RAC_Scheduler.m

/*
RACImmediateScheduler
Private scheduler used in ReactiveCocoa internally and and supports only synchronous scheduling. It simply execute the block right away. Delayed scheduling works by blocking current thread with -[NSThread sleepUntilDate:]. Obviously, there's no way to control cancellation of such scheduling, so disposables retuned by this scheduler will do nothing (in fact, scheduling methods of this scheduler return nil).

RACQueueScheduler
This scheduler uses GCD queues for scheduling blocks. It's functionality is pretty straightforward if you know what GCD does. It's actually a very thin layer over dispatching blocks in GCD queues.

RACSubscriptionScheduler
Another private scheduler used by framework internally. It forwards scheduling to current thread's scheduler (scheduler can be associated with the thread) if it exists or to default background queue scheduler.
*/

///methods look like this
- (RACDisposable *)schedule:(void (^)(void))block;

- (RACDisposable *)after:(NSDate *)date schedule:(void (^)(void))block;

- (RACDisposable *)afterDelay:(NSTimeInterval)delay schedule:(void (^)(void))block;

- (RACDisposable *)after:(NSDate *)date repeatingEvery:(NSTimeInterval)interval withLeeway:(NSTimeInterval)leeway schedule:(void (^)(void))block;


//implementation

RACDisposable *disposable = [[RACScheduler mainThreadScheduler] afterDelay:5.0 schedule:^{
    //do something
}];

//if you changed your mind
[disposable dispose]; // block scheduling cancelled, it won't be executed.