MediaStream audio: Refactor 3 separate "glue" implementations into one.

content/renderer/media/media_stream_audio_deliverer.h

+// 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.
+
+#ifndef CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_DELIVERER_H_
+#define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_DELIVERER_H_
+
+#include <algorithm>
+#include <vector>
+
+#include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.h"
+#include "media/base/audio_parameters.h"
+
+namespace content {
+
+// Template containing functionality common to both MediaStreamAudioSource and
+// MediaStreamAudioTrack. This is used for managing the connections between
+// objects through which audio data flows, and doing so in a thread-safe manner.
+//
+// The Consumer parameter of the template is the type of the objects to which
+// audio data is delivered: MediaStreamAudioTrack or MediaStreamAudioSink. It's
+// assumed the Consumer class defines methods named OnSetFormat() and OnData()
+// that have the same signature as the ones defined in this template.
+// MediaStreamAudioDeliverer will always guarantee the Consumer's OnSetFormat()
+// and OnData() methods are called sequentially.
+template <typename Consumer>
+class MediaStreamAudioDeliverer {
+ public:
+  MediaStreamAudioDeliverer() {}
+  ~MediaStreamAudioDeliverer() {}
+
+  // Returns the current audio parameters. These will be invalid before the
+  // first call to OnSetFormat(). This method is thread-safe.
+  media::AudioParameters GetAudioParameters() const {
+    base::AutoLock auto_lock(params_lock_);
+    return params_;
+  }
+
+  // Begin delivering audio to |consumer|. The caller must guarantee |consumer|
+  // is not destroyed until after calling RemoveConsumer(consumer). This method
+  // must be called on the main thread.
+  void AddConsumer(Consumer* consumer) {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    DCHECK(consumer);
+    base::AutoLock auto_lock(consumers_lock_);
+    DCHECK(std::find(consumers_.begin(), consumers_.end(), consumer) ==
+           consumers_.end());
+    DCHECK(std::find(pending_consumers_.begin(), pending_consumers_.end(),
+                     consumer) == pending_consumers_.end());
+    pending_consumers_.push_back(consumer);
+  }
+
+  // Stop delivering audio to |consumer|. Returns true if |consumer| was the
+  // last consumer removed, false otherwise. When this method returns, no
+  // further calls will be made to OnSetFormat() or OnData() on any thread.
+  // This method must be called on the main thread.
+  bool RemoveConsumer(Consumer* consumer) {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    base::AutoLock auto_lock(consumers_lock_);
+    const bool had_consumers =
+        !consumers_.empty() || !pending_consumers_.empty();
+    auto it = std::find(consumers_.begin(), consumers_.end(), consumer);
+    if (it != consumers_.end()) {
+      consumers_.erase(it);
+    } else {
+      it = std::find(pending_consumers_.begin(), pending_consumers_.end(),
+                     consumer);
+      if (it != pending_consumers_.end())
+        pending_consumers_.erase(it);
+    }
+    return had_consumers && consumers_.empty() && pending_consumers_.empty();
+  }
+
+  // Returns the current list of connected Consumers. This is normally used to
+  // send a notification to all consumers. This method must be called on the
+  // main thread.
+  void GetConsumerList(std::vector<Consumer*>* consumer_list) const {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    base::AutoLock auto_lock(consumers_lock_);
+    *consumer_list = consumers_;
+    consumer_list->insert(consumer_list->end(),
+                          pending_consumers_.begin(), pending_consumers_.end());
+  }
+
+  // Change the format of the audio passed in the next call to OnData(). This
+  // method may be called on any thread but, logically, should only be called
+  // between calls to OnData().
+  void OnSetFormat(const media::AudioParameters& params) {
+    DCHECK(params.IsValid());
+    base::AutoLock auto_lock(consumers_lock_);
+    {
+      base::AutoLock auto_params_lock(params_lock_);
+      if (params_.Equals(params))
+        return;
+      params_ = params;
+    }
+    pending_consumers_.insert(pending_consumers_.end(),
+                              consumers_.begin(), consumers_.end());
+    consumers_.clear();
+  }
+
+  // Deliver data to all consumers. This method may be called on any thread.
+  void OnData(const media::AudioBus& audio_bus,
+              base::TimeTicks reference_time) {
+    base::AutoLock auto_lock(consumers_lock_);
+
+    // Call OnSetFormat() for all pending consumers and move them to the
+    // active-delivery list.
+    if (!pending_consumers_.empty()) {
+      const media::AudioParameters params = GetAudioParameters();
+      DCHECK(params.IsValid());
+      for (Consumer* consumer : pending_consumers_)
+        consumer->OnSetFormat(params);
+      consumers_.insert(consumers_.end(),
+                        pending_consumers_.begin(), pending_consumers_.end());
+      pending_consumers_.clear();
+    }
+
+    // Deliver the audio data to each consumer.
+    for (Consumer* consumer : consumers_)
+      consumer->OnData(audio_bus, reference_time);
+  }
+
+ private:
+  // In debug builds, check that all methods that could cause object graph or
+  // data flow changes are being called on the main thread.
+  base::ThreadChecker thread_checker_;
+
+  // Protects concurrent access to |pending_consumers_| and |consumers_|.
+  mutable base::Lock consumers_lock_;
+
+  // Any consumers needing a call to OnSetFormat(), to be notified of the
+  // changed audio format, are placed in this list. This includes consumers
+  // added via AddConsumer() that need to have an initial OnSetFormat() call
+  // before audio data is first delivered. Consumers are moved from this list to
+  // |consumers_| on the audio thread.
+  std::vector<Consumer*> pending_consumers_;
+
+  // Consumers that are up-to-date on the current audio format and are receiving
+  // audio data are placed in this list.
+  std::vector<Consumer*> consumers_;
+
+  // Protects concurrent access to |params_|.
+  mutable base::Lock params_lock_;
+
+  // Specifies the current format of the audio passing through this
+  // MediaStreamAudioDeliverer.
+  media::AudioParameters params_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaStreamAudioDeliverer);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_DELIVERER_H_