Call AvSetMmThreadCharacteristicsW on the WASAPI mixing threads

CMakeLists.txt

@@ -1044,6 +1044,11 @@ if(WIN32)
             set(HAVE_WASAPI 1)
             set(BACKENDS  "${BACKENDS} WASAPI,")
             set(ALC_OBJS  ${ALC_OBJS} alc/backends/wasapi.cpp alc/backends/wasapi.h)
+
+            find_library(AVRT_LIBRARY NAMES avrt DOC "The AVRT library")
+            if(AVRT_LIBRARY)
+                set(EXTRA_LIBS ${AVRT_LIBRARY} ${EXTRA_LIBS})
+            endif()
         endif()
     endif()
 

alc/backends/wasapi.cpp

@@ -29,6 +29,7 @@
 #include <cstdlib>
 #include <memory.h>
 
+#include <avrt.h>
 #include <wtypes.h>
 #include <mmdeviceapi.h>
 #include <audiosessiontypes.h>
@@ -319,6 +320,13 @@ struct DeviceListLock : public std::unique_lock<DeviceList> {
 DeviceList gDeviceList;
 
 
+#ifdef AVRTAPI
+struct AvrtHandleCloser {
+    void operator()(HANDLE handle) { AvRevertMmThreadCharacteristics(handle); }
+};
+using AvrtHandlePtr = std::unique_ptr<std::remove_pointer_t<HANDLE>,AvrtHandleCloser>;
+#endif
+
 #if defined(ALSOFT_UWP)
 enum EDataFlow {
     eRender              = 0,
@@ -968,6 +976,7 @@ struct WasapiProxy {
     static inline std::deque<Msg> mMsgQueue;
     static inline std::mutex mMsgQueueLock;
     static inline std::condition_variable mMsgQueueCond;
+    static inline DWORD sAvIndex{};
 
     static inline std::optional<DeviceHelper> sDeviceHelper;
 
@@ -1169,6 +1178,15 @@ FORCE_ALIGN int WasapiPlayback::mixerProc()
     const UINT32 buffer_len{mOrigBufferSize};
     const void *resbufferptr{};
 
+#ifdef AVRTAPI
+    /* TODO: "Audio" or "Pro Audio"? The suggestion is to use "Pro Audio" for
+     * device periods less than 10ms, and "Audio" for greater than or equal to
+     * 10ms.
+     */
+    auto taskname = (update_size < mFormat.Format.nSamplesPerSec/100) ? L"Pro Audio" : L"Audio";
+    auto avhandle = AvrtHandlePtr{AvSetMmThreadCharacteristicsW(taskname, &sAvIndex)};
+#endif
+
     mBufferFilled = 0;
     while(!mKillNow.load(std::memory_order_relaxed))
     {
@@ -1257,6 +1275,11 @@ FORCE_ALIGN int WasapiPlayback::mixerSpatialProc()
     std::vector<void*> resbuffers;
     std::vector<const void*> tmpbuffers;
 
+#ifdef AVRTAPI
+    auto taskname = (mOrigUpdateSize<mFormat.Format.nSamplesPerSec/100) ? L"Pro Audio" : L"Audio";
+    auto avhandle = AvrtHandlePtr{AvSetMmThreadCharacteristicsW(taskname, &sAvIndex)};
+#endif
+
     /* TODO: Set mPadding appropriately. There doesn't seem to be a way to
      * update it dynamically based on the stream, so a fixed size may be the
      * best we can do.