--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pseudo-weak-refs/pseudo-weak-refs.js	Sat Apr 25 13:38:25 2009 -0700
@@ -0,0 +1,55 @@
+// This Ubiquity page-load function injects the following functions for memory
+// debugging into webpages:
+//
+// * window.PseudoWeakRef(object) makes a pseudo-weak reference for the
+//   object.  It has one method, exists(), which returns whether or not
+//   the referent still exists (i.e., has not been garbage collected).
+//
+// * window.forceGC() forces garbage collection.
+
+function pageLoad_injectPseudoWeakRefs(document) {
+  var sandbox = Components.utils.Sandbox(document.defaultView);
+  var weakrefs = [];
+
+  function makePseudoWeakRef(object) {
+    var weakref = new Components.utils.getWeakReference(object);
+    object = null;
+    weakrefs.push(weakref);
+    return weakrefs.length - 1;
+  }
+
+  function isReferentAlive(id) {
+    if (typeof(id) == "number" && weakrefs[id]) {
+      if (weakrefs[id].get() != null)
+        return true;
+      else
+        delete weakrefs[id];
+    }
+    return false;
+  }
+
+  function forceGC() {
+    Components.utils.forceGC();
+  }
+
+  sandbox.importFunction(makePseudoWeakRef);
+  sandbox.importFunction(isReferentAlive);
+  sandbox.importFunction(forceGC);
+
+  function PseudoWeakRef(object) {
+    var id = makePseudoWeakRef(object);
+    object = null;
+    this.exists = function() {
+      return isReferentAlive(id);
+    };
+  }
+
+  Components.utils.evalInSandbox(PseudoWeakRef.toString(), sandbox);
+
+  sandbox.window = document.defaultView.wrappedJSObject;
+  Components.utils.evalInSandbox(
+    ("window.PseudoWeakRef = PseudoWeakRef;" +
+     "window.forceGC = forceGC;"),
+    sandbox
+  );
+}