Prepare CompositorWorker for per thread heap

third_party/WebKit/Source/web/CompositorMutatorImpl.cpp

Index: third_party/WebKit/Source/web/CompositorMutatorImpl.cpp
diff --git a/third_party/WebKit/Source/web/CompositorMutatorImpl.cpp b/third_party/WebKit/Source/web/CompositorMutatorImpl.cpp
index eddb7cb5972855c792cb2a2e48e854c5f32239ae..3a0ee6e698f421c997c28b702e8a5371f12d1f22 100644
--- a/third_party/WebKit/Source/web/CompositorMutatorImpl.cpp
+++ b/third_party/WebKit/Source/web/CompositorMutatorImpl.cpp
@@ -64,8 +64,9 @@ bool CompositorMutatorImpl::mutate(double monotonicTimeNow, CompositorMutableSta
     // 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;
     }
 
@@ -75,7 +76,21 @@ bool CompositorMutatorImpl::mutate(double monotonicTimeNow, CompositorMutableSta
 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();
 }