Thread-safe singleton pattern using dispatch_once

gistfile1.m

@interface Something : NSObject

+(Something *)somethingSingleton;

@end


@implementation Something

+(Something *)somethingSingleton {
     static Something *something = nil;
     static dispatch_once_t onceToken;
     dispatch_once(&onceToken, ^{
          something = [[self alloc] init];
     });
     return something;
}

@end

More information: http://objcolumnist.com/2011/07/06/creating-singletons-using-dispatch_once/