Patch to fix Reference/natReference.

Thu Aug 21 18:10:00 GMT 2003

David> If Reference.clear() is called and then the Reference is finalized
David> before its referent, a dangling pointer is created in the object_list
David> structure in natReference.cc. This happens because the 'copy' field
David> of the Reference is cleared and that is what is used to find the slot
David> in the object_list table.
Could you try the appended patch instead?
I can't try it right now, since I've got other patches in my tree
that break things all over.
This is based on the idea that we shouldn't clear `copy'. It also
removes the disappearing link registration; I think that is a leftover
from an earlier implementation where `referent' was an Object (and
thus traced by the GC). If this works I think we can remove
_Jv_GCRegisterDisappearingLink altogether.
Tom
Index: java/lang/ref/Reference.java
===================================================================
RCS file: /cvs/gcc/gcc/libjava/java/lang/ref/Reference.java,v
retrieving revision 1.4
diff -u -r1.4 Reference.java

--- java/lang/ref/Reference.java 19 Nov 2002 21:59:40 -0000 1.4
+++ java/lang/ref/Reference.java 21 Aug 2003 18:05:06 -0000
@@ -1,5 +1,5 @@
 /* java.lang.ref.Reference
- Copyright (C) 1999, 2002 Free Software Foundation, Inc.
+ Copyright (C) 1999, 2002, 2003 Free Software Foundation, Inc.
 
 This file is part of GNU Classpath.
 
@@ -85,8 +85,8 @@
 * This is like REFERENT but is not scanned by the GC. We keep a
 * copy around so that we can see when clear() has been called.
 * GCJ LOCAL:
- * This field doesn't exist in Classpath; we use it to detect
- * clearing.
+ * This field doesn't exist in Classpath; we use it to let us clean
+ * up some internal data structures after clearing.
 * END GCJ LOCAL
 */
 gnu.gcj.RawData copy;
@@ -167,7 +167,6 @@
 public void clear()
 {
 referent = null;
- copy = null;
 }
 
 /**
Index: java/lang/ref/natReference.cc
===================================================================
RCS file: /cvs/gcc/gcc/libjava/java/lang/ref/natReference.cc,v
retrieving revision 1.4
diff -u -r1.4 natReference.cc
--- java/lang/ref/natReference.cc 20 Aug 2003 15:30:04 -0000 1.4
+++ java/lang/ref/natReference.cc 21 Aug 2003 18:05:06 -0000
@@ -258,10 +258,16 @@
 	{
 	 java::lang::ref::Reference *ref
 	 = reinterpret_cast<java::lang::ref::Reference *> (head->reference);
-	 // If the copy is already NULL then the user must have
+	 // If reference is already NULL then the user must have
 	 // called Reference.clear().
-	 if (ref->copy != NULL)
-	 ref->enqueue ();
+	 if (ref->referent != NULL)
+	 {
+	 // The JDK doesn't appear to call clear() internally,
+	 // so we don't either.
+	 if (w != PHANTOM)
+		ref->referent = NULL;
+	 ref->enqueue ();
+	 }
 
 	 object_list *next = head->next;
 	 _Jv_Free (head);
@@ -303,8 +309,6 @@
 // finalizer for ourselves as well.
 _Jv_RegisterFinalizer (this, finalize_reference);
 _Jv_RegisterFinalizer (referent, finalize_referred_to_object);
- jobject *objp = reinterpret_cast<jobject *> (&referent);
- _Jv_GCRegisterDisappearingLink (objp);
 add_to_hash (this);
 }
 }
