Struct tokio::prelude::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, 

pub fn new() -> FuturesOrdered<T>

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

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

Returns true if the queue contains no futures

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

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> Debug for FuturesOrdered<T> where
    T: Debug + Future, 

fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error>

Formats the value using the given formatter.

impl<T> Default for FuturesOrdered<T> where
    T: Future, 

fn default() -> FuturesOrdered<T>

Returns the "default value" for a type.

impl<F> FromIterator<F> for FuturesOrdered<F> where
    F: Future, 

fn from_iter<T>(iter: T) -> FuturesOrdered<F> where
    T: IntoIterator<Item = F>, 

Creates a value from an iterator.

impl<T> Stream for FuturesOrdered<T> where
    T: Future, 

type Item = <T as Future>::Item

The type of item this stream will yield on success.

type Error = <T as Future>::Error

The type of error this stream may generate.

fn poll(
    &mut self
) -> Result<Async<Option<<FuturesOrdered<T> as Stream>::Item>>, <FuturesOrdered<T> as Stream>::Error>

Attempt to pull out the next value of this stream, returning None if the stream is finished.

fn wait(self) -> Wait<Self>

Creates an iterator which blocks the current thread until each item of this stream is resolved.

fn into_future(self) -> StreamFuture<Self>

Converts this stream into a Future.

fn map<U, F>(self, f: F) -> Map<Self, F> where
    F: FnMut(Self::Item) -> U, 

Converts a stream of type T to a stream of type U.

fn map_err<U, F>(self, f: F) -> MapErr<Self, F> where
    F: FnMut(Self::Error) -> U, 

Converts a stream of error type T to a stream of error type U.

fn filter<F>(self, f: F) -> Filter<Self, F> where
    F: FnMut(&Self::Item) -> bool, 

Filters the values produced by this stream according to the provided predicate.

fn filter_map<F, B>(self, f: F) -> FilterMap<Self, F> where
    F: FnMut(Self::Item) -> Option<B>, 

Filters the values produced by this stream while simultaneously mapping them to a different type.

fn then<F, U>(self, f: F) -> Then<Self, F, U> where
    F: FnMut(Result<Self::Item, Self::Error>) -> U,
    U: IntoFuture, 

Chain on a computation for when a value is ready, passing the resulting item to the provided closure f.

fn and_then<F, U>(self, f: F) -> AndThen<Self, F, U> where
    F: FnMut(Self::Item) -> U,
    U: IntoFuture<Error = Self::Error>, 

Chain on a computation for when a value is ready, passing the successful results to the provided closure f.

fn or_else<F, U>(self, f: F) -> OrElse<Self, F, U> where
    F: FnMut(Self::Error) -> U,
    U: IntoFuture<Item = Self::Item>, 

Chain on a computation for when an error happens, passing the erroneous result to the provided closure f.

fn collect(self) -> Collect<Self>

Collect all of the values of this stream into a vector, returning a future representing the result of that computation.

fn concat2(self) -> Concat2<Self> where
    Self::Item: Extend<<Self::Item as IntoIterator>::Item>,
    Self::Item: IntoIterator,
    Self::Item: Default, 

Concatenate all results of a stream into a single extendable destination, returning a future representing the end result.

fn concat(self) -> Concat<Self> where
    Self::Item: Extend<<Self::Item as IntoIterator>::Item>,
    Self::Item: IntoIterator, 

Deprecated since 0.1.14:

please use Stream::concat2 instead

Concatenate all results of a stream into a single extendable destination, returning a future representing the end result.

fn fold<F, T, Fut>(self, init: T, f: F) -> Fold<Self, F, Fut, T> where
    F: FnMut(T, Self::Item) -> Fut,
    Fut: IntoFuture<Item = T>,
    Self::Error: From<<Fut as IntoFuture>::Error>, 

Execute an accumulating computation over a stream, collecting all the values into one final result.

fn flatten(self) -> Flatten<Self> where
    Self::Item: Stream,
    <Self::Item as Stream>::Error: From<Self::Error>, 

Flattens a stream of streams into just one continuous stream.

fn skip_while<P, R>(self, pred: P) -> SkipWhile<Self, P, R> where
    P: FnMut(&Self::Item) -> R,
    R: IntoFuture<Item = bool, Error = Self::Error>, 

Skip elements on this stream while the predicate provided resolves to true.

fn take_while<P, R>(self, pred: P) -> TakeWhile<Self, P, R> where
    P: FnMut(&Self::Item) -> R,
    R: IntoFuture<Item = bool, Error = Self::Error>, 

Take elements from this stream while the predicate provided resolves to true.

fn for_each<F, U>(self, f: F) -> ForEach<Self, F, U> where
    F: FnMut(Self::Item) -> U,
    U: IntoFuture<Item = (), Error = Self::Error>, 

Runs this stream to completion, executing the provided closure for each element on the stream.

fn from_err<E>(self) -> FromErr<Self, E> where
    E: From<Self::Error>, 

Map this stream's error to any error implementing From for this stream's Error, returning a new stream.

fn take(self, amt: u64) -> Take<Self>

Creates a new stream of at most amt items of the underlying stream.

fn skip(self, amt: u64) -> Skip<Self>

Creates a new stream which skips amt items of the underlying stream.

fn fuse(self) -> Fuse<Self>

Fuse a stream such that poll will never again be called once it has finished.

fn by_ref(&mut self) -> &mut Self

Borrows a stream, rather than consuming it.

fn catch_unwind(self) -> CatchUnwind<Self> where
    Self: UnwindSafe, 

Catches unwinding panics while polling the stream.

fn buffered(self, amt: usize) -> Buffered<Self> where
    Self::Item: IntoFuture,
    <Self::Item as IntoFuture>::Error == Self::Error, 

An adaptor for creating a buffered list of pending futures.

fn buffer_unordered(self, amt: usize) -> BufferUnordered<Self> where
    Self::Item: IntoFuture,
    <Self::Item as IntoFuture>::Error == Self::Error, 

An adaptor for creating a buffered list of pending futures (unordered).

fn merge<S>(self, other: S) -> Merge<Self, S> where
    S: Stream<Error = Self::Error>, 

Deprecated:

functionality provided by select now

An adapter for merging the output of two streams.

fn zip<S>(self, other: S) -> Zip<Self, S> where
    S: Stream<Error = Self::Error>, 

An adapter for zipping two streams together.

fn chain<S>(self, other: S) -> Chain<Self, S> where
    S: Stream<Item = Self::Item, Error = Self::Error>, 

Adapter for chaining two stream.

fn peekable(self) -> Peekable<Self>

Creates a new stream which exposes a peek method.

fn chunks(self, capacity: usize) -> Chunks<Self>

An adaptor for chunking up items of the stream inside a vector.

fn select<S>(self, other: S) -> Select<Self, S> where
    S: Stream<Item = Self::Item, Error = Self::Error>, 

Creates a stream that selects the next element from either this stream or the provided one, whichever is ready first.

fn forward<S>(self, sink: S) -> Forward<Self, S> where
    S: Sink<SinkItem = Self::Item>,
    Self::Error: From<<S as Sink>::SinkError>, 

A future that completes after the given stream has been fully processed into the sink, including flushing.

fn split(self) -> (SplitSink<Self>, SplitStream<Self>) where
    Self: Sink, 

Splits this Stream + Sink object into separate Stream and Sink objects.

fn inspect<F>(self, f: F) -> Inspect<Self, F> where
    F: FnMut(&Self::Item), 

Do something with each item of this stream, afterwards passing it on.

fn inspect_err<F>(self, f: F) -> InspectErr<Self, F> where
    F: FnMut(&Self::Error), 

Do something with the error of this stream, afterwards passing it on.