--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/components/src/nsJSWeakRef.cpp	Thu Apr 16 15:23:22 2009 -0700
@@ -0,0 +1,178 @@
+#include "nsJSWeakRef.h"
+
+#include "jsapi.h"
+#include "nsIXPConnect.h"
+#include "nsAXPCNativeCallContext.h"
+#include "nsServiceManagerUtils.h"
+#include "nsComponentManagerUtils.h"
+
+class nsJSWeakRefListNode {
+public:
+  nsJSWeakRef *data;
+  nsJSWeakRefListNode *next;
+};
+
+class nsJSWeakRefImpl {
+public:
+  JSObject *weakRef;
+  JSContext *weakCx;
+  nsJSWeakRefListNode *node;
+};
+
+static nsJSWeakRefListNode *gList;
+static JSGCCallback gOldJSGCCallback;
+
+void processGarbage() {
+  nsJSWeakRefListNode *node = gList;
+  nsJSWeakRefListNode *prevNode = nsnull;
+  nsJSWeakRefListNode *nextNode = nsnull;
+  while (node) {
+    nextNode = node->next;
+    if (node->data) {
+      if (JS_IsAboutToBeFinalized(node->data->impl->weakCx,
+                                  node->data->impl->weakRef)) {
+        // Tell the weak reference holder that its target no longer exists.
+        node->data->impl->weakRef = nsnull;
+        node->data->impl->weakCx = nsnull;
+        node->data->impl->node = nsnull;
+
+        // Delete this node.
+        if (prevNode)
+          prevNode->next = nextNode;
+        else
+          gList = nextNode;
+        delete node;
+      } else
+        // This is our general case; just move on to the next node.
+        prevNode = node;
+    } else {
+      // The weak reference holder went away, so just delete this node.
+      if (prevNode)
+        prevNode->next = nextNode;
+      else
+        gList = nextNode;
+      delete node;
+    }
+    node = nextNode;
+  }
+}
+
+static JSBool XPCCycleCollectGCCallback(JSContext *cx, JSGCStatus status) {
+  if (status == JSGC_MARK_END)
+    processGarbage();
+  return gOldJSGCCallback ? gOldJSGCCallback(cx, status) : JS_TRUE;
+}
+
+nsJSWeakRef::nsJSWeakRef()
+{
+  this->impl = new nsJSWeakRefImpl();
+  this->impl->weakRef = nsnull;
+  this->impl->weakCx = nsnull;
+  this->impl->node = nsnull;
+}
+
+nsJSWeakRef::~nsJSWeakRef()
+{
+  if (this->impl->node)
+    // Tell the GC callback to remove our node from the list next time around.
+    this->impl->node->data = nsnull;
+
+  delete this->impl;
+  this->impl = nsnull;
+}
+
+NS_IMETHODIMP nsJSWeakRef::Set()
+{
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsIXPConnect> xpc = do_GetService(
+    "@mozilla.org/js/xpc/XPConnect;1",
+    &rv
+  );
+  if (NS_FAILED(rv))
+    return NS_ERROR_FAILURE;
+
+  // get the xpconnect native call context
+  nsAXPCNativeCallContext *cc = nsnull;
+  xpc->GetCurrentNativeCallContext(&cc);
+  if(!cc)
+    return NS_ERROR_FAILURE;
+
+  // Get JSContext of current call
+  JSContext* cx;
+  rv = cc->GetJSContext(&cx);
+  if(NS_FAILED(rv) || !cx)
+    return NS_ERROR_FAILURE;
+
+  // get place for return value
+  jsval *rval = nsnull;
+  rv = cc->GetRetValPtr(&rval);
+  if(NS_FAILED(rv) || !rval)
+    return NS_ERROR_FAILURE;
+
+  // get argc and argv and verify arg count
+  PRUint32 argc;
+  rv = cc->GetArgc(&argc);
+  if(NS_FAILED(rv))
+    return rv;
+
+  if (argc < 1)
+    return NS_ERROR_XPC_NOT_ENOUGH_ARGS;
+
+  jsval *argv;
+  rv = cc->GetArgvPtr(&argv);
+  if (NS_FAILED(rv))
+    return rv;
+
+  if (!JSVAL_IS_OBJECT(argv[0]))
+    return NS_ERROR_ILLEGAL_VALUE;
+
+  this->impl->weakRef = JSVAL_TO_OBJECT(argv[0]);
+  this->impl->weakCx = cx;
+
+  // Insert a new node at the head of the global list.
+  nsJSWeakRefListNode *newNode = new nsJSWeakRefListNode();
+  newNode->data = this;
+  newNode->next = gList;
+  this->impl->node = newNode;
+  gList = newNode;
+
+  // TODO: Note that this is never removed.
+  if (!gOldJSGCCallback)
+    gOldJSGCCallback = JS_SetGCCallback(cx, XPCCycleCollectGCCallback);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsJSWeakRef::Get()
+{
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsIXPConnect> xpc = do_GetService(
+    "@mozilla.org/js/xpc/XPConnect;1",
+    &rv
+  );
+  if (NS_FAILED(rv))
+    return NS_ERROR_FAILURE;
+
+  // get the xpconnect native call context
+  nsAXPCNativeCallContext *cc = nsnull;
+  xpc->GetCurrentNativeCallContext(&cc);
+  if(!cc)
+    return NS_ERROR_FAILURE;
+
+  // get place for return value
+  jsval *rval = nsnull;
+  rv = cc->GetRetValPtr(&rval);
+  if(NS_FAILED(rv) || !rval)
+    return NS_ERROR_FAILURE;
+
+  // TODO: Do we have to increase the reference count of the object
+  // or anything?
+
+  // This automatically is set to JSVAL_NULL if weakRef is nsnull.
+  *rval = OBJECT_TO_JSVAL(this->impl->weakRef);
+  cc->SetReturnValueWasSet(PR_TRUE);
+
+  return NS_OK;
+}
+
+NS_IMPL_ISUPPORTS1(nsJSWeakRef, nsIJSWeakRef);