Introduce command buffer control thread

mojo/services/gles2/gpu_impl.h

Index: mojo/services/gles2/gpu_impl.h
diff --git a/mojo/services/gles2/gpu_impl.h b/mojo/services/gles2/gpu_impl.h
index 62a8af69c5407a8049805dc3c9abc45faf8c7fab..b5e7948c4acb8c444517f9ed19f01a84822b40e3 100644
--- a/mojo/services/gles2/gpu_impl.h
+++ b/mojo/services/gles2/gpu_impl.h
@@ -4,6 +4,7 @@
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/threading/thread.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "mojo/public/cpp/bindings/strong_binding.h"
 #include "mojo/services/public/interfaces/geometry/geometry.mojom.h"
@@ -24,10 +25,30 @@ namespace mojo {
 
 class GpuImpl : public Gpu {
  public:
-  GpuImpl(InterfaceRequest<Gpu> request,
-          const scoped_refptr<gfx::GLShareGroup>& share_group,
-          const scoped_refptr<gpu::gles2::MailboxManager> mailbox_manager);
+  // We need to share these across all CommandBuffer instances so that contexts
+  // they create can share resources with each other via mailboxes.
+  class State : public base::RefCounted<State> {
+   public:
+    State();
+
+    scoped_refptr<base::SingleThreadTaskRunner> control_task_runner() {
+      return control_thread_.task_runner();

[jamesr, 2014/11/19 06:43:02]

the threading rules for these objects is not clear to me - are they only safe
for use on the driver thread? could we make that more explicit if so (i.e. add a
threadchecker member to this, perhaps?)

[abarth-chromium, 2014/11/19 15:42:11]

I'm happy to add comments about which thread these objects should be used on,
but I'm not sure adding a threadchecker to this state object buys us much.  We
take references to these objects directly in CommandBufferDriver rather than
using State as a bundle.

I just made them into a bundle to make it easier for code that allocates GpuImpl
objects not to have to worry about what all state the GpuImpl object needs (and
because that code is duplicate for Desktop and Android).

+    }
+    gfx::GLShareGroup* share_group() const { return share_group_.get(); }
+    gpu::gles2::MailboxManager* mailbox_manager() const {
+      return mailbox_manager_.get();
+    }
+
+   private:
+    friend class base::RefCounted<State>;
+    ~State();
 
+    base::Thread control_thread_;
+    scoped_refptr<gfx::GLShareGroup> share_group_;
+    scoped_refptr<gpu::gles2::MailboxManager> mailbox_manager_;
+  };
+
+  GpuImpl(InterfaceRequest<Gpu> request, const scoped_refptr<State>& state);
   ~GpuImpl() override;
 
   void CreateOnscreenGLES2Context(
@@ -39,12 +60,8 @@ class GpuImpl : public Gpu {
       InterfaceRequest<CommandBuffer> command_buffer_request) override;
 
  private:
-  // We need to share these across all CommandBuffer instances so that contexts
-  // they create can share resources with each other via mailboxes.
-  scoped_refptr<gfx::GLShareGroup> share_group_;
-  scoped_refptr<gpu::gles2::MailboxManager> mailbox_manager_;
-
   StrongBinding<Gpu> binding_;
+  scoped_refptr<State> state_;
 
   DISALLOW_COPY_AND_ASSIGN(GpuImpl);
 };