Moved the fake input stream's processing onto the audio worker thread.

media/audio/fake_audio_provider.h

+// Copyright (c) 2015 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.
+
+#ifndef MEDIA_AUDIO_FAKE_AUDIO_PROVIDER_H_
+#define MEDIA_AUDIO_FAKE_AUDIO_PROVIDER_H_
+
+#include "base/callback_forward.h"
+#include "base/memory/ref_counted.h"
+#include "media/base/media_export.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+class FilePath;
+}
+
+namespace media {
+class AudioBus;
+class AudioParameters;
+
+// A fake audio provider.  Using a provided message loop, the FakeAudioProvider
+// will generate real-time audio data.
+class MEDIA_EXPORT FakeAudioProvider {
+ public:
+  // |worker_task_runner| is the task runner on which the InputCB provided to
+  // Start() will be executed on.  This may or may not be the be for the same
+  // thread that invokes the Start/Stop methods.
+  // |params| is used to determine the frequency of callbacks.
+  FakeAudioProvider(
+      const scoped_refptr<base::SingleThreadTaskRunner>& worker_task_runner,
+      const AudioParameters& params);
+  ~FakeAudioProvider();
+
+  void OpenInBeepMode();
+  void OpenInFileMode(const base::FilePath& path_to_wav_file);
+
+  // Start executing |input_cb| at a regular intervals.  Stop() must be called
+  // by the same thread before destroying FakeAudioProvider. The callback will
+  // be called with an audio bus filled with input data.
+  typedef base::Callback<void(AudioBus* audio_bus, int buffer_size)> InputCB;
+  void Start(const InputCB& input_cb);
+
+  // Stop executing the InputCB provided to Start().  Blocks until the worker
+  // loop is not inside a InputCB invocation.  Safe to call multiple times.
+  // Must be called on the same thread that called Start().
+  void Stop();
+
+  // TODO(phoglund): See TODO on FakeAudioInputStream::BeepOnce.
+  static void BeepOnce();

[DaleCurtis, 2015/02/17 23:27:49]

Why static?

[phoglund_chromium, 2015/02/18 10:22:05]

It's static because BeepOnce is called from the fake video input stream. The
beeps are synchronized to the spinning green ball generated by that device.
Since the video stream doesn't have a ref to the audio stream it cheats by
making a static call. Somebody should perhaps redesign that at some point :)

+
+ private:
+  // All state and implementation is kept within this ref-counted class because
+  // cancellation of posted tasks must happen on the worker thread some time
+  // after the call to Stop() (on the main thread) returns.
+  class Worker;
+  const scoped_refptr<Worker> worker_;
+
+  DISALLOW_COPY_AND_ASSIGN(FakeAudioProvider);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_FAKE_AUDIO_PROVIDER_H_