Trait actix::prelude::Future1.36.0[][src]

#[must_use = "futures do nothing unless you `.await` or poll them"]
#[lang = "future_trait"]pub trait Future {
    type Output;
#[lang = "poll"]    pub fn poll(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>
    ) -> Poll<Self::Output>; }

A future represents an asynchronous computation.

A future is a value that may not have finished computing yet. This kind of “asynchronous value” makes it possible for a thread to continue doing useful work while it waits for the value to become available.

The poll method

The core method of future, poll, attempts to resolve the future into a final value. This method does not block if the value is not ready. Instead, the current task is scheduled to be woken up when it’s possible to make further progress by polling again. The context passed to the poll method can provide a Waker, which is a handle for waking up the current task.

When using a future, you generally won’t call poll directly, but instead .await the value.

Associated Types

type Output[src]

The type of value produced on completion.

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Required methods

#[lang = "poll"]pub fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>[src]

Attempt to resolve the future to a final value, registering the current task for wakeup if the value is not yet available.

Return value

This function returns:

Once a future has finished, clients should not poll it again.

When a future is not ready yet, poll returns Poll::Pending and stores a clone of the Waker copied from the current Context. This Waker is then woken once the future can make progress. For example, a future waiting for a socket to become readable would call .clone() on the Waker and store it. When a signal arrives elsewhere indicating that the socket is readable, Waker::wake is called and the socket future’s task is awoken. Once a task has been woken up, it should attempt to poll the future again, which may or may not produce a final value.

Note that on multiple calls to poll, only the Waker from the Context passed to the most recent call should be scheduled to receive a wakeup.

Runtime characteristics

Futures alone are inert; they must be actively polled to make progress, meaning that each time the current task is woken up, it should actively re-poll pending futures that it still has an interest in.

The poll function is not called repeatedly in a tight loop – instead, it should only be called when the future indicates that it is ready to make progress (by calling wake()). If you’re familiar with the poll(2) or select(2) syscalls on Unix it’s worth noting that futures typically do not suffer the same problems of “all wakeups must poll all events”; they are more like epoll(4).

An implementation of poll should strive to return quickly, and should not block. Returning quickly prevents unnecessarily clogging up threads or event loops. If it is known ahead of time that a call to poll may end up taking awhile, the work should be offloaded to a thread pool (or something similar) to ensure that poll can return quickly.

Panics

Once a future has completed (returned Ready from poll), calling its poll method again may panic, block forever, or cause other kinds of problems; the Future trait places no requirements on the effects of such a call. However, as the poll method is not marked unsafe, Rust’s usual rules apply: calls must never cause undefined behavior (memory corruption, incorrect use of unsafe functions, or the like), regardless of the future’s state.

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Trait Implementations

impl<'a, T> UnsafeFutureObj<'a, T> for &'a mut (dyn Future<Output = T> + 'a + Unpin)[src]

Implementations on Foreign Types

impl<F> Future for AssertUnwindSafe<F> where
    F: Future
[src]

type Output = <F as Future>::Output

impl<T> Future for Pending<T>[src]

type Output = T

impl<'_, F> Future for &'_ mut F where
    F: Unpin + Future + ?Sized
[src]

type Output = <F as Future>::Output

impl<P> Future for Pin<P> where
    P: Unpin + DerefMut,
    <P as Deref>::Target: Future
[src]

type Output = <<P as Deref>::Target as Future>::Output

impl<T> Future for Ready<T>[src]

type Output = T

impl<T, F> Future for PollFn<F> where
    F: FnMut(&mut Context<'_>) -> Poll<T>, 
[src]

type Output = T

impl<F, A> Future for Box<F, A> where
    F: Unpin + Future + ?Sized,
    A: Allocator + 'static, 
[src]

type Output = <F as Future>::Output

impl<T> Future for Receiver<T>[src]

type Output = Result<T, RecvError>

impl<T> Future for JoinHandle<T>[src]

type Output = Result<T, JoinError>

impl Future for LocalSet[src]

type Output = ()

impl<Fut, E> Future for ErrInto<Fut, E> where
    MapErr<Fut, IntoFn<E>>: Future
[src]

type Output = <MapErr<Fut, IntoFn<E>> as Future>::Output

impl<Fut, F> Future for MapErr<Fut, F> where
    Map<IntoFuture<Fut>, MapErrFn<F>>: Future
[src]

type Output = <Map<IntoFuture<Fut>, MapErrFn<F>> as Future>::Output

impl<St, Fut, T, F> Future for Fold<St, Fut, T, F> where
    F: FnMut(T, <St as Stream>::Item) -> Fut,
    Fut: Future<Output = T>,
    St: Stream
[src]

type Output = T

impl<Fut> Future for Fuse<Fut> where
    Fut: Future
[src]

type Output = <Fut as Future>::Output

impl<Fut, E> Future for OkInto<Fut, E> where
    MapOk<Fut, IntoFn<E>>: Future
[src]

type Output = <MapOk<Fut, IntoFn<E>> as Future>::Output

impl<F> Future for OptionFuture<F> where
    F: Future
[src]

type Output = Option<<F as Future>::Output>

impl<Fut, F> Future for InspectErr<Fut, F> where
    Inspect<IntoFuture<Fut>, InspectErrFn<F>>: Future
[src]

type Output = <Inspect<IntoFuture<Fut>, InspectErrFn<F>> as Future>::Output

impl<Fut1, Fut2> Future for TryFlatten<Fut1, Fut2> where
    TryFlatten<Fut1, Fut2>: Future
[src]

type Output = <TryFlatten<Fut1, Fut2> as Future>::Output

impl<St> Future for Concat<St> where
    St: Stream,
    <St as Stream>::Item: Extend<<<St as Stream>::Item as IntoIterator>::Item>,
    <St as Stream>::Item: IntoIterator,
    <St as Stream>::Item: Default
[src]

type Output = <St as Stream>::Item

impl<F, R> Future for Lazy<F> where
    F: FnOnce(&mut Context<'_>) -> R, 
[src]

type Output = R

impl<T, F> Future for PollFn<F> where
    F: FnMut(&mut Context<'_>) -> Poll<T>, 
[src]

type Output = T

impl<Fut> Future for IntoFuture<Fut> where
    Fut: TryFuture
[src]

type Output = Result<<Fut as TryFuture>::Ok, <Fut as TryFuture>::Error>

impl<Fut, F> Future for InspectOk<Fut, F> where
    Inspect<IntoFuture<Fut>, InspectOkFn<F>>: Future
[src]

type Output = <Inspect<IntoFuture<Fut>, InspectOkFn<F>> as Future>::Output

impl<F> Future for Flatten<F> where
    F: Future,
    Flatten<F, <F as Future>::Output>: Future
[src]

type Output = <Flatten<F, <F as Future>::Output> as Future>::Output

impl<A, B> Future for Select<A, B> where
    A: Future + Unpin,
    B: Future + Unpin
[src]

type Output = Either<(<A as Future>::Output, B), (<B as Future>::Output, A)>

impl<Fut1, Fut2, Fut3> Future for Join3<Fut1, Fut2, Fut3> where
    Fut1: Future,
    Fut2: Future,
    Fut3: Future
[src]

type Output = (<Fut1 as Future>::Output, <Fut2 as Future>::Output, <Fut3 as Future>::Output)

impl<St, Fut, T, F> Future for TryFold<St, Fut, T, F> where
    F: FnMut(T, <St as TryStream>::Ok) -> Fut,
    Fut: TryFuture<Ok = T, Error = <St as TryStream>::Error>,
    St: TryStream
[src]

type Output = Result<T, <St as TryStream>::Error>

impl<Fut> Future for MaybeDone<Fut> where
    Fut: Future
[src]

type Output = ()

impl<St> Future for StreamFuture<St> where
    St: Unpin + Stream
[src]

type Output = (Option<<St as Stream>::Item>, St)

impl<St, A, B, FromA, FromB> Future for Unzip<St, FromA, FromB> where
    St: Stream<Item = (A, B)>,
    FromA: Default + Extend<A>,
    FromB: Default + Extend<B>, 
[src]

type Output = (FromA, FromB)

impl<Fut, F, G> Future for MapOkOrElse<Fut, F, G> where
    Map<IntoFuture<Fut>, ChainFn<MapOkFn<F>, ChainFn<MapErrFn<G>, MergeResultFn>>>: Future
[src]

type Output = <Map<IntoFuture<Fut>, ChainFn<MapOkFn<F>, ChainFn<MapErrFn<G>, MergeResultFn>>> as Future>::Output

impl<T> Future for Pending<T>[src]

type Output = T

impl<Fut, T> Future for MapInto<Fut, T> where
    Map<Fut, IntoFn<T>>: Future
[src]

type Output = <Map<Fut, IntoFn<T>> as Future>::Output

impl<St, C> Future for Collect<St, C> where
    C: Default + Extend<<St as Stream>::Item>,
    St: Stream
[src]

type Output = C

impl<A, B> Future for TrySelect<A, B> where
    A: Unpin + TryFuture,
    B: Unpin + TryFuture
[src]

type Output = Result<Either<(<A as TryFuture>::Ok, B), (<B as TryFuture>::Ok, A)>, Either<(<A as TryFuture>::Error, B), (<B as TryFuture>::Error, A)>>

impl<Fut, F> Future for MapOk<Fut, F> where
    Map<IntoFuture<Fut>, MapOkFn<F>>: Future
[src]

type Output = <Map<IntoFuture<Fut>, MapOkFn<F>> as Future>::Output

impl<'a, St> Future for Peek<'a, St> where
    St: Stream
[src]

type Output = Option<&'a <St as Stream>::Item>

impl<Fut> Future for UnitError<Fut> where
    Map<Fut, OkFn<()>>: Future
[src]

type Output = <Map<Fut, OkFn<()>> as Future>::Output

impl<Fut1, Fut2, F> Future for OrElse<Fut1, Fut2, F> where
    TryFlattenErr<MapErr<Fut1, F>, Fut2>: Future
[src]

type Output = <TryFlattenErr<MapErr<Fut1, F>, Fut2> as Future>::Output

impl<'_, St> Future for TryNext<'_, St> where
    St: Unpin + TryStream + ?Sized
[src]

type Output = Result<Option<<St as TryStream>::Ok>, <St as TryStream>::Error>

impl<Fut> Future for TryMaybeDone<Fut> where
    Fut: TryFuture
[src]

type Output = Result<(), <Fut as TryFuture>::Error>

impl<Fut1, Fut2> Future for TryJoin<Fut1, Fut2> where
    Fut1: TryFuture,
    Fut2: TryFuture<Error = <Fut1 as TryFuture>::Error>, 
[src]

type Output = Result<(<Fut1 as TryFuture>::Ok, <Fut2 as TryFuture>::Ok), <Fut1 as TryFuture>::Error>

impl<Fut, F> Future for Inspect<Fut, F> where
    Map<Fut, InspectFn<F>>: Future
[src]

type Output = <Map<Fut, InspectFn<F>> as Future>::Output

impl<Fut1, Fut2, Fut3> Future for TryJoin3<Fut1, Fut2, Fut3> where
    Fut1: TryFuture,
    Fut2: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut3: TryFuture<Error = <Fut1 as TryFuture>::Error>, 
[src]

type Output = Result<(<Fut1 as TryFuture>::Ok, <Fut2 as TryFuture>::Ok, <Fut3 as TryFuture>::Ok), <Fut1 as TryFuture>::Error>

impl<Fut1, Fut2, Fut3, Fut4, Fut5> Future for Join5<Fut1, Fut2, Fut3, Fut4, Fut5> where
    Fut1: Future,
    Fut2: Future,
    Fut3: Future,
    Fut4: Future,
    Fut5: Future
[src]

type Output = (<Fut1 as Future>::Output, <Fut2 as Future>::Output, <Fut3 as Future>::Output, <Fut4 as Future>::Output, <Fut5 as Future>::Output)

impl<St> Future for TryConcat<St> where
    St: TryStream,
    <St as TryStream>::Ok: Extend<<<St as TryStream>::Ok as IntoIterator>::Item>,
    <St as TryStream>::Ok: IntoIterator,
    <St as TryStream>::Ok: Default
[src]

type Output = Result<<St as TryStream>::Ok, <St as TryStream>::Error>

impl<St, Fut, F> Future for ForEach<St, Fut, F> where
    F: FnMut(<St as Stream>::Item) -> Fut,
    Fut: Future<Output = ()>,
    St: Stream
[src]

type Output = ()

impl<'_, St> Future for SelectNextSome<'_, St> where
    St: Unpin + FusedStream + ?Sized
[src]

type Output = <St as Stream>::Item

impl<Fut1, Fut2, Fut3, Fut4> Future for Join4<Fut1, Fut2, Fut3, Fut4> where
    Fut1: Future,
    Fut2: Future,
    Fut3: Future,
    Fut4: Future
[src]

type Output = (<Fut1 as Future>::Output, <Fut2 as Future>::Output, <Fut3 as Future>::Output, <Fut4 as Future>::Output)

impl<St, Fut, F> Future for TryForEach<St, Fut, F> where
    F: FnMut(<St as TryStream>::Ok) -> Fut,
    Fut: TryFuture<Ok = (), Error = <St as TryStream>::Error>,
    St: TryStream
[src]

type Output = Result<(), <St as TryStream>::Error>

impl<'_, St> Future for Next<'_, St> where
    St: Unpin + Stream + ?Sized
[src]

type Output = Option<<St as Stream>::Item>

impl<St, C> Future for TryCollect<St, C> where
    C: Default + Extend<<St as TryStream>::Ok>,
    St: TryStream
[src]

type Output = Result<C, <St as TryStream>::Error>

impl<Fut, F> Future for Map<Fut, F> where
    Map<Fut, F>: Future
[src]

type Output = <Map<Fut, F> as Future>::Output

impl<Fut1, Fut2, Fut3, Fut4> Future for TryJoin4<Fut1, Fut2, Fut3, Fut4> where
    Fut1: TryFuture,
    Fut2: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut3: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut4: TryFuture<Error = <Fut1 as TryFuture>::Error>, 
[src]

type Output = Result<(<Fut1 as TryFuture>::Ok, <Fut2 as TryFuture>::Ok, <Fut3 as TryFuture>::Ok, <Fut4 as TryFuture>::Ok), <Fut1 as TryFuture>::Error>

impl<Fut1, Fut2, F> Future for AndThen<Fut1, Fut2, F> where
    TryFlatten<MapOk<Fut1, F>, Fut2>: Future
[src]

type Output = <TryFlatten<MapOk<Fut1, F>, Fut2> as Future>::Output

impl<Fut1, Fut2, F> Future for Then<Fut1, Fut2, F> where
    Flatten<Map<Fut1, F>, Fut2>: Future
[src]

type Output = <Flatten<Map<Fut1, F>, Fut2> as Future>::Output

impl<Fut, F> Future for UnwrapOrElse<Fut, F> where
    Map<IntoFuture<Fut>, UnwrapOrElseFn<F>>: Future
[src]

type Output = <Map<IntoFuture<Fut>, UnwrapOrElseFn<F>> as Future>::Output

impl<Fut1, Fut2, Fut3, Fut4, Fut5> Future for TryJoin5<Fut1, Fut2, Fut3, Fut4, Fut5> where
    Fut1: TryFuture,
    Fut2: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut3: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut4: TryFuture<Error = <Fut1 as TryFuture>::Error>,
    Fut5: TryFuture<Error = <Fut1 as TryFuture>::Error>, 
[src]

type Output = Result<(<Fut1 as TryFuture>::Ok, <Fut2 as TryFuture>::Ok, <Fut3 as TryFuture>::Ok, <Fut4 as TryFuture>::Ok, <Fut5 as TryFuture>::Ok), <Fut1 as TryFuture>::Error>

impl<Fut> Future for NeverError<Fut> where
    Map<Fut, OkFn<Infallible>>: Future
[src]

type Output = <Map<Fut, OkFn<Infallible>> as Future>::Output

impl<Fut1, Fut2> Future for Join<Fut1, Fut2> where
    Fut1: Future,
    Fut2: Future
[src]

type Output = (<Fut1 as Future>::Output, <Fut2 as Future>::Output)

impl<'_, T> Future for LocalFutureObj<'_, T>[src]

type Output = T

impl<'_, T> Future for FutureObj<'_, T>[src]

type Output = T

impl<L, R, O> Future for Either<L, R> where
    R: Future<Output = O>,
    L: Future<Output = O>, 
[src]

type Output = O

impl<'a> Future for WaitForCancellationFuture<'a>[src]

type Output = ()

impl<T> Future for ReusableBoxFuture<T>[src]

type Output = T

pub fn poll(
    self: Pin<&mut ReusableBoxFuture<T>>,
    cx: &mut Context<'_>
) -> Poll<T>
[src]

Poll the future stored inside this box.

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Implementors

impl Future for Sleep[src]

type Output = ()

impl<A, B> Future for actix::fut::Either<A, B> where
    A: Future,
    B: Future<Output = <A as Future>::Output>, 
[src]

type Output = <A as Future>::Output

impl<T> Future for Timeout<T> where
    T: Future
[src]

type Output = Result<<T as Future>::Output, Elapsed>

impl<T> Future for actix::fut::future::result::Ready<T>[src]

type Output = T

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