Silence warnings from portaudio ALSA backend during device enumeration. Do device enumeration on background thread

cmake/portaudio.cmake

@@ -2,6 +2,7 @@
 if(LASP_HAS_PORTAUDIO)
     message("Building with Portaudio backend")
     if(WIN32)
+        set(PA_USE_ALSA FALSE CACHE BOOL "Build PortAudio with ALSA backend")
     else()
         # Unix
         set(PA_USE_ALSA TRUE CACHE BOOL "Build PortAudio with ALSA backend")
@@ -9,7 +10,15 @@ if(LASP_HAS_PORTAUDIO)
         set(PA_USE_PULSEAUDIO FALSE CACHE BOOL "Build PortAudio with PulseAudio backend")
         set(PA_BUILD_SHARED_LIBS FALSE CACHE BOOL "Build static library")
     endif()
+
     add_subdirectory(third_party/portaudio)
     include_directories(third_party/portaudio/include)
     link_directories(third_party/portaudio)
+
+    if(PA_USE_ALSA)
+    add_definitions(-DLASP_HAS_PA_ALSA=1)
+    else()
+    add_definitions(-DLASP_HAS_PA_ALSA=0)
+    endif()
+
 endif()

cpp_src/device/lasp_streammgr.cpp

@@ -75,7 +75,7 @@ StreamMgr::StreamMgr()
 {
   DEBUGTRACE_ENTER;
   // Trigger a scan for the available devices, in the background.
-  rescanDAQDevices(false);
+  rescanDAQDevices(true);
 }
 #if LASP_DEBUG == 1
 void StreamMgr::checkRightThread() const {
@@ -107,13 +107,44 @@ void StreamMgr::rescanDAQDevices(bool background,
     _pool.push_task(&StreamMgr::rescanDAQDevices_impl, this, callback);
   }
 }
+#if LASP_HAS_PORTAUDIO && LASP_HAS_PA_ALSA
+#include <alsa/asoundlib.h>
+void empty_handler(const char *file, int line, const char *function, int err,
+                   const char *fmt, ...) {}
+
+// Temporarily set the ALSA eror handler to something that does nothing, to
+// prevent ALSA from spitting out all kinds of misconfiguration errors.
+class MuteErrHandler {
+ private:
+  snd_lib_error_handler_t _default_handler;
+
+ public:
+  explicit MuteErrHandler() {
+    _default_handler = snd_lib_error;
+    snd_lib_error_set_handler(empty_handler);
+  }
+
+  ~MuteErrHandler() { snd_lib_error_set_handler(_default_handler); }
+};
+#else
+// Does nothin in case of no ALSA
+class MuteErrHandler {};
+#endif
+
 void StreamMgr::rescanDAQDevices_impl(std::function<void()> callback) {
   DEBUGTRACE_ENTER;
+  assert(!_inputStream && !_outputStream);
   Lck lck(_mtx);
+  // Alsa spits out annoying messages that are not useful
+  {
+    MuteErrHandler guard;
+
     _devices = DeviceInfo::getDeviceInfo();
+  }
   if (callback) {
     callback();
   }
+
   _scanningDevices = false;
 }
 void StreamMgr::inCallback(const DaqData &data) {

cpp_src/device/portaudio/lasp_portaudiodaq.cpp

@@ -93,6 +93,7 @@ void fillPortAudioDeviceInfo(DeviceInfoList &devinfolist) {
           d.api = portaudioALSAApi;
           break;
         case paASIO:
+          hasDuplexMode = true;
           d.api = portaudioASIOApi;
           break;
         case paDirectSound: