Fix erratic HTML5 audio playback

media/audio/audio_output_dispatcher.cc

-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// 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.
 
 #include "media/audio/audio_output_dispatcher.h"
 
 #include "base/compiler_specific.h"
 #include "base/message_loop.h"
+#include "base/time.h"
 #include "media/audio/audio_io.h"
 
 AudioOutputDispatcher::AudioOutputDispatcher(
     AudioManager* audio_manager, const AudioParameters& params,
     int close_delay_ms)
     : audio_manager_(audio_manager),
       message_loop_(audio_manager->GetMessageLoop()),
       params_(params),
+      pause_delay_milliseconds_(2 * params.samples_per_packet *
+          base::Time::kMillisecondsPerSecond / params.sample_rate),
       paused_proxies_(0),
       ALLOW_THIS_IN_INITIALIZER_LIST(close_timer_(
           base::TimeDelta::FromMilliseconds(close_delay_ms),
           this, &AudioOutputDispatcher::ClosePendingStreams)) {
 }
 
 AudioOutputDispatcher::~AudioOutputDispatcher() {
 }
 
 bool AudioOutputDispatcher::StreamOpened() {
   DCHECK_EQ(MessageLoop::current(), message_loop_);
   paused_proxies_++;
 
   // Ensure that there is at least one open stream.
-  if (streams_.empty() && !CreateAndOpenStream()) {
+  if (idle_streams_.empty() && !CreateAndOpenStream()) {
     return false;
   }
 
   close_timer_.Reset();
 
   return true;
 }
 
 AudioOutputStream* AudioOutputDispatcher::StreamStarted() {
   DCHECK_EQ(MessageLoop::current(), message_loop_);
 
-  if (streams_.empty() && !CreateAndOpenStream()) {
+  if (idle_streams_.empty() && !CreateAndOpenStream()) {
     return NULL;
   }
 
-  AudioOutputStream* stream = streams_.back();
-  streams_.pop_back();
+  AudioOutputStream* stream = idle_streams_.back();
+  idle_streams_.pop_back();
 
   DCHECK_GT(paused_proxies_, 0u);
   paused_proxies_--;
 
   close_timer_.Reset();
 
   // Schedule task to allocate streams for other proxies if we need to.
   message_loop_->PostTask(FROM_HERE, NewRunnableMethod(
       this, &AudioOutputDispatcher::OpenTask));
 
   return stream;
 }
 
 void AudioOutputDispatcher::StreamStopped(AudioOutputStream* stream) {
   DCHECK_EQ(MessageLoop::current(), message_loop_);
+
   paused_proxies_++;
-  streams_.push_back(stream);
+
+  pausing_streams_.push_front(stream);
   close_timer_.Reset();
+
+  // Don't recycle stream until two buffers worth of time has elapsed.
+  message_loop_->PostDelayedTask(
+      FROM_HERE,
+      NewRunnableMethod(this, &AudioOutputDispatcher::StopStreamTask),
+      pause_delay_milliseconds_);
+}
+
+void AudioOutputDispatcher::StopStreamTask() {
+  if (pausing_streams_.empty())
+    return;
+  AudioOutputStream* stream = pausing_streams_.back();
+  pausing_streams_.pop_back();
+  idle_streams_.push_back(stream);
 }
 
 void AudioOutputDispatcher::StreamClosed() {
   DCHECK_EQ(MessageLoop::current(), message_loop_);
 

[davejcool, 2011/04/14 00:43:26]

When a stream is finally closed, it should be added to idle_streams_ and not
just stick around in the pausing_streams_.  Also, unit tests fail without this
since a close stream is expected to be closed for real right away.

+  while (!pausing_streams_.empty()) {
+    idle_streams_.push_back(pausing_streams_.back());

[Sergey Ulanov, 2011/04/14 18:05:09]

I don't like this. Basically when a single stream closing, you are moving all
other streams from pausing_streams_ to idle_streams_, so playback on other
streams may be disrupted.
Can we update tests to reflect new behaviour instead of cleaning
|pausing_streams_| here?

[davejcool, 2011/04/15 01:12:51]

Closing the pausing_streams_ later can not be done in the constructor because
that's not on the right thread.  Some other ideas are:
(1) If we knew what physical stream the caller was using when StreamClosed() is
called, we could just move that one only.
(2) If idle_streams_ was also a <list>, the pausing streams could be pushed to
the front, so at they'd be getting closed later than the other streams, and much
less likely to be disrupted.

+    pausing_streams_.pop_back();
+  }
+
   DCHECK_GT(paused_proxies_, 0u);
   paused_proxies_--;
 
-  while (streams_.size() > paused_proxies_) {
-    streams_.back()->Close();
-    streams_.pop_back();
+  while (idle_streams_.size() > paused_proxies_) {
+    idle_streams_.back()->Close();
+    idle_streams_.pop_back();
   }
 }
 
 MessageLoop* AudioOutputDispatcher::message_loop() {
   return message_loop_;
 }
 
 bool AudioOutputDispatcher::CreateAndOpenStream() {
   AudioOutputStream* stream =
       audio_manager_->MakeAudioOutputStream(params_);
   if (!stream) {
     return false;
   }
   if (!stream->Open()) {
     stream->Close();
     return false;
   }
-  streams_.push_back(stream);
+  idle_streams_.push_back(stream);
   return true;
 }
 
 void AudioOutputDispatcher::OpenTask() {
   // Make sure that we have at least one stream allocated if there
   // are paused streams.
-  if (paused_proxies_ > 0 && streams_.empty()) {
+  if (paused_proxies_ > 0 && idle_streams_.empty()
+      && pausing_streams_.empty()) {

[scherkus (not reviewing), 2011/04/14 17:11:08]

nit: && goes on end of previous line

     CreateAndOpenStream();
   }
 
   close_timer_.Reset();
 }
 
 // This method is called by |close_timer_|.
 void AudioOutputDispatcher::ClosePendingStreams() {
-  while (!streams_.empty()) {
-    streams_.back()->Close();
-    streams_.pop_back();
+  while (!idle_streams_.empty()) {
+    idle_streams_.back()->Close();
+    idle_streams_.pop_back();
   }
 }