Running code on a specified queue

gistfile1.txt

// queue name
static const char* s_myqueue = "myqueue";

// return the specific queue
dispatch_queue_t my_queue() {
    static dispatch_queue_t _q;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _q = dispatch_queue_create(s_myqueue, 0);
        // sets the key/value data for the specified dispatch queue
        dispatch_queue_set_specific(_q,                 // queue 
                                    s_myqueue,          // context key (only compared as pointer)
                                    (void*) s_myqueue,  // context data
                                    NULL);              // destructor for the context data
    });
    return _q;
}

static int foo()
{
    // returns the value for the key associated with the current dispatch queue
    if (dispatch_get_specific(s_myqueue) == s_myqueue) {
        // we are running on the queue created at my_queue() so just do the work
        return do_foo();
    }
    // dispath sync to the my_queue
    __block int result;
    dispatch_sync(my_queue(), ^{
        result = do_foo();
    });
    return result;
}