Bug 1250963 part 1. Change NotifyRunnable::Dispatch to not require a JSContext. r=khuey

The only reason NotifyRunnable::Dispatch needs a JSContext is so that it can call
ModifyBusyCount in Pre/PostDispatch.  The only reason that needs a JSContext is
to call Cancel(), which only needs it to call Notify(), which only needs it to
call NotifyPrivate, which only needs it to dispatch a NotifyRunnable.

dom/workers/RuntimeService.cpp

@@ -2146,19 +2146,13 @@ RuntimeService::CancelWorkersForWindow(nsPIDOMWindowInner* aWindow)
   GetWorkersForWindow(aWindow, workers);
 
   if (!workers.IsEmpty()) {
-    AutoJSAPI jsapi;
-    if (NS_WARN_IF(!jsapi.InitWithLegacyErrorReporting(aWindow))) {
-      return;
-    }
-    JSContext* cx = jsapi.cx();
-
     for (uint32_t index = 0; index < workers.Length(); index++) {
       WorkerPrivate*& worker = workers[index];
 
       if (worker->IsSharedWorker()) {
         worker->CloseSharedWorkersForWindow(aWindow);
-      } else if (!worker->Cancel(cx)) {
-        JS_ReportPendingException(cx);
+      } else {
+        worker->Cancel();
       }
     }
   }

dom/workers/WorkerPrivate.cpp

@@ -847,10 +847,19 @@ public:
                aStatus == Canceling || aStatus == Killing);
   }
 
+  // We can be dispatched without a JSContext, because all we do with the
+  // JSContext passed to Dispatch() normally for worker runnables is call
+  // ModifyBusyCount... but that doesn't actually use its JSContext argument.
+  bool Dispatch()
+  {
+    return WorkerControlRunnable::Dispatch(nullptr);
+  }
+
 private:
   virtual bool
   PreDispatch(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override
   {
+    aWorkerPrivate->AssertIsOnParentThread();
     // Modify here, but not in PostRun! This busy count addition will be matched
     // by the CloseEventRunnable.
     return aWorkerPrivate->ModifyBusyCount(aCx, true);
@@ -860,6 +869,7 @@ private:
   PostDispatch(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
                bool aDispatchResult) override
   {
+    aWorkerPrivate->AssertIsOnParentThread();
     if (!aDispatchResult) {
       // We couldn't dispatch to the worker, which means it's already dead.
       // Undo the busy count modification.
@@ -2519,7 +2529,7 @@ WorkerPrivateParent<Derived>::Start()
 // aCx is null when called from the finalizer
 template <class Derived>
 bool
-WorkerPrivateParent<Derived>::NotifyPrivate(JSContext* aCx, Status aStatus)
+WorkerPrivateParent<Derived>::NotifyPrivate(Status aStatus)
 {
   AssertIsOnParentThread();
 
@@ -2571,7 +2581,7 @@ WorkerPrivateParent<Derived>::NotifyPrivate(JSContext* aCx, Status aStatus)
 
   RefPtr<NotifyRunnable> runnable =
     new NotifyRunnable(ParentAsWorkerPrivate(), aStatus);
-  return runnable->Dispatch(aCx);
+  return runnable->Dispatch();
 }
 
 template <class Derived>
@@ -2778,7 +2788,8 @@ WorkerPrivateParent<Derived>::Close()
 
 template <class Derived>
 bool
-WorkerPrivateParent<Derived>::ModifyBusyCount(JSContext* aCx, bool aIncrease)
+WorkerPrivateParent<Derived>::ModifyBusyCount(JSContext* /* unused */,
+                                              bool aIncrease)
 {
   AssertIsOnParentThread();
 
@@ -2797,7 +2808,7 @@ WorkerPrivateParent<Derived>::ModifyBusyCount(JSContext* aCx, bool aIncrease)
       shouldCancel = mParentStatus == Terminating;
     }
 
-    if (shouldCancel && !Cancel(aCx)) {
+    if (shouldCancel && !Cancel()) {
       return false;
     }
   }
@@ -3332,8 +3343,8 @@ WorkerPrivateParent<Derived>::CloseSharedWorkersForWindow(
     if (!Freeze(cx, nullptr)) {
       JS_ReportPendingException(cx);
     }
-  } else if (!Cancel(cx)) {
-    JS_ReportPendingException(cx);
+  } else {
+    Cancel();
   }
 }
 
@@ -3350,10 +3361,7 @@ WorkerPrivateParent<Derived>::CloseAllSharedWorkers()
 
   mSharedWorkers.Clear();
 
-  AutoSafeJSContext cx;
-  if (!Cancel(cx)) {
-    JS_ReportPendingException(cx);
-  }
+  Cancel();
 }
 
 template <class Derived>
@@ -5185,7 +5193,7 @@ WorkerPrivate::NotifyFeatures(JSContext* aCx, Status aStatus)
   children.AppendElements(mChildWorkers);
 
   for (uint32_t index = 0; index < children.Length(); index++) {
-    if (!children[index]->Notify(aCx, aStatus)) {
+    if (!children[index]->Notify(aStatus)) {
       NS_WARNING("Failed to notify child worker!");
     }
   }

dom/workers/WorkerPrivate.h

@@ -218,13 +218,13 @@ private:
 
   // aCx is null when called from the finalizer
   bool
-  NotifyPrivate(JSContext* aCx, Status aStatus);
+  NotifyPrivate(Status aStatus);
 
   // aCx is null when called from the finalizer
   bool
   TerminatePrivate(JSContext* aCx)
   {
-    return NotifyPrivate(aCx, Terminating);
+    return NotifyPrivate(Terminating);
   }
 
   void
@@ -282,21 +282,21 @@ public:
 
   // Called on the parent thread.
   bool
-  Notify(JSContext* aCx, Status aStatus)
+  Notify(Status aStatus)
   {
-    return NotifyPrivate(aCx, aStatus);
+    return NotifyPrivate(aStatus);
   }
 
   bool
-  Cancel(JSContext* aCx)
+  Cancel()
   {
-    return Notify(aCx, Canceling);
+    return Notify(Canceling);
   }
 
   bool
   Kill(JSContext* aCx)
   {
-    return Notify(aCx, Killing);
+    return Notify(Killing);
   }
 
   // We can assume that an nsPIDOMWindow will be available for Freeze, Thaw
@@ -323,8 +323,10 @@ public:
   bool
   Close();
 
+  // The JSContext argument can be null, since it's not used for anything.  It's
+  // about to go away.
   bool
-  ModifyBusyCount(JSContext* aCx, bool aIncrease);
+  ModifyBusyCount(JSContext* /* unused */, bool aIncrease);
 
   void
   ForgetOverridenLoadGroup(nsCOMPtr<nsILoadGroup>& aLoadGroupOut);