sealed abstract class CancelablePromise[A] extends Promise[A]
CancelablePromise is a scala.concurrent.Promise implementation that
allows listeners to unsubscribe from receiving future results.
It does so by:
- adding a low-level subscribe method, that allows for callbacks to be subscribed
- returning CancelableFuture in its future method implementation, allowing created future objects to unsubscribe (being the high-level subscribe that should be preferred for most usage)
Being able to unsubscribe listeners helps with avoiding memory leaks in case of listeners or futures that are being timed-out due to promises that take a long time to complete.
- Source
- CancelablePromise.scala
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Abstract Value Members
- abstract def future: CancelableFuture[A]
Returns a future that can unsubscribe from this promise's notifications via cancelation.
Returns a future that can unsubscribe from this promise's notifications via cancelation.
val promise = CancelablePromise[Int]() val future1 = promise.future val future2 = promise.future for (r <- future1) println(s"Future1 completed with: $$r") for (r <- future2) println(s"Future2 completed with: $$r") // Unsubscribing from the future notification, but only for future1 future1.cancel() // Completing our promise promise.success(99) //=> Future2 completed with: 99
Note that in the above example
future1becomes non-terminating after cancellation. By unsubscribing its listener, it will never complete.This helps with avoiding memory leaks for futures that are being timed-out due to promises that take a long time to complete.
- Definition Classes
- CancelablePromise → Promise
- abstract def isCompleted: Boolean
- Definition Classes
- Promise
- abstract def subscribe(cb: (Try[A]) => Unit): Cancelable
Low-level subscription method that registers a callback to be called when this promise will complete.
Low-level subscription method that registers a callback to be called when this promise will complete.
val promise = CancelablePromise[Int]() def subscribe(n: Int): Cancelable = promise.subscribe { case Success(str) => println(s"Callback ($$n) completed with: $$str") case Failure(e) => println(s"Callback ($$n) completed with: $$e") } val token1 = subscribe(1) val token2 = subscribe(2) // Unsubscribing from the future notification token1.cancel() // Completing our promise promise.success(99) //=> Callback (2) completed with: 99
UNSAFE PROTOCOL: the implementation does not protect against stack-overflow exceptions. There's no point in doing it for such low level methods, because this is useful as middleware and different implementations will have different ways to deal with stack safety (e.g.
monix.eval.Task).- cb
is a callback that will be called when the promise completes with a result, assuming that the returned cancelable token isn't canceled
- returns
a cancelable token that can be used to unsubscribe the given callback, in order to prevent memory leaks, at which point the callback will never be called (if it wasn't called already)
- abstract def tryComplete(result: Try[A]): Boolean
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- Promise
Concrete Value Members
- final def !=(arg0: Any): Boolean
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- final def ##(): Int
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- def complete(result: Try[A]): CancelablePromise.this.type
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- Promise
- def completeWith(other: Future[A]): CancelablePromise.this.type
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- Promise
- final def eq(arg0: AnyRef): Boolean
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- def equals(arg0: AnyRef): Boolean
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- def failure(cause: Throwable): CancelablePromise.this.type
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- def finalize(): Unit
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- final def notify(): Unit
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- final def notifyAll(): Unit
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- def success(value: A): CancelablePromise.this.type
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- Promise
- final def synchronized[T0](arg0: => T0): T0
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- def toString(): String
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- def tryFailure(cause: Throwable): Boolean
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- Promise
- def trySuccess(value: A): Boolean
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- final def wait(): Unit
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- final def wait(arg0: Long, arg1: Int): Unit
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Deprecated Value Members
- final def tryCompleteWith(other: Future[A]): CancelablePromise.this.type
- Definition Classes
- Promise
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- @deprecated
- Deprecated
(Since version 2.13.0) Since this method is semantically equivalent to
completeWith, use that instead.
This is the API documentation for the Monix library.
Package Overview
monix.execution exposes lower level primitives for dealing with asynchronous execution:
Atomictypes, as alternative tojava.util.concurrent.atomicmonix.catnap exposes pure abstractions built on top of the Cats-Effect type classes:
monix.eval is for dealing with evaluation of results, thus exposing Task and Coeval.
monix.reactive exposes the
Observablepattern:Observableimplementationsmonix.tail exposes Iterant for purely functional pull based streaming:
BatchandBatchCursor, the alternatives to Scala'sIterableandIteratorrespectively that we are using within Iterant's encodingYou can control evaluation with type you choose - be it Task, Coeval, cats.effect.IO or your own as long as you provide correct cats-effect or cats typeclass instance.