futures_util::stream

Struct FuturesOrdered

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pub struct FuturesOrdered<T>
where T: Future,
{ /* private fields */ }
Expand description

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::Pending) if the future has not yet completed. When multiple futures are submitted to the queue, FuturesOrdered::poll will return Ok(Async::Pending) 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.

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

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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)).

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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.

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pub fn is_empty(&self) -> bool

Returns true if the queue contains no futures

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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§

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

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

Formats the value using the given formatter. Read more
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impl<F: Future> FromIterator<F> for FuturesOrdered<F>

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

Creates a value from an iterator. Read more
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impl<T> Stream for FuturesOrdered<T>
where T: Future,

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type Item = <T as Future>::Item

Values yielded by the stream.
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type Error = <T as Future>::Error

Errors yielded by the stream.
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fn poll_next( &mut self, cx: &mut Context<'_>, ) -> Poll<Option<Self::Item>, Self::Error>

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted. Read more

Auto Trait Implementations§

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impl<T> Freeze for FuturesOrdered<T>

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impl<T> !RefUnwindSafe for FuturesOrdered<T>

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

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

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

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impl<T> !UnwindSafe for FuturesOrdered<T>

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

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> IntoEither for T

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fn into_either(self, into_left: bool) -> Either<Self, Self>

Converts self into a Left variant of Either<Self, Self> if into_left is true. Converts self into a Right variant of Either<Self, Self> otherwise. Read more
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fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
where F: FnOnce(&Self) -> bool,

Converts self into a Left variant of Either<Self, Self> if into_left(&self) returns true. Converts self into a Right variant of Either<Self, Self> otherwise. Read more
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impl<T> StreamExt for T
where T: Stream + ?Sized,

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fn next(self) -> StreamFuture<Self>
where Self: Sized,

Converts this stream into a Future. Read more
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fn map<U, F>(self, f: F) -> Map<Self, F>
where F: FnMut(Self::Item) -> U, Self: Sized,

Converts a stream of type T to a stream of type U. Read more
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fn map_err<U, F>(self, f: F) -> MapErr<Self, F>
where F: FnMut(Self::Error) -> U, Self: Sized,

Converts a stream of error type T to a stream of error type U. Read more
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fn filter<R, P>(self, pred: P) -> Filter<Self, R, P>
where P: FnMut(&Self::Item) -> R, R: IntoFuture<Item = bool, Error = Self::Error>, Self: Sized,

Filters the values produced by this stream according to the provided predicate. Read more
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fn filter_map<R, B, F>(self, f: F) -> FilterMap<Self, R, F>
where F: FnMut(Self::Item) -> R, R: IntoFuture<Item = Option<B>, Error = Self::Error>, Self: Sized,

Filters the values produced by this stream while simultaneously mapping them to a different type. Read more
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fn then<U, F>(self, f: F) -> Then<Self, U, F>
where F: FnMut(Result<Self::Item, Self::Error>) -> U, U: IntoFuture, Self: Sized,

Chain on a computation for when a value is ready, passing the resulting item to the provided closure f. Read more
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fn and_then<U, F>(self, f: F) -> AndThen<Self, U, F>
where F: FnMut(Self::Item) -> U, U: IntoFuture<Error = Self::Error>, Self: Sized,

Chain on a computation for when a value is ready, passing the successful results to the provided closure f. Read more
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fn or_else<U, F>(self, f: F) -> OrElse<Self, U, F>
where F: FnMut(Self::Error) -> U, U: IntoFuture<Item = Self::Item>, Self: Sized,

Chain on a computation for when an error happens, passing the erroneous result to the provided closure f. Read more
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fn collect<C: Default + Extend<Self::Item>>(self) -> Collect<Self, C>
where Self: Sized,

Collect all of the values of this stream into a vector, returning a future representing the result of that computation. Read more
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fn concat(self) -> Concat<Self>
where Self: Sized, Self::Item: Extend<<<Self as Stream>::Item as IntoIterator>::Item> + IntoIterator + Default,

Concatenate all results of a stream into a single extendable destination, returning a future representing the end result. Read more
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fn fold<T, Fut, F>(self, init: T, f: F) -> Fold<Self, Fut, T, F>
where F: FnMut(T, Self::Item) -> Fut, Fut: IntoFuture<Item = T, Error = Self::Error>, Self: Sized,

Execute an accumulating computation over a stream, collecting all the values into one final result. Read more
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fn flatten(self) -> Flatten<Self>
where Self::Item: Stream<Error = Self::Error>, Self: Sized,

Flattens a stream of streams into just one continuous stream. Read more
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fn skip_while<R, P>(self, pred: P) -> SkipWhile<Self, R, P>
where P: FnMut(&Self::Item) -> R, R: IntoFuture<Item = bool, Error = Self::Error>, Self: Sized,

Skip elements on this stream while the predicate provided resolves to true. Read more
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fn take_while<R, P>(self, pred: P) -> TakeWhile<Self, R, P>
where P: FnMut(&Self::Item) -> R, R: IntoFuture<Item = bool, Error = Self::Error>, Self: Sized,

Take elements from this stream while the predicate provided resolves to true. Read more
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fn for_each<U, F>(self, f: F) -> ForEach<Self, U, F>
where F: FnMut(Self::Item) -> U, U: IntoFuture<Item = (), Error = Self::Error>, Self: Sized,

Runs this stream to completion, executing the provided closure for each element on the stream. Read more
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fn for_each_concurrent<U, F>(self, f: F) -> ForEachConcurrent<Self, U, F>
where F: FnMut(Self::Item) -> U, U: IntoFuture<Item = (), Error = Self::Error>, Self: Sized,

Runs this stream to completion, executing the provided closure for each element on the stream. This is similar to for_each but may begin processing an element while previous elements are still being processed. Read more
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fn err_into<E>(self) -> ErrInto<Self, E>
where Self: Sized, Self::Error: Into<E>,

Map this stream’s error to a different type using the Into trait. Read more
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fn take(self, amt: u64) -> Take<Self>
where Self: Sized,

Creates a new stream of at most amt items of the underlying stream. Read more
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fn skip(self, amt: u64) -> Skip<Self>
where Self: Sized,

Creates a new stream which skips amt items of the underlying stream. Read more
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fn fuse(self) -> Fuse<Self>
where Self: Sized,

Fuse a stream such that poll will never again be called once it has finished. Read more
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fn by_ref(&mut self) -> &mut Self
where Self: Sized,

Borrows a stream, rather than consuming it. Read more
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fn catch_unwind(self) -> CatchUnwind<Self>
where Self: Sized + UnwindSafe,

Catches unwinding panics while polling the stream. Read more
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fn buffered(self, amt: usize) -> Buffered<Self>
where Self::Item: IntoFuture<Error = <Self as Stream>::Error>, Self: Sized,

An adaptor for creating a buffered list of pending futures. Read more
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fn buffer_unordered(self, amt: usize) -> BufferUnordered<Self>
where Self::Item: IntoFuture<Error = <Self as Stream>::Error>, Self: Sized,

An adaptor for creating a buffered list of pending futures (unordered). Read more
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fn zip<S>(self, other: S) -> Zip<Self, S>
where S: Stream<Error = Self::Error>, Self: Sized,

An adapter for zipping two streams together. Read more
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fn chain<S>(self, other: S) -> Chain<Self, S>
where S: Stream<Item = Self::Item, Error = Self::Error>, Self: Sized,

Adapter for chaining two stream. Read more
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fn peekable(self) -> Peekable<Self>
where Self: Sized,

Creates a new stream which exposes a peek method. Read more
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fn chunks(self, capacity: usize) -> Chunks<Self>
where Self: Sized,

An adaptor for chunking up items of the stream inside a vector. Read more
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fn select<S>(self, other: S) -> Select<Self, S>
where S: Stream<Item = Self::Item, Error = Self::Error>, Self: Sized,

Creates a stream that selects the next element from either this stream or the provided one, whichever is ready first. Read more
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fn forward<S>(self, sink: S) -> Forward<Self, S>
where S: Sink<SinkItem = Self::Item>, Self::Error: From<S::SinkError>, Self: Sized,

A future that completes after the given stream has been fully processed into the sink, including flushing. Read more
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fn split(self) -> (SplitSink<Self>, SplitStream<Self>)
where Self: Sink + Sized,

Splits this Stream + Sink object into separate Stream and Sink objects. Read more
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fn inspect<F>(self, f: F) -> Inspect<Self, F>
where F: FnMut(&Self::Item), Self: Sized,

Do something with each item of this stream, afterwards passing it on. Read more
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fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
where F: FnMut(&Self::Error), Self: Sized,

Do something with the error of this stream, afterwards passing it on. Read more
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fn recover<E, F>(self, f: F) -> Recover<Self, E, F>
where F: FnMut(Self::Error) -> Option<Self::Item>, Self: Sized,

Handle errors generated by this stream by converting them into Option<Self::Item>, such that a None value terminates the stream. Read more
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fn left<B>(self) -> Either<Self, B>
where B: Stream<Item = Self::Item, Error = Self::Error>, Self: Sized,

👎Deprecated: use left_stream instead
Wrap this stream in an Either stream, making it the left-hand variant of that Either. Read more
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fn right<B>(self) -> Either<B, Self>
where B: Stream<Item = Self::Item, Error = Self::Error>, Self: Sized,

👎Deprecated: use right_stream instead
Wrap this stream in an Either stream, making it the right-hand variant of that Either. Read more
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fn left_stream<B>(self) -> Either<Self, B>
where B: Stream<Item = Self::Item, Error = Self::Error>, Self: Sized,

Wrap this stream in an Either stream, making it the left-hand variant of that Either. Read more
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fn right_stream<B>(self) -> Either<B, Self>
where B: Stream<Item = Self::Item, Error = Self::Error>, Self: Sized,

Wrap this stream in an Either stream, making it the right-hand variant of that Either. Read more
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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.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.