Remove device enumeration, caching and monitoring from MediaStreamManager.

content/browser/renderer_host/media/media_devices_manager.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_BROWSER_RENDERER_HOST_MEDIA_MEDIA_DEVICES_MANAGER_H_
+#define CONTENT_BROWSER_RENDERER_HOST_MEDIA_MEDIA_DEVICES_MANAGER_H_
+
+#include <array>
+#include <vector>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/system_monitor/system_monitor.h"
+#include "content/common/content_export.h"
+#include "content/common/media/media_devices.h"
+#include "media/capture/video/video_capture_device_descriptor.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace media {
+class AudioManager;
+}
+
+namespace content {
+
+class MediaStreamManager;
+class VideoCaptureManager;
+
+// Use MediaDeviceType values to index on this type.
+using MediaDeviceEnumeration =
+    std::array<MediaDeviceInfoArray, NUM_MEDIA_DEVICE_TYPES>;
+
+// MediaDevicesManager is responsible for doing media-device enumerations.
+// In addition it implements caching for enumeration results and device
+// monitoring in order to keep caches consistent.
+// All its methods must be called on the IO thread.
+class CONTENT_EXPORT MediaDevicesManager
+    : public base::SystemMonitor::DevicesChangedObserver {
+ public:
+  // Use MediaDeviceType values to index on this type.
+  using BoolDeviceTypes = std::array<bool, NUM_MEDIA_DEVICE_TYPES>;
+
+  using EnumerationCallback =
+      base::Callback<void(const MediaDeviceEnumeration&)>;
+
+  enum class CachePolicy {
+    NO_CACHE,
+    SYSTEM_MONITOR,
+  };
+
+  MediaDevicesManager(
+      media::AudioManager* audio_manager,
+      const scoped_refptr<VideoCaptureManager>& video_capture_manager,
+      MediaStreamManager* media_stream_manager);
+  ~MediaDevicesManager() override;
+
+  // Performs a possibly cached device enumeration for the requested device
+  // types and reports the results to |callback|.
+  // The enumeration results passed to |callback| are guaranteed to be valid
+  // only for the types specified in |requested_types|.
+  // Note that this function is not reentrant, so if |callback| needs to perform
+  // another call to EnumerateDevices, it must do so by posting a task to the
+  // IO thread.
+  void EnumerateDevices(const BoolDeviceTypes& requested_types,
+                        const EnumerationCallback& callback);
+
+  // Manually sets a caching policy for a given device type.
+  // Note that manually setting the SYSTEM_MONITOR policy without having
+  // monitoring enabled may result in incorrect behavior.
+  void SetCachePolicy(MediaDeviceType type, CachePolicy policy);

[hta - Chromium, 2016/09/20 10:55:29]

Why not return a failure when SYSTEM_MONITOR is set manually?

A return bool saying "this succeeded/failed" should be enough.

Given that the only values are SYSTEM_MONITOR (set by StartMonitoring() if
available) and NO_CACHE (set by StopMonitoring()), the utility of this function
seems doubtful.
Is it for testing?

[Guido Urdaneta, 2016/09/20 13:59:27]

I originally made it public mainly for testing purposes. Since in practice it's
used only by the unit test, I just made it private and made the unit test a
friend.

+
+  // Tries to starts device monitoring. If successful, sets the caching policy
+  // to SYSTEM_MONITOR for the device types supported by the monitor.
+  void StartMonitoring();
+
+  // Stops device monitoring and sets the caching policy to NO_CACHE for all
+  // device types.
+  void StopMonitoring();
+  bool IsMonitoringStarted();
+
+  // Implements base::SystemMonitor::DevicesChangedObserver.
+  // This function is only called in response to physical audio/video device
+  // changes.
+  void OnDevicesChanged(base::SystemMonitor::DeviceType device_type) override;
+
+  // TODO(guidou): Remove this function once content::GetMediaDeviceIDForHMAC
+  // is rewritten to receive devices via a callback.
+  // See http://crbug.com/648155.
+  MediaDeviceInfoArray GetCachedDeviceInfo(MediaDeviceType type);
+
+ private:
+  struct EnumerationRequest;
+
+  void DoEnumerateDevices(MediaDeviceType type);
+  void EnumerateAudioDevices(bool is_input);
+
+  // Callback for VideoCaptureManager::EnumerateDevices.
+  void VideoInputDevicesEnumerated(
+      const media::VideoCaptureDeviceDescriptors& descriptors);
+
+  // Helpers to handle enumeration results.
+  void DevicesEnumerated(MediaDeviceType type,
+                         const MediaDeviceInfoArray& snapshot);
+  void UpdateSnapshot(MediaDeviceType type,
+                      const MediaDeviceInfoArray& new_snapshot);
+  void ProcessRequests();
+  bool IsEnumerationRequestReady(const EnumerationRequest& request_info);
+
+  // Helpers to handle device-change notification.
+  void HandleDevicesChanged(MediaDeviceType type);
+  void NotifyMediaStreamManager(MediaDeviceType type,
+                                const MediaDeviceInfoArray& new_snapshot);
+  void NotifyDeviceChangeSubscribers(MediaDeviceType type,
+                                     const MediaDeviceInfoArray& snapshot);
+
+#if defined(OS_MACOSX)
+  void StartMonitoringOnUIThread();
+#endif
+
+  bool use_fake_devices_;
+  media::AudioManager* const audio_manager_;  // not owned
+  scoped_refptr<VideoCaptureManager> video_capture_manager_;
+  MediaStreamManager* const media_stream_manager_;  // not owned
+
+  using CachePolicies = std::array<CachePolicy, NUM_MEDIA_DEVICE_TYPES>;

[hta - Chromium, 2016/09/20 10:55:29]

This is a pattern I haven't seen before. Is it a newer version of "typedef"?

[Guido Urdaneta, 2016/09/20 13:59:27]

Yes, it is. It's preferred over typedef, according to
http://chromium-cpp.appspot.com

+  CachePolicies cache_policies_;
+
+  class CacheInfo;
+  using CacheInfos = std::vector<CacheInfo>;
+  CacheInfos cache_infos_;
+
+  BoolDeviceTypes has_seen_result_;
+  std::vector<EnumerationRequest> requests_;
+  MediaDeviceEnumeration current_snapshot_;
+  bool monitoring_started_;
+
+  base::WeakPtrFactory<MediaDevicesManager> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaDevicesManager);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_MEDIA_DEVICES_MANAGER_H_