From 852c66497eb39cdbb8e6969bf7b6500d13807548 Mon Sep 17 00:00:00 2001
From: Andrzej Kapolka <andrzej@threerings.net>
Date: Sat, 12 Jun 2010 01:15:22 +0000
Subject: [PATCH] Allow adding/removing listeners by weak reference so as not
 to prevent garbage collection.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@6076 542714f4-19e9-0310-aa3c-eee0fc999fb1
---
 .../com/threerings/presents/dobj/DObject.java | 78 +++++++++++++++++++
 1 file changed, 78 insertions(+)

diff --git a/src/java/com/threerings/presents/dobj/DObject.java b/src/java/com/threerings/presents/dobj/DObject.java
index ac05709cd..9c39446d8 100644
--- a/src/java/com/threerings/presents/dobj/DObject.java
+++ b/src/java/com/threerings/presents/dobj/DObject.java
@@ -21,6 +21,7 @@
 
 package com.threerings.presents.dobj;
 
+import java.lang.ref.WeakReference;
 import java.lang.reflect.Field;
 
 import java.util.Arrays;
@@ -200,6 +201,31 @@ public class DObject
         _deathWish = deathWish;
     }
 
+    /**
+     * Adds a listener using a weak reference that will not prevent the listener from being
+     * garbage-collected.
+     */
+    public void addWeakListener (ChangeListener listener)
+    {
+        if (getWeakListenerIndex(listener) == -1) {
+            _listeners = ListUtil.add(_listeners, new WeakListenerWrapper(listener));
+        } else {
+            log.warning("Refusing repeat weak listener registration",
+                "dobj", which(), "list", listener, new Exception());
+        }
+    }
+
+    /**
+     * Removes a weak event listener.
+     */
+    public void removeWeakListener (ChangeListener listener)
+    {
+        int idx = getWeakListenerIndex(listener);
+        if (idx != -1) {
+            _listeners[idx] = null;
+        }
+    }
+
     /**
      * Adds an event listener to this object. The listener will be notified when any events are
      * dispatched on this object that match their particular listener interface.
@@ -975,6 +1001,58 @@ public class DObject
         return null; // key not found.
     }
 
+    /**
+     * Returns the index of the identified wrapped weak listener, or -1 if not found.
+     */
+    protected int getWeakListenerIndex (ChangeListener listener)
+    {
+        if (_listeners == null) {
+            return -1;
+        }
+        for (int ii = 0, ll = _listeners.length; ii < ll; ii++) {
+            Object olistener = _listeners[ii];
+            if (!(olistener instanceof WeakListenerWrapper)) {
+                continue;
+            }
+            if (((WeakListenerWrapper)olistener).ref.get() == listener) {
+                return ii;
+            }
+        }
+        return -1;
+    }
+
+    /**
+     * A listener that wraps a weak reference to another listener.
+     */
+    protected class WeakListenerWrapper
+        implements EventListener
+    {
+        /** The weak reference to our underlying listener. */
+        public final WeakReference<ChangeListener> ref;
+
+        /**
+         * Creates a new weak listener wrapper.
+         */
+        public WeakListenerWrapper (ChangeListener listener)
+        {
+            ref = new WeakReference<ChangeListener>(listener);
+        }
+
+        // documentation inherited from interface EventListener
+        public void eventReceived (DEvent event)
+        {
+            ChangeListener listener = ref.get();
+            if (listener == null) {
+                removeListener(this);
+            } else {
+                event.notifyListener(listener);
+                if (listener instanceof EventListener) {
+                    ((EventListener)listener).eventReceived(event);
+                }
+            }
+        }
+    }
+
     /** Our object id. */
     protected int _oid;