Thread safe instantiation of a singleton

Question

Which one synchronization method to use to ensure a singleton remains a singleton?

+(Foo*)sharedInstance
{
   @synchronized(self)
   {
      if (nil == _shar         


        

Answer 1

The fastest thread safe way to do this is with Grand Central Dispatch ( libdispatch ) and dispatch_once()

+(MyClass *)sharedInstance
{   
    static MyClass *sharedInstance = nil;
    static dispatch_once_t pred;

    dispatch_once(&pred, ^{
        sharedInstance = [[MyClass alloc] init];
    });

    return sharedInstance;
}