Use GpuPreferences to avoid directly accessing switches in gpu related code

content/gpu/gpu_child_thread.h

 // 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.
 
 #ifndef CONTENT_GPU_GPU_CHILD_THREAD_H_
 #define CONTENT_GPU_GPU_CHILD_THREAD_H_
 
 #include <stdint.h>
 
 #include <queue>
 #include <string>
 
 #include "base/command_line.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "content/child/child_thread_impl.h"
 #include "content/common/gpu/gpu_channel.h"
 #include "content/common/gpu/gpu_channel_manager.h"
 #include "content/common/gpu/gpu_channel_manager_delegate.h"
 #include "content/common/gpu/gpu_config.h"
 #include "content/common/gpu/x_util.h"
 #include "content/common/process_control.mojom.h"
+#include "gpu/command_buffer/service/gpu_preferences.h"
 #include "gpu/config/gpu_info.h"
 #include "mojo/public/cpp/bindings/binding_set.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace gpu {
 class SyncPointManager;
 }
 
 namespace sandbox {
 class TargetServices;
 }
 
 namespace content {
 class GpuMemoryBufferFactory;
 class GpuProcessControlImpl;
 class GpuWatchdogThread;
 
 // The main thread of the GPU child process. There will only ever be one of
 // these per process. It does process initialization and shutdown. It forwards
 // IPC messages to GpuChannelManager, which is responsible for issuing rendering
 // commands to the GPU.
 class GpuChildThread : public ChildThreadImpl,
                        public GpuChannelManagerDelegate {
  public:
   typedef std::queue<IPC::Message*> DeferredMessages;
 
-  GpuChildThread(GpuWatchdogThread* gpu_watchdog_thread,
+  GpuChildThread(const gpu::GpuPreferences* gpu_preferences,

[boliu, 2016/02/26 22:17:32]

these should be const&

[Peng, 2016/02/29 16:09:22]

pointer is necessary, so the caller can use a nullptr and the GpuChildThread
will construct a GpuPreferences by itself.

[boliu, 2016/02/29 16:26:40]

Then maybe you want another constructor instead.

[Peng, 2016/02/29 19:29:50]

Do we really need another constructor with duplicate code in it, since const
pointer is allowed by our code style?

[boliu, 2016/02/29 19:48:22]

Just a general preference to not have parameters that can be missing if at all
possible. It's easy to have a mistake become a silent failure.

cs.chromium.org claims there is only a single callsite to each constructor, both
from content/gpu, so you don't have to duplicate more code by making
GpuPreference a required argument in these constructors.

[Peng, 2016/02/29 20:30:50]

I do agree it is better to avoid using const pointer in general. But in this
case, if use const reference,
1. we have to put GetGpuPreferences() in somewhere both gpu_main.cc and
in_process_gpu_thread.cc can access.
2. The InProcessGpuThread also need keep a duplicate GpuPreference instance.
3. With follow up CLs, the parameter gpu_preferences will be changed to const
reference.
So I think it is not necessary to do it in this short term CL.

[boliu, 2016/02/29 20:40:07]

content/gpu then? You can just expose that as a static method on GpuChildThread.
That's better than const* imo.

[Peng, 2016/02/29 21:18:29]

Done.

+                 GpuWatchdogThread* gpu_watchdog_thread,
                  bool dead_on_arrival,
                  const gpu::GPUInfo& gpu_info,
                  const DeferredMessages& deferred_messages,
                  GpuMemoryBufferFactory* gpu_memory_buffer_factory,
                  gpu::SyncPointManager* sync_point_manager);
 
-  GpuChildThread(const InProcessChildThreadParams& params,
+  GpuChildThread(const gpu::GpuPreferences* gpu_preferences,
+                 const InProcessChildThreadParams& params,
                  GpuMemoryBufferFactory* gpu_memory_buffer_factory,
                  gpu::SyncPointManager* sync_point_manager);
 
   ~GpuChildThread() override;
 
   void Shutdown() override;
 
   void Init(const base::Time& process_start_time);
   void StopWatchdog();
 
+ private:
   // ChildThread overrides.
   bool Send(IPC::Message* msg) override;
   bool OnControlMessageReceived(const IPC::Message& msg) override;
   bool OnMessageReceived(const IPC::Message& msg) override;
 
- private:
   // GpuChannelManagerDelegate implementation.
   void AddSubscription(int32_t client_id, unsigned int target) override;
   void ChannelEstablished(const IPC::ChannelHandle& channel_handle) override;
   void DidCreateOffscreenContext(const GURL& active_url) override;
   void DidDestroyChannel(int client_id) override;
   void DidDestroyOffscreenContext(const GURL& active_url) override;
   void DidLoseContext(bool offscreen,
                       gpu::error::ContextLostReason reason,
                       const GURL& active_url) override;
   void GpuMemoryUmaStats(const GPUMemoryUmaStats& params) override;
@@ skipping 37 matching lines @@
                           unsigned int target,
                           const gpu::ValueState& state);
 #if defined(OS_ANDROID)
   void OnWakeUpGpu();
 #endif
   void OnLoseAllContexts();
 
   void BindProcessControlRequest(
       mojo::InterfaceRequest<ProcessControl> request);
 
+  gpu::GpuPreferences gpu_preferences_;
+
   // Set this flag to true if a fatal error occurred before we receive the
   // OnInitialize message, in which case we just declare ourselves DOA.
   bool dead_on_arrival_;
   base::Time process_start_time_;
   scoped_refptr<GpuWatchdogThread> watchdog_thread_;
 
 #if defined(OS_WIN)
   // Windows specific client sandbox interface.
   sandbox::TargetServices* target_services_;
 #endif
@@ skipping 20 matching lines @@
 
   // Bindings to the ProcessControl impl.
   mojo::BindingSet<ProcessControl> process_control_bindings_;
 
   DISALLOW_COPY_AND_ASSIGN(GpuChildThread);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_GPU_GPU_CHILD_THREAD_H_