Bug 702036 - JSEventListener could have weak mTarget to reduce CC overhead, r=bz

content/events/src/nsEventListenerManager.cpp

@@ -405,7 +405,7 @@ nsEventListenerManager::SetJSEventListener(nsIScriptContext *aContext,
   if (!ls) {
     // If we didn't find a script listener or no listeners existed
     // create and add a new one.
-    nsCOMPtr<nsIDOMEventListener> scriptListener;
+    nsCOMPtr<nsIJSEventListener> scriptListener;
     rv = NS_NewJSEventListener(aContext, aScopeObject, mTarget, aName,
                                aHandler, getter_AddRefs(scriptListener));
     if (NS_SUCCEEDED(rv)) {

content/events/src/nsEventListenerManager.h

@@ -63,7 +63,8 @@ class nsCxPusher;
 class nsIEventListenerInfo;
 class nsIDocument;
 
-typedef struct {
+struct nsListenerStruct
+{
   nsRefPtr<nsIDOMEventListener> mListener;
   PRUint32                      mEventType;
   nsCOMPtr<nsIAtom>             mTypeAtom;
@@ -74,7 +75,14 @@ typedef struct {
     return (mFlags & NS_PRIV_EVENT_FLAG_SCRIPT) ?
       static_cast<nsIJSEventListener *>(mListener.get()) : nsnull;
   }
-} nsListenerStruct;
+
+  ~nsListenerStruct()
+  {
+    if ((mFlags & NS_PRIV_EVENT_FLAG_SCRIPT) && mListener) {
+      static_cast<nsIJSEventListener*>(mListener.get())->Disconnect();
+    }
+  }
+};
 
 /*
  * Event listener manager

content/xbl/src/nsXBLPrototypeHandler.cpp

@@ -327,7 +327,7 @@ nsXBLPrototypeHandler::ExecuteHandler(nsIDOMEventTarget* aTarget,
   NS_ENSURE_SUCCESS(rv, rv);
 
   // Execute it.
-  nsCOMPtr<nsIDOMEventListener> eventListener;
+  nsCOMPtr<nsIJSEventListener> eventListener;
   rv = NS_NewJSEventListener(boundContext, scope,
                              scriptTarget, onEventAtom,
                              boundHandler.getObject(),
@@ -336,6 +336,7 @@ nsXBLPrototypeHandler::ExecuteHandler(nsIDOMEventTarget* aTarget,
 
   // Handle the event.
   eventListener->HandleEvent(aEvent);
+  eventListener->Disconnect();
   return NS_OK;
 }
 

dom/base/nsIJSEventListener.h

@@ -46,13 +46,16 @@ class nsIScriptObjectOwner;
 class nsIAtom;
 
 #define NS_IJSEVENTLISTENER_IID \
-{ 0xafc5d047, 0xdb6b, 0x4076, \
-  { 0xb3, 0xfa, 0x57, 0x96, 0x1e, 0x21, 0x48, 0x42 } }
+{ 0x92f9212b, 0xa6aa, 0x4867, \
+  { 0x93, 0x8a, 0x56, 0xbe, 0x17, 0x67, 0x4f, 0xd4 } }
 
 // Implemented by script event listeners. Used to retrieve the
 // script object corresponding to the event target and the handler itself.
 // (Note this interface is now used to store script objects for all
 // script languages, so is no longer JS specific)
+//
+// Note, mTarget is a raw pointer and the owner of the nsIJSEventListener object
+// is expected to call Disconnect()!
 class nsIJSEventListener : public nsIDOMEventListener
 {
 public:
@@ -60,9 +63,10 @@ public:
 
   nsIJSEventListener(nsIScriptContext* aContext, JSObject* aScopeObject,
                      nsISupports *aTarget, JSObject *aHandler)
-    : mContext(aContext), mScopeObject(aScopeObject),
-      mTarget(do_QueryInterface(aTarget)), mHandler(aHandler)
+    : mContext(aContext), mScopeObject(aScopeObject), mHandler(aHandler)
   {
+    nsCOMPtr<nsISupports> base = do_QueryInterface(aTarget);
+    mTarget = base.get();
   }
 
   nsIScriptContext *GetEventContext() const
@@ -75,6 +79,11 @@ public:
     return mTarget;
   }
 
+  void Disconnect()
+  {
+    mTarget = nsnull;
+  }
+
   JSObject* GetEventScope() const
   {
     return mScopeObject;
@@ -94,10 +103,11 @@ public:
 protected:
   virtual ~nsIJSEventListener()
   {
+    NS_ASSERTION(!mTarget, "Should have called Disconnect()!");
   }
   nsCOMPtr<nsIScriptContext> mContext;
   JSObject* mScopeObject;
-  nsCOMPtr<nsISupports> mTarget;
+  nsISupports* mTarget;
   JSObject *mHandler;
 };
 
@@ -107,6 +117,6 @@ NS_DEFINE_STATIC_IID_ACCESSOR(nsIJSEventListener, NS_IJSEVENTLISTENER_IID)
 nsresult NS_NewJSEventListener(nsIScriptContext *aContext,
                                JSObject* aScopeObject, nsISupports* aTarget,
                                nsIAtom* aType, JSObject* aHandler,
-                               nsIDOMEventListener **aReturn);
+                               nsIJSEventListener **aReturn);
 
 #endif // nsIJSEventListener_h__

dom/src/events/nsJSEventListener.cpp

@@ -103,7 +103,6 @@ nsJSEventListener::~nsJSEventListener()
 
 NS_IMPL_CYCLE_COLLECTION_CLASS(nsJSEventListener)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsJSEventListener)
-  NS_IMPL_CYCLE_COLLECTION_UNLINK_NSCOMPTR(mTarget)
   if (tmp->mContext) {
     if (tmp->mContext->GetScriptTypeID() == nsIProgrammingLanguage::JAVASCRIPT) {
       NS_DROP_JS_OBJECTS(tmp, nsJSEventListener);
@@ -117,7 +116,6 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsJSEventListener)
   }
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsJSEventListener)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR(mTarget)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR(mContext)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
@@ -274,7 +272,7 @@ nsJSEventListener::SetHandler(JSObject *aHandler)
 nsresult
 NS_NewJSEventListener(nsIScriptContext* aContext, JSObject* aScopeObject,
                       nsISupports*aTarget, nsIAtom* aEventType,
-                      JSObject* aHandler, nsIDOMEventListener ** aReturn)
+                      JSObject* aHandler, nsIJSEventListener** aReturn)
 {
   NS_ENSURE_ARG(aEventType);
   nsJSEventListener* it =