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//! Definition of the `JoinAll` combinator, waiting for all of a list of futures
//! to finish.
use std::prelude::v1::*;
use std::fmt;
use std::mem;
use {Future, IntoFuture, Poll, Async};
#[derive(Debug)]
enum ElemState<T> where T: Future {
Pending(T),
Done(T::Item),
}
/// A future which takes a list of futures and resolves with a vector of the
/// completed values.
///
/// This future is created with the `join_all` method.
#[must_use = "futures do nothing unless polled"]
pub struct JoinAll<I>
where I: IntoIterator,
I::Item: IntoFuture,
{
elems: Vec<ElemState<<I::Item as IntoFuture>::Future>>,
}
impl<I> fmt::Debug for JoinAll<I>
where I: IntoIterator,
I::Item: IntoFuture,
<<I as IntoIterator>::Item as IntoFuture>::Future: fmt::Debug,
<<I as IntoIterator>::Item as IntoFuture>::Item: fmt::Debug,
{
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
fmt.debug_struct("JoinAll")
.field("elems", &self.elems)
.finish()
}
}
/// Creates a future which represents a collection of the results of the futures
/// given.
///
/// The returned future will drive execution for all of its underlying futures,
/// collecting the results into a destination `Vec<T>` in the same order as they
/// were provided. If any future returns an error then all other futures will be
/// canceled and an error will be returned immediately. If all futures complete
/// successfully, however, then the returned future will succeed with a `Vec` of
/// all the successful results.
///
/// # Examples
///
/// ```
/// use futures::future::*;
///
/// let f = join_all(vec![
/// ok::<u32, u32>(1),
/// ok::<u32, u32>(2),
/// ok::<u32, u32>(3),
/// ]);
/// let f = f.map(|x| {
/// assert_eq!(x, [1, 2, 3]);
/// });
///
/// let f = join_all(vec![
/// Box::new(ok::<u32, u32>(1)),
/// Box::new(err::<u32, u32>(2)),
/// Box::new(ok::<u32, u32>(3)),
/// ]);
/// let f = f.then(|x| {
/// assert_eq!(x, Err(2));
/// x
/// });
/// ```
pub fn join_all<I>(i: I) -> JoinAll<I>
where I: IntoIterator,
I::Item: IntoFuture,
{
let elems = i.into_iter().map(|f| {
ElemState::Pending(f.into_future())
}).collect();
JoinAll { elems: elems }
}
impl<I> Future for JoinAll<I>
where I: IntoIterator,
I::Item: IntoFuture,
{
type Item = Vec<<I::Item as IntoFuture>::Item>;
type Error = <I::Item as IntoFuture>::Error;
fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
let mut all_done = true;
for idx in 0 .. self.elems.len() {
let done_val = match self.elems[idx] {
ElemState::Pending(ref mut t) => {
match t.poll() {
Ok(Async::Ready(v)) => Ok(v),
Ok(Async::NotReady) => {
all_done = false;
continue
}
Err(e) => Err(e),
}
}
ElemState::Done(ref mut _v) => continue,
};
match done_val {
Ok(v) => self.elems[idx] = ElemState::Done(v),
Err(e) => {
// On completion drop all our associated resources
// ASAP.
self.elems = Vec::new();
return Err(e)
}
}
}
if all_done {
let elems = mem::replace(&mut self.elems, Vec::new());
let result = elems.into_iter().map(|e| {
match e {
ElemState::Done(t) => t,
_ => unreachable!(),
}
}).collect();
Ok(Async::Ready(result))
} else {
Ok(Async::NotReady)
}
}
}
|
