From 38c5e9de6df4bc4ca52c53e31759bcdfe9fccd3d Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Fri, 4 Aug 2017 03:12:29 +0200
Subject: CoreAudio: Set MachThread RT Priority

---
 libs/backends/coreaudio/coreaudio_backend.cc | 48 +++++++++++++++++++++++++---
 libs/backends/coreaudio/coreaudio_backend.h  |  1 +
 2 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/libs/backends/coreaudio/coreaudio_backend.cc b/libs/backends/coreaudio/coreaudio_backend.cc
index 7137b1d65a..b488091632 100644
--- a/libs/backends/coreaudio/coreaudio_backend.cc
+++ b/libs/backends/coreaudio/coreaudio_backend.cc
@@ -21,6 +21,9 @@
 #include <sys/mman.h>
 #include <sys/time.h>
 
+#include <mach/thread_policy.h>
+#include <mach/thread_act.h>
+
 #include <glibmm.h>
 
 #include "coreaudio_backend.h"
@@ -327,6 +330,12 @@ CoreAudioBackend::set_buffer_size (uint32_t bs)
 	}
 	_samples_per_period = bs;
 	_pcmio->set_samples_per_period(bs);
+	if (_run) {
+		coreaudio_set_realtime_policy (_main_thread);
+	}
+	for (std::vector<pthread_t>::const_iterator i = _threads.begin (); i != _threads.end (); ++i) {
+		coreaudio_set_realtime_policy (*i);
+	}
 	engine.buffer_size_change (bs);
 	return 0;
 }
@@ -603,11 +612,6 @@ CoreAudioBackend::_start (bool for_latency_measurement)
 		PBD::info << _("CoreAudioBackend: adjusted input channel count to match device.") << endmsg;
 	}
 
-	if (_pcmio->samples_per_period() != _samples_per_period) {
-		_samples_per_period = _pcmio->samples_per_period();
-		PBD::warning << _("CoreAudioBackend: samples per period does not match.") << endmsg;
-	}
-
 	if (_pcmio->sample_rate() != _samplerate) {
 		_samplerate = _pcmio->sample_rate();
 		engine.sample_rate_change (_samplerate);
@@ -816,6 +820,34 @@ CoreAudioBackend::coreaudio_process_thread (void *arg)
 	return 0;
 }
 
+bool
+CoreAudioBackend::coreaudio_set_realtime_policy (pthread_t thread_id) const
+{
+	thread_time_constraint_policy_data_t policy;
+#ifndef NDEBUG
+	mach_msg_type_number_t msgt = 4;
+	boolean_t dflt = false;
+	kern_return_t rv = thread_policy_get (pthread_mach_thread_np (_main_thread),
+			THREAD_TIME_CONSTRAINT_POLICY, (thread_policy_t) &policy,
+			&msgt, &dflt);
+	printf ("Coreaudio Main Thread(%p) %d %d %d %d DFLT %d OK: %d\n", _main_thread, policy.period, policy.computation, policy.constraint, policy.preemptible, dflt, rv == KERN_SUCCESS);
+#endif
+
+	double period_ns = 1e9 * _samples_per_period / _samplerate;
+	policy.period = AudioConvertNanosToHostTime (period_ns);
+	policy.computation = AudioConvertNanosToHostTime (period_ns * .9);
+	policy.constraint = AudioConvertNanosToHostTime (period_ns * .95);
+	policy.preemptible = true;
+	kern_return_t res = thread_policy_set (pthread_mach_thread_np (thread_id),
+			THREAD_TIME_CONSTRAINT_POLICY, (thread_policy_t) &policy,
+			THREAD_TIME_CONSTRAINT_POLICY_COUNT);
+
+#ifndef NDEBUG
+	printf ("Coreaudio Proc Thread(%p) %d %d %d %d OK: %d\n", thread_id, policy.period, policy.computation, policy.constraint, policy.preemptible, res == KERN_SUCCESS);
+#endif
+	return res != KERN_SUCCESS;
+}
+
 int
 CoreAudioBackend::create_process_thread (boost::function<void()> func)
 {
@@ -838,6 +870,10 @@ CoreAudioBackend::create_process_thread (boost::function<void()> func)
 		pthread_attr_destroy (&attr);
 	}
 
+	if (coreaudio_set_realtime_policy (thread_id)) {
+		PBD::warning << _("AudioEngine: process thread failed to set mach realtime policy.") << endmsg;
+	}
+
 	_threads.push_back (thread_id);
 	return 0;
 }
@@ -1673,6 +1709,7 @@ CoreAudioBackend::freewheel_thread ()
 			AudioEngine::thread_init_callback (this);
 			_midiio->set_enabled(false);
 			reset_midi_parsers ();
+			coreaudio_set_realtime_policy (_main_thread);
 		}
 
 		// process port updates first in every cycle.
@@ -1738,6 +1775,7 @@ CoreAudioBackend::process_callback (const uint32_t n_samples, const uint64_t hos
 		_reinit_thread_callback = false;
 		_main_thread = pthread_self();
 		AudioEngine::thread_init_callback (this);
+		coreaudio_set_realtime_policy (_main_thread);
 	}
 
 	if (pthread_mutex_trylock (&_process_callback_mutex)) {
diff --git a/libs/backends/coreaudio/coreaudio_backend.h b/libs/backends/coreaudio/coreaudio_backend.h
index 5211839a9c..03edf4f6ed 100644
--- a/libs/backends/coreaudio/coreaudio_backend.h
+++ b/libs/backends/coreaudio/coreaudio_backend.h
@@ -447,6 +447,7 @@ class CoreAudioBackend : public AudioBackend {
 
 	/* process threads */
 	static void* coreaudio_process_thread (void *);
+	bool coreaudio_set_realtime_policy (pthread_t) const;
 	std::vector<pthread_t> _threads;
 
 	struct ThreadData {
-- 
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