Use a lock to deal with concurrent access to the m_evictedBackings

cc/thread_proxy.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/thread_proxy.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "cc/delay_based_time_source.h"
 #include "cc/draw_quad.h"
@@ skipping 498 matching lines @@
 
 void ThreadProxy::scheduledActionBeginFrame()
 {
     TRACE_EVENT0("cc", "ThreadProxy::scheduledActionBeginFrame");
     scoped_ptr<BeginFrameAndCommitState> beginFrameState(new BeginFrameAndCommitState);
     beginFrameState->monotonicFrameBeginTime = base::TimeTicks::Now();
     beginFrameState->scrollInfo = m_layerTreeHostImpl->processScrollDeltas();
     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) {
         m_beginFrameCompletionEventOnImplThread->signal();
         m_beginFrameCompletionEventOnImplThread = 0;
     }
 }
 
 void ThreadProxy::beginFrame(scoped_ptr<BeginFrameAndCommitState> beginFrameState)
 {
     TRACE_EVENT0("cc", "ThreadProxy::beginFrame");
     DCHECK(isMainThread());
     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();
         TRACE_EVENT0("cc", "EarlyOut_DeferCommits");
         return;
     }
 
     if (m_layerTreeHost->needsSharedContext() && !WebSharedGraphicsContext3D::haveCompositorThreadContext())
         WebSharedGraphicsContext3D::createCompositorThreadContext();
 
@@ skipping 19 matching lines @@
         m_commitRequested = false;
         m_commitRequestSentToImplThread = false;
 
         TRACE_EVENT0("cc", "EarlyOut_NotVisible");
         Proxy::implThread()->postTask(base::Bind(&ThreadProxy::beginFrameAbortedOnImplThread, base::Unretained(this)));
         return;
     }
 
     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();
 
     // Clear the commit flag after updating animations and layout here --- objects that only
     // layout when painted will trigger another setNeedsCommit inside
     // updateLayers.
     m_commitRequested = false;
     m_commitRequestSentToImplThread = false;
 
@@ skipping 384 matching lines @@
 ThreadProxy::BeginFrameAndCommitState::BeginFrameAndCommitState()
     : memoryAllocationLimitBytes(0)
 {
 }
 
 ThreadProxy::BeginFrameAndCommitState::~BeginFrameAndCommitState()
 {
 }
 
 }  // namespace cc