Merge "viewcapture: guarantee happens-before relationship" into main

            captureViewTree(mRoot, mViewPropertyRef);

            ViewPropertyRef captured = mViewPropertyRef.next;

            if (captured != null) {

                captured.callback = mCaptureCallback;

                captured.elapsedRealtimeNanos = SystemClock.elapsedRealtimeNanos();

                // Main thread writes volatile field:

                // guarantee that variable changes prior the field write are visible to bg thread

                captured.volatileCallback = mCaptureCallback;

                mBgExecutor.execute(captured);

            }

            mIsFirstFrame = false;

        public ViewPropertyRef next;

        public Consumer<ViewPropertyRef> callback = null;

        public long elapsedRealtimeNanos = 0;

        // Volatile field to establish happens-before relationship between main and bg threads

        // (see JSR-133: Java Memory Model and Thread Specification)

        public volatile Consumer<ViewPropertyRef> volatileCallback = null;

        public void transferFrom(View in) {

            view = in;

        @Override

        public void run() {

            Consumer<ViewPropertyRef> oldCallback = callback;

            callback = null;

            // Bg thread reads volatile field:

            // guarantee that variable changes in main thread prior the field write are visible

            Consumer<ViewPropertyRef> oldCallback = volatileCallback;

            volatileCallback = null;

            if (oldCallback != null) {

                oldCallback.accept(this);

            }