Bug 675068 - change off-main-thread cycle collection not to use a (thread-local) safe JS context (r=mrbkap)

--HG--
extra : rebase_source : b5a8a4ffa590bc9d0f2491d6a14bb95a37ff55e9

js/src/xpconnect/src/nsXPConnect.cpp

@@ -468,10 +468,22 @@ nsresult
 nsXPConnect::BeginCycleCollection(nsCycleCollectionTraversalCallback &cb,
                                   bool explainLiveExpectedGarbage)
 {
+    // It is important not to call GetSafeJSContext while on the
+    // cycle-collector thread since this context will be destroyed
+    // asynchronously and race with the main thread. In particular, we must
+    // ensure that a context is passed to the XPCCallContext constructor.
+    JSContext *cx = mRuntime->GetJSCycleCollectionContext();
+    if (!cx)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    // Clear after mCycleCollectionContext is destroyed
+    JS_SetContextThread(cx);
+
     NS_ASSERTION(!mCycleCollectionContext, "Didn't call FinishTraverse?");
-    mCycleCollectionContext = new XPCCallContext(NATIVE_CALLER);
+    mCycleCollectionContext = new XPCCallContext(NATIVE_CALLER, cx);
     if (!mCycleCollectionContext->IsValid()) {
         mCycleCollectionContext = nsnull;
+        JS_ClearContextThread(cx);
         return NS_ERROR_FAILURE;
     }
 
@@ -521,8 +533,11 @@ nsXPConnect::BeginCycleCollection(nsCycleCollectionTraversalCallback &cb,
 nsresult 
 nsXPConnect::FinishTraverse()
 {
-    if (mCycleCollectionContext)
+    if (mCycleCollectionContext) {
+        JSContext *cx = mCycleCollectionContext->GetJSContext();
         mCycleCollectionContext = nsnull;
+        JS_ClearContextThread(cx);
+    }
     return NS_OK;
 }
 

js/src/xpconnect/src/xpcjsruntime.cpp

@@ -1057,6 +1057,18 @@ void XPCJSRuntime::SystemIsBeingShutDown(JSContext* cx)
             Enumerate(DetachedWrappedNativeProtoShutdownMarker, cx);
 }
 
+JSContext *
+XPCJSRuntime::GetJSCycleCollectionContext()
+{
+    if(!mJSCycleCollectionContext) {
+        mJSCycleCollectionContext = JS_NewContext(mJSRuntime, 0);
+        if(!mJSCycleCollectionContext)
+            return nsnull;
+        JS_ClearContextThread(mJSCycleCollectionContext);
+    }
+    return mJSCycleCollectionContext;
+}
+
 XPCJSRuntime::~XPCJSRuntime()
 {
     if (mWatchdogWakeup)
@@ -1077,6 +1089,12 @@ XPCJSRuntime::~XPCJSRuntime()
         mWatchdogWakeup = nsnull;
     }
 
+    if(mJSCycleCollectionContext)
+    {
+        JS_SetContextThread(mJSCycleCollectionContext);
+        JS_DestroyContextNoGC(mJSCycleCollectionContext);
+    }
+
 #ifdef XPC_DUMP_AT_SHUTDOWN
     {
     // count the total JSContexts in use
@@ -1905,6 +1923,7 @@ DiagnosticMemoryCallback(void *ptr, size_t size)
 XPCJSRuntime::XPCJSRuntime(nsXPConnect* aXPConnect)
  : mXPConnect(aXPConnect),
    mJSRuntime(nsnull),
+   mJSCycleCollectionContext(nsnull),
    mWrappedJSMap(JSObject2WrappedJSMap::newMap(XPC_JS_MAP_SIZE)),
    mWrappedJSClassMap(IID2WrappedJSClassMap::newMap(XPC_JS_CLASS_MAP_SIZE)),
    mIID2NativeInterfaceMap(IID2NativeInterfaceMap::newMap(XPC_NATIVE_INTERFACE_MAP_SIZE)),

js/src/xpconnect/src/xpcprivate.h

@@ -654,6 +654,7 @@ public:
 
     JSRuntime*     GetJSRuntime() const {return mJSRuntime;}
     nsXPConnect*   GetXPConnect() const {return mXPConnect;}
+    JSContext*     GetJSCycleCollectionContext();
 
     JSObject2WrappedJSMap*     GetWrappedJSMap()        const
         {return mWrappedJSMap;}
@@ -800,8 +801,9 @@ private:
     jsid mStrIDs[IDX_TOTAL_COUNT];
     jsval mStrJSVals[IDX_TOTAL_COUNT];
 
-    nsXPConnect* mXPConnect;
-    JSRuntime*  mJSRuntime;
+    nsXPConnect*             mXPConnect;
+    JSRuntime*               mJSRuntime;
+    JSContext*               mJSCycleCollectionContext;
     JSObject2WrappedJSMap*   mWrappedJSMap;
     IID2WrappedJSClassMap*   mWrappedJSClassMap;
     IID2NativeInterfaceMap*  mIID2NativeInterfaceMap;