Add an initial revision of an audio server.

services/media/audio/audio_output.cc

Index: services/media/audio/audio_output.cc
diff --git a/services/media/audio/audio_output.cc b/services/media/audio/audio_output.cc
new file mode 100644
index 0000000000000000000000000000000000000000..be2b89556d7ffb242000b18660b01bf3c97c15b3
--- /dev/null
+++ b/services/media/audio/audio_output.cc
@@ -0,0 +1,215 @@
+// Copyright 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.
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/logging.h"
+
+#include "services/media/audio/audio_output.h"
+#include "services/media/audio/audio_output_manager.h"
+#include "services/media/audio/audio_track_to_output_link.h"
+
+namespace mojo {
+namespace media {
+namespace audio {
+
+// Function used in a base::Closure to defer the final part of a shutdown task
+// to the main event loop.
+static void FinishShutdownSelf(AudioOutputManager* manager,
+                               AudioOutputWeakPtr weak_output) {
+  auto output  = weak_output.lock();
+  if (output) {
+    manager->ShutdownOutput(output);
+  }
+}
+
+AudioOutput::AudioOutput(AudioOutputManager* manager)
+  : manager_(manager) {
+  DCHECK(manager_);
+}
+
+AudioOutput::~AudioOutput() {
+  DCHECK(!task_runner_ && shutting_down_);
+}
+
+MediaResult AudioOutput::AddTrackLink(AudioTrackToOutputLinkPtr link) {
+  MediaResult res = InitializeLink(link);
+
+  if (res == MediaResult::OK) {
+    base::AutoLock lock(processing_lock_);
+
+    // Assert that we are the output in this link.
+    DCHECK(this == link->GetOutput().get());
+
+    if (shutting_down_) {
+      return MediaResult::SHUTTING_DOWN;
+    }
+
+    auto insert_result = links_.emplace(link);
+    DCHECK(insert_result.second);
+  } else {
+    // TODO(johngro): Output didn't like this track for some reason...  Should
+    // probably log something about this.
+  }
+
+  return res;
+}
+
+MediaResult AudioOutput::RemoveTrackLink(
+    const AudioTrackToOutputLinkPtr& link) {
+  base::AutoLock lock(processing_lock_);
+
+  if (shutting_down_) {
+    return MediaResult::SHUTTING_DOWN;
+  }
+
+  auto iter = links_.find(link);
+  if (iter == links_.end()) {
+    return MediaResult::NOT_FOUND;
+  }
+
+  links_.erase(iter);
+  return MediaResult::OK;
+}
+
+MediaResult AudioOutput::Init() {
+  return MediaResult::OK;
+}
+
+void AudioOutput::Cleanup() {
+}
+
+MediaResult AudioOutput::InitializeLink(const AudioTrackToOutputLinkPtr& link) {
+  DCHECK(link);
+  return MediaResult::OK;
+}
+
+void AudioOutput::ScheduleCallback(LocalTime when) {
+  base::AutoLock lock(shutdown_lock_);
+
+  // If we are in the process of shutting down, then we are no longer permitted
+  // to schedule callbacks.
+  if (shutting_down_) {
+    DCHECK(!task_runner_);
+    return;
+  }
+  DCHECK(task_runner_);
+
+  // TODO(johngro):  Someday, if there is ever a way to schedule delayed tasks
+  // with absolute time, or with resolution better than microseconds, do so.
+  // Until then figure out the relative time for scheduling the task and do so.
+  LocalTime now = LocalClock::now();
+  base::TimeDelta sched_time = (now > when)
+    ? base::TimeDelta::FromMicroseconds(0)
+    : base::TimeDelta::FromMicroseconds(
+        local_time::to_usec<int64_t>(when - now));
+
+  task_runner_->PostNonNestableDelayedTask(
+      FROM_HERE,
+      base::Bind(&ProcessThunk, weak_self_),
+      sched_time);
+}
+
+void AudioOutput::ShutdownSelf() {
+  // If we are not already in the process of shutting down, send a message to
+  // the main message loop telling it to complete the shutdown process.
+  if (!BeginShutdown()) {
+    DCHECK(manager_);
+    manager_->ScheduleMessageLoopTask(
+        FROM_HERE,
+        base::Bind(&FinishShutdownSelf, manager_, weak_self_));
+  }
+}
+
+void AudioOutput::ProcessThunk(AudioOutputWeakPtr weak_output) {
+  // If we are still around by the time this callback fires, enter the procesing
+  // lock and dispatch to our derived class's implementation.
+  auto output  = weak_output.lock();
+  if (output) {
+    base::AutoLock lock(output->processing_lock_);
+    output->Process();
+  }
+}
+
+MediaResult AudioOutput::Init(
+    const AudioOutputPtr& self,
+    scoped_refptr<base::SequencedTaskRunner> task_runner) {
+  DCHECK(this == self.get());
+  DCHECK(task_runner);
+
+  // If our derived class failed to initialize, don't bother to hold onto the
+  // state we will need drive our callback engine.  Begin the process of
+  // shutting ourselves down, the output manager will eventually finish the job
+  // for us.
+  MediaResult res = Init();
+  if (res != MediaResult::OK) {
+    ShutdownSelf();
+    return res;
+  }
+
+  // Stash our callback state and schedule an immediate callback to get things
+  // running.
+  task_runner_ = task_runner;
+  weak_self_   = self;
+  task_runner_->PostNonNestableTask(FROM_HERE,
+                                    base::Bind(&ProcessThunk, weak_self_));
+
+  return MediaResult::OK;
+}
+
+bool AudioOutput::BeginShutdown() {
+  // Start the process of shutting down if we have not already.  This method may
+  // be called from either a processing context, or from the audio output
+  // manager.  After it finishes, any pending processing callbacks will have
+  // been nerfed, although there may still be callbacks in flight.
+  base::AutoLock lock(shutdown_lock_);
+
+  if (shutting_down_) { return true; }
+
+  shutting_down_ = true;
+  task_runner_   = nullptr;
+
+  return false;
+}
+
+void AudioOutput::Shutdown() {
+  if (shut_down_) { return; }
+
+  // TODO(johngro): Assert that we are running on the audio server's main
+  // message loop thread.
+
+  // Make sure no new callbacks can be generated, and that pending callbacks
+  // have been nerfed.
+  BeginShutdown();
+
+  // Synchronize with any callbacks in flight.  By acquiring and releasing the
+  // processing lock, we are guaranteed that we have no callbacks which are in
+  // the middle of processing, and that any pending callbacks will be nerfed.
+  // It is safe to destroy this audio output at any point in time after this.
+  processing_lock_.Acquire();
+  processing_lock_.Release();
+
+  // Unlink ourselves from all of our tracks.  Then go ahead and clear the track
+  // set.
+  for (const auto& link : links_) {
+    DCHECK(link);
+    AudioTrackImplPtr track = link->GetTrack();
+    if (track) {
+      track->RemoveOutput(link);
+    }
+  }
+  links_.clear();
+
+  // Give our derived class a chance to clean up its resources.
+  Cleanup();
+
+  // We are now completely shut down.  The only reason we have this flag is to
+  // make sure that Shutdown is idempotent.
+  shut_down_ = true;
+}
+
+}  // namespace audio
+}  // namespace media
+}  // namespace mojo
+