Ensure the wedge timer isn't started until after StartStream().

media/audio/audio_output_controller.cc

 // Copyright (c) 2012 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_controller.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
@@ skipping 180 matching lines @@
 #if defined(AUDIO_POWER_MONITORING)
   power_monitor_.Reset();
   power_poll_callback_.Reset(
       base::Bind(&AudioOutputController::ReportPowerMeasurementPeriodically,
                  this));
   // Run the callback to send an initial notification that we're starting in
   // silence, and to schedule periodic callbacks.
   power_poll_callback_.callback().Run();
 #endif
 
+  AllowEntryToOnMoreIOData();
+  stream_->Start(this);
+
   // For UMA tracking purposes, start the wedge detection timer.  This allows us
   // to record statistics about the number of wedged playbacks in the field.
   //
   // WedgeCheck() will look to see if |on_more_io_data_called_| is true after
   // the timeout expires.  Care must be taken to ensure the wedge check delay is
   // large enough that the value isn't queried while OnMoreDataIO() is setting
   // it.
   //
   // Timer self-manages its lifetime and WedgeCheck() will only record the UMA
   // statistic if state is still kPlaying.  Additional Start() calls will
   // invalidate the previous timer.
   wedge_timer_.reset(new base::OneShotTimer<AudioOutputController>());
   wedge_timer_->Start(
       FROM_HERE, TimeDelta::FromSeconds(3), this,
       &AudioOutputController::WedgeCheck);
   on_more_io_data_called_ = 0;

[miu, 2013/11/07 23:18:41]

Should this statement (setting on_more_io_data_called_ to 0) occur before
AllowEntryToOnMoreIOData() above?  It's possible, in a race condition, for
on_more_io_data_called_ to be incremented on the audio device thread, and then
set back to zero on this thread, right?

[DaleCurtis, 2013/11/07 23:22:54]

Good catch!

 
-  AllowEntryToOnMoreIOData();
-  stream_->Start(this);
-
   handler_->OnPlaying();
 }
 
 #if defined(AUDIO_POWER_MONITORING)
 void AudioOutputController::ReportPowerMeasurementPeriodically() {
   DCHECK(message_loop_->BelongsToCurrentThread());
   const std::pair<float, bool>& reading =
       power_monitor_.ReadCurrentPowerAndClip();
   handler_->OnPowerMeasured(reading.first, reading.second);
   message_loop_->PostDelayedTask(
@@ skipping 246 matching lines @@
   if (state_ == kPlaying) {
     UMA_HISTOGRAM_BOOLEAN("Media.AudioOutputControllerPlaybackStartupSuccess",
                           base::AtomicRefCountIsOne(&on_more_io_data_called_));
 
     // TODO(dalecurtis): Temporary debugging measure for http://crbug.com/160920
     CHECK(base::AtomicRefCountIsOne(&on_more_io_data_called_));
   }
 }
 
 }  // namespace media