[Chromecast] Limit number of concurrent audio and video decoders

chromecast/media/cma/backend/media_pipeline_backend_manager.h

 // Copyright 2016 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 CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_MANAGER_H_
 #define CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_MANAGER_H_
 
 #include <map>
 #include <memory>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #include "chromecast/public/media/media_pipeline_backend.h"
 #include "chromecast/public/media/media_pipeline_device_params.h"
 
 namespace chromecast {
 namespace media {
 
 // This class manages created media pipelines, and provides volume control by
 // stream type.
 // All functions in this class should be called on the media thread.
 class MediaPipelineBackendManager {
  public:
+  enum DecoderType { AUDIO_DECODER, VIDEO_DECODER, NUM_DECODER_TYPES };
+
   explicit MediaPipelineBackendManager(
       scoped_refptr<base::SingleThreadTaskRunner> media_task_runner);
   ~MediaPipelineBackendManager();
 
   // Create media pipeline backend.
   std::unique_ptr<MediaPipelineBackend> CreateMediaPipelineBackend(
       const MediaPipelineDeviceParams& params);
 
   // Create media pipeline backend with a specific stream_type.
   std::unique_ptr<MediaPipelineBackend> CreateMediaPipelineBackend(
       const MediaPipelineDeviceParams& params,
       int stream_type);
 
   // Sets the relative volume for a specified stream type,
   // with range [0.0, 1.0] inclusive. If |multiplier| is outside the
   // range [0.0, 1.0], it is clamped to that range.
   // TODO(tianyuwang): change stream_type to use a enum.
   void SetVolumeMultiplier(int stream_type, float volume);
 
   base::SingleThreadTaskRunner* task_runner() const {
     return media_task_runner_.get();
   }
 
  private:
   friend class MediaPipelineBackendWrapper;
 
+  // Backend wrapper instances must use these APIs when allocating and releasing
+  // decoder objects, so we can enforce global limit on #concurrent decoders.
+  bool IncrementDecoderCount(DecoderType type);
+  void DecrementDecoderCount(DecoderType type);
+
   // Internal clean up when a new media pipeline backend is destroyed.
   void OnMediaPipelineBackendDestroyed(const MediaPipelineBackend* backend);
 
   float GetVolumeMultiplier(int stream_type);
 
   const scoped_refptr<base::SingleThreadTaskRunner> media_task_runner_;
 
   // A vector that stores all of the existing media_pipeline_backends_.
   std::vector<MediaPipelineBackend*> media_pipeline_backends_;
 
+  // Total count of decoders created
+  int decoder_count_[NUM_DECODER_TYPES];
+
   // Volume multiplier for each type of audio streams.
   std::map<int, float> volume_by_stream_type_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaPipelineBackendManager);
 };
 
 }  // namespace media
 }  // namespace chromecast
 
 #endif  // CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_MANAGER_H_