Let default device in PulseAudio be the system default device

media/audio/pulse/pulse_input.cc

Index: media/audio/pulse/pulse_input.cc
diff --git a/media/audio/pulse/pulse_input.cc b/media/audio/pulse/pulse_input.cc
index 8d4aeea2079d201a69e52fb48e4344680c467d70..f8f69b0b82be2a597b16ea8484aba1206a5c3ce6 100644
--- a/media/audio/pulse/pulse_input.cc
+++ b/media/audio/pulse/pulse_input.cc
@@ -12,6 +12,22 @@
 
 namespace media {
 
+namespace {
+
+// pa_context_get_server_info callback. It's used by
+// GetSystemDefaultInputDevice to set |default_system_device_name_| to the
+// default system input device.
+void GetSystemDefaultInputDeviceCallback(pa_context* context,
+                                         const pa_server_info* info,
+                                         void* user_data) {
+  media::PulseAudioInputStream* stream =
+      reinterpret_cast<media::PulseAudioInputStream*>(user_data);
+  stream->SetDefaultSystemDeviceName(info->default_source_name);
+  pa_threaded_mainloop_signal(stream->GetPAMainloop(), 0);
+}
+
+}  // namespace
+
 using pulse::AutoPulseLock;
 using pulse::WaitForOperationCompletion;
 
@@ -51,8 +67,15 @@ PulseAudioInputStream::~PulseAudioInputStream() {
 bool PulseAudioInputStream::Open() {
   DCHECK(thread_checker_.CalledOnValidThread());
   AutoPulseLock auto_lock(pa_mainloop_);
+  std::string device_name_to_use = device_name_;
+  if (device_name_ == AudioManagerBase::kDefaultDeviceId) {
+    GetSystemDefaultInputDevice();
+    device_name_to_use = default_system_device_name_;
+  }
+
   if (!pulse::CreateInputStream(pa_mainloop_, pa_context_, &handle_, params_,
-                                device_name_, &StreamNotifyCallback, this)) {
+                                device_name_to_use, &StreamNotifyCallback,
+                                this)) {
     return false;
   }
 
@@ -197,6 +220,15 @@ bool PulseAudioInputStream::IsMuted() {
   return muted_;
 }
 
+pa_threaded_mainloop* PulseAudioInputStream::GetPAMainloop() {
+  return pa_mainloop_;

[Henrik Grunell, 2016/03/10 20:07:34]

Could this function be called at the same time as setting the variable in
Open()? I don't think so, but can you verify that not possible?

[rchtara, 2016/03/11 10:13:09]

PulseAudioInputStream::Open is going to lock the main loop until the stream is
open (which includes calling: PulseAudioInputStream::GetPAMainloop).
In case a concurrent call to Open happens, it's going to wait until the first 
one has finished. 
so this function could not be called at the same time as setting the variable in
Open()

[Henrik Grunell, 2016/03/11 18:54:41]

Acknowledged.

[rchtara, 2016/03/13 15:12:00]

Done.

+}
+
+void PulseAudioInputStream::SetDefaultSystemDeviceName(
+    const std::string& name) {
+  default_system_device_name_ = name;
+}
+
 // static, used by pa_stream_set_read_callback.
 void PulseAudioInputStream::ReadCallback(pa_stream* handle,
                                          size_t length,
@@ -268,6 +300,14 @@ void PulseAudioInputStream::StreamNotifyCallback(pa_stream* s,
   pa_threaded_mainloop_signal(stream->pa_mainloop_, 0);
 }
 
+void PulseAudioInputStream::GetSystemDefaultInputDevice() {
+  DCHECK(pa_mainloop_);
+  DCHECK(pa_context_);
+  pa_operation* operation = pa_context_get_server_info(
+      pa_context_, GetSystemDefaultInputDeviceCallback, this);
+  WaitForOperationCompletion(pa_mainloop_, operation);
+}
+
 void PulseAudioInputStream::ReadData() {
   uint32_t hardware_delay = pulse::GetHardwareLatencyInBytes(
       handle_, params_.sample_rate(), params_.GetBytesPerFrame());