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

Answer 1

My way is simple like this:

static id instanceOfXXX = nil;

+ (id) sharedXXX
{
    static volatile BOOL initialized = NO;

    if (!initialized)
    {
        @synchronized([XXX class])
        {
            if (!initialized)
            {
                instanceOfXXX = [[XXX alloc] init];
                initialized = YES;
            }
        }
    }

    return instanceOfXXX;
}

If the singleton is initialized already, the LOCK block will not be entered. The second check if(!initialized) is to make sure it is not initialized yet when the current thread acquires the LOCK.