From 6bd0bf1dc531b0ba09a32fa521d1ba03bd845dda Mon Sep 17 00:00:00 2001
From: Christopher Snowhill <kode54@gmail.com>
Date: Thu, 9 Jun 2022 18:53:58 -0700
Subject: [PATCH] [Audio Threads] Set realtime priority on old OS

Set baseline real-time priority for audio threads even on old macOS,
since that API is available there. Only set it once, and do not attempt
again if it fails, only once per thread.

Signed-off-by: Christopher Snowhill <kode54@gmail.com>
---
 Audio/Chain/Node.h |  1 +
 Audio/Chain/Node.m | 25 +++++++++++++++++--------
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/Audio/Chain/Node.h b/Audio/Chain/Node.h
index 723801db0..c0bdadacf 100644
--- a/Audio/Chain/Node.h
+++ b/Audio/Chain/Node.h
@@ -29,6 +29,7 @@
 	BOOL shouldContinue;
 	BOOL endOfStream; // All data is now in buffer
 	BOOL initialBufferFilled;
+	BOOL isRealtime, isRealtimeError; // If was successfully set realtime, or if error
 
 	AudioStreamBasicDescription nodeFormat;
 	uint32_t nodeChannelConfig;
diff --git a/Audio/Chain/Node.m b/Audio/Chain/Node.m
index d02953569..7e96ec344 100644
--- a/Audio/Chain/Node.m
+++ b/Audio/Chain/Node.m
@@ -31,7 +31,7 @@ static const os_clockid_t clockId = OS_CLOCK_MACH_ABSOLUTE_TIME;
 
 // Enables time-contraint policy and priority suitable for low-latency,
 // glitch-resistant audio.
-void SetPriorityRealtimeAudio(mach_port_t mach_thread_id) {
+BOOL SetPriorityRealtimeAudio(mach_port_t mach_thread_id) {
 	kern_return_t result;
 
 	// Increase thread priority to real-time.
@@ -50,7 +50,7 @@ void SetPriorityRealtimeAudio(mach_port_t mach_thread_id) {
 	                           THREAD_EXTENDED_POLICY_COUNT);
 	if(result != KERN_SUCCESS) {
 		DLog(@"thread_policy_set extended policy failure: %d", result);
-		return;
+		return NO;
 	}
 
 	// Set to relatively high priority.
@@ -62,7 +62,7 @@ void SetPriorityRealtimeAudio(mach_port_t mach_thread_id) {
 	                           THREAD_PRECEDENCE_POLICY_COUNT);
 	if(result != KERN_SUCCESS) {
 		DLog(@"thread_policy_set precedence policy failure: %d", result);
-		return;
+		return NO;
 	}
 
 	// Most important, set real-time constraints.
@@ -106,7 +106,10 @@ void SetPriorityRealtimeAudio(mach_port_t mach_thread_id) {
 	                           THREAD_TIME_CONSTRAINT_POLICY_COUNT);
 	if(result != KERN_SUCCESS) {
 		DLog(@"thread_policy_set constraint policy failure: %d", result);
+		return NO;
 	}
+	
+	return YES;
 }
 
 @implementation Node
@@ -213,10 +216,11 @@ void SetPriorityRealtimeAudio(mach_port_t mach_thread_id) {
 		if(!wg) {
 			if(!workgroup) {
 				workgroup = AudioWorkIntervalCreate([[NSString stringWithFormat:@"%@ Work Interval", [self className]] UTF8String], clockId, &attr);
-				SetPriorityRealtimeAudio(pthread_mach_thread_np(pthread_self()));
+				isRealtimeError = !SetPriorityRealtimeAudio(pthread_mach_thread_np(pthread_self()));
+				isRealtime = !isRealtimeError;
 			}
 			wg = workgroup;
-			if(wg) {
+			if(wg && !isRealtimeError) {
 				int result = os_workgroup_join(wg, &wgToken);
 				if(result == 0) return;
 				if(result == EALREADY) {
@@ -226,12 +230,17 @@ void SetPriorityRealtimeAudio(mach_port_t mach_thread_id) {
 				}
 			}
 		}
+	} else {
+		if(!isRealtime && !isRealtimeError) {
+			isRealtimeError = SetPriorityRealtimeAudio(pthread_mach_thread_np(pthread_self()));
+			isRealtime = !isRealtimeError;
+		}
 	}
 }
 
 - (void)leaveWorkgroup {
 	if(@available(macOS 11, *)) {
-		if(wg) {
+		if(wg && !isRealtimeError) {
 			os_workgroup_leave(wg, &wgToken);
 			wg = nil;
 		}
@@ -240,7 +249,7 @@ void SetPriorityRealtimeAudio(mach_port_t mach_thread_id) {
 
 - (void)startWorkslice {
 	if(@available(macOS 11, *)) {
-		if(wg) {
+		if(wg && !isRealtimeError) {
 			const uint64_t currentTime = mach_absolute_time();
 			const uint64_t deadline = currentTime + intervalMachLength;
 			int result = os_workgroup_interval_start(wg, currentTime, deadline, nil);
@@ -253,7 +262,7 @@ void SetPriorityRealtimeAudio(mach_port_t mach_thread_id) {
 
 - (void)endWorkslice {
 	if(@available(macOS 11, *)) {
-		if(wg) {
+		if(wg && !isRealtimeError) {
 			int result = os_workgroup_interval_finish(wg, nil);
 			if(result != 0) {
 				DLog(@"Deadline end error = %d", result);