What should my Objective-C singleton look like? [closed]

Answer 1

Shouln't this be threadsafe and avoid the expensive locking after the first call?

+ (MySingleton*)sharedInstance
{
    if (sharedInstance == nil) {
        @synchronized(self) {
            if (sharedInstance == nil) {
                sharedInstance = [[MySingleton alloc] init];
            }
        }
    }
    return (MySingleton *)sharedInstance;
}