Possible WeakReference Bug

Mon Nov 18 15:34:00 GMT 2002

>>>>> "Jesse" == Jesse Rosenstock <jmr@ugcs.caltech.edu> writes:

Jesse> It seems that the WeakReference is being enqueued even though
Jesse> the referent is still live and WeakReference.get() returns
Jesse> non-null.
Yes, that's a bug. Oops.
The spec requires weak and soft references to be cleared before
enqueueing.
Jesse> Also, it seems that the finalizer is never called, is that
Jesse> expected?
Nope, another bug.
The appended patch is a start, but not complete.
It just addresses a couple obvious problems.
I wouldn't be surprised to find other bugs in this area.
The code to implement java.lang.ref is pretty horrible.
Tom
Index: ChangeLog
from Tom Tromey <tromey@redhat.com>
	* java/lang/ref/natReference.cc (add_to_hash): Look at `copy', not
	`referent'.
	(finalize_referred_to_object): Don't modify `referent' or `copy'
	fields.
	* java/lang/ref/Reference.java (enqueue): Return false if already
	enqueued.
Index: java/lang/ref/Reference.java
===================================================================
RCS file: /cvs/gcc/gcc/libjava/java/lang/ref/Reference.java,v
retrieving revision 1.3
diff -u -r1.3 Reference.java

--- java/lang/ref/Reference.java 22 Jan 2002 22:40:18 -0000 1.3
+++ java/lang/ref/Reference.java 18 Nov 2002 22:26:22 -0000
@@ -1,5 +1,5 @@
 /* java.lang.ref.Reference
- Copyright (C) 1999 Free Software Foundation, Inc.
+ Copyright (C) 1999, 2002 Free Software Foundation, Inc.
 
 This file is part of GNU Classpath.
 
@@ -185,7 +185,7 @@
 */
 public boolean enqueue() 
 {
- if (queue != null)
+ if (queue != null && nextOnQueue != null)
 {
 	queue.enqueue(this);
 	queue = null;
Index: java/lang/ref/natReference.cc
===================================================================
RCS file: /cvs/gcc/gcc/libjava/java/lang/ref/natReference.cc,v
retrieving revision 1.2
diff -u -r1.2 natReference.cc
--- java/lang/ref/natReference.cc 3 Oct 2001 16:47:02 -0000 1.2
+++ java/lang/ref/natReference.cc 18 Nov 2002 22:26:22 -0000
@@ -1,6 +1,6 @@
 // natReference.cc - Native code for References
 
-/* Copyright (C) 2001 Free Software Foundation
+/* Copyright (C) 2001, 2002 Free Software Foundation
 
 This file is part of libgcj.
 
@@ -165,7 +165,8 @@
 if (3 * hash_count >= 2 * hash_size)
 rehash ();
 
- jobject referent = the_reference->referent;
+ // Use `copy' here because the `referent' field has been cleared.
+ jobject referent = the_reference->copy;
 object_list *item = find_slot (referent);
 if (item->reference == NULL)
 {
@@ -249,13 +250,7 @@
 	 // If the copy is already NULL then the user must have
 	 // called Reference.clear().
 	 if (ref->copy != NULL)
-	 {
-	 if (w == PHANTOM)
-		ref->referent = ref->copy;
-	 else
-		ref->copy = NULL;
-	 ref->enqueue ();
-	 }
+	 ref->enqueue ();
 
 	 object_list *next = head->next;
 	 _Jv_Free (head);
