Implement AudioOutputProxy.

media/audio/audio_output_dispatcher.cc

+// Copyright (c) 2010 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/message_loop.h"
+#include "media/audio/audio_io.h"
+
+namespace {
+// Delay in milliseconds after since the stream is paused untill the

[scherkus (not reviewing), 2010/11/22 06:43:15]

untill -> until

[Sergey Ulanov, 2010/11/23 19:51:46]

Done.

+// audio device is closed.
+const int kStreamCloseDelayMs = 5000;
+}  // namespace
+
+AudioOutputDispatcher::AudioOutputDispatcher(
+    AudioManager* audio_manager, const AudioParameters& params)
+    : audio_manager_(audio_manager),
+      message_loop_(audio_manager->GetMessageLoop()),
+      params_(params),
+      close_delay_(base::TimeDelta::FromMilliseconds(
+          kStreamCloseDelayMs)),
+      paused_proxies_(0),
+      last_activity_time_(base::Time::Now()),
+      close_task_scheduled_(false) {
+}
+
+AudioOutputDispatcher::~AudioOutputDispatcher() {
+}
+
+bool AudioOutputDispatcher::StreamOpened() {
+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+  paused_proxies_++;

[scherkus (not reviewing), 2010/11/22 06:43:15]

I'm not really sure what this variable is tracking... also do we want to still
increase this even if we return false?

[Sergey Ulanov, 2010/11/23 19:51:46]

Number of streams that are currently paused.
Yes: the proxy will call StreamClosed() later anyway.

+  last_activity_time_ = base::Time::Now();
+
+  // Ensure that there is at least one open stream.

[scherkus (not reviewing), 2010/11/22 06:43:15]

out of curiosity do we need to have an open stream right away?

it's a bit confusing considering you attempt to schedule a close right away

what are the implications of waiting until a stream is started?

[Sergey Ulanov, 2010/11/23 19:51:46]

It is just so that a page that created media element can be notified that the
stream is unplayable (e.g. invalid sample rate) before it actually tries to
starts playing. I discussed this design with Alpha a while ago, and he seemed to
agree. Do you think this isn't necessary?
Yes, it is closed 5 seconds later if Start() isn't called before that.

+  if (streams_.size() == 0) {
+    AudioOutputStream* stream = CreateAndOpenStream();
+    if (!stream) {
+      return false;
+    }
+    streams_.push_back(stream);
+  }
+
+  // Schedule close task so that the stream is closed later if it is
+  // not used.
+  ScheduleCloseTask();
+
+  return true;
+}
+
+AudioOutputStream* AudioOutputDispatcher::StreamStarted() {

[scherkus (not reviewing), 2010/11/22 06:43:15]

so to help me understand... ownership is passed back and forth via
StreamStarted() and StreamStopped()

[Sergey Ulanov, 2010/11/23 19:51:46]

Yes. Added more comments about it in .h

+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+  AudioOutputStream* stream;
+  if (streams_.size() == 0) {
+    stream = CreateAndOpenStream();

[scherkus (not reviewing), 2010/11/22 06:43:15]

you might be able to de-duplicate this + StreamOpened() logic if
CreateAndOpenStream() also adds it to streams_ and returns true if it was added,
false otherwise

[Sergey Ulanov, 2010/11/23 19:51:46]

Good catch. Fixed!

+    if (!stream) {
+      return NULL;
+    }
+  } else {
+    stream = streams_.back();
+    streams_.pop_back();
+  }
+
+  paused_proxies_--;
+  DCHECK_GE(paused_proxies_, 0);
+
+  last_activity_time_ = base::Time::Now();
+
+  // 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);
+  last_activity_time_ = base::Time::Now();
+  ScheduleCloseTask();
+}
+
+void AudioOutputDispatcher::StreamClosed() {
+  DCHECK_EQ(MessageLoop::current(), message_loop_);
+  paused_proxies_--;
+  DCHECK_GE(paused_proxies_, 0);
+  ClosePendingStreams();
+}
+
+MessageLoop* AudioOutputDispatcher::message_loop() {
+  return message_loop_;
+}
+
+AudioOutputStream* AudioOutputDispatcher::CreateAndOpenStream() {
+  AudioOutputStream* stream =
+      audio_manager_->MakeAudioOutputStream(params_);
+  if (!stream) {
+    return NULL;
+  }
+  if (!stream->Open()) {
+    stream->Close();
+    return NULL;;
+  }
+  return stream;
+}
+
+void AudioOutputDispatcher::OpenTask() {
+  base::TimeDelta last_activity_delay =
+      base::Time::Now() - last_activity_time_;
+
+  if (last_activity_delay < close_delay_) {
+    // Make sure that we have at least one stream allocated if there
+    // are paused streams.
+    if (paused_proxies_ > 0 && streams_.size() == 0) {
+      AudioOutputStream* stream = CreateAndOpenStream();
+      if (stream) {
+        streams_.push_back(stream);
+      }
+    }
+  }
+
+  // Schedule close task, so that the stream is closed if it is not
+  // used.
+  ScheduleCloseTask();
+}
+
+void AudioOutputDispatcher::CloseTask() {
+  close_task_scheduled_ = false;
+  ClosePendingStreams();
+}
+
+void AudioOutputDispatcher::ClosePendingStreams() {
+  bool delay_expired = (base::Time::Now() - last_activity_time_) >=
+      close_delay_;
+
+  // We never need to have more than |paused_proxies_| streams.
+  int max_pending_streams =  paused_proxies_;

[scherkus (not reviewing), 2010/11/22 06:43:15]

nit: remove one space between = and paused_proxies_

[Sergey Ulanov, 2010/11/23 19:51:46]

Done.

+
+  if (delay_expired) {
+    // Enough time has expired since the last activity. Close all
+    // pending streams.
+    max_pending_streams = 0;
+  }
+
+  // Close streams we don't need anymore.
+  while (static_cast<int>(streams_.size()) > max_pending_streams) {
+    streams_.back()->Close();
+    streams_.pop_back();
+  }
+
+  if (!delay_expired && streams_.size() > 0) {
+    ScheduleCloseTask();
+  }
+}
+
+void AudioOutputDispatcher::ScheduleCloseTask() {
+  if (close_task_scheduled_) {

[scherkus (not reviewing), 2010/11/22 06:43:15]

nit: DCHECK for the message loop

[Sergey Ulanov, 2010/11/23 19:51:46]

Done.

+    // There is a pending task. Don't schedule another one.
+    return;
+  }
+
+  base::TimeDelta last_activity_delay =
+      base::Time::Now() - last_activity_time_;
+  int64 next_task_delay_ms =
+      (close_delay_ - last_activity_delay).InMillisecondsRoundedUp();
+  if (next_task_delay_ms <= 0)
+    next_task_delay_ms = 0;
+
+  message_loop_->PostDelayedTask(
+      FROM_HERE,
+      NewRunnableMethod(this, &AudioOutputDispatcher::CloseTask),
+      next_task_delay_ms);
+
+  close_task_scheduled_ = true;
+}
+
+void AudioOutputDispatcher::set_close_delay(base::TimeDelta delay) {
+  close_delay_ = delay;
+}