media/audio/fake_audio_consumer.cc

// Copyright (c) 2013 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/fake_audio_consumer.h"

#include "base/bind.h"
#include "base/bind_helpers.h"
#include "base/cancelable_callback.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/single_thread_task_runner.h"
#include "base/synchronization/lock.h"
#include "base/threading/thread_checker.h"
#include "base/time/time.h"
#include "media/audio/audio_parameters.h"
#include "media/base/audio_bus.h"

namespace media {

class FakeAudioConsumer::Worker
    : public base::RefCountedThreadSafe<FakeAudioConsumer::Worker> {
 public:
  Worker(const scoped_refptr<base::SingleThreadTaskRunner>& worker_task_runner,
         const AudioParameters& params);

  bool IsStopped();
  void Start(const ReadCB& read_cb);
  void Stop();

 private:
  friend class base::RefCountedThreadSafe<Worker>;
  ~Worker();

  // Initialize and start regular calls to DoRead() on the worker thread.
  void DoStart();

  // Cancel any delayed callbacks to DoRead() in the worker loop's queue.
  void DoCancel();

  // Task that regularly calls |read_cb_| according to the playback rate as
  // determined by the audio parameters given during construction.  Runs on
  // the worker loop.
  void DoRead();

  const scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner_;
  const scoped_ptr<AudioBus> audio_bus_;
  const base::TimeDelta buffer_duration_;

  base::Lock read_cb_lock_;  // Held while mutating or running |read_cb_|.
  ReadCB read_cb_;
  base::TimeTicks next_read_time_;

  // Used to cancel any delayed tasks still inside the worker loop's queue.
  base::CancelableClosure read_task_cb_;

  base::ThreadChecker thread_checker_;

  DISALLOW_COPY_AND_ASSIGN(Worker);
};

FakeAudioConsumer::FakeAudioConsumer(
    const scoped_refptr<base::SingleThreadTaskRunner>& worker_task_runner,
    const AudioParameters& params)
    : worker_(new Worker(worker_task_runner, params)) {
}

FakeAudioConsumer::~FakeAudioConsumer() {
  DCHECK(worker_->IsStopped());
}

void FakeAudioConsumer::Start(const ReadCB& read_cb) {
  DCHECK(worker_->IsStopped());
  worker_->Start(read_cb);
}

void FakeAudioConsumer::Stop() {
  worker_->Stop();
}

FakeAudioConsumer::Worker::Worker(
    const scoped_refptr<base::SingleThreadTaskRunner>& worker_task_runner,
    const AudioParameters& params)
    : worker_task_runner_(worker_task_runner),
      audio_bus_(AudioBus::Create(params)),
      buffer_duration_(base::TimeDelta::FromMicroseconds(
          params.frames_per_buffer() * base::Time::kMicrosecondsPerSecond /
          static_cast<float>(params.sample_rate()))) {
  audio_bus_->Zero();

  // Worker can be constructed on any thread, but will DCHECK that its
  // Start/Stop methods are called from the same thread.
  thread_checker_.DetachFromThread();
}

FakeAudioConsumer::Worker::~Worker() {
  DCHECK(read_cb_.is_null());
}

bool FakeAudioConsumer::Worker::IsStopped() {
  base::AutoLock scoped_lock(read_cb_lock_);
  return read_cb_.is_null();
}

void FakeAudioConsumer::Worker::Start(const ReadCB& read_cb)  {
  DCHECK(thread_checker_.CalledOnValidThread());
  DCHECK(!read_cb.is_null());
  {
    base::AutoLock scoped_lock(read_cb_lock_);
    DCHECK(read_cb_.is_null());
    read_cb_ = read_cb;
  }
  worker_task_runner_->PostTask(FROM_HERE, base::Bind(&Worker::DoStart, this));
}

void FakeAudioConsumer::Worker::DoStart() {
  DCHECK(worker_task_runner_->BelongsToCurrentThread());
  next_read_time_ = base::TimeTicks::Now();
  read_task_cb_.Reset(base::Bind(&Worker::DoRead, this));
  read_task_cb_.callback().Run();
}

void FakeAudioConsumer::Worker::Stop() {
  DCHECK(thread_checker_.CalledOnValidThread());
  {
    base::AutoLock scoped_lock(read_cb_lock_);
    if (read_cb_.is_null())
      return;
    read_cb_.Reset();
  }
  worker_task_runner_->PostTask(FROM_HERE, base::Bind(&Worker::DoCancel, this));
}

void FakeAudioConsumer::Worker::DoCancel() {
  DCHECK(worker_task_runner_->BelongsToCurrentThread());
  read_task_cb_.Cancel();
}

void FakeAudioConsumer::Worker::DoRead() {
  DCHECK(worker_task_runner_->BelongsToCurrentThread());

  {
    base::AutoLock scoped_lock(read_cb_lock_);
    if (!read_cb_.is_null())
      read_cb_.Run(audio_bus_.get());
  }

  // Need to account for time spent here due to the cost of |read_cb_| as well
  // as the imprecision of PostDelayedTask().
  const base::TimeTicks now = base::TimeTicks::Now();
  base::TimeDelta delay = next_read_time_ + buffer_duration_ - now;

  // If we're behind, find the next nearest ontime interval.
  if (delay < base::TimeDelta())
    delay += buffer_duration_ * (-delay / buffer_duration_ + 1);
  next_read_time_ = now + delay;

  worker_task_runner_->PostDelayedTask(
      FROM_HERE, read_task_cb_.callback(), delay);
}

}  // namespace media