From 06e2e9cf4c3fe1eaac3271c9a346d5cc7fe5c3a8 Mon Sep 17 00:00:00 2001
From: Chris Craik <ccraik@google.com>
Date: Wed, 31 Aug 2016 17:32:46 -0700
Subject: [PATCH] Wait on frame work fences when frames are dropped

bug:30895941

Prevents a race where frame work could interleave between frames,
causing SurfaceView position updates to be delivered out of order.

Change-Id: I01e4cc557b69dcf33e877a0e16c0d115ec95e4cc
---
 libs/hwui/renderthread/CanvasContext.cpp | 3 +++
 libs/hwui/renderthread/CanvasContext.h   | 4 ++--
 libs/hwui/renderthread/DrawFrameTask.cpp | 3 +++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/libs/hwui/renderthread/CanvasContext.cpp b/libs/hwui/renderthread/CanvasContext.cpp
index dcaec428449c3..70b9a436dee26 100644
--- a/libs/hwui/renderthread/CanvasContext.cpp
+++ b/libs/hwui/renderthread/CanvasContext.cpp
@@ -633,6 +633,9 @@ void CanvasContext::prepareAndDraw(RenderNode* node) {
     prepareTree(info, frameInfo, systemTime(CLOCK_MONOTONIC), node);
     if (info.out.canDrawThisFrame) {
         draw();
+    } else {
+        // wait on fences so tasks don't overlap next frame
+        waitOnFences();
     }
 }
 
diff --git a/libs/hwui/renderthread/CanvasContext.h b/libs/hwui/renderthread/CanvasContext.h
index 3eef29b24473b..e1821751b57fe 100644
--- a/libs/hwui/renderthread/CanvasContext.h
+++ b/libs/hwui/renderthread/CanvasContext.h
@@ -168,6 +168,8 @@ public:
 
     ANDROID_API int64_t getFrameNumber();
 
+    void waitOnFences();
+
 private:
     friend class RegisterFrameCallbackTask;
     // TODO: Replace with something better for layer & other GL object
@@ -178,8 +180,6 @@ private:
 
     void freePrefetchedLayers(TreeObserver* observer);
 
-    void waitOnFences();
-
     bool isSwapChainStuffed();
 
     EGLint mLastFrameWidth = 0;
diff --git a/libs/hwui/renderthread/DrawFrameTask.cpp b/libs/hwui/renderthread/DrawFrameTask.cpp
index c9c07b3df292c..e3b6dc6fd9fee 100644
--- a/libs/hwui/renderthread/DrawFrameTask.cpp
+++ b/libs/hwui/renderthread/DrawFrameTask.cpp
@@ -104,6 +104,9 @@ void DrawFrameTask::run() {
 
     if (CC_LIKELY(canDrawThisFrame)) {
         context->draw();
+    } else {
+        // wait on fences so tasks don't overlap next frame
+        context->waitOnFences();
     }
 
     if (!canUnblockUiThread) {