From 89520b7407b6c3c545a3936bb4bdc77860ab0276 Mon Sep 17 00:00:00 2001
From: Andrew McCreight <continuation@gmail.com>
Date: Mon, 2 Dec 2013 13:17:29 -0800
Subject: [PATCH] Bug 942528 - Make XPCWN more of a normal cycle collected
 class. r=smaug

---
 js/xpconnect/src/XPCWrappedNative.cpp | 18 +++++++++++++++---
 js/xpconnect/src/xpcprivate.h         | 22 ++--------------------
 2 files changed, 17 insertions(+), 23 deletions(-)

diff --git a/js/xpconnect/src/XPCWrappedNative.cpp b/js/xpconnect/src/XPCWrappedNative.cpp
index 7d9dcfadbb8d..b88aee46839b 100644
--- a/js/xpconnect/src/XPCWrappedNative.cpp
+++ b/js/xpconnect/src/XPCWrappedNative.cpp
@@ -41,6 +41,10 @@ xpc_OkToHandOutWrapper(nsWrapperCache *cache)
 
 NS_IMPL_CYCLE_COLLECTION_CLASS(XPCWrappedNative)
 
+// No need to unlink the JS objects: if the XPCWrappedNative is cycle
+// collected then its mFlatJSObject will be cycle collected too and
+// finalization of the mFlatJSObject will unlink the JS objects (see
+// XPC_WN_NoHelper_Finalize and FlatJSObjectFinalized).
 NS_IMETHODIMP_(void)
 NS_CYCLE_COLLECTION_CLASSNAME(XPCWrappedNative)::Unlink(void *p)
 {
@@ -600,6 +604,8 @@ XPCWrappedNative::XPCWrappedNative(already_AddRefed<nsISupports> aIdentity,
       mSet(aProto->GetSet()),
       mScriptableInfo(nullptr)
 {
+    MOZ_ASSERT(NS_IsMainThread());
+
     mIdentity = aIdentity.get();
     mFlatJSObject.setFlags(FLAT_JS_OBJECT_VALID);
 
@@ -616,6 +622,8 @@ XPCWrappedNative::XPCWrappedNative(already_AddRefed<nsISupports> aIdentity,
       mSet(aSet),
       mScriptableInfo(nullptr)
 {
+    MOZ_ASSERT(NS_IsMainThread());
+
     mIdentity = aIdentity.get();
     mFlatJSObject.setFlags(FLAT_JS_OBJECT_VALID);
 
@@ -905,10 +913,14 @@ NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(XPCWrappedNative)
   NS_INTERFACE_MAP_ENTRY(nsIXPConnectWrappedNative)
   NS_INTERFACE_MAP_ENTRY(nsIXPConnectJSObjectHolder)
   NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIXPConnectWrappedNative)
-NS_INTERFACE_MAP_END_THREADSAFE
+NS_INTERFACE_MAP_END
 
-NS_IMPL_ADDREF(XPCWrappedNative)
-NS_IMPL_RELEASE(XPCWrappedNative)
+NS_IMPL_CYCLE_COLLECTING_ADDREF(XPCWrappedNative)
+
+// Release calls Destroy() immediately when the refcount drops to 0 to
+// clear the weak references nsXPConnect has to XPCWNs and to ensure there
+// are no pointers to dying protos.
+NS_IMPL_CYCLE_COLLECTING_RELEASE_WITH_LAST_RELEASE(XPCWrappedNative, Destroy())
 
 /*
  *  Wrapped Native lifetime management is messy!
diff --git a/js/xpconnect/src/xpcprivate.h b/js/xpconnect/src/xpcprivate.h
index 7eaf6be3f237..81fb18097306 100644
--- a/js/xpconnect/src/xpcprivate.h
+++ b/js/xpconnect/src/xpcprivate.h
@@ -2007,29 +2007,11 @@ TraceXPCGlobal(JSTracer *trc, JSObject *obj);
 class XPCWrappedNative : public nsIXPConnectWrappedNative
 {
 public:
-    NS_DECL_THREADSAFE_ISUPPORTS
+    NS_DECL_CYCLE_COLLECTING_ISUPPORTS
     NS_DECL_NSIXPCONNECTJSOBJECTHOLDER
     NS_DECL_NSIXPCONNECTWRAPPEDNATIVE
-    // No need to unlink the JS objects, if the XPCWrappedNative will be cycle
-    // collected then its mFlatJSObject will be cycle collected too and
-    // finalization of the mFlatJSObject will unlink the js objects (see
-    // XPC_WN_NoHelper_Finalize and FlatJSObjectFinalized).
-    // We also give XPCWrappedNative empty Root/Unroot methods, to avoid
-    // root/unrooting the JS objects from addrefing/releasing the
-    // XPCWrappedNative during unlinking, which would make the JS objects
-    // uncollectable to the JS GC.
-    class NS_CYCLE_COLLECTION_INNERCLASS
-     : public nsXPCOMCycleCollectionParticipant
-    {
-      NS_DECL_CYCLE_COLLECTION_CLASS_BODY(XPCWrappedNative, XPCWrappedNative)
-      NS_IMETHOD_(void) Root(void *p) { }
-      NS_IMETHOD_(void) Unroot(void *p) { }
-      NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(XPCWrappedNative)
-    };
-    NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(XPCWrappedNative);
-    static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
 
-    void DeleteCycleCollectable() {}
+    NS_DECL_CYCLE_COLLECTION_CLASS(XPCWrappedNative)
 
     nsIPrincipal* GetObjectPrincipal() const;