[][src]Struct futures::stream::FuturesOrdered

#[must_use = "streams do nothing unless polled"]
pub struct FuturesOrdered<T> where
    T: Future
{ /* fields omitted */ }

An unbounded queue of futures.

This "combinator" is similar to FuturesUnordered, but it imposes an order on top of the set of futures. While futures in the set will race to completion in parallel, results will only be returned in the order their originating futures were added to the queue.

Futures are pushed into this queue and their realized values are yielded in order. This structure is optimized to manage a large number of futures. Futures managed by FuturesOrdered will only be polled when they generate notifications. This reduces the required amount of work needed to coordinate large numbers of futures.

When a FuturesOrdered is first created, it does not contain any futures. Calling poll in this state will result in Ok(Async::Ready(None)) to be returned. Futures are submitted to the queue using push; however, the future will not be polled at this point. FuturesOrdered will only poll managed futures when FuturesOrdered::poll is called. As such, it is important to call poll after pushing new futures.

If FuturesOrdered::poll returns Ok(Async::Ready(None)) this means that the queue is currently not managing any futures. A future may be submitted to the queue at a later time. At that point, a call to FuturesOrdered::poll will either return the future's resolved value or Ok(Async::NotReady) if the future has not yet completed. When multiple futures are submitted to the queue, FuturesOrdered::poll will return Ok(Async::NotReady) until the first future completes, even if some of the later futures have already completed.

Note that you can create a ready-made FuturesOrdered via the futures_ordered function in the stream module, or you can start with an empty queue with the FuturesOrdered::new constructor.

Methods

impl<T> FuturesOrdered<T> where
    T: Future
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pub fn new() -> FuturesOrdered<T>[src]

Constructs a new, empty FuturesOrdered

The returned FuturesOrdered does not contain any futures and, in this state, FuturesOrdered::poll will return Ok(Async::Ready(None)).

pub fn len(&self) -> usize[src]

Returns the number of futures contained in the queue.

This represents the total number of in-flight futures, both those currently processing and those that have completed but which are waiting for earlier futures to complete.

pub fn is_empty(&self) -> bool[src]

Returns true if the queue contains no futures

pub fn push(&mut self, future: T)[src]

Push a future into the queue.

This function submits the given future to the internal set for managing. This function will not call poll on the submitted future. The caller must ensure that FuturesOrdered::poll is called in order to receive task notifications.

Trait Implementations

impl<T> Stream for FuturesOrdered<T> where
    T: Future
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type Item = T::Item

The type of item this stream will yield on success.

type Error = T::Error

The type of error this stream may generate.

impl<T: Debug> Debug for FuturesOrdered<T> where
    T: Future
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impl<F: Future> FromIterator<F> for FuturesOrdered<F>[src]

impl<T> Default for FuturesOrdered<T> where
    T: Future
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Auto Trait Implementations

impl<T> Unpin for FuturesOrdered<T> where
    <T as Future>::Item: Unpin

impl<T> Send for FuturesOrdered<T> where
    T: Send,
    <T as Future>::Item: Send

impl<T> Sync for FuturesOrdered<T> where
    T: Sync,
    <T as Future>::Item: Sync

impl<T> !UnwindSafe for FuturesOrdered<T>

impl<T> !RefUnwindSafe for FuturesOrdered<T>

Blanket Implementations

impl<T> From<T> for T[src]

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
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type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> Into<U> for T where
    U: From<T>, 
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impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T> Borrow<T> for T where
    T: ?Sized
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impl<T> BorrowMut<T> for T where
    T: ?Sized
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impl<T> Any for T where
    T: 'static + ?Sized
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