Made an attempt to consolidate serialisation and clock rate adherence, allowing a floating-point clock rate.

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -318,6 +318,7 @@
 		4BC9DF451D044FCA00F44158 /* ROMImages in Resources */ = {isa = PBXBuildFile; fileRef = 4BC9DF441D044FCA00F44158 /* ROMImages */; };
 		4BC9DF4F1D04691600F44158 /* 6560.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BC9DF4D1D04691600F44158 /* 6560.cpp */; };
 		4BCA98C31D065CA20062F44C /* 6522.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 4BCA98C11D065CA20062F44C /* 6522.cpp */; };
+		4BD5F1951D13528900631CD1 /* CSBestEffortUpdater.m in Sources */ = {isa = PBXBuildFile; fileRef = 4BD5F1941D13528900631CD1 /* CSBestEffortUpdater.m */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXContainerItemProxy section */
@@ -692,6 +693,8 @@
 		4BC9DF4E1D04691600F44158 /* 6560.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = 6560.hpp; sourceTree = "<group>"; };
 		4BCA98C11D065CA20062F44C /* 6522.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = 6522.cpp; sourceTree = "<group>"; };
 		4BCA98C21D065CA20062F44C /* 6522.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = 6522.hpp; sourceTree = "<group>"; };
+		4BD5F1931D13528900631CD1 /* CSBestEffortUpdater.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = CSBestEffortUpdater.h; path = Updater/CSBestEffortUpdater.h; sourceTree = "<group>"; };
+		4BD5F1941D13528900631CD1 /* CSBestEffortUpdater.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; name = CSBestEffortUpdater.m; path = Updater/CSBestEffortUpdater.m; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -1192,6 +1195,7 @@
 		4BB73EA01B587A5100552FC2 /* Clock Signal */ = {
 			isa = PBXGroup;
 			children = (
+				4BE5F85A1C3E1C2500C43F01 /* Resources */,
 				4BB73ECF1B587A6700552FC2 /* Clock Signal.entitlements */,
 				4B1414501B58848C00E04248 /* ClockSignal-Bridging-Header.h */,
 				4BB73EAA1B587A5100552FC2 /* MainMenu.xib */,
@@ -1201,7 +1205,7 @@
 				4B2A538F1D117D36003C6002 /* Audio */,
 				4B55CE551C3B7D360093A61B /* Documents */,
 				4B2A53921D117D36003C6002 /* Machine */,
-				4BE5F85A1C3E1C2500C43F01 /* Resources */,
+				4BD5F1961D1352A000631CD1 /* Updater */,
 				4B55CE5A1C3B7D6F0093A61B /* Views */,
 			);
 			path = "Clock Signal";
@@ -1311,6 +1315,15 @@
 			path = 6560;
 			sourceTree = "<group>";
 		};
+		4BD5F1961D1352A000631CD1 /* Updater */ = {
+			isa = PBXGroup;
+			children = (
+				4BD5F1931D13528900631CD1 /* CSBestEffortUpdater.h */,
+				4BD5F1941D13528900631CD1 /* CSBestEffortUpdater.m */,
+			);
+			name = Updater;
+			sourceTree = "<group>";
+		};
 		4BE5F85A1C3E1C2500C43F01 /* Resources */ = {
 			isa = PBXGroup;
 			children = (
@@ -1733,6 +1746,7 @@
 				4BC3B74F1CD194CC00F86E85 /* Shader.cpp in Sources */,
 				4B55CE581C3B7D360093A61B /* Atari2600Document.swift in Sources */,
 				4BBB14311CD2CECE00BDB55C /* IntermediateShader.cpp in Sources */,
+				4BD5F1951D13528900631CD1 /* CSBestEffortUpdater.m in Sources */,
 				4B73C71A1D036BD90074D992 /* Vic20Document.swift in Sources */,
 				4BBF99181C8FBA6F0075DAFB /* TextureTarget.cpp in Sources */,
 				4BC76E691C98E31700E6EF73 /* FIRFilter.cpp in Sources */,

OSBindings/Mac/Clock Signal/Updater/CSBestEffortUpdater.h

@@ -0,0 +1,28 @@
+//
+//  CSBestEffortUpdater.h
+//  Clock Signal
+//
+//  Created by Thomas Harte on 16/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+@import CoreVideo;
+
+@class CSBestEffortUpdater;
+
+@protocol CSBestEffortUpdaterDelegate <NSObject>
+
+- (void)bestEffortUpdater:(CSBestEffortUpdater *)bestEffortUpdater runForCycles:(NSUInteger)cycles didSkipPreviousUpdate:(BOOL)didSkipPreviousUpdate;
+
+@end
+
+
+@interface CSBestEffortUpdater : NSObject
+
+@property (nonatomic, assign) double clockRate;
+@property (nonatomic, weak) id<CSBestEffortUpdaterDelegate> delegate;
+
+- (void)update;
+
+@end

OSBindings/Mac/Clock Signal/Updater/CSBestEffortUpdater.m

@@ -0,0 +1,65 @@
+//
+//  CSBestEffortUpdater.m
+//  Clock Signal
+//
+//  Created by Thomas Harte on 16/06/2016.
+//  Copyright © 2016 Thomas Harte. All rights reserved.
+//
+
+#import "CSBestEffortUpdater.h"
+
+@implementation CSBestEffortUpdater
+{
+	// these are inherently handled only by thread-safe constructions
+	uint32_t _updateIsOngoing;
+	dispatch_queue_t _serialDispatchQueue;
+
+	// these are permitted for modification on _serialDispatchQueue only
+	NSTimeInterval _previousTimeInterval;
+	NSTimeInterval _cyclesError;
+	BOOL _hasSkipped;
+}
+
+- (instancetype)init
+{
+	if(self = [super init])
+	{
+		_serialDispatchQueue = dispatch_queue_create("Best Effort Updater", DISPATCH_QUEUE_SERIAL);
+	}
+	return self;
+}
+
+- (void)update
+{
+	const uint32_t processingMask = 0x01;
+
+	// Always post an -openGLView:didUpdateToTime: if a previous one isn't still ongoing. This is the hook upon which the substantial processing occurs.
+	if(!OSAtomicTestAndSet(processingMask, &_updateIsOngoing))
+	{
+		dispatch_async(_serialDispatchQueue, ^{
+			NSTimeInterval timeInterval = [NSDate timeIntervalSinceReferenceDate];
+			if(_previousTimeInterval > DBL_EPSILON)
+			{
+				NSTimeInterval timeToRunFor = timeInterval - _previousTimeInterval;
+				double cyclesToRunFor = timeToRunFor * self.clockRate + _cyclesError;
+
+				_cyclesError = fmod(cyclesToRunFor, 1.0);
+				NSUInteger integerCyclesToRunFor = (NSUInteger)cyclesToRunFor;
+
+				[self.delegate bestEffortUpdater:self runForCycles:integerCyclesToRunFor didSkipPreviousUpdate:_hasSkipped];
+
+				_previousTimeInterval = timeInterval;
+			}
+			_hasSkipped = NO;
+			OSAtomicTestAndClear(processingMask, &_updateIsOngoing);
+		});
+	}
+	else
+	{
+		dispatch_async(_serialDispatchQueue, ^{
+			_hasSkipped = YES;
+		});
+	}
+}
+
+@end