Add an option for real-time priority mixing

Default to disable for now, as a safety precaution

Alc/ALc.c

@@ -208,6 +208,9 @@ static tls_type LocalContext;
 // Context Error
 static ALCenum g_eLastContextError = ALC_NO_ERROR;
 
+// Mixing Priority Level
+ALint RTPrioLevel;
+
 ///////////////////////////////////////////////////////
 
 
@@ -253,6 +256,8 @@ static void alc_init(void)
 
     tls_create(&LocalContext);
 
+    RTPrioLevel = GetConfigValueInt(NULL, "rt-prio", 0);
+
     devs = GetConfigValue(NULL, "drivers", "");
     if(devs[0])
     {
@@ -424,6 +429,39 @@ DECL_APPEND_LIST_FUNC(AllDevice)
 DECL_APPEND_LIST_FUNC(CaptureDevice)
 
 
+void EnableRTPrio(ALint level)
+{
+    ALboolean failed;
+
+#ifdef _WIN32
+    if(level > 0)
+        failed = !SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_TIME_CRITICAL);
+    else
+        failed = !SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_NORMAL);
+#elif defined(HAVE_PTHREAD_SETSCHEDPARAM)
+    struct sched_param param;
+
+    if(level > 0)
+    {
+        /* Use the minimum real-time priority possible for now (on Linux this
+         * should be 1 for SCHED_RR) */
+        param.sched_priority = sched_get_priority_min(SCHED_RR);
+        failed = !!pthread_setschedparam(pthread_self(), SCHED_RR, &param);
+    }
+    else
+    {
+        param.sched_priority = 0;
+        failed = !!pthread_setschedparam(pthread_self(), SCHED_OTHER, &param);
+    }
+#else
+    /* Real-time priority not available */
+    failed = !!level;
+#endif
+    if(failed)
+        AL_PRINT("Failed to set priority level for thread\n");
+}
+
+
 /*
     IsDevice
 

Alc/alsa.c

@@ -271,7 +271,7 @@ static ALuint ALSAProc(ALvoid *ptr)
     char *WritePtr;
     int err;
 
-    EnableRTPrio();
+    EnableRTPrio(RTPrioLevel);
 
     while(!data->killNow)
     {
@@ -345,7 +345,7 @@ static ALuint ALSANoMMapProc(ALvoid *ptr)
     snd_pcm_sframes_t avail;
     char *WritePtr;
 
-    EnableRTPrio();
+    EnableRTPrio(RTPrioLevel);
 
     while(!data->killNow)
     {
@@ -400,7 +400,7 @@ static ALuint ALSANoMMapCaptureProc(ALvoid *ptr)
     alsa_data *data = (alsa_data*)pDevice->ExtraData;
     snd_pcm_sframes_t avail;
 
-    EnableRTPrio();
+    EnableRTPrio(RTPrioLevel);
 
     while(!data->killNow)
     {

Alc/dsound.c

@@ -134,7 +134,7 @@ static ALuint DSoundProc(ALvoid *ptr)
     DWORD avail;
     HRESULT err;
 
-    EnableRTPrio();
+    EnableRTPrio(RTPrioLevel);
 
     memset(&DSBCaps, 0, sizeof(DSBCaps));
     DSBCaps.dwSize = sizeof(DSBCaps);

Alc/oss.c

@@ -82,7 +82,7 @@ static ALuint OSSProc(ALvoid *ptr)
     ALint frameSize;
     ssize_t wrote;
 
-    EnableRTPrio();
+    EnableRTPrio(RTPrioLevel);
 
     frameSize = aluChannelsFromFormat(pDevice->Format) *
                 aluBytesFromFormat(pDevice->Format);
@@ -124,7 +124,7 @@ static ALuint OSSCaptureProc(ALvoid *ptr)
     int frameSize;
     int amt;
 
-    EnableRTPrio();
+    EnableRTPrio(RTPrioLevel);
 
     frameSize  = aluBytesFromFormat(pDevice->Format);
     frameSize *= aluChannelsFromFormat(pDevice->Format);

Alc/solaris.c

@@ -57,6 +57,8 @@ static ALuint SolarisProc(ALvoid *ptr)
     ALint frameSize;
     int wrote;
 
+    EnableRTPrio(RTPrioLevel);
+
     frameSize = aluChannelsFromFormat(pDevice->Format) *
                 aluBytesFromFormat(pDevice->Format);
 

OpenAL32/Include/alMain.h

@@ -181,22 +181,6 @@ static __inline ALuint NextPowerOf2(ALuint value)
     return powerOf2;
 }
 
-static __inline void EnableRTPrio()
-{
-#ifdef _WIN32
-    SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_TIME_CRITICAL);
-#elif defined(HAVE_PTHREAD_SETSCHEDPARAM)
-    struct sched_param param;
-
-    /* Use the minimum real-time priority possible for now (on Linux this
-     * should be 1 for SCHED_RR) */
-    param.sched_priority = sched_get_priority_min(SCHED_RR);
-    pthread_setschedparam(pthread_self(), SCHED_RR, &param);
-#else
-    /* Real-time priority not available */
-#endif
-}
-
 
 typedef struct {
     ALCboolean (*OpenPlayback)(ALCdevice*, const ALCchar*);
@@ -343,6 +327,8 @@ struct ALCcontext_struct
     ALCcontext *next;
 };
 
+extern ALint RTPrioLevel;
+
 ALCvoid ReleaseALC(ALCvoid);
 
 void AppendDeviceList(const ALCchar *name);
@@ -373,6 +359,8 @@ int GetConfigValueInt(const char *blockName, const char *keyName, int def);
 float GetConfigValueFloat(const char *blockName, const char *keyName, float def);
 int GetConfigValueBool(const char *blockName, const char *keyName, float def);
 
+void EnableRTPrio(ALint level);
+
 ALCboolean  ALCAPIENTRY alcMakeCurrent(ALCcontext *context);
 ALCcontext* ALCAPIENTRY alcGetThreadContext(void);
 

alsoftrc.sample

@@ -52,6 +52,15 @@
 #  Sets the output frequency.
 #frequency = 44100
 
+## rt-prio:
+#  Sets real-time priority for the mixing thread. Not all drivers may use this
+#  (eg. PulseAudio) as they already control the priority of the mixing thread.
+#  0 and negative values will disable it. Note that this may constitute a
+#  security risk since a real-time priority thread can indefinitely block
+#  normal-priority threads if it fails to wait. As such, the default is
+#  disabled.
+#rt-prio = 0
+
 ## period_size:
 #  Sets the update period size, in frames. This is the number of frames needed
 #  for each mixing update. If the deprecated 'refresh' option is specified and