Struct FuturesOrderedBounded

pub struct FuturesOrderedBounded<T: Future> { /* private fields */ }

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 FuturesOrderedBounded will only be polled when they generate notifications. This reduces the required amount of work needed to coordinate large numbers of futures.

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

If FuturesOrderedBounded::poll returns Poll::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 FuturesOrderedBounded::poll will either return the future’s resolved value or Poll::Pending if the future has not yet completed. When multiple futures are submitted to the queue, FuturesOrderedBounded::poll will return Poll::Pending until the first future completes, even if some of the later futures have already completed.

Note that you can create a ready-made FuturesOrderedBounded via the collect method, or you can start with an empty queue with the FuturesOrderedBounded::new constructor.

Implementations

impl<Fut: Future> FuturesOrderedBounded<Fut>

pub fn new(capacity: usize) -> Self

Constructs a new, empty FuturesOrderedBounded

The returned FuturesOrderedBounded does not contain any futures and, in this state, FuturesOrderedBounded::poll_next will return Poll::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 try_push_back(&mut self, future: Fut) -> Result<(), Fut>

Pushes a future to the back of 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 FuturesOrderedBounded::poll is called in order to receive task notifications.

Errors

This method will error if the buffer is currently full, returning the future back

pub fn try_push_front(&mut self, future: Fut) -> Result<(), Fut>

Pushes a future to the front of 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 FuturesOrderedBounded::poll is called in order to receive task notifications. This future will be the next future to be returned complete.

Errors

This method will error if the buffer is currently full, returning the future back

pub fn push_back(&mut self, future: Fut)

Pushes a future to the back of 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 FuturesOrderedBounded::poll is called in order to receive task notifications.

Panics

This method will panic if the buffer is currently full. See FuturesOrderedBounded::try_push_back to get a result instead

pub fn push_front(&mut self, future: Fut)

Pushes a future to the front of 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 FuturesOrderedBounded::poll is called in order to receive task notifications. This future will be the next future to be returned complete.

Panics

This method will panic if the buffer is currently full. See FuturesOrderedBounded::try_push_front to get a result instead

Trait Implementations

impl<Fut: Future> Debug for FuturesOrderedBounded<Fut>

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

Formats the value using the given formatter.

impl<Fut: Future> Extend<Fut> for FuturesOrderedBounded<Fut>

fn extend<I>(&mut self, iter: I)

where I: IntoIterator<Item = Fut>,

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<Fut: Future> FromIterator<Fut> for FuturesOrderedBounded<Fut>

fn from_iter<T>(iter: T) -> Self

where T: IntoIterator<Item = Fut>,

Creates a value from an iterator.

impl<Fut: Future> FusedStream for FuturesOrderedBounded<Fut>

fn is_terminated(&self) -> bool

Returns true if the stream should no longer be polled.

impl<Fut: Future> Stream for FuturesOrderedBounded<Fut>

type Item = <Fut as Future>::Output

Values yielded by the stream.

fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll<Option<Self::Item>>

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.

fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream.

impl<T: Future> Unpin for FuturesOrderedBounded<T>