Use MMCSS to elevate the thread priorities for audio and MIDI threads

use AVRT_PRIORITY_NORMAL for audio threads and AVRT_PRIORITY_HIGH for MIDI
threads

libs/backends/portaudio/portaudio_backend.cc

@@ -37,6 +37,8 @@
 #include "i18n.h"
 
 #include "win_utils.h"
+#include "mmcss.h"
+
 #include "debug.h"
 
 using namespace ARDOUR;
@@ -79,6 +81,8 @@ PortAudioBackend::PortAudioBackend (AudioEngine& e, AudioBackendInfo& info)
 	_instance_name = s_instance_name;
 	pthread_mutex_init (&_port_callback_mutex, 0);
 
+	mmcss::initialize ();
+
 	_pcmio = new PortAudioIO ();
 	_midiio = new WinMMEMidiIO ();
 }
@@ -87,6 +91,9 @@ PortAudioBackend::~PortAudioBackend ()
 {
 	delete _pcmio; _pcmio = 0;
 	delete _midiio; _midiio = 0;
+
+	mmcss::deinitialize ();
+
 	pthread_mutex_destroy (&_port_callback_mutex);
 }
 
@@ -636,7 +643,23 @@ PortAudioBackend::portaudio_process_thread (void *arg)
 	ThreadData* td = reinterpret_cast<ThreadData*> (arg);
 	boost::function<void ()> f = td->f;
 	delete td;
+
+#ifdef USE_MMCSS_THREAD_PRIORITIES
+	HANDLE task_handle;
+
+	mmcss::set_thread_characteristics ("Pro Audio", &task_handle);
+	mmcss::set_thread_priority (task_handle, mmcss::AVRT_PRIORITY_NORMAL);
+#endif
+
+	DWORD tid = GetThreadId (GetCurrentThread ());
+	DEBUG_THREADS (string_compose ("Process Thread Child ID: %1\n", tid));
+
 	f ();
+
+#ifdef USE_MMCSS_THREAD_PRIORITIES
+	mmcss::revert_thread_characteristics (task_handle);
+#endif
+
 	return 0;
 }
 
@@ -1308,6 +1331,16 @@ PortAudioBackend::main_process_thread ()
 		engine.halted_callback("PortAudio I/O error.");
 	}
 
+#ifdef USE_MMCSS_THREAD_PRIORITIES
+	HANDLE task_handle;
+
+	mmcss::set_thread_characteristics ("Pro Audio", &task_handle);
+	mmcss::set_thread_priority (task_handle, mmcss::AVRT_PRIORITY_NORMAL);
+#endif
+
+	DWORD tid = GetThreadId (GetCurrentThread ());
+	DEBUG_THREADS (string_compose ("Process Thread Master ID: %1\n", tid));
+
 	while (_run) {
 
 		if (_freewheeling != _freewheel) {
@@ -1511,6 +1544,11 @@ PortAudioBackend::main_process_thread ()
 	if (_run) {
 		engine.halted_callback("PortAudio I/O error.");
 	}
+
+#ifdef USE_MMCSS_THREAD_PRIORITIES
+	mmcss::revert_thread_characteristics (task_handle);
+#endif
+
 	return 0;
 }
 

libs/backends/portaudio/winmmemidi_input_device.cc

@@ -26,6 +26,8 @@
 #include "win_utils.h"
 #include "midi_util.h"
 
+#include "mmcss.h"
+
 #include "debug.h"
 
 static const uint32_t MIDI_BUFFER_SIZE = 32768;
@@ -175,6 +177,30 @@ WinMMEMidiInputDevice::winmm_input_callback(HMIDIIN handle,
 {
 	WinMMEMidiInputDevice* midi_input = (WinMMEMidiInputDevice*)instance;
 
+#ifdef USE_MMCSS_THREAD_PRIORITIES
+
+	static HANDLE input_thread = GetCurrentThread ();
+	static bool priority_boosted = false;
+
+	if (input_thread != GetCurrentThread ()) {
+		DWORD otid = GetThreadId (input_thread);
+		DWORD ntid = GetThreadId (GetCurrentThread ());
+		// There was a reference on the internet somewhere that it is possible
+		// for the callback to come from different threads(thread pool) this
+		// could be problematic but I haven't seen this behaviour yet
+		DEBUG_THREADS (string_compose (
+		    "WinMME input Thread ID Changed: was %1, now %2\n", otid, ntid));
+	}
+
+	HANDLE task_handle;
+
+	if (!priority_boosted) {
+		mmcss::set_thread_characteristics ("Pro Audio", &task_handle);
+		mmcss::set_thread_priority (task_handle, mmcss::AVRT_PRIORITY_HIGH);
+		priority_boosted = true;
+	}
+#endif
+
 	switch (msg) {
 	case MIM_OPEN:
 	case MIM_CLOSE:

libs/backends/portaudio/winmmemidi_output_device.cc

@@ -27,6 +27,7 @@
 #include "win_utils.h"
 #include "midi_util.h"
 
+#include "mmcss.h"
 #include "debug.h"
 
 // remove dup with input_device
@@ -349,6 +350,13 @@ WinMMEMidiOutputDevice::midi_output_thread ()
 
 	DEBUG_MIDI ("WinMMEMidiOut: MIDI output thread started\n");
 
+#ifdef USE_MMCSS_THREAD_PRIORITIES
+	HANDLE task_handle;
+
+	mmcss::set_thread_characteristics ("Pro Audio", &task_handle);
+	mmcss::set_thread_priority (task_handle, mmcss::AVRT_PRIORITY_HIGH);
+#endif
+
 	while (!m_thread_quit) {
 		if (!wait (m_queue_semaphore)) {
 			break;
@@ -471,6 +479,10 @@ WinMMEMidiOutputDevice::midi_output_thread ()
 #endif
 	}
 
+#ifdef USE_MMCSS_THREAD_PRIORITIES
+	mmcss::revert_thread_characteristics (task_handle);
+#endif
+
 	m_thread_running = false;
 }
 

libs/backends/portaudio/wscript

@@ -36,5 +36,6 @@ def build(bld):
     obj.uselib   = ['PORTAUDIO']
     obj.install_path  = os.path.join(bld.env['LIBDIR'], 'backends')
     obj.defines = ['PACKAGE="' + I18N_PACKAGE + '"',
-                   'ARDOURBACKEND_DLL_EXPORTS'
+                   'ARDOURBACKEND_DLL_EXPORTS',
+                   'USE_MMCSS_THREAD_PRIORITIES'
                   ]