From 62b6224e37e180498990ba7d79a09bf87889e520 Mon Sep 17 00:00:00 2001
From: Nirbheek Chauhan <nirbheek@centricular.com>
Date: Tue, 6 Feb 2018 23:45:02 +0530
Subject: [PATCH] wasapi: Increase thread priority to reduce glitches

This is particularly important when running in exclusive mode because
any delays will immediately cause glitching.

The MinGW version in Cerbero is too old, so we can only enable this when
building with MSVC or when people build GStreamer for MSYS2 or other
MinGW-based distributions.

To force-enable this code when building with MinGW, build with
CFLAGS="-DGST_FORCE_WIN_AVRT -lavrt".

https://bugzilla.gnome.org/show_bug.cgi?id=793289
---
 sys/wasapi/gstwasapisink.c | 18 ++++++++++++++++++
 sys/wasapi/gstwasapisink.h |  1 +
 sys/wasapi/gstwasapisrc.c  | 18 ++++++++++++++++++
 sys/wasapi/gstwasapisrc.h  |  1 +
 4 files changed, 38 insertions(+)

diff --git a/sys/wasapi/gstwasapisink.c b/sys/wasapi/gstwasapisink.c
index 0f0d299d48..8a9d3f89dc 100644
--- a/sys/wasapi/gstwasapisink.c
+++ b/sys/wasapi/gstwasapisink.c
@@ -40,6 +40,8 @@
 
 #include "gstwasapisink.h"
 
+#include <avrt.h>
+
 GST_DEBUG_CATEGORY_STATIC (gst_wasapi_sink_debug);
 #define GST_CAT_DEFAULT gst_wasapi_sink_debug
 
@@ -472,6 +474,15 @@ gst_wasapi_sink_prepare (GstAudioSink * asink, GstAudioRingBufferSpec * spec)
   gst_audio_ring_buffer_set_channel_positions (GST_AUDIO_BASE_SINK
       (self)->ringbuffer, self->positions);
 
+#if defined(_MSC_VER) || defined(GST_FORCE_WIN_AVRT)
+  /* Increase the thread priority to reduce glitches */
+  {
+    DWORD taskIndex = 0;
+    self->thread_priority_handle =
+        AvSetMmThreadCharacteristics (TEXT ("Pro Audio"), &taskIndex);
+  }
+#endif
+
   res = TRUE;
 
 beach:
@@ -489,6 +500,13 @@ gst_wasapi_sink_unprepare (GstAudioSink * asink)
   if (self->sharemode == AUDCLNT_SHAREMODE_EXCLUSIVE)
     CoUninitialize ();
 
+#if defined(_MSC_VER) || defined(GST_FORCE_WIN_AVRT)
+  if (self->thread_priority_handle != NULL) {
+    AvRevertMmThreadCharacteristics (self->thread_priority_handle);
+    self->thread_priority_handle = NULL;
+  }
+#endif
+
   if (self->client != NULL) {
     IAudioClient_Stop (self->client);
   }
diff --git a/sys/wasapi/gstwasapisink.h b/sys/wasapi/gstwasapisink.h
index 882f46e2c6..588d5807db 100644
--- a/sys/wasapi/gstwasapisink.h
+++ b/sys/wasapi/gstwasapisink.h
@@ -44,6 +44,7 @@ struct _GstWasapiSink
   IAudioClient *client;
   IAudioRenderClient *render_client;
   HANDLE event_handle;
+  HANDLE thread_priority_handle;
 
   /* Actual size of the allocated buffer */
   guint buffer_frame_count;
diff --git a/sys/wasapi/gstwasapisrc.c b/sys/wasapi/gstwasapisrc.c
index dec93f8293..49f1d31b54 100644
--- a/sys/wasapi/gstwasapisrc.c
+++ b/sys/wasapi/gstwasapisrc.c
@@ -38,6 +38,8 @@
 
 #include "gstwasapisrc.h"
 
+#include <avrt.h>
+
 GST_DEBUG_CATEGORY_STATIC (gst_wasapi_src_debug);
 #define GST_CAT_DEFAULT gst_wasapi_src_debug
 
@@ -477,6 +479,15 @@ gst_wasapi_src_prepare (GstAudioSrc * asrc, GstAudioRingBufferSpec * spec)
   gst_audio_ring_buffer_set_channel_positions (GST_AUDIO_BASE_SRC
       (self)->ringbuffer, self->positions);
 
+#if defined(_MSC_VER) || defined(GST_FORCE_WIN_AVRT)
+  /* Increase the thread priority to reduce glitches */
+  {
+    DWORD taskIndex = 0;
+    self->thread_priority_handle =
+        AvSetMmThreadCharacteristics (TEXT ("Pro Audio"), &taskIndex);
+  }
+#endif
+
   res = TRUE;
 
 beach:
@@ -499,6 +510,13 @@ gst_wasapi_src_unprepare (GstAudioSrc * asrc)
   if (self->sharemode == AUDCLNT_SHAREMODE_EXCLUSIVE)
     CoUninitialize ();
 
+#if defined(_MSC_VER) || defined(GST_FORCE_WIN_AVRT)
+  if (self->thread_priority_handle != NULL) {
+    AvRevertMmThreadCharacteristics (self->thread_priority_handle);
+    self->thread_priority_handle = NULL;
+  }
+#endif
+
   if (self->client != NULL) {
     IAudioClient_Stop (self->client);
   }
diff --git a/sys/wasapi/gstwasapisrc.h b/sys/wasapi/gstwasapisrc.h
index fc89391a9b..530fb2b927 100644
--- a/sys/wasapi/gstwasapisrc.h
+++ b/sys/wasapi/gstwasapisrc.h
@@ -46,6 +46,7 @@ struct _GstWasapiSrc
   guint64 client_clock_freq;
   IAudioCaptureClient *capture_client;
   HANDLE event_handle;
+  HANDLE thread_priority_handle;
 
   /* Actual size of the allocated buffer */
   guint buffer_frame_count;