ConcurrentAccessors.m

#import <Foundation/Foundation.h>
#include <pthread.h>

@interface Getty : NSObject {
	@protected
	id _object;
}
@property (nonatomic, strong, readonly) id object;
@end

@implementation Getty
- (instancetype)init {
	self = [super init];
	if (self) {
		_object = [NSObject new];
	}
	return self;
}

- (id)object {
	return _object;
}
@end

@interface SynchronisedGetty : Getty
@end

@implementation SynchronisedGetty {
}

- (id)object {
	id object = nil;
	@synchronized (self) {
		object = _object;
	}
	return object;
}
@end

@interface RWLockGetty : Getty
@end

@implementation RWLockGetty {
	pthread_rwlock_t _theLock;	
}
- (instancetype)init {
	self = [super init];
	if (self) {
		pthread_rwlock_init(&_theLock, NULL);
	}
	return self;
}

- (void)dealloc {
	pthread_rwlock_destroy(&_theLock);
}

- (id)object {
	pthread_rwlock_rdlock(&_theLock);
	return _object;
	pthread_rwlock_unlock(&_theLock);	
}
@end

@interface DispatchGetty : Getty
@end

@implementation DispatchGetty {
	dispatch_queue_t _queue;
}
- (instancetype)init {
	self = [super init];
	if (self) {
		_queue = dispatch_queue_create("array q", DISPATCH_QUEUE_SERIAL);
	}
	return self;
}

- (void)dealloc {
}

- (id)object {
	__block id object = nil;
	dispatch_sync(_queue, ^(void) {
		object = _object;
	});
	return object;
}
@end

CFAbsoluteTime timeRun(Getty *getty) {
	CFAbsoluteTime startTime = CFAbsoluteTimeGetCurrent();

	for (NSUInteger i=0; i<1000000; i++) {
		(void)[getty object];
	}

	CFAbsoluteTime endTime = CFAbsoluteTimeGetCurrent();
	return 	endTime-startTime;
}

CFAbsoluteTime timeParallelRun(Getty *getty) {
	CFAbsoluteTime startTime = CFAbsoluteTimeGetCurrent();

	dispatch_queue_t queue = dispatch_queue_create("parallel queue", DISPATCH_QUEUE_CONCURRENT);
	dispatch_group_t group = dispatch_group_create();

	for (NSUInteger i=0; i<1000000; i++) {
		dispatch_group_async(group, queue, ^{
			(void)[getty object];			
		});
	}
	
	dispatch_group_wait(group, DISPATCH_TIME_FOREVER);

	CFAbsoluteTime endTime = CFAbsoluteTimeGetCurrent();
	return 	endTime-startTime;
}

int main(int argc, const char * argv[])
{
	@autoreleasepool {
		CFAbsoluteTime baseTime = timeRun([Getty new]);
		CFAbsoluteTime rwlockTime = timeRun([RWLockGetty new]) - baseTime;
		CFAbsoluteTime dispatchTime = timeRun([DispatchGetty new]) - baseTime;
		CFAbsoluteTime syncTime = timeRun([SynchronisedGetty new]) - baseTime;
		
		NSLog(@"Serial:");
		NSLog(@"base    : %0.8f", baseTime);
		NSLog(@"rwlock  :+%0.8f (%0.4f%%)", rwlockTime, rwlockTime/baseTime*100.0);
		NSLog(@"dispatch:+%0.8f (%0.4f%%)", dispatchTime, dispatchTime/baseTime*100.0);				
		NSLog(@"@sync   :+%0.8f (%0.4f%%)", syncTime, syncTime/baseTime*100.0);				

		NSLog(@"Parallel:");
		CFAbsoluteTime baseTimeP = timeParallelRun([Getty new]);
		CFAbsoluteTime rwlockTimeP = timeParallelRun([RWLockGetty new]) - baseTimeP;
		CFAbsoluteTime dispatchTimeP = timeParallelRun([DispatchGetty new]) - baseTimeP;
		CFAbsoluteTime syncTimeP = timeParallelRun([SynchronisedGetty new]) - baseTimeP;
		
		NSLog(@"base    : %0.8f", baseTimeP);
		NSLog(@"rwlock  :+%0.8f (%0.4f%%)", rwlockTimeP, rwlockTimeP/baseTimeP*100.0);
		NSLog(@"dispatch:+%0.8f (%0.4f%%)", dispatchTimeP, dispatchTimeP/baseTimeP*100.0);	
		NSLog(@"@sync   :+%0.8f (%0.4f%%)", syncTimeP, syncTimeP/baseTimeP*100.0);				
					
	}
    return 0;
}

Serial:
base    : 0.01133299
rwlock  :+0.00428009 (37.7667%)
dispatch:+0.06589592 (581.4522%)
@sync   :+0.09532309 (841.1116%)
Parallel:
base    : 0.55236197
rwlock  :+0.01732695 (3.1369%)
dispatch:+3.11447012 (563.8459%)
@sync   :+4.23668313 (767.0121%)