Don't background processes with active audio output.

If a process is actively rendering audio, it should not be put into
the background state.  "Active" is determined by having any stream
in the playing state as considered by AudioRendererHost.

When a tab has active audio, it's already being woken up ~ every
10-20ms, so I expect the power impact of this change to be negligible.

This should reduce glitching under load.

BUG=362294
TEST=Ensure Windows playback under load no longer glitches.

Review URL: https://codereview.chromium.org/298253004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274020 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/renderer_host/media/audio_renderer_host.cc

@@ -61,6 +61,9 @@ class AudioRendererHost::AudioEntry
     return reader_.get();
   }
 
+  bool playing() const { return playing_; }
+  void set_playing(bool playing) { playing_ = playing; }
+
  private:
   // media::AudioOutputController::EventHandler implementation.
   virtual void OnCreated() OVERRIDE;
@@ -85,6 +88,8 @@ class AudioRendererHost::AudioEntry
 
   // The AudioOutputController that manages the audio stream.
   const scoped_refptr<media::AudioOutputController> controller_;
+
+  bool playing_;
 };
 
 AudioRendererHost::AudioEntry::AudioEntry(
@@ -106,7 +111,8 @@ AudioRendererHost::AudioEntry::AudioEntry(
                                                        this,
                                                        params,
                                                        output_device_id,
-                                                       reader_.get())) {
+                                                       reader_.get())),
+      playing_(false) {
   DCHECK(controller_.get());
 }
 
@@ -127,7 +133,8 @@ AudioRendererHost::AudioRendererHost(
       mirroring_manager_(mirroring_manager),
       audio_log_(media_internals->CreateAudioLog(
           media::AudioLogFactory::AUDIO_OUTPUT_CONTROLLER)),
-      media_stream_manager_(media_stream_manager) {
+      media_stream_manager_(media_stream_manager),
+      num_playing_streams_(0) {
   DCHECK(audio_manager_);
   DCHECK(media_stream_manager_);
 }
@@ -275,10 +282,18 @@ void AudioRendererHost::DoNotifyStreamStateChanged(int stream_id,
           entry->stream_id(),
           base::Bind(&media::AudioOutputController::ReadCurrentPowerAndClip,
                      entry->controller()));
+      if (!entry->playing()) {
+        entry->set_playing(true);
+        base::AtomicRefCountInc(&num_playing_streams_);
+      }
     } else {
       media_observer->OnAudioStreamStopped(render_process_id_,
                                            entry->render_frame_id(),
                                            entry->stream_id());
+      if (entry->playing()) {
+        entry->set_playing(false);
+        base::AtomicRefCountDec(&num_playing_streams_);
+      }
     }
   }
 }
@@ -458,6 +473,8 @@ void AudioRendererHost::DeleteEntry(scoped_ptr<AudioEntry> entry) {
     media_observer->OnAudioStreamStopped(render_process_id_,
                                          entry->render_frame_id(),
                                          entry->stream_id());
+    if (entry->playing())
+      base::AtomicRefCountDec(&num_playing_streams_);
   }
 }
 
@@ -483,4 +500,8 @@ AudioRendererHost::AudioEntry* AudioRendererHost::LookupById(int stream_id) {
   return i != audio_entries_.end() ? i->second : NULL;
 }
 
+bool AudioRendererHost::HasActiveAudio() {
+  return !base::AtomicRefCountIsZero(&num_playing_streams_);
+}
+
 }  // namespace content

content/browser/renderer_host/media/audio_renderer_host.h

@@ -39,6 +39,7 @@
 
 #include <map>
 
+#include "base/atomic_ref_count.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ -84,6 +85,10 @@ class CONTENT_EXPORT AudioRendererHost : public BrowserMessageFilter {
   virtual void OnDestruct() const OVERRIDE;
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
+  // Returns true if any streams managed by this host are actively playing.  Can
+  // be called from any thread.
+  bool HasActiveAudio();
+
  private:
   friend class AudioRendererHostTest;
   friend class BrowserThread;
@@ -165,6 +170,9 @@ class CONTENT_EXPORT AudioRendererHost : public BrowserMessageFilter {
   // A map of stream IDs to audio sources.
   AudioEntryMap audio_entries_;
 
+  // The number of streams in the playing state.
+  base::AtomicRefCount num_playing_streams_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioRendererHost);
 };
 

content/browser/renderer_host/render_process_host_impl.cc

@@ -1960,6 +1960,10 @@ void RenderProcessHostImpl::SetBackgrounded(bool backgrounded) {
   if (!child_process_launcher_.get() || child_process_launcher_->IsStarting())
     return;
 
+  // Don't background processes which have active audio streams.
+  if (backgrounded_ && audio_renderer_host_->HasActiveAudio())
+    return;
+
 #if defined(OS_WIN)
   // The cbstext.dll loads as a global GetMessage hook in the browser process
   // and intercepts/unintercepts the kernel32 API SetPriorityClass in a