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 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
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).
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.
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
Extends a collection with the contents of an iterator. Read more
extend_one)Extends a collection with exactly one element.
extend_one)Reserves capacity in a collection for the given number of additional elements. Read more
Creates a value from an iterator. Read more
Returns true if the stream should no longer be polled.
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