content/browser/media/audio_stream_monitor.h

// Copyright 2014 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_MEDIA_AUDIO_STREAM_MONITOR_H_
#define CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_

#include <map>
#include <utility>

#include "base/callback_forward.h"
#include "base/containers/flat_map.h"
#include "base/macros.h"
#include "base/threading/thread_checker.h"
#include "base/time/default_tick_clock.h"
#include "base/time/time.h"
#include "base/timer/timer.h"
#include "build/build_config.h"
#include "content/common/content_export.h"
#include "content/public/browser/web_contents_observer.h"
#include "media/audio/audio_output_controller.h"

namespace base {
class TickClock;
}

namespace content {

class WebContents;

// Keeps track of the audible state of audio output streams and uses it to
// maintain a "was recently audible" binary state for the audio indicators in
// the tab UI.  The logic is to: 1) Turn on immediately when sound is audible;
// and 2) Hold on for X amount of time after sound has gone silent, then turn
// off if no longer audible.  Said another way, we don't want tab indicators to
// turn on/off repeatedly and annoy the user.  AudioStreamMonitor sends UI
// update notifications only when needed, but may be queried at any time.
//
// When monitoring is not available, audibility is approximated with having
// active audio streams.
//
// Each WebContentsImpl owns an AudioStreamMonitor.
class CONTENT_EXPORT AudioStreamMonitor : public WebContentsObserver {
 public:
  explicit AudioStreamMonitor(WebContents* contents);
  ~AudioStreamMonitor() override;

  // Returns true if audio has recently been audible from the tab.  This is
  // usually called whenever the tab data model is refreshed; but there are
  // other use cases as well (e.g., the OOM killer uses this to de-prioritize
  // the killing of tabs making sounds).
  bool WasRecentlyAudible() const;

  // Returns true if the audio is currently audible from the given WebContents.
  // The difference from WasRecentlyAudible() is that this method will return
  // false as soon as the WebContents stop producing sound.
  bool IsCurrentlyAudible() const;

  // Called by the WebContentsImpl if |render_process_id| dies; used to clear
  // any outstanding poll callbacks.
  void RenderProcessGone(int render_process_id);

  // Starts or stops monitoring respectively for the stream owned by the
  // specified renderer.  Safe to call from any thread.
  static void StartMonitoringStream(int render_process_id,
                                    int render_frame_id,
                                    int stream_id);
  static void StopMonitoringStream(int render_process_id,
                                   int render_frame_id,
                                   int stream_id);
  // Updates the audible state for the given stream. Safe to call from any
  // thread.
  static void UpdateStreamAudibleState(int render_process_id,
                                       int render_frame_id,
                                       int stream_id,
                                       bool is_audible);

  // WebContentsObserver implementation
  void RenderFrameDeleted(RenderFrameHost* render_frame_host) override;
  // Overloaded to avoid conflict with RenderProcessGone(int).
  void RenderProcessGone(base::TerminationStatus status) override {}

  void set_was_recently_audible_for_testing(bool value) {
    indicator_is_on_ = value;
  }

  void set_is_currently_audible_for_testing(bool value) { is_audible_ = value; }

 private:
  friend class AudioStreamMonitorTest;

  enum {
    // Minimum amount of time to hold a tab indicator on after it becomes
    // silent.
    kHoldOnMilliseconds = 2000
  };

  struct CONTENT_EXPORT StreamID {
    int render_process_id;
    int render_frame_id;
    int stream_id;
    bool operator<(const StreamID& other) const;
    bool operator==(const StreamID& other) const;
  };

  // Starts monitoring the audible state for the given stream.
  void StartMonitoringStreamOnUIThread(const StreamID& sid);

  // Stops monitoring the audible state for the given stream.
  void StopMonitoringStreamOnUIThread(const StreamID& sid);

  // Updates the audible state for the given stream.
  void UpdateStreamAudibleStateOnUIThread(const StreamID& sid, bool is_audible);

  // Compares last known indicator state with what it should be, and triggers UI
  // updates through |web_contents_| if needed.  When the indicator is turned
  // on, |off_timer_| is started to re-invoke this method in the future.
  void MaybeToggle();
  void UpdateStreams();

  // void OnStreamRemoved();

  // The WebContents instance to receive indicator toggle notifications.  This
  // pointer should be valid for the lifetime of AudioStreamMonitor.
  WebContents* const web_contents_;

  // Note: |clock_| is always a DefaultTickClock, except during unit
  // testing.
  const base::TickClock* const clock_;

  // Confirms single-threaded access in debug builds.
  base::ThreadChecker thread_checker_;

  // The audible state for each stream.  Only playing (i.e., not paused)
  // streams will have an entry in this map.
  base::flat_map<StreamID, bool> streams_;

  // Records the last time at which all streams became silent.
  base::TimeTicks last_became_silent_time_;

  // Set to true if the last call to MaybeToggle() determined the indicator
  // should be turned on.
  bool indicator_is_on_;

  // Whether the WebContents is currently audible.
  bool is_audible_;

  // Started only when an indicator is toggled on, to turn it off again in the
  // future.
  base::OneShotTimer off_timer_;

  DISALLOW_COPY_AND_ASSIGN(AudioStreamMonitor);
};

}  // namespace content

#endif  // CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_