Bug 1276112. Stop using GetScriptContextFromJSContext in CycleCollectedJSRuntime::UsefulToMergeZones. r=mccr8

js/xpconnect/src/XPCJSRuntime.cpp

@@ -596,6 +596,38 @@ CompartmentSizeOfIncludingThisCallback(MallocSizeOf mallocSizeOf, JSCompartment*
     return priv ? priv->SizeOfIncludingThis(mallocSizeOf) : 0;
 }
 
+/*
+ * Return true if there exists a non-system inner window which is a current
+ * inner window and whose reflector is gray.  We don't merge system
+ * compartments, so we don't use them to trigger merging CCs.
+ */
+bool XPCJSRuntime::UsefulToMergeZones() const
+{
+    MOZ_ASSERT(NS_IsMainThread());
+
+    nsGlobalWindow::WindowByIdTable* windowsById =
+        nsGlobalWindow::GetWindowsTable();
+    if (!windowsById) {
+        return false;
+    }
+
+    for (auto iter = windowsById->Iter(); !iter.Done(); iter.Next()) {
+        nsGlobalWindow* window = iter.Data();
+        if (!window->IsInnerWindow() ||
+            !window->AsInner()->IsCurrentInnerWindow()) {
+            continue;
+        }
+
+        JSObject* reflector = window->FastGetGlobalJSObject();
+        if (JS::ObjectIsMarkedGray(reflector) &&
+            !js::IsSystemCompartment(js::GetObjectCompartment(reflector))) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
 void XPCJSRuntime::TraceNativeBlackRoots(JSTracer* trc)
 {
     // Skip this part if XPConnect is shutting down. We get into

js/xpconnect/src/xpcprivate.h

@@ -543,6 +543,7 @@ public:
         return mStrings[index];
     }
 
+    virtual bool UsefulToMergeZones() const override;
     void TraceNativeBlackRoots(JSTracer* trc) override;
     void TraceAdditionalNativeGrayRoots(JSTracer* aTracer) override;
     void TraverseAdditionalNativeRoots(nsCycleCollectionNoteRootCallback& cb) override;

xpcom/base/CycleCollectedJSRuntime.cpp

@@ -1176,39 +1176,9 @@ CycleCollectedJSRuntime::TraverseRoots(nsCycleCollectionNoteRootCallback& aCb)
   return NS_OK;
 }
 
-/*
- * Return true if there exists a JSContext with a default global whose current
- * inner is gray. The intent is to look for JS Object windows. We don't merge
- * system compartments, so we don't use them to trigger merging CCs.
- */
 bool
 CycleCollectedJSRuntime::UsefulToMergeZones() const
 {
-  MOZ_ASSERT(mJSRuntime);
-
-  if (!NS_IsMainThread()) {
-    return false;
-  }
-
-  JSContext* iter = nullptr;
-  JSContext* cx;
-  JSAutoRequest ar(nsContentUtils::GetSafeJSContext());
-  while ((cx = JS_ContextIterator(mJSRuntime, &iter))) {
-    // Skip anything without an nsIScriptContext.
-    nsIScriptContext* scx = GetScriptContextFromJSContext(cx);
-    JS::RootedObject obj(cx, scx ? scx->GetWindowProxyPreserveColor() : nullptr);
-    if (!obj) {
-      continue;
-    }
-    MOZ_ASSERT(js::IsWindowProxy(obj));
-    // Grab the global from the WindowProxy.
-    obj = js::ToWindowIfWindowProxy(obj);
-    MOZ_ASSERT(JS_IsGlobalObject(obj));
-    if (JS::ObjectIsMarkedGray(obj) &&
-        !js::IsSystemCompartment(js::GetObjectCompartment(obj))) {
-      return true;
-    }
-  }
   return false;
 }
 

xpcom/base/CycleCollectedJSRuntime.h

@@ -299,7 +299,7 @@ public:
   nsCycleCollectionParticipant* ZoneParticipant();
 
   nsresult TraverseRoots(nsCycleCollectionNoteRootCallback& aCb);
-  bool UsefulToMergeZones() const;
+  virtual bool UsefulToMergeZones() const;
   void FixWeakMappingGrayBits() const;
   bool AreGCGrayBitsValid() const;
   void GarbageCollect(uint32_t aReason) const;