cc: Implement shared worker contexts.

content/common/gpu/client/context_provider_command_buffer.cc

Index: content/common/gpu/client/context_provider_command_buffer.cc
diff --git a/content/common/gpu/client/context_provider_command_buffer.cc b/content/common/gpu/client/context_provider_command_buffer.cc
index ba9f0ebfbed6a6f75196c29a7bf89da933557773..fb76ee481050ca01bc18abbd4d1ddd9052fe5a8c 100644
--- a/content/common/gpu/client/context_provider_command_buffer.cc
+++ b/content/common/gpu/client/context_provider_command_buffer.cc
@@ -59,17 +59,8 @@ ContextProviderCommandBuffer::ContextProviderCommandBuffer(
 }
 
 ContextProviderCommandBuffer::~ContextProviderCommandBuffer() {
-  DCHECK(main_thread_checker_.CalledOnValidThread() ||
-         context_thread_checker_.CalledOnValidThread());
-
   base::AutoLock lock(main_thread_lock_);
-
-  // Destroy references to the context3d_ before leaking it.
-  if (context3d_->GetCommandBufferProxy()) {
-    context3d_->GetCommandBufferProxy()->SetLock(nullptr);
-    context3d_->GetCommandBufferProxy()->SetMemoryAllocationChangedCallback(
-        CommandBufferProxyImpl::MemoryAllocationChangedCallback());
-  }
+  DestroyWithMainThreadLockAcquired();
   lost_context_callback_proxy_.reset();
 }
 
@@ -78,6 +69,15 @@ CommandBufferProxyImpl* ContextProviderCommandBuffer::GetCommandBufferProxy() {
   return context3d_->GetCommandBufferProxy();
 }
 
+void ContextProviderCommandBuffer::Destroy() {
+  DCHECK(context_thread_checker_.CalledOnValidThread());
+  // Verify that SetupLock() has been called.
+  DCHECK(context3d_->GetCommandBufferProxy()->lock());
+
+  base::AutoLock lock(main_thread_lock_);
+  DestroyWithMainThreadLockAcquired();
+}
+
 WebGraphicsContext3DCommandBufferImpl*
 ContextProviderCommandBuffer::WebContext3D() {
   DCHECK(context3d_);
@@ -151,6 +151,7 @@ void ContextProviderCommandBuffer::InvalidateGrContext(uint32_t state) {
 
 void ContextProviderCommandBuffer::SetupLock() {
   DCHECK(context3d_);
+  DCHECK(!context3d_->GetCommandBufferProxy()->lock());
   context3d_->GetCommandBufferProxy()->SetLock(&context_lock_);
 }
 
@@ -247,4 +248,16 @@ void ContextProviderCommandBuffer::SetMemoryPolicyChangedCallback(
   }
 }
 
+void ContextProviderCommandBuffer::DestroyWithMainThreadLockAcquired() {
+  main_thread_lock_.AssertAcquired();
+
+  if (context3d_->GetCommandBufferProxy()) {
+    context3d_->GetCommandBufferProxy()->SetLock(nullptr);

[piman, 2015/09/09 19:14:23]

That's unsafe if the lock wasn't taken (or this is the only thread). Another
thread might be checking whether lock_ is set on the context.

I'm not convinced that this is ok. If you reset the lock (even while it is held,
and even if on the context thread), won't IPC messages after that fail to take
the lock, causing data races on some of CommandBufferProxyImpl members if
read/modified on other threads, even though they take the lock?

+    context3d_->GetCommandBufferProxy()->SetMemoryAllocationChangedCallback(
+        CommandBufferProxyImpl::MemoryAllocationChangedCallback());
+    context3d_->GetCommandBufferProxy()->Destroy();
+  }
+  destroyed_ = true;
+}
+
 }  // namespace content