * <code>null</code> otherwise.  
    */
-  public synchronized Reference poll()
+  public Reference poll()
   { 
     return dequeue();
   }
@@ -84,14 +90,23 @@ public class ReferenceQueue
   /**
    * This is called by reference to enqueue itself on this queue.  
    * @param ref the reference that should be enqueued.
+   * @return true if successful, false if not.
    */
-  synchronized void enqueue(Reference ref)
+  final boolean enqueue(Reference ref)
   {
-    /* last reference will point to itself */
-    ref.nextOnQueue = first == null ? ref : first;
-    first = ref;
-    /* this wakes only one remove thread. */
-    notify();
+    synchronized (lock)
+      {
+        if (ref.queue != this)
+          return false;
+
+        /* last reference will point to itself */
+        ref.nextOnQueue = first == null ? ref : first;
+        ref.queue = null;
+        first = ref;
+        /* this wakes only one remove thread. */
+        lock.notify();
+        return true;
+      }
   }
 
   /**
@@ -100,13 +115,16 @@ public class ReferenceQueue
    */
   private Reference dequeue()
   {
-    if (first == null)
-      return null;
+    synchronized (lock)
+      {
+        if (first == null)
+          return null;
 
-    Reference result = first;
-    first = (first == first.nextOnQueue) ? null : first.nextOnQueue;
-    result.nextOnQueue = null;
-    return result;
+        Reference result = first;
+        first = (first == first.nextOnQueue) ? null : first.nextOnQueue;
+        result.nextOnQueue = null;
+        return result;
+      }
   }
 
   /**
@@ -118,12 +136,13 @@ public class ReferenceQueue
    * <code>null</code> if timeout period expired.  
    * @exception InterruptedException if the wait was interrupted.
    */
-  public synchronized Reference remove(long timeout)
+  public Reference remove(long timeout)
     throws InterruptedException
   {
-    if (first == null)
+    synchronized (lock)
       {
-	wait(timeout);
+        if (first == null)
+          lock.wait(timeout);
       }
 
     return dequeue();