Promise
Related Docs:
object Promise
| package util
Register a FutureEventListener to be invoked when the computation completes.
Register a FutureEventListener to be invoked when the computation completes. This method is typically used by Java programs because it avoids the use of small Function objects.
this should be used for side-effects
transformedBy for a Java friendly way to produce
a new Future from the result of a computation.
respond for a Scala API.
Become the other promise.
Become the other promise. become declares an equivalence
relation: this and other are the same.
By becoming other, its waitlists are now merged into this's,
and this becomes canonical. The same is true of interrupt
handlers: other's interrupt handler is overwritten with the
handlers installed for this.
Note: Using become and setInterruptHandler on the same
promise is not recommended. Consider the following, which
demonstrates unexpected behavior related to this usage.
val a, b = new Promise[Unit] a.setInterruptHandler { case _ => println("A") } b.become(a) b.setInterruptHandler { case _ => println("B") } a.raise(new Exception)
This prints "B", the action in the interrupt handler for b,
which is unexpected because we raised on a. In this case and
others, using com.twitter.util.Future.proxyTo may be more
appropriate.
Note that this must be unsatisfied at the time of the call,
and not race with any other setters. become is a form of
satisfying the promise.
This has the combined effect of compressing the other into
this, effectively providing a form of tail-call elimination
when used in recursion constructs. transform (and thus any
other combinator) use this to compress Futures, freeing them
from space leaks when used with recursive constructions.
Note: do not use become with cyclic graphs of futures: the
behavior of racing a.become(b) with b.become(a) is undefined
(where a and b may resolve as such transitively).
Sequentially compose this with f.
Returns a new Future that fails if it is not satisfied before the given time.
Returns a new Future that fails if it is not satisfied before the given time.
Note: On timeout, the underlying future is not interrupted.
Note: Interrupting a returned future would not prevent it from being satisfied with a given exception (when the time comes).
to run timeout on.
indicates when to stop waiting for the result to be available.
exception to throw.
Returns a new Future that fails if it is not satisfied before the given time.
Returns a new Future that fails if it is not satisfied before the given time.
Note: On timeout, the underlying future is not interrupted.
Returns a new Future that fails if it is not satisfied before the given time.
Returns a new Future that fails if it is not satisfied before the given time.
Same as the other by, but with an implicit timer. Sometimes this is more convenient.
Note: On timeout, the underlying future is not interrupted.
Should only be called when this Promise has already been fulfilled
or it is becoming another Future via become.
Should only be called when this Promise has already been fulfilled
or it is becoming another Future via become.
Delay the completion of this Future for at least howlong from now.
Delay the completion of this Future for at least howlong from now.
Note: Interrupting a returned future would not prevent it from becoming this future (when the time comes).
Invoked regardless of whether the computation completed successfully or unsuccessfully.
Invoked regardless of whether the computation completed successfully or unsuccessfully. Implemented in terms of respond so that subclasses control evaluation order. Returns a chained Future.
The returned Future will be satisfied when this,
the original future, is done.
the side-effect to apply when the computation completes.
If this, the original future, succeeds, run f on the result.
If this, the original future, succeeds, run f on the result.
The returned result is a Future that is satisfied when the original future
and the callback, f, are done.
If the original future fails, this one will also fail, without executing f
and preserving the failed computation of this.
Converts a Future[Future[B]] into a Future[B].
Converts a Future[Future[B]] into a Future[B].
Invoke the callback only if the Future returns successfully.
Forward interrupts to another future.
Forward interrupts to another future. If the other future is fulfilled, this is a no-op. Calling this multiple times is not recommended as the resulting state may not be as expected.
the Future to which interrupts are forwarded.
If this, the original future, results in an exceptional computation,
rescueException may convert the failure into a new result.
If this, the original future, results in an exceptional computation,
rescueException may convert the failure into a new result.
The returned result is a Future that is satisfied when the original
future and the callback, rescueException, are done.
This is the equivalent of map for failed computations.
Makes a derivative Future which will be satisfied with the result
of the parent.
Makes a derivative Future which will be satisfied with the result
of the parent. However, if it's interrupted, it will detach from
the parent Future, satisfy itself with the exception raised to
it, and won't propagate the interruption back to the parent
Future.
This is useful for when a Future is shared between many contexts,
where it may not be useful to discard the underlying computation
if just one context is no longer interested in the result. In
particular, this is different from Future.masked in that it will
prevent memory leaks if the parent Future will never be
satisfied, because closures that are attached to this derivative
Future will not be held onto by the killer Future.
Is the result of the Future available yet?
Checks whether a Unit-typed Future is done.
Checks whether a Unit-typed Future is done. By convention, futures of type Future[Unit] are used for signalling.
Returns this promise's interrupt if it is interrupted.
Is this Awaitable ready? In other words: would calling Awaitable.ready block?
Is this Awaitable ready? In other words: would calling Awaitable.ready block?
Joins this future with a given other future into a Future[(A, B)]
(future of a Tuple2).
Joins this future with a given other future into a Future[(A, B)]
(future of a Tuple2). If this or other future fails, the returned Future
is immediately satisfied by that failure.
Joins this future with a given other future and applies fn to its result.
Joins this future with a given other future and applies fn to its result.
If this or other future fails, the returned Future is immediately satisfied
by that failure.
Before (using join):
val ab = a.join(b).map { case (a, b) => Foo(a, b) }
After (using joinWith):
val ab = a.joinWith(b)(Foo.apply)
Returns the result of the computation as a Future[Try[A]].
Returns the result of the computation as a Future[Try[A]].
Lowers a Future[Try[T]] into a Future[T].
Lowers a Future[Try[T]] into a Future[T].
If this, the original future, succeeds, run f on the result.
If this, the original future, succeeds, run f on the result.
The returned result is a Future that is satisfied when the original future
and the callback, f, are done.
If the original future fails, this one will also fail, without executing f
and preserving the failed computation of this.
Returns an identical future except that it ignores interrupts which match a predicate
Returns an identical future except that it ignores interrupts which match a predicate
Returns an identical future that ignores all interrupts
Returns an identical future that ignores all interrupts
Invoke the function on the error, if the computation was unsuccessful.
Invoke the function on the error, if the computation was
unsuccessful. Returns a chained Future as in respond.
chained Future
if fn is a PartialFunction and the input is not defined for a given
Throwable, the resulting MatchError will propagate to the current
Monitor. This will happen if you use a construct such as
future.onFailure { case NonFatal(e) => ... } when the Throwable
is "fatal".
this should be used for side-effects.
handle and rescue to produce a new Future from the result of
the computation.
Invoke the function on the result, if the computation was successful.
A synonym for select: Choose the first Future to be satisfied.
Polls for an available result.
Send updates from this Future to the other.
Send updates from this Future to the other.
other must not yet be satisfied at the time of the call.
After this call, nobody else should satisfy other.
using proxyTo will mask interrupts to this future, and it's
the user's responsibility to set an interrupt handler on other
to raise on f. In some cases, using
com.twitter.util.Promise.become may be more appropriate.
Raise the given throwable as an interrupt.
Raise the given throwable as an interrupt. Interrupts are
one-shot and latest-interrupt wins. That is, the last interrupt
to have been raised is delivered exactly once to the Promise
responsible for making progress on the future (multiple such
promises may be involved in flatMap chains).
Raising an interrupt does not alter the externally observable state of the Future. They are used to signal to the producer of the future's value that the result is no longer desired (for whatever reason given in the passed Throwable).
Returns a new Future that fails if this Future does not return in time.
Returns a new Future that fails if this Future does not return in time.
Note: On timeout, the underlying future is interrupted.
Returns a new Future that fails if this Future does not return in time.
Returns a new Future that fails if this Future does not return in time.
Same as the other raiseWithin, but with an implicit timer. Sometimes this is more convenient.
Note: On timeout, the underlying future is interrupted.
Returns a new Future that fails if this Future does not return in time.
Returns a new Future that fails if this Future does not return in time.
Same as the other raiseWithin, but with an implicit timer. Sometimes this is more convenient.
Note: On timeout, the underlying future is interrupted.
Support for Await.ready.
If this, the original future, results in an exceptional computation,
rescueException may convert the failure into a new result.
If this, the original future, results in an exceptional computation,
rescueException may convert the failure into a new result.
The returned result is a Future that is satisfied when the original
future and the callback, rescueException, are done.
This is the equivalent of flatMap for failed computations.
Note: exceptions in responds are monitored.
Support for Await.result.
Choose the first Future to be satisfied.
Choose the first Future to be satisfied.
another Future
a new Future whose result is that of the first of this and other to return
Sets a Unit-typed future.
Sets a Unit-typed future. By convention, futures of type Future[Unit] are used for signalling.
Populate the Promise with the given exception.
Populate the Promise with the given exception.
ImmutableResult if the Promise is already populated
(Re)sets the interrupt handler.
(Re)sets the interrupt handler. There is only one active interrupt handler.
the new interrupt handler
Populate the Promise with the given result.
Populate the Promise with the given result.
ImmutableResult if the Promise is already populated
Convert a Twitter Future to a Java native Future.
Convert a Twitter Future to a Java native Future. This should match the semantics of a Java Future as closely as possible to avoid issues with the way another API might use them. See:
http://download.oracle.com/javase/6/docs/api/java/util/concurrent/Future.html#cancel(boolean)
An Offer for this future.
Transform the Future[A] into a Future[B] using the
FutureTransformer.
Transform the Future[A] into a Future[B] using the
FutureTransformer. The FutureTransformer handles both success
(Return) and failure (Throw) values by implementing map/flatMap
and handle/rescue. This method is typically used by Java
programs because it avoids the use of small Function objects.
The FutureTransformer must implement either flatMap
or map and may optionally implement handle. Failing to
implement a method will result in a run-time error (AbstractMethodError).
addEventListener for a Java friendly way to perform side-effects.
transform for a Scala API.
Convert this Future[A] to a Future[Unit] by discarding the result.
Convert this Future[A] to a Future[Unit] by discarding the result.
failed futures will remain as is.
Populate the Promise with the given Try.
Populate the Promise with the given Try.
Populate the Promise with the given Try. The Try can either be a
value or an exception. setValue and setException are generally
more readable methods to use.
true only if the result is updated, false if it was already set.
Invoking updateIfEmpty without checking the boolean result is almost
never the right approach. Doing so is generally unsafe unless race
conditions are acceptable.
Convert this Future[A] to a Future[Void] by discarding the result.
Convert this Future[A] to a Future[Void] by discarding the result.
failed futures will remain as is.
Returns a Future[Boolean] indicating whether two Futures are equivalent.
Returns a Future[Boolean] indicating whether two Futures are equivalent.
Note that
Future.exception(e).willEqual(Future.exception(e)) == Future.value(true).
Future.exception(e).willEqual(Future.exception(e)) == Future.value(true) }}}
Returns a new Future that fails if it is not satisfied in time.
Returns a new Future that fails if it is not satisfied in time.
Note: On timeout, the underlying future is not interrupted.
to run timeout on.
indicates how long you are willing to wait for the result to be available.
exception to throw.
Returns a new Future that fails if it is not satisfied in time.
Returns a new Future that fails if it is not satisfied in time.
Note: On timeout, the underlying future is not interrupted.
Returns a new Future that fails if it is not satisfied in time.
Returns a new Future that fails if it is not satisfied in time.
Same as the other within, but with an implicit timer. Sometimes this is more convenient.
Note: On timeout, the underlying future is not interrupted.
A writeable com.twitter.util.Future that supports merging. Callbacks (responders) of Promises are scheduled with com.twitter.concurrent.Scheduler.
Implementation details
A Promise is in one of six states:
Waiting,Interruptible,Interrupted,Transforming,DoneandLinkedwhereInterruptible,Interrupted, andTransformingare variants ofWaitingto deal with future interrupts. Promises are concurrency-safe, using lock-free operations throughout. Callback dispatch is scheduled with Scheduler.Waiters (i.e., continuations) are stored in a Promise.WaitQueue and executed in the LIFO order.
Promise.becomemerges two promises: they are declared equivalent.becomemerges the states of the two promises, and links one to the other. Thus promises support the analog to tail-call elimination: no space leak is incurred fromflatMapin the tail position since intermediate promises are merged into the root promise.