Struct futures::stream::FuturesOrdered
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#[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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T: Future,
pub fn new() -> FuturesOrdered<T>
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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
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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: T)
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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<T> Stream for FuturesOrdered<T> where
T: Future,
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T: Future,
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.
fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error>
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Attempt to pull out the next value of this stream, returning None
if the stream is finished. Read more
ⓘImportant traits for Wait<S>fn wait(self) -> Wait<Self> where
Self: Sized,
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Self: Sized,
Creates an iterator which blocks the current thread until each item of this stream is resolved. Read more
fn into_future(self) -> StreamFuture<Self> where
Self: Sized,
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Self: Sized,
Converts this stream into a Future
. Read more
fn map<U, F>(self, f: F) -> Map<Self, F> where
F: FnMut(Self::Item) -> U,
Self: Sized,
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F: FnMut(Self::Item) -> U,
Self: Sized,
Converts a stream of type T
to a stream of type U
. Read more
fn map_err<U, F>(self, f: F) -> MapErr<Self, F> where
F: FnMut(Self::Error) -> U,
Self: Sized,
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F: FnMut(Self::Error) -> U,
Self: Sized,
Converts a stream of error type T
to a stream of error type U
. Read more
fn filter<F>(self, f: F) -> Filter<Self, F> where
F: FnMut(&Self::Item) -> bool,
Self: Sized,
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F: FnMut(&Self::Item) -> bool,
Self: Sized,
Filters the values produced by this stream according to the provided predicate. Read more
fn filter_map<F, B>(self, f: F) -> FilterMap<Self, F> where
F: FnMut(Self::Item) -> Option<B>,
Self: Sized,
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F: FnMut(Self::Item) -> Option<B>,
Self: Sized,
Filters the values produced by this stream while simultaneously mapping them to a different type. Read more
fn then<F, U>(self, f: F) -> Then<Self, F, U> where
F: FnMut(Result<Self::Item, Self::Error>) -> U,
U: IntoFuture,
Self: Sized,
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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
fn and_then<F, U>(self, f: F) -> AndThen<Self, F, U> where
F: FnMut(Self::Item) -> U,
U: IntoFuture<Error = Self::Error>,
Self: Sized,
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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
fn or_else<F, U>(self, f: F) -> OrElse<Self, F, U> where
F: FnMut(Self::Error) -> U,
U: IntoFuture<Item = Self::Item>,
Self: Sized,
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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
fn collect(self) -> Collect<Self> where
Self: Sized,
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Self: Sized,
Collect all of the values of this stream into a vector, returning a future representing the result of that computation. Read more
fn concat2(self) -> Concat2<Self> where
Self: Sized,
Self::Item: Extend<<Self::Item as IntoIterator>::Item> + IntoIterator + Default,
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Self: Sized,
Self::Item: Extend<<Self::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
fn concat(self) -> Concat<Self> where
Self: Sized,
Self::Item: Extend<<Self::Item as IntoIterator>::Item> + IntoIterator,
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Self: Sized,
Self::Item: Extend<<Self::Item as IntoIterator>::Item> + IntoIterator,
: please use Stream::concat2
instead
Concatenate all results of a stream into a single extendable destination, returning a future representing the end result. Read more
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::Error>,
Self: Sized,
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F: FnMut(T, Self::Item) -> Fut,
Fut: IntoFuture<Item = T>,
Self::Error: From<Fut::Error>,
Self: Sized,
Execute an accumulating computation over a stream, collecting all the values into one final result. Read more
fn flatten(self) -> Flatten<Self> where
Self::Item: Stream,
<Self::Item as Stream>::Error: From<Self::Error>,
Self: Sized,
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Self::Item: Stream,
<Self::Item as Stream>::Error: From<Self::Error>,
Self: Sized,
Flattens a stream of streams into just one continuous stream. Read more
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>,
Self: Sized,
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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
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>,
Self: Sized,
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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
fn for_each<F, U>(self, f: F) -> ForEach<Self, F, U> where
F: FnMut(Self::Item) -> U,
U: IntoFuture<Item = (), Error = Self::Error>,
Self: Sized,
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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
fn from_err<E: From<Self::Error>>(self) -> FromErr<Self, E> where
Self: Sized,
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Self: Sized,
Map this stream's error to any error implementing From
for this stream's Error
, returning a new stream. Read more
fn take(self, amt: u64) -> Take<Self> where
Self: Sized,
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Self: Sized,
Creates a new stream of at most amt
items of the underlying stream. Read more
fn skip(self, amt: u64) -> Skip<Self> where
Self: Sized,
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Self: Sized,
Creates a new stream which skips amt
items of the underlying stream. Read more
fn fuse(self) -> Fuse<Self> where
Self: Sized,
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Self: Sized,
Fuse a stream such that poll
will never again be called once it has finished. Read more
fn by_ref(&mut self) -> &mut Self where
Self: Sized,
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Self: Sized,
Borrows a stream, rather than consuming it. Read more
fn catch_unwind(self) -> CatchUnwind<Self> where
Self: Sized + UnwindSafe,
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Self: Sized + UnwindSafe,
Catches unwinding panics while polling the stream. Read more
fn buffered(self, amt: usize) -> Buffered<Self> where
Self::Item: IntoFuture<Error = Self::Error>,
Self: Sized,
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Self::Item: IntoFuture<Error = Self::Error>,
Self: Sized,
An adaptor for creating a buffered list of pending futures. Read more
fn buffer_unordered(self, amt: usize) -> BufferUnordered<Self> where
Self::Item: IntoFuture<Error = Self::Error>,
Self: Sized,
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Self::Item: IntoFuture<Error = Self::Error>,
Self: Sized,
An adaptor for creating a buffered list of pending futures (unordered). Read more
fn merge<S>(self, other: S) -> Merge<Self, S> where
S: Stream<Error = Self::Error>,
Self: Sized,
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S: Stream<Error = Self::Error>,
Self: Sized,
: functionality provided by select
now
An adapter for merging the output of two streams. Read more
fn zip<S>(self, other: S) -> Zip<Self, S> where
S: Stream<Error = Self::Error>,
Self: Sized,
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S: Stream<Error = Self::Error>,
Self: Sized,
An adapter for zipping two streams together. Read more
fn chain<S>(self, other: S) -> Chain<Self, S> where
S: Stream<Item = Self::Item, Error = Self::Error>,
Self: Sized,
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S: Stream<Item = Self::Item, Error = Self::Error>,
Self: Sized,
Adapter for chaining two stream. Read more
fn peekable(self) -> Peekable<Self> where
Self: Sized,
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Self: Sized,
Creates a new stream which exposes a peek
method. Read more
fn chunks(self, capacity: usize) -> Chunks<Self> where
Self: Sized,
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Self: Sized,
An adaptor for chunking up items of the stream inside a vector. Read more
fn select<S>(self, other: S) -> Select<Self, S> where
S: Stream<Item = Self::Item, Error = Self::Error>,
Self: Sized,
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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
fn forward<S>(self, sink: S) -> Forward<Self, S> where
S: Sink<SinkItem = Self::Item>,
Self::Error: From<S::SinkError>,
Self: Sized,
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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
fn split(self) -> (SplitSink<Self>, SplitStream<Self>) where
Self: Sink + Sized,
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Self: Sink + Sized,
Splits this Stream + Sink
object into separate Stream
and Sink
objects. Read more
fn inspect<F>(self, f: F) -> Inspect<Self, F> where
F: FnMut(&Self::Item),
Self: Sized,
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F: FnMut(&Self::Item),
Self: Sized,
Do something with each item of this stream, afterwards passing it on. Read more
fn inspect_err<F>(self, f: F) -> InspectErr<Self, F> where
F: FnMut(&Self::Error),
Self: Sized,
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F: FnMut(&Self::Error),
Self: Sized,
Do something with the error of this stream, afterwards passing it on. Read more
impl<T: Debug> Debug for FuturesOrdered<T> where
T: Future,
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T: Future,
fn fmt(&self, fmt: &mut Formatter) -> Result
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Formats the value using the given formatter. Read more
impl<F: Future> FromIterator<F> for FuturesOrdered<F>
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fn from_iter<T>(iter: T) -> Self where
T: IntoIterator<Item = F>,
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T: IntoIterator<Item = F>,
Creates a value from an iterator. Read more