MJPEG acceleration for video capture using VAAPI, the GPU and IPC part

content/common/gpu/client/gpu_jpeg_decode_accelerator_host.h

+// Copyright 2015 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_COMMON_GPU_CLIENT_GPU_JPEG_DECODE_ACCELERATOR_HOST_H_
+#define CONTENT_COMMON_GPU_CLIENT_GPU_JPEG_DECODE_ACCELERATOR_HOST_H_
+
+#include "base/memory/weak_ptr.h"
+#include "base/threading/non_thread_safe.h"
+#include "ipc/ipc_listener.h"
+#include "media/video/jpeg_decode_accelerator.h"
+
+namespace content {
+class GpuChannelHost;
+
+// This class is used to talk to JpegDecodeAccelerator in the GPU process
+// through IPC messages.
+class GpuJpegDecodeAcceleratorHost
+    : public IPC::Listener,
+      public media::JpegDecodeAccelerator,
+      public base::NonThreadSafe,
+      public base::SupportsWeakPtr<GpuJpegDecodeAcceleratorHost> {
+ public:
+  // |this| is guaranteed not to outlive |channel|.  (See comments for
+  // |channel_|.)

[piman, 2015/05/18 22:46:18]

I'm confused by this comment. Comments for channel_ mention it can be NULL,
which would suggest |this| could outlive |channel_|.

More generally, what guarantees that GpuJpegDecodeAcceleratorHost will be
Destroy'ed before the channel is? In particular after a lost channel (e.g. GPU
process dying), the GpuChannelHost could get destroyed as a side effect of
context recreation - see RenderThreadImpl::EstablishGpuChannelSync /
BrowserGpuChannelHostFactory::EstablishGpuChannel, and this might happen before
this class had a chance to get the OnChannelError notification.

[kcwu, 2015/06/02 15:07:25]

Done.
The life cycle issue is fixed (together with the other CL,
https://codereview.chromium.org/1132683004/ )

+  GpuJpegDecodeAcceleratorHost(GpuChannelHost* channel, int32 route_id);
+
+  // IPC::Listener implementation.
+  void OnChannelError() override;
+  bool OnMessageReceived(const IPC::Message& message) override;
+
+  // media::JpegDecodeAccelerator implementation.
+  bool Initialize(media::JpegDecodeAccelerator::Client* client) override;
+  void Decode(const media::BitstreamBuffer& bitstream_buffer,
+              const scoped_refptr<media::VideoFrame>& video_frame) override;
+  void Destroy() override;
+
+ private:
+  // Only Destroy() should be deleting |this|.
+  ~GpuJpegDecodeAcceleratorHost() override;
+
+  void Send(IPC::Message* message);
+
+  void OnVideoFrameReady(int32_t bitstream_buffer_id);
+  void OnNotifyError(int32_t bitstream_buffer_id, Error error);
+
+  // Unowned reference to the GpuChannelHost to send IPC messages to the GPU
+  // process.  |channel_| is always valid as long as it is not NULL.
+  GpuChannelHost* channel_;
+
+  Client* client_;
+
+  // Route ID for the associated decoder in the GPU process.
+  int32 decoder_route_id_;
+
+  DISALLOW_COPY_AND_ASSIGN(GpuJpegDecodeAcceleratorHost);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_GPU_CLIENT_GPU_JPEG_DECODE_ACCELERATOR_HOST_H_