thread & lock

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait;

create new thread to do something

- (void)performSelectorInBackground:(SEL)aSelector withObject:(id)arg;

sleep

[NSThread sleepForTimeInterval:0.5]

lock:

ex:

NSLock *testLock = [[NSLock alloc] init];

[testLock lock];

[testLock unlock];

[testLock release];