[Chromecast] Limit number of concurrent audio and video decoders

chromecast/media/cma/backend/media_pipeline_backend_manager.cc

 // 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.
 
 #include "chromecast/media/cma/backend/media_pipeline_backend_manager.h"
 
 #include <algorithm>
 
 #include "base/memory/ptr_util.h"
 #include "chromecast/media/cma/backend/media_pipeline_backend_wrapper.h"
 #include "chromecast/public/cast_media_shlib.h"
 
 namespace chromecast {
 namespace media {
 
 MediaPipelineBackendManager::MediaPipelineBackendManager(
     scoped_refptr<base::SingleThreadTaskRunner> media_task_runner)
-    : media_task_runner_(std::move(media_task_runner)) {
-}
+    : media_task_runner_(std::move(media_task_runner)),
+      audio_decoder_count_(0),
+      video_decoder_count_(0) {}
 
 MediaPipelineBackendManager::~MediaPipelineBackendManager() {
 }
 
 std::unique_ptr<MediaPipelineBackend>
 MediaPipelineBackendManager::CreateMediaPipelineBackend(
     const media::MediaPipelineDeviceParams& params) {
   DCHECK(media_task_runner_->BelongsToCurrentThread());
   return CreateMediaPipelineBackend(params, 0);
 }
 
 std::unique_ptr<MediaPipelineBackend>
 MediaPipelineBackendManager::CreateMediaPipelineBackend(
     const media::MediaPipelineDeviceParams& params,
     int stream_type) {
   DCHECK(media_task_runner_->BelongsToCurrentThread());
   std::unique_ptr<MediaPipelineBackend> backend_ptr(
       new MediaPipelineBackendWrapper(
           base::WrapUnique(
               media::CastMediaShlib::CreateMediaPipelineBackend(params)),
           stream_type, GetVolumeMultiplier(stream_type), this));
-  media_pipeline_backends_.push_back(backend_ptr.get());
+  media_pipeline_backends_[backend_ptr.get()] = BackendInfo();
   return backend_ptr;
 }
 
+bool MediaPipelineBackendManager::CanCreateAudioDecoder(

[alokp, 2016/07/22 04:59:46]

The function name is a bit weird. In addition to replying yes it also assumes
that the decoder has been created.

Would it make more sense to:
1. Move the decoder count for each backend from BackendInfo into
MediaPipelineBackendWrapper?
2. Keep the global decoder counts here but expose functions to
increment/decrement audio/video decoder count.
3. Let MediaPipelineBackendWrapper decide whether it should create decoder or
not.

That way you can also handle the case when one of the decoders is deleted from a
backend (which you do not seem to handle currently)

[halliwell, 2016/07/22 16:34:50]

Agreed :)  I moved the count into the wrapper (actually just a flag, wrappers
don't currently support multiple decoders) and rephrased the API as
increment/decrement.

+    MediaPipelineBackend* backend) {
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
+
+  if (audio_decoder_count_ >= 2) {
+    LOG(WARNING) << "Unable to create AudioDecoder: global limit exceeded";
+    return false;
+  }
+
+  auto itr = media_pipeline_backends_.find(backend);
+  DCHECK(itr != media_pipeline_backends_.end());
+  itr->second.audio_decoder_count_++;
+  audio_decoder_count_++;
+
+  return true;
+}
+
+bool MediaPipelineBackendManager::CanCreateVideoDecoder(
+    MediaPipelineBackend* backend) {
+  DCHECK(media_task_runner_->BelongsToCurrentThread());
+
+  if (video_decoder_count_ >= 1) {
+    LOG(WARNING) << "Unable to create VideoDecoder: global limit exceeded";
+    return false;
+  }
+
+  auto itr = media_pipeline_backends_.find(backend);
+  DCHECK(itr != media_pipeline_backends_.end());
+  itr->second.video_decoder_count_++;
+  video_decoder_count_++;
+
+  return true;
+}
+
 void MediaPipelineBackendManager::OnMediaPipelineBackendDestroyed(
-    const MediaPipelineBackend* backend) {
+    MediaPipelineBackend* backend) {
   DCHECK(media_task_runner_->BelongsToCurrentThread());
-  media_pipeline_backends_.erase(
-      std::remove(media_pipeline_backends_.begin(),
-                  media_pipeline_backends_.end(), backend),
-      media_pipeline_backends_.end());
+
+  auto itr = media_pipeline_backends_.find(backend);
+  DCHECK(itr != media_pipeline_backends_.end());
+
+  audio_decoder_count_ -= itr->second.audio_decoder_count_;
+  video_decoder_count_ -= itr->second.video_decoder_count_;
+
+  media_pipeline_backends_.erase(itr);
 }
 
 void MediaPipelineBackendManager::SetVolumeMultiplier(int stream_type,
                                                       float volume) {
   DCHECK(media_task_runner_->BelongsToCurrentThread());
   volume = std::max(0.0f, std::min(volume, 1.0f));
   volume_by_stream_type_[stream_type] = volume;
 
   // Set volume for each open media pipeline backends.
   for (auto it = media_pipeline_backends_.begin();
        it != media_pipeline_backends_.end(); it++) {
     MediaPipelineBackendWrapper* wrapper =
-        static_cast<MediaPipelineBackendWrapper*>(*it);
+        static_cast<MediaPipelineBackendWrapper*>(it->first);
     if (wrapper->GetStreamType() == stream_type)
       wrapper->SetStreamTypeVolume(volume);
   }
 }
 
 float MediaPipelineBackendManager::GetVolumeMultiplier(int stream_type) {
   DCHECK(media_task_runner_->BelongsToCurrentThread());
   auto it = volume_by_stream_type_.find(stream_type);
   if (it == volume_by_stream_type_.end()) {
     return 1.0;
   } else {
     return it->second;
   }
 }
 
 }  // namespace media
 }  // namespace chromecast