Use a lock to deal with concurrent access to the m_evictedBackings

cc/thread_proxy.cc

Index: cc/thread_proxy.cc
diff --git a/cc/thread_proxy.cc b/cc/thread_proxy.cc
index 2281164263a28f51999db0dc8d1923bc5618a32b..0f550ce2a0cca17d24cbce4917045ecb8c650e84 100644
--- a/cc/thread_proxy.cc
+++ b/cc/thread_proxy.cc
@@ -516,9 +516,6 @@ void ThreadProxy::scheduledActionBeginFrame()
     beginFrameState->implTransform = m_layerTreeHostImpl->implTransform();
     DCHECK_GT(m_layerTreeHostImpl->memoryAllocationLimitBytes(), 0u);
     beginFrameState->memoryAllocationLimitBytes = m_layerTreeHostImpl->memoryAllocationLimitBytes();
-    if (m_layerTreeHost->contentsTextureManager())
-        m_layerTreeHost->contentsTextureManager()->getEvictedBackings(beginFrameState->evictedContentsTexturesBackings);
-
     m_mainThreadProxy->postTask(FROM_HERE, base::Bind(&ThreadProxy::beginFrame, base::Unretained(this), base::Passed(beginFrameState.Pass())));
 
     if (m_beginFrameCompletionEventOnImplThread) {
@@ -534,13 +531,6 @@ void ThreadProxy::beginFrame(scoped_ptr<BeginFrameAndCommitState> beginFrameStat
     if (!m_layerTreeHost)
         return;
 
-    // Be sure to never early-out of unlinking evicted textures whenever, so that
-    // the each evicted backing is sent to the main thread exactly once.
-    if (beginFrameState && !beginFrameState->evictedContentsTexturesBackings.empty()) {
-        DCHECK(m_layerTreeHost->contentsTextureManager());
-        m_layerTreeHost->contentsTextureManager()->unlinkEvictedBackings(beginFrameState->evictedContentsTexturesBackings);
-    }
-
     if (m_deferCommits) {
         m_pendingDeferredCommit = beginFrameState.Pass();
         m_layerTreeHost->didDeferCommit();
@@ -580,6 +570,9 @@ void ThreadProxy::beginFrame(scoped_ptr<BeginFrameAndCommitState> beginFrameStat
 
     m_layerTreeHost->willBeginFrame();
 
+    if (m_layerTreeHost->contentsTextureManager())
+        m_layerTreeHost->contentsTextureManager()->unlinkAndClearEvictedBackings();

[jamesr, 2012/11/29 22:06:16]

we don't need to know about unlinked state until updateLayers() - the animation
/ layout calls definitely don't need to know about this (and they might take
some time).  could you move the call down?

[ccameron, 2012/11/29 22:25:35]

Good point -- and I can get rid of the conditional by putting it after
initializeRenderer.

[ccameron, 2012/11/29 23:51:43]

This turns out to be very complicated -- there are tests
(LayerTreeHostTestEvictTextures.runMultiThread, in particular) which are built
around the assumption that the call to layout() will be called after the
textures are unlinked.

This can be easily fixed by adding a new hook to LayerTreeHostClient, but that
will involve touching a dozen files (all with different owners). Doing that in
this CL will add a lot of additional time, and make merging it into M24 much
more difficult.

+
     if (beginFrameState)
         m_layerTreeHost->updateAnimations(beginFrameState->monotonicFrameBeginTime);
     m_layerTreeHost->layout();