Move Alsa device opening into the audio thread, and add in support for multi-channel audio.

media/audio/linux/alsa_output.h

 // Copyright (c) 2009 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.
 //
 // Creates an output stream based on the ALSA PCM interface.
 //
 // On device write failure, the stream will move itself to an invalid state.
 // No more data will be pulled from the data source, or written to the device.
 // All calls to public API functions will either no-op themselves, or return an
 // error if possible.  Specifically, If the stream is in an error state, Open()
@@ skipping 28 matching lines @@
 #include "media/audio/audio_output.h"
 #include "testing/gtest/include/gtest/gtest_prod.h"
 
 class AlsaWrapper;
 class AudioManagerLinux;
 
 class AlsaPcmOutputStream :
     public AudioOutputStream,
     public base::RefCountedThreadSafe<AlsaPcmOutputStream> {
  public:
-  // Set to "default" which should avoid locking the sound device and allow
-  // ALSA to multiplex sound from different processes that want to write PCM
-  // data.
+  // String for the generic "default" ALSA device that has the highest
+  // compatibility and chance of working.
   static const char kDefaultDevice[];
 
+  // Pass this to the AlsaPcmOutputStream if you want to attempt auto-selection
+  // of the audio device.
+  static const char kAutoSelectDevice[];
+
+  // Prefix for device names to enable ALSA library resampling.
+  static const char kPlugPrefix[];
+
+  // The minimum latency that is accepted by the device.
+  static const int kMinLatencyMicros;
+
   // Create a PCM Output stream for the ALSA device identified by
   // |device_name|.  The AlsaPcmOutputStream uses |wrapper| to communicate with
   // the alsa libraries, allowing for dependency injection during testing.  All
   // requesting of data, and writing to the alsa device will be done on
   // |message_loop|.
   //
-  // If unsure of what to use for |device_name|, use |kDefaultDevice|.
+  // If unsure of what to use for |device_name|, use |kAutoSelectDevice|.
   AlsaPcmOutputStream(const std::string& device_name,
                       AudioManager::Format format,
                       int channels,
                       int sample_rate,
                       int bits_per_sample,
                       AlsaWrapper* wrapper,
                       AudioManagerLinux* manager,
                       MessageLoop* message_loop);
   virtual ~AlsaPcmOutputStream();
 
   // Implementation of AudioOutputStream.
   virtual bool Open(size_t packet_size);
   virtual void Close();
   virtual void Start(AudioSourceCallback* callback);
   virtual void Stop();
   virtual void SetVolume(double left_level, double right_level);
   virtual void GetVolume(double* left_level, double* right_level);
 
  private:
   friend class AlsaPcmOutputStreamTest;
+  FRIEND_TEST(AlsaPcmOutputStreamTest, AutoSelectDevice_DeviceSelect);
+  FRIEND_TEST(AlsaPcmOutputStreamTest, AutoSelectDevice_FallbackDevices);
+  FRIEND_TEST(AlsaPcmOutputStreamTest, AutoSelectDevice_HintFail);
   FRIEND_TEST(AlsaPcmOutputStreamTest, BufferPacket);
   FRIEND_TEST(AlsaPcmOutputStreamTest, BufferPacket_StopStream);
   FRIEND_TEST(AlsaPcmOutputStreamTest, BufferPacket_UnfinishedPacket);
   FRIEND_TEST(AlsaPcmOutputStreamTest, ConstructedState);
+  FRIEND_TEST(AlsaPcmOutputStreamTest, LatencyFloor);
   FRIEND_TEST(AlsaPcmOutputStreamTest, OpenClose);
   FRIEND_TEST(AlsaPcmOutputStreamTest, PcmOpenFailed);
   FRIEND_TEST(AlsaPcmOutputStreamTest, PcmSetParamsFailed);
   FRIEND_TEST(AlsaPcmOutputStreamTest, ScheduleNextWrite);
   FRIEND_TEST(AlsaPcmOutputStreamTest, ScheduleNextWrite_StopStream);
   FRIEND_TEST(AlsaPcmOutputStreamTest, StartStop);
   FRIEND_TEST(AlsaPcmOutputStreamTest, WritePacket_FinishedPacket);
   FRIEND_TEST(AlsaPcmOutputStreamTest, WritePacket_NormalPacket);
   FRIEND_TEST(AlsaPcmOutputStreamTest, WritePacket_StopStream);
   FRIEND_TEST(AlsaPcmOutputStreamTest, WritePacket_WriteFails);
@@ skipping 19 matching lines @@
     kInError = 0,
     kCreated,
     kIsOpened,
     kIsPlaying,
     kIsStopped,
     kIsClosed
   };
   friend std::ostream& ::operator<<(std::ostream& os, InternalState);
 
   // Various tasks that complete actions started in the public API.
-  void FinishOpen(snd_pcm_t* playback_handle, size_t packet_size);
+  void OpenTask(size_t packet_size);
   void StartTask();
   void CloseTask();
 
   // Functions to get another packet from the data source and write it into the
   // ALSA device.
   void BufferPacket(Packet* packet);
   void WritePacket(Packet* packet);
   void WriteTask();
   void ScheduleNextWrite(Packet* current_packet);
 
   // Utility functions for talking with the ALSA API.
   static snd_pcm_sframes_t FramesInPacket(const Packet& packet,
                                           int bytes_per_frame);
   static int64 FramesToMicros(int frames, int sample_rate);
   static int64 FramesToMillis(int frames, int sample_rate);
+  std::string FindDeviceForChannels(int channels);
+  snd_pcm_t* OpenDevice(const std::string& device_name,
+                        int channels,
+                        unsigned int latency);
   bool CloseDevice(snd_pcm_t* handle);
   snd_pcm_sframes_t GetAvailableFrames();
 
+  // Attempts to find the best matching linux audio device for the given number
+  // of channels.  This function will set |device_name_| and |should_downmix_|.
+  snd_pcm_t* AutoSelectDevice(unsigned int latency);
+
   // Thread-asserting accessors for member variables.
   AudioManagerLinux* manager();
 
   // Struct holding all mutable the data that must be shared by the
   // message_loop() and the thread that created the object.
   class SharedData {
    public:
     explicit SharedData(MessageLoop* state_transition_loop);
 
     // Functions to safeguard state transitions and ensure that transitions are
@@ skipping 32 matching lines @@
 
     AudioSourceCallback* source_callback_;
 
     MessageLoop* const state_transition_loop_;
 
     DISALLOW_COPY_AND_ASSIGN(SharedData);
   } shared_data_;
 
   // Configuration constants from the constructor.  Referenceable by all threads
   // since they are constants.
-  const std::string device_name_;
+  const std::string requested_device_name_;
   const snd_pcm_format_t pcm_format_;
   const int channels_;
   const int sample_rate_;
   const int bytes_per_sample_;
   const int bytes_per_frame_;
 
+  // Device configuration data. Populated after OpenTask() completes.
+  std::string device_name_;
+  bool should_downmix_;
+  int latency_micros_;
+  int micros_per_packet_;
+  int bytes_per_output_frame_;
+
   // Flag indicating the code should stop reading from the data source or
   // writing to the ALSA device.  This is set because the device has entered
   // an unrecoverable error state, or the ClosedTask() has executed.
   bool stop_stream_;
 
   // Wrapper class to invoke all the ALSA functions.
   AlsaWrapper* wrapper_;
 
   // Audio manager that created us.  Used to report that we've been closed.
   // This should only be used on the |client_thread_loop_|.  Access via
@@ skipping 10 matching lines @@
   MessageLoop* client_thread_loop_;
 
   // The message loop responsible for querying the data source, and writing to
   // the output device.
   MessageLoop* message_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(AlsaPcmOutputStream);
 };
 
 #endif  // MEDIA_AUDIO_LINUX_ALSA_OUTPUT_H_