Struct futures_util::stream::FuturesOrdered
source · [−]pub struct FuturesOrdered<T: Future> { /* private fields */ }
Expand description
An unbounded queue of futures.
This “combinator” is similar to FuturesUnordered
, but it imposes a FIFO 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
sourceimpl<Fut: Future> FuturesOrdered<Fut>
impl<Fut: Future> FuturesOrdered<Fut>
sourcepub fn new() -> Self
pub fn new() -> Self
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)
.
sourcepub fn len(&self) -> usize
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.
sourcepub fn push(&mut self, future: Fut)
👎Deprecated: use push_back
instead
pub fn push(&mut self, future: Fut)
push_back
insteadPush 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.
sourcepub fn push_back(&mut self, future: Fut)
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 FuturesOrdered::poll
is called in order to receive
task notifications.
sourcepub fn push_front(&mut self, future: Fut)
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 FuturesOrdered::poll
is called in order to receive
task notifications. This future will be the next future to be returned
complete.
Trait Implementations
sourceimpl<Fut: Future> Debug for FuturesOrdered<Fut>
impl<Fut: Future> Debug for FuturesOrdered<Fut>
sourceimpl<Fut: Future> Default for FuturesOrdered<Fut>
impl<Fut: Future> Default for FuturesOrdered<Fut>
sourceimpl<Fut: Future> Extend<Fut> for FuturesOrdered<Fut>
impl<Fut: Future> Extend<Fut> for FuturesOrdered<Fut>
sourcefn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = Fut>,
fn extend<I>(&mut self, iter: I)where
I: IntoIterator<Item = Fut>,
sourcefn extend_one(&mut self, item: A)
fn extend_one(&mut self, item: A)
extend_one
)sourcefn extend_reserve(&mut self, additional: usize)
fn extend_reserve(&mut self, additional: usize)
extend_one
)sourceimpl<Fut: Future> FromIterator<Fut> for FuturesOrdered<Fut>
impl<Fut: Future> FromIterator<Fut> for FuturesOrdered<Fut>
sourcefn from_iter<T>(iter: T) -> Selfwhere
T: IntoIterator<Item = Fut>,
fn from_iter<T>(iter: T) -> Selfwhere
T: IntoIterator<Item = Fut>,
sourceimpl<Fut: Future> FusedStream for FuturesOrdered<Fut>
impl<Fut: Future> FusedStream for FuturesOrdered<Fut>
sourcefn is_terminated(&self) -> bool
fn is_terminated(&self) -> bool
true
if the stream should no longer be polled.