Prepare CompositorWorker for per thread heap

third_party/WebKit/Source/web/CompositorMutatorImpl.cpp

 // Copyright 2016 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 "web/CompositorMutatorImpl.h"
 
 #include "core/animation/CustomCompositorAnimationManager.h"
 #include "core/dom/CompositorProxy.h"
 #include "platform/CrossThreadFunctional.h"
 #include "platform/TraceEvent.h"
@@ skipping 46 matching lines @@
     return new CompositorMutatorImpl();
 }
 
 bool CompositorMutatorImpl::mutate(double monotonicTimeNow, CompositorMutableStateProvider* stateProvider)
 {
     TRACE_EVENT0("compositor-worker", "CompositorMutatorImpl::mutate");
     bool needToReinvoke = false;
     // TODO(vollick): we should avoid executing the animation frame
     // callbacks if none of the proxies in the global scope are affected by
     // m_mutations.
-    for (CompositorProxyClientImpl* client : m_proxyClients) {
-        if (client->mutate(monotonicTimeNow, stateProvider))
+    for (auto& it : m_proxyClients) {
+        CrossThreadPersistent<CompositorProxyClientImpl> client = CrossThreadPersistent<CompositorProxyClientImpl>::protectWeak(it);
+        if (client && client->mutate(monotonicTimeNow, stateProvider))
             needToReinvoke = true;
     }
 
     return needToReinvoke;
 }
 
 void CompositorMutatorImpl::registerProxyClient(CompositorProxyClientImpl* client)
 {
     TRACE_EVENT0("compositor-worker", "CompositorMutatorImpl::registerClient");
-    m_proxyClients.add(client);
+    CrossThreadWeakPersistent<CompositorProxyClientImpl>* insertPosition = nullptr;
+    for (auto& it : m_proxyClients) {
+        CrossThreadPersistent<CompositorProxyClientImpl> protect = CrossThreadPersistent<CompositorProxyClientImpl>::protectWeak(it);
+        if (!protect && !insertPosition) {
+            insertPosition = &it;
+#if !DCHECK_IS_ON()
+            break;
+#endif
+        }
+        DCHECK_NE(protect, client);
+    }
+    if (insertPosition)
+        *insertPosition = client;
+    else
+        m_proxyClients.append(client);

[haraken, 2016/09/07 15:10:30]

Hmm, this looks very complicated and I'm not sure if this code is really
thread-safe...

Maybe can we use HeapHashSet<UntracedMember<CompositorProxyClientImpl>> and
introduce CompositorMutatorImpl::unregisterProxyClient, which removes the
UntracedMember at some explicit point?

If that is not easy, let's chat offline.

(I begin to think that CrossThreadWeakPersistent is a dangerous thing in
general, and maybe it should be just forbidden...)

[keishi, 2016/09/12 09:00:48]

I used WorkerGlobalScope::dispose for explicit removal instead of relying on
weak. dispose is called when the worker is terminated so it should work.

     setNeedsMutate();
 }
 
 void CompositorMutatorImpl::setNeedsMutate()
 {
     TRACE_EVENT0("compositor-worker", "CompositorMutatorImpl::setNeedsMutate");
     m_client->setNeedsMutate();
 }
 
 } // namespace blink