chrome/browser/chromeos/audio_mixer_alsa.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_ALSA_H_
   6 #define CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_ALSA_H_
   7 #pragma once
   8
   9 #include <string>
  10
  11 #include "base/basictypes.h"
  12 #include "base/compiler_specific.h"
  13 #include "base/memory/scoped_ptr.h"
  14 #include "base/synchronization/lock.h"
  15 #include "base/synchronization/waitable_event.h"
  16 #include "base/threading/thread.h"
  17 #include "chrome/browser/chromeos/audio_mixer.h"
  18
  19 class PrefService;
  20
  21 struct _snd_mixer_elem;
  22 struct _snd_mixer;
  23
  24 namespace chromeos {
  25
  26 // Simple wrapper around ALSA's mixer functions.
  27 // Interaction with ALSA takes place on a background thread.
  28 class AudioMixerAlsa : public AudioMixer {
  29  public:
  30   AudioMixerAlsa();
  31   virtual ~AudioMixerAlsa();
  32
  33   // AudioMixer implementation.
  34   virtual void Init() OVERRIDE;
  35   virtual bool IsInitialized() OVERRIDE;
  36   virtual void GetVolumeLimits(double* min_volume_db,
  37                                double* max_volume_db) OVERRIDE;
  38   virtual double GetVolumeDb() OVERRIDE;
  39   virtual void SetVolumeDb(double volume_db) OVERRIDE;
  40   virtual bool IsMuted() OVERRIDE;
  41   virtual void SetMuted(bool muted) OVERRIDE;
  42
  43   // Registers volume and mute preferences.
  44   // TODO(derat): Move prefs into AudioHandler.
  45   static void RegisterPrefs(PrefService* local_state);
  46
  47  private:
  48   // Tries to connect to ALSA.  On failure, posts a delayed Connect() task to
  49   // try again.
  50   void Connect();
  51
  52   // Helper method called by Connect().  On success, initializes
  53   // |min_volume_db_|, |max_volume_db_|, |alsa_mixer_|, and |element_*| and
  54   // returns true.
  55   bool ConnectInternal();
  56
  57   // Disconnects from ALSA if currently connected and signals
  58   // |disconnected_event_|.
  59   void Disconnect();
  60
  61   // Updates |alsa_mixer_| for current values of |volume_db_| and |is_muted_|.
  62   // No-op if not connected.
  63   void ApplyState();
  64
  65   // Finds the element named |element_name|.  Returns NULL on failure.
  66   _snd_mixer_elem* FindElementWithName(_snd_mixer* handle,
  67                                        const std::string& element_name) const;
  68
  69   // Queries |element|'s current volume, copying it to |new_volume_db|.
  70   // Returns true on success.
  71   bool GetElementVolume(_snd_mixer_elem* element, double* current_volume_db);
  72
  73   // Sets |element|'s volume.  Since volume is done in steps, we may not get the
  74   // exact volume asked for.  |rounding_bias| is added in before rounding to the
  75   // nearest volume step (use 0.5 to round to nearest).
  76   bool SetElementVolume(_snd_mixer_elem* element,
  77                         double new_volume_db,
  78                         double rounding_bias);
  79
  80   // Mutes or unmutes |element|.
  81   void SetElementMuted(_snd_mixer_elem* element, bool mute);
  82
  83   // Guards |min_volume_db_|, |max_volume_db_|, |volume_db_|, |is_muted_|, and
  84   // |apply_is_pending_|.
  85   base::Lock lock_;
  86
  87   // Volume range limits are computed once in ConnectInternal().
  88   double min_volume_db_;
  89   double max_volume_db_;
  90
  91   // Most recently requested volume, in decibels.  This variable is updated
  92   // immediately by GetVolumeDb(); the actual mixer volume is updated later on
  93   // |thread_| by ApplyState().
  94   double volume_db_;
  95
  96   // Most recently requested muting state.
  97   bool is_muted_;
  98
  99   // Is there already a pending call to ApplyState() scheduled on |thread_|?
 100   bool apply_is_pending_;
 101
 102   // Connection to ALSA.  NULL if not connected.
 103   _snd_mixer* alsa_mixer_;
 104
 105   // Master mixer.
 106   _snd_mixer_elem* master_element_;
 107
 108   // PCM mixer.  May be NULL if the driver doesn't expose one.
 109   _snd_mixer_elem* pcm_element_;
 110
 111   PrefService* prefs_;
 112
 113   // Signalled after Disconnect() finishes (which is itself invoked by the
 114   // d'tor).
 115   base::WaitableEvent disconnected_event_;
 116
 117   // Background thread used for interacting with ALSA.
 118   scoped_ptr<base::Thread> thread_;
 119
 120   // Number of times that we've attempted to connect to ALSA.  Just used to keep
 121   // us from spamming the logs.
 122   int num_connection_attempts_;
 123
 124   DISALLOW_COPY_AND_ASSIGN(AudioMixerAlsa);
 125 };
 126
 127 }  // namespace chromeos
 128
 129 #endif  // CHROME_BROWSER_CHROMEOS_AUDIO_MIXER_ALSA_H_