Pepper takes ownership of a mailbox before passing it to the texture layer.

gpu/ipc/client/command_buffer_proxy_impl.cc

 // Copyright (c) 2012 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 "gpu/ipc/client/command_buffer_proxy_impl.h"
 
 #include <utility>
 #include <vector>
 
 #include "base/callback.h"
@@ skipping 599 matching lines @@
   // catches upwith the command buffer.
   // A malicious caller trying to create a collision by making next_signal_id
   // would have to make calls at an astounding rate (300B/s) and even if they
   // could do that, all they would do is to prevent some callbacks from getting
   // called, leading to stalled threads and/or memory leaks.
   uint32_t signal_id = next_signal_id_++;
   Send(new GpuCommandBufferMsg_SignalQuery(route_id_, query, signal_id));
   signal_tasks_.insert(std::make_pair(signal_id, callback));
 }
 
-bool CommandBufferProxyImpl::ProduceFrontBuffer(const gpu::Mailbox& mailbox) {
-  CheckLock();
+void CommandBufferProxyImpl::TakeFrontBuffer(const gpu::Mailbox& mailbox) {

[piman, 2016/04/27 23:00:58]

nit: CheckLock();

[erikchen, 2016/04/27 23:59:24]

Done

[piman, 2016/04/28 02:15:05]

I don't see it in the latest PS (PS#18)

[erikchen, 2016/04/28 17:07:23]

I do see it.
https://codereview.chromium.org/1912833002/diff2/240001:330001/gpu/ipc/client...

It's been there since PS 15.

   if (last_state_.error != gpu::error::kNoError)
-    return false;
+    return;
 
-  Send(new GpuCommandBufferMsg_ProduceFrontBuffer(route_id_, mailbox));
-  return true;
+  Send(new GpuCommandBufferMsg_TakeFrontBuffer(route_id_, mailbox));
+}
+
+void CommandBufferProxyImpl::ReturnFrontBuffer(const gpu::Mailbox& mailbox,
+                                               const gpu::SyncToken& sync_token,
+                                               bool is_lost) {

[piman, 2016/04/27 23:00:58]

nit: CheckLock();

[erikchen, 2016/04/27 23:59:24]

Done.

[piman, 2016/04/28 02:15:05]

ditto

+  if (last_state_.error != gpu::error::kNoError)
+    return;
+
+  Send(new GpuCommandBufferMsg_ReturnFrontBuffer(route_id_, mailbox, sync_token,
+                                                 is_lost));
 }
 
 gpu::error::Error CommandBufferProxyImpl::GetLastError() {
   return last_state_.error;
 }
 
 bool CommandBufferProxyImpl::Send(IPC::Message* msg) {
   // Caller should not intentionally send a message if the context is lost.
   DCHECK(last_state_.error == gpu::error::kNoError);
   DCHECK(channel_);
@@ skipping 82 matching lines @@
 }
 
 void CommandBufferProxyImpl::InvalidGpuReplyOnClientThread() {
   std::unique_ptr<base::AutoLock> lock;
   if (lock_)
     lock.reset(new base::AutoLock(*lock_));
   OnDestroyed(gpu::error::kInvalidGpuMessage, gpu::error::kLostContext);
 }
 
 }  // namespace gpu