Add a proxy for thread-hopping VideoCapture::EventHandler.

media/video/capture/video_capture_proxy.h

+// Copyright (c) 2011 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 MEDIA_VIDEO_CAPTURE_VIDEO_CAPTURE_PROXY_H_
+#define MEDIA_VIDEO_CAPTURE_VIDEO_CAPTURE_PROXY_H_
+
+#include "base/compiler_specific.h"
+#include "base/memory/ref_counted.h"
+#include "base/task.h"
+#include "media/video/capture/video_capture.h"
+
+namespace base {
+class MessageLoopProxy;
+}
+
+namespace media {
+
+// This is a helper class to proxy a VideoCapture::EventHandler. In the renderer
+// process, the VideoCaptureImpl calls its handler on a "Video Capture" thread,
+// this class allows seamless proxying to another thread ("main thread"), which
+// would be the thread where the instance of this class is created. The
+// "proxied" handler is then called on that thread.
+// Since the VideoCapture is living on the "Video Capture" thread, querying its
+// state from the "main thread" is fundamentally racy. Instead this class keeps
+// track of the state every time it is called by the VideoCapture (on the VC
+// thread), and forwards that information to the main thread.
+class VideoCaptureHandlerProxy : public VideoCapture::EventHandler {
+ public:
+  struct VideoCaptureState {
+    VideoCaptureState() : started(false), width(0), height(0), frame_rate(0) {}
+    bool started;
+    int width;
+    int height;
+    int frame_rate;
+  };
+
+  // Called on main thread.
+  VideoCaptureHandlerProxy(
+      VideoCapture::EventHandler* proxied,
+      scoped_refptr<base::MessageLoopProxy> main_message_loop);
+  virtual ~VideoCaptureHandlerProxy();
+
+  // Retrieves the state of the VideoCapture. Must be called on main thread.
+  const VideoCaptureState& state() const { return state_; }
+  VideoCapture::EventHandler* proxied() const { return proxied_; }
+
+  // VideoCapture::EventHandler implementation, called on VC thread.
+  virtual void OnStarted(VideoCapture* capture) OVERRIDE;
+  virtual void OnStopped(VideoCapture* capture) OVERRIDE;
+  virtual void OnPaused(VideoCapture* capture) OVERRIDE;
+  virtual void OnError(VideoCapture* capture, int error_code) OVERRIDE;
+  virtual void OnBufferReady(
+      VideoCapture* capture,
+      scoped_refptr<VideoCapture::VideoFrameBuffer> buffer) OVERRIDE;
+  virtual void OnDeviceInfoReceived(
+      VideoCapture* capture,
+      const VideoCaptureParams& device_info) OVERRIDE;
+
+ private:
+  // Called on main thread.
+  void OnStartedOnMainThread(
+      VideoCapture* capture,
+      const VideoCaptureState& state);
+  void OnStoppedOnMainThread(
+      VideoCapture* capture,
+      const VideoCaptureState& state);
+  void OnPausedOnMainThread(
+      VideoCapture* capture,
+      const VideoCaptureState& state);
+  void OnErrorOnMainThread(
+      VideoCapture* capture,
+      const VideoCaptureState& state,
+      int error_code);
+  void OnBufferReadyOnMainThread(
+      VideoCapture* capture,
+      const VideoCaptureState& state,
+      scoped_refptr<VideoCapture::VideoFrameBuffer> buffer);
+  void OnDeviceInfoReceivedOnMainThread(
+      VideoCapture* capture,
+      const VideoCaptureState& state,
+      const VideoCaptureParams& device_info);
+
+  // Only accessed from main thread.
+  VideoCapture::EventHandler* proxied_;
+  VideoCaptureState state_;
+
+  scoped_refptr<base::MessageLoopProxy> main_message_loop_;
+};
+
+}  // namespace media
+DISABLE_RUNNABLE_METHOD_REFCOUNT(media::VideoCaptureHandlerProxy);
+
+#endif  // MEDIA_VIDEO_CAPTURE_VIDEO_CAPTURE_PROXY_H_