Implement AudioRendererMixerInput::CurrentThreadIsRenderingThread().

media/base/audio_renderer_mixer_input.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/base/audio_renderer_mixer_input.h"
 
 #include <cmath>
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
@@ skipping 105 matching lines @@
 }
 
 OutputDeviceInfo AudioRendererMixerInput::GetOutputDeviceInfo() {
   return mixer_
              ? mixer_->GetOutputDeviceInfo()
              : mixer_pool_->GetOutputDeviceInfo(owner_id_, 0 /* session_id */,
                                                 device_id_, security_origin_);
 }
 
 bool AudioRendererMixerInput::CurrentThreadIsRenderingThread() {
-  NOTIMPLEMENTED();
-  return false;
+  // The users of this class are required to handle thread safety. In
+  // particular, the AudioConverter uses a lock when calling Stop(), where
+  // |mixer_| is cleared, and also in its render call, where this function is
+  // called.
+  return mixer_ && mixer_->CurrentThreadIsRenderingThread();

[o1ka, 2016/06/21 12:43:09]

I would say something like:
This method is expected to be called in callback_->Render().
|mixer_| access on rendering thread is safe:
AudioRendererMixer::AddInput()/RemoveInput()/Render() take lock for
AudioConverter operations, which guarantees that there are no
ARMI::ProvideInput()(=>callback_->Render()) calls coming before/during
AddInput() and during/after RemoveInput().

[DaleCurtis, 2016/06/21 19:50:03]

Can we just DCHECK(mixer_)?

[Henrik Grunell, 2016/06/23 06:19:55]

No need to DCHECK since it'll crash when dereferencing. And as a means to
document the code, it doesn't document why it's safe throughout the execution of
the function. So I think a a comment is better, but "mixer_ &&" can be removed.

[Henrik Grunell, 2016/06/23 06:19:55]

I'd prefer a more general and shorter comment. :) Since the details are about
something outside of this class, which can change. What about describing the
contract in the header?

 }
 
 void AudioRendererMixerInput::SwitchOutputDevice(
     const std::string& device_id,
     const url::Origin& security_origin,
     const OutputDeviceStatusCB& callback) {
   if (!mixer_) {
     if (pending_switch_callback_.is_null()) {
       pending_switch_callback_ = callback;
       pending_switch_device_id_ = device_id;
@@ skipping 50 matching lines @@
     base::AutoLock auto_lock(volume_lock_);
     return frames_filled > 0 ? volume_ : 0;
   }
 }
 
 void AudioRendererMixerInput::OnRenderError() {
   callback_->OnRenderError();
 }
 
 }  // namespace media