Objective-C SingletonClass in GCD

MySingletonClass.m

#import "MySingletonClass.h"

static MySingletonClass *singleton = nil;

@implementation MySingletonClass

+ (MySingletonClass *)defaultSingleton{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        singleton = [[MySingletonClass alloc] init];
    });
    return singleton;
}