Merge pull request #612 from TomHarte/HighPrecisionTimer

Sketches a high-precision timer class.

OSBindings/Mac/Clock Signal/High Precision Timer/CSHighPrecisionTimer.h

@@ -0,0 +1,27 @@
+//
+//  CSHighPrecisionTimer.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 07/03/2019.
+//  Copyright © 2019 Thomas Harte. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+
+/*!
+	Provides a high-precision timer; provide it with a block and an
+	interval, and it will ensure the block is performed as regularly
+	as the system will allow at the specified intervals.
+
+	The block will be executed on an arbitrary thread.
+*/
+@interface CSHighPrecisionTimer: NSObject
+
+/// Initialises a new instance of the high precision timer; the timer will begin
+/// ticking immediately.
+- (instancetype)initWithTask:(dispatch_block_t)task interval:(uint64_t)interval;
+
+/// Stops the timer.
+- (void)invalidate;
+
+@end

OSBindings/Mac/Clock Signal/High Precision Timer/CSHighPrecisionTimer.m

@@ -0,0 +1,37 @@
+//
+//  CSHighPrecisionTimer.m
+//  Clock Signal
+//
+//  Created by Thomas Harte on 07/03/2019.
+//  Copyright © 2019 Thomas Harte. All rights reserved.
+//
+
+#import "CSHighPrecisionTimer.h"
+
+@implementation CSHighPrecisionTimer {
+	dispatch_source_t _timer;
+	dispatch_queue_t _queue;
+}
+
+- (instancetype)initWithTask:(dispatch_block_t)task interval:(uint64_t)interval {
+	self = [super init];
+	if(self) {
+		_queue = dispatch_queue_create("High precision timer queue", DISPATCH_QUEUE_SERIAL);
+		_timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, _queue);
+		if(_timer) {
+			dispatch_source_set_timer(_timer, dispatch_walltime(NULL, 0), interval, 0);
+			dispatch_source_set_event_handler(_timer, task);
+
+			// TODO: dispatch_activate is preferred to dispatch_resume, but arrives only
+			// as of macOS 10.12. So switch if/when upping the OS requirements.
+			dispatch_resume(_timer);
+		}
+	}
+	return self;
+}
+
+- (void)invalidate {
+	dispatch_suspend(_timer);
+}
+
+@end