cc: Implement shared worker contexts.

content/common/gpu/client/context_provider_command_buffer.cc

 // Copyright (c) 2013 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 "content/common/gpu/client/context_provider_command_buffer.h"
 
 #include <set>
 #include <vector>
 
 #include "base/callback_helpers.h"
@@ skipping 41 matching lines @@
     : context3d_(context3d.Pass()),
       context_type_(type),
       debug_name_(CommandBufferContextTypeToString(type)),
       destroyed_(false) {
   DCHECK(main_thread_checker_.CalledOnValidThread());
   DCHECK(context3d_);
   context_thread_checker_.DetachFromThread();
 }
 
 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();
 }
 
 
 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_);
   DCHECK(lost_context_callback_proxy_);  // Is bound to thread.
   DCHECK(context_thread_checker_.CalledOnValidThread());
 
   return context3d_.get();
 }
 
 bool ContextProviderCommandBuffer::BindToCurrentThread() {
@@ skipping 53 matching lines @@
 void ContextProviderCommandBuffer::InvalidateGrContext(uint32_t state) {
   if (gr_context_) {
     DCHECK(lost_context_callback_proxy_);  // Is bound to thread.
     DCHECK(context_thread_checker_.CalledOnValidThread());
     gr_context_->get()->resetContext(state);
   }
 }
 
 void ContextProviderCommandBuffer::SetupLock() {
   DCHECK(context3d_);
+  DCHECK(!context3d_->GetCommandBufferProxy()->lock());
   context3d_->GetCommandBufferProxy()->SetLock(&context_lock_);
 }
 
 base::Lock* ContextProviderCommandBuffer::GetLock() {
   return &context_lock_;
 }
 
 cc::ContextProvider::Capabilities
 ContextProviderCommandBuffer::ContextCapabilities() {
   DCHECK(lost_context_callback_proxy_);  // Is bound to thread.
@@ skipping 76 matching lines @@
   memory_policy_changed_callback_ = memory_policy_changed_callback;
 
   if (!memory_policy_changed_callback_.is_null()) {
     DCHECK(context3d_->GetCommandBufferProxy());
     context3d_->GetCommandBufferProxy()->SetMemoryAllocationChangedCallback(
         base::Bind(&ContextProviderCommandBuffer::OnMemoryAllocationChanged,
                    base::Unretained(this)));
   }
 }
 
+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