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

content/renderer/pepper/ppb_graphics_3d_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 "content/renderer/pepper/ppb_graphics_3d_impl.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/location.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 10 matching lines @@
 #include "gpu/ipc/client/command_buffer_proxy_impl.h"
 #include "gpu/ipc/client/gpu_channel_host.h"
 #include "ppapi/c/ppp_graphics_3d.h"
 #include "ppapi/thunk/enter.h"
 #include "third_party/WebKit/public/platform/WebString.h"
 #include "third_party/WebKit/public/web/WebConsoleMessage.h"
 #include "third_party/WebKit/public/web/WebDocument.h"
 #include "third_party/WebKit/public/web/WebElement.h"
 #include "third_party/WebKit/public/web/WebLocalFrame.h"
 #include "third_party/WebKit/public/web/WebPluginContainer.h"
+#include "third_party/khronos/GLES2/gl2.h"
 
 using ppapi::thunk::EnterResourceNoLock;
 using ppapi::thunk::PPB_Graphics3D_API;
 using blink::WebConsoleMessage;
 using blink::WebLocalFrame;
 using blink::WebPluginContainer;
 using blink::WebString;
 
 namespace content {
 
@@ skipping 66 matching lines @@
     int32_t start,
     int32_t end) {
   GetCommandBuffer()->WaitForGetOffsetInRange(start, end);
   return GetCommandBuffer()->GetLastState();
 }
 
 void PPB_Graphics3D_Impl::EnsureWorkVisible() {
   command_buffer_->EnsureWorkVisible();
 }
 
+void PPB_Graphics3D_Impl::TakeFrontBuffer() {
+  DCHECK(taken_front_buffer_.IsZero());

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

This DCHECK is not valid. The plugin side may be untrusted (NaCl plugin) and
could call TakeFrontBuffer several times without a SwapBuffers.

It's ok to ignore redundant calls.

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

Done.

+  taken_front_buffer_ = GenerateMailbox();
+  command_buffer_->TakeFrontBuffer(taken_front_buffer_);
+}
+
+void PPB_Graphics3D_Impl::ReturnFrontBuffer(const gpu::Mailbox& mailbox,
+                                            const gpu::SyncToken& sync_token,
+                                            bool is_lost) {
+  command_buffer_->ReturnFrontBuffer(mailbox, sync_token, is_lost);
+  mailboxes_to_reuse_.push_back(mailbox);
+}
+
 bool PPB_Graphics3D_Impl::BindToInstance(bool bind) {
   bound_to_instance_ = bind;
   return true;
 }
 
 bool PPB_Graphics3D_Impl::IsOpaque() { return !has_alpha_; }
 
 void PPB_Graphics3D_Impl::ViewInitiatedPaint() {
   commit_pending_ = false;
 
   if (HasPendingSwap())
     SwapBuffersACK(PP_OK);
 }
 
 gpu::CommandBufferProxyImpl* PPB_Graphics3D_Impl::GetCommandBufferProxy() {
   DCHECK(command_buffer_);
   return command_buffer_.get();
 }
 
 gpu::CommandBuffer* PPB_Graphics3D_Impl::GetCommandBuffer() {
   return command_buffer_.get();
 }
 
 gpu::GpuControl* PPB_Graphics3D_Impl::GetGpuControl() {
   return command_buffer_.get();
 }
 
 int32_t PPB_Graphics3D_Impl::DoSwapBuffers(const gpu::SyncToken& sync_token) {
   DCHECK(command_buffer_);
-  if (sync_token.HasData())
-    sync_token_ = sync_token;
+  DCHECK(!taken_front_buffer_.IsZero());

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

Here too, the DCHECK is invalid.

It's ok to return failure.

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

Done.

 
   if (bound_to_instance_) {
     // If we are bound to the instance, we need to ask the compositor
     // to commit our backing texture so that the graphics appears on the page.
     // When the backing texture will be committed we get notified via
     // ViewFlushedPaint().
     //
     // Don't need to check for NULL from GetPluginInstance since when we're
     // bound, we know our instance is valid.
-    HostGlobals::Get()->GetInstance(pp_instance())->CommitBackingTexture();
+    cc::TextureMailbox texture_mailbox(taken_front_buffer_, sync_token,
+                                       GL_TEXTURE_2D);
+    taken_front_buffer_.SetZero();
+    HostGlobals::Get()
+        ->GetInstance(pp_instance())
+        ->CommitTextureMailbox(texture_mailbox);
     commit_pending_ = true;
   } else {
     // Wait for the command to complete on the GPU to allow for throttling.
     command_buffer_->SignalSyncToken(
-        sync_token_,
-        base::Bind(&PPB_Graphics3D_Impl::OnSwapBuffers,
-                   weak_ptr_factory_.GetWeakPtr()));
+        sync_token, base::Bind(&PPB_Graphics3D_Impl::OnSwapBuffers,
+                               weak_ptr_factory_.GetWeakPtr()));
   }
 
   return PP_OK_COMPLETIONPENDING;
 }
 
 bool PPB_Graphics3D_Impl::InitRaw(PPB_Graphics3D_API* share_context,
                                   const int32_t* attrib_list,
                                   gpu::Capabilities* capabilities,
                                   base::SharedMemoryHandle* shared_state_handle,
                                   gpu::CommandBufferId* command_buffer_id) {
@@ skipping 80 matching lines @@
   if (!command_buffer_->Initialize())
     return false;
 
   if (shared_state_handle)
     *shared_state_handle = command_buffer_->GetSharedStateHandle();
   if (capabilities)
     *capabilities = command_buffer_->GetCapabilities();
   if (command_buffer_id)
     *command_buffer_id = command_buffer_->GetCommandBufferID();
 
-  mailbox_ = gpu::Mailbox::Generate();
-  if (!command_buffer_->ProduceFrontBuffer(mailbox_))
-    return false;
-
   return true;
 }
 
 void PPB_Graphics3D_Impl::OnGpuControlErrorMessage(const char* message,
                                                    int32_t id) {
   if (!bound_to_instance_)
     return;
   WebPluginContainer* container =
       HostGlobals::Get()->GetInstance(pp_instance())->container();
   if (!container)
@@ skipping 53 matching lines @@
   const PPP_Graphics3D* ppp_graphics_3d = static_cast<const PPP_Graphics3D*>(
       instance->module()->GetPluginInterface(PPP_GRAPHICS_3D_INTERFACE));
   // We have to check *again* that the instance exists, because it could have
   // been deleted during GetPluginInterface(). Even the PluginModule could be
   // deleted, but in that case, the instance should also be gone, so the
   // GetInstance check covers both cases.
   if (ppp_graphics_3d && HostGlobals::Get()->GetInstance(this_pp_instance))
     ppp_graphics_3d->Graphics3DContextLost(this_pp_instance);
 }
 
+gpu::Mailbox PPB_Graphics3D_Impl::GenerateMailbox() {
+  if (mailboxes_to_reuse_.size()) {

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

nit: !mailboxes_to_reuse_.empty()

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

Done.

+    gpu::Mailbox mailbox = mailboxes_to_reuse_[0];
+    mailboxes_to_reuse_.erase(mailboxes_to_reuse_.begin());
+    return mailbox;
+  }
+
+  return gpu::Mailbox::Generate();
+}
+
 }  // namespace content