Bug 718899 - Implement Cu.forceShrinkingGC / Cu.schedulePreciseShrinkingGC r=gwagner

js/xpconnect/idl/xpccomponents.idl

@@ -152,7 +152,7 @@ interface ScheduledGCCallback : nsISupports
 /**
 * interface of Components.utils
 */
-[scriptable, uuid(b032a8f1-9149-4cbe-bee6-4ac5dfe7c80a)]
+[scriptable, uuid(9e9ba9d6-a0fa-4767-9f49-9b74bb2368cd)]
 interface nsIXPCComponents_Utils : nsISupports
 {
 
@@ -263,6 +263,14 @@ interface nsIXPCComponents_Utils : nsISupports
      */
     [implicit_jscontext]
     void forceGC();
+    
+    /*
+     * To be called from JS only.
+     *
+     * Force an immediate shrinking garbage collection cycle.
+     */
+    [implicit_jscontext]
+    void forceShrinkingGC();
 
     /*
      * Schedule a garbage collection cycle for a point in the future when no JS
@@ -270,6 +278,13 @@ interface nsIXPCComponents_Utils : nsISupports
      */
     [implicit_jscontext]
     void schedulePreciseGC(in ScheduledGCCallback callback);
+    
+    /*
+     * Schedule a shrinking garbage collection cycle for a point in the future
+     * when no JS is running. Call the provided function once this has occured.
+     */
+    [implicit_jscontext]
+    void schedulePreciseShrinkingGC(in ScheduledGCCallback callback);
 
     /**
      * Return the keys in a weak map.  This operation is

js/xpconnect/src/XPCComponents.cpp

@@ -3604,11 +3604,19 @@ nsXPCComponents_Utils::ForceGC(JSContext *cx)
     return NS_OK;
 }
 
+/* void forceShrinkingGC (); */
+NS_IMETHODIMP
+nsXPCComponents_Utils::ForceShrinkingGC(JSContext *cx)
+{
+    JS_ShrinkingGC(cx);
+    return NS_OK;
+}
+
 class PreciseGCRunnable : public nsRunnable
 {
   public:
-    PreciseGCRunnable(JSContext *aCx, ScheduledGCCallback* aCallback)
-    : mCallback(aCallback), mCx(aCx) {}
+    PreciseGCRunnable(JSContext *aCx, ScheduledGCCallback* aCallback, bool aShrinking)
+    : mCallback(aCallback), mCx(aCx), mShrinking(aShrinking) {}
 
     NS_IMETHOD Run()
     {
@@ -3627,7 +3635,10 @@ class PreciseGCRunnable : public nsRunnable
             }
         }
 
-        JS_GC(mCx);
+        if (mShrinking)
+            JS_ShrinkingGC(mCx);
+        else
+            JS_GC(mCx);
 
         mCallback->Callback();
         return NS_OK;
@@ -3636,13 +3647,22 @@ class PreciseGCRunnable : public nsRunnable
   private:
     nsRefPtr<ScheduledGCCallback> mCallback;
     JSContext *mCx;
+    bool mShrinking;
 };
 
 /* [inline_jscontext] void schedulePreciseGC(in ScheduledGCCallback callback); */
 NS_IMETHODIMP
 nsXPCComponents_Utils::SchedulePreciseGC(ScheduledGCCallback* aCallback, JSContext* aCx)
 {
-    nsRefPtr<PreciseGCRunnable> event = new PreciseGCRunnable(aCx, aCallback);
+    nsRefPtr<PreciseGCRunnable> event = new PreciseGCRunnable(aCx, aCallback, false);
+    return NS_DispatchToMainThread(event);
+}
+
+/* [inline_jscontext] void schedulePreciseShrinkingGC(in ScheduledGCCallback callback); */
+NS_IMETHODIMP
+nsXPCComponents_Utils::SchedulePreciseShrinkingGC(ScheduledGCCallback* aCallback, JSContext* aCx)
+{
+    nsRefPtr<PreciseGCRunnable> event = new PreciseGCRunnable(aCx, aCallback, true);
     return NS_DispatchToMainThread(event);
 }