Promise
Related Docs:
object Promise
| package async
Like get but returns an F[Unit] that can be used to cancel the subscription.
If this Promise is empty, *synchronously* sets the current value to a, and notifies
any and all readers currently blocked on a get.
If this Promise is empty, *synchronously* sets the current value to a, and notifies
any and all readers currently blocked on a get.
Note that the returned action completes after the reference has been successfully set:
use async.fork(r.complete) if you want asynchronous behaviour.
If this Promise has already been completed, the returned action immediately fails with a Promise.AlreadyCompletedException.
In the uncommon scenario where this behaviour is problematic, you can handle failure explicitly
using attempt or any other ApplicativeError/MonadError combinator on the returned action.
Satisfies:
Promise.empty[F, A].flatMap(r => r.complete(a) *> r.get) == a.pure[F]
Obtains the value of the Promise, or waits until it has been completed.
Like get but if the Promise has not been completed when the timeout is reached, a None
is returned.
A purely functional synchronisation primitive.
When created, a
Promiseis empty. It can then be completed exactly once, and never be made empty again.geton an emptyPromisewill block until thePromiseis completed.geton a completedPromisewill always immediately return its content.complete(a)on an emptyPromisewill set it toa, and notify any and all readers currently blocked on a call toget.complete(a)on aPromisethat's already been completed will not modify its content, and result in a failedF.Albeit simple,
Promisecan be used in conjunction with Ref to build complex concurrent behaviour and data structures like queues and semaphores.Finally, the blocking mentioned above is semantic only, no actual threads are blocked by the implementation.