Add mojo interface+impl for audio stream control.

media/mojo/services/mojo_audio_output.cc

+// Copyright 2016 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/mojo/services/mojo_audio_output.h"
+
+#include <memory>
+#include <utility>
+
+#include "base/memory/shared_memory.h"
+#include "base/sync_socket.h"
+#include "mojo/public/cpp/system/platform_handle.h"
+
+namespace media {
+
+MojoAudioOutput::MojoAudioOutput(
+    mojom::AudioOutputRequest request,
+    CreateDelegateCallback create_delegate_callback,
+    FinishedCallback finished_callback)
+    : binding_(this, std::move(request)),
+      create_delegate_callback_(std::move(create_delegate_callback)),
+      finished_callback_(std::move(finished_callback)) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(finished_callback_);
+  // |this| owns |binding_|, so unretained is safe.
+  binding_.set_connection_error_handler(
+      base::Bind(&MojoAudioOutput::OnError, base::Unretained(this)));
+}
+
+MojoAudioOutput::~MojoAudioOutput() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+}
+
+void MojoAudioOutput::Start(const AudioParameters& params,
+                            const StartCallback& callback) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (delegate_) {
+    // Already started.

[o1ka, 2017/02/22 13:26:30]

Add logging on error in all places like this? Will help us to triage bugs.

[Max Morin, 2017/03/02 23:11:32]

Done.

+    OnError();
+    return;
+  }
+  delegate_ = std::move(create_delegate_callback_).Run(this, params);

[DaleCurtis, 2017/02/21 18:18:32]

Hmm, post std::move the contents of create_delegate_callback_ are undefined I
thought? I notice this is how the examples in OnceCallback do it, so no problem,
just surprising since we now potentially have a member variable in some weird
state.

[Max Morin, 2017/02/22 10:08:43]

The C++ standard requires that it is in a "valid but unspecified state" after
moving. This is only a minimal requirement, for example we know that
std::unique_ptr is null after moving. I think it is implicit that a OnceCallback
also become null/empty, though having it explicitly documented would be nice. I
filed crbug.com/694945 to ask for clarification.

[o1ka, 2017/02/22 13:26:30]

Here is what I found it unit tests:
https://cs.chromium.org/chromium/src/base/bind_unittest.cc?type=cs&q=OnceCall....
So it is null pre implementation, and you are right that it should be
documented.

[Max Morin, 2017/02/22 16:07:44]

The comment actually contradicts the test, since the comment says it's
"undefined" but the test prescribes a certain state. :)

+  DCHECK(delegate_);
+  start_callback_ = callback;
+}
+
+void MojoAudioOutput::Play() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (!delegate_) {
+    // Not started yet.
+    OnError();
+    return;
+  }
+  delegate_->OnPlayStream();
+}
+
+void MojoAudioOutput::Pause() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (!delegate_) {
+    // Not started yet.
+    OnError();
+    return;
+  }
+  delegate_->OnPauseStream();
+}
+
+void MojoAudioOutput::SetVolume(double volume) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (!delegate_ || volume < 0 || volume > 1) {
+    // Not started yet.

[o1ka, 2017/02/22 13:26:30]

...or volume is out of range

+    OnError();
+    return;
+  }
+  delegate_->OnSetVolume(volume);
+}
+
+void MojoAudioOutput::OnStreamCreated(
+    int stream_id,
+    base::SharedMemory* shared_memory,
+    base::CancelableSyncSocket* foreign_socket) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (!binding_.is_bound()) {
+    // Already closed, make sure we are properly cleaned up.
+    OnError();
+    return;
+  }
+  DCHECK(start_callback_);
+  DCHECK(shared_memory);
+  DCHECK(foreign_socket);
+
+  base::SharedMemoryHandle foreign_memory_handle =
+      base::SharedMemory::DuplicateHandle(shared_memory->handle());
+  DCHECK(base::SharedMemory::IsHandleValid(foreign_memory_handle));
+
+  mojo::ScopedSharedBufferHandle buffer_handle = mojo::WrapSharedMemoryHandle(
+      foreign_memory_handle, shared_memory->requested_size(), false);
+  mojo::ScopedHandle socket_handle =
+      mojo::WrapPlatformFile(foreign_socket->handle());
+
+  DCHECK(buffer_handle.is_valid());
+  DCHECK(socket_handle.is_valid());
+
+  start_callback_.Run(std::move(buffer_handle), std::move(socket_handle));

[DaleCurtis, 2017/02/21 18:18:32]

base::ResetAndReturn?

[Max Morin, 2017/02/22 10:08:43]

Done.

+  start_callback_ = StartCallback();
+}
+
+void MojoAudioOutput::OnStreamError(int stream_id) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  OnError();
+}
+
+void MojoAudioOutput::OnError() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (!finished_callback_) {

[DaleCurtis, 2017/02/21 18:18:32]

Hmm, this is relying on finished_callback_ being null, so my understanding of
oncecallback post std::move above must be wrong?

[Max Morin, 2017/02/22 10:08:43]

I'm pretty sure it's null after being moved from, but this check is not
necessary anyways (since this object is synchronously destroyed when running
|finished_callback_|, OnError cannot be called multiple times). I simplified
this method and added a comment to the constructor stating that |this| must be
destroyed by |finished_callback_| synchronously.

[o1ka, 2017/02/22 13:26:30]

Hmm... |finished_callback_| acts as a deleter for MojoAudioOutput, and will also
remove the instance from some owner container.
Something like what StrongBindingSet does
(https://cs.chromium.org/chromium/src/media/mojo/services/strong_binding_set.h...).
Won't Close() call below
(https://cs.chromium.org/chromium/src/mojo/public/cpp/bindings/binding.h?type=...)
result in disconnecting the pipe? If it will, do we need |finished_callback_|,
or we can store a pointer to a strong binding and just close it (not sure, this
may be unsafe)?

BTW, I would rename the callback into |deleter_| - it's more clear

[Max Morin, 2017/03/02 23:11:32]

Renamed to deleter_.

+    // There is already a destruction in progress.
+    return;
+  }
+  // Notify the renderer.
+  binding_.Close();
+  // The rest of the cleanup is done when |this| is destructed.
+  std::move(finished_callback_).Run(this);
+}
+
+}  // namespace media