Shared instances for all

Log.txt

2011-05-11 03:25:07.462 GlobalSingletonSupportTest[63618:1803] irSharedInstance instance NSObject 15f980, 181511 ns
2011-05-11 03:25:07.465 GlobalSingletonSupportTest[63618:5303] irSharedInstance instance NSObject 15f980, 614 ns
2011-05-11 03:25:07.465 GlobalSingletonSupportTest[63618:5403] irSharedInstance instance NSObject 15f980, 584 ns
2011-05-11 03:25:07.464 GlobalSingletonSupportTest[63618:a0f] irSharedInstance instance NSObject 15f980, 1546 ns
2011-05-11 03:25:07.466 GlobalSingletonSupportTest[63618:a0f] irSharedInstance instance NSObject 15f980, 1545 ns

NSObject+IRSharedInstance.h

//
//  NSObject+IRSharedInstance.h
//  GlobalSingletonSupportTest
//
//  Created by Evadne Wu on 5/11/11.
//  Copyright 2011 Iridia Productions. All rights reserved.
//

#import <objc/runtime.h>
#import <Foundation/Foundation.h>

extern NSString * const kIRSharedInstancePredicate;
extern NSString * const kIRSharedInstanceObject;

@interface NSObject (IRSharedInstance)

+ (id) irSharedInstance;

@end

NSObject+IRSharedInstance.m

//
//  NSObject+IRSharedInstance.m
//  GlobalSingletonSupportTest
//
//  Created by Evadne Wu on 5/11/11.
//  Copyright 2011 Iridia Productions. All rights reserved.
//

#import "NSObject+IRSharedInstance.h"

#include <mach/mach.h>
#include <mach/mach_time.h>
#include <unistd.h>

NSString * const kIRSharedInstancePredicate = @"IRSharedInstance_Predicate";
NSString * const kIRSharedInstanceObject = @"IRSharedInstance_Object";

@implementation NSObject (IRSharedInstance)

+ (id) irSharedInstance {

	//	uint64_t begin = mach_absolute_time();

	__block dispatch_once_t predicate = 0;
	__block id returned = objc_getAssociatedObject(self, kIRSharedInstanceObject); 
	
	if (!returned) @synchronized(self) {
		
		returned = objc_getAssociatedObject(self, kIRSharedInstanceObject); 
		
		if (!returned) {
		
			[(NSValue *)objc_getAssociatedObject(self, kIRSharedInstancePredicate) getValue:&predicate];
			
			dispatch_once(&predicate, ^ {
			
				returned = [[self alloc] init];
				objc_setAssociatedObject(self, kIRSharedInstanceObject, returned, OBJC_ASSOCIATION_ASSIGN);
				objc_setAssociatedObject(self, kIRSharedInstancePredicate, [NSValue valueWithBytes:&predicate objCType:@encode(__typeof__(predicate))], OBJC_ASSOCIATION_RETAIN);
			
			});
		
		}
					
	}
	
	//	uint64_t end = mach_absolute_time();
	//	NSLog(@"irSharedInstance instance %@ %x, %i ns", NSStringFromClass([returned class]), returned, (end - begin));

	return returned;

}

@end

Note: http://developer.apple.com/library/mac/#qa/qa1398/_index.html — not really nanoseconds