Struct futures_util::stream::FuturesOrdered [−][src]
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 Poll::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 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
FuturesOrdered::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, FuturesOrdered::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 FuturesOrdered
via the
collect
method, or you can start with an empty queue
with the FuturesOrdered::new
constructor.
This type is only available when the std
or alloc
feature of this
library is activated, and it is activated by default.
Implementations
impl<Fut: Future> FuturesOrdered<Fut>
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pub fn new() -> Self
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Constructs a new, empty FuturesOrdered
The returned FuturesOrdered
does not contain any futures and, in this
state, FuturesOrdered::poll_next
will return Poll::Ready(None)
.
pub fn len(&self) -> usize
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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
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Returns true
if the queue contains no futures
pub fn push(&mut self, future: Fut)
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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<Fut: Future> Debug for FuturesOrdered<Fut>
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impl<Fut: Future> Default for FuturesOrdered<Fut>
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impl<Fut: Future> Extend<Fut> for FuturesOrdered<Fut>
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fn extend<I>(&mut self, iter: I) where
I: IntoIterator<Item = Fut>,
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I: IntoIterator<Item = Fut>,
pub fn extend_one(&mut self, item: A)
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pub fn extend_reserve(&mut self, additional: usize)
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impl<Fut: Future> FromIterator<Fut> for FuturesOrdered<Fut>
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fn from_iter<T>(iter: T) -> Self where
T: IntoIterator<Item = Fut>,
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T: IntoIterator<Item = Fut>,
impl<Fut: Future> FusedStream for FuturesOrdered<Fut>
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fn is_terminated(&self) -> bool
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impl<Fut: Future> Stream for FuturesOrdered<Fut>
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type Item = Fut::Output
Values yielded by the stream.
fn poll_next(
self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Option<Self::Item>>
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self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Option<Self::Item>>
fn size_hint(&self) -> (usize, Option<usize>)
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impl<T: Future> Unpin for FuturesOrdered<T>
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Auto Trait Implementations
impl<T> Send for FuturesOrdered<T> where
T: Send,
<T as Future>::Output: Send,
T: Send,
<T as Future>::Output: Send,
impl<T> Sync for FuturesOrdered<T> where
T: Sync,
<T as Future>::Output: Sync,
T: Sync,
<T as Future>::Output: Sync,
Blanket Implementations
impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,
impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
pub fn borrow_mut(&mut self) -> &mut T
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impl<T> From<T> for T
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<S, T, E> TryStream for S where
S: Stream<Item = Result<T, E>> + ?Sized,
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S: Stream<Item = Result<T, E>> + ?Sized,