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use crate::common::*;
/// The trait extends [TryStream](futures::stream::TryStream) types with ordering manipulation combinators.
pub trait TryIndexStreamExt
where
Self: Stream<Item = Result<(usize, Self::Ok), Self::Error>>,
{
type Ok;
type Error;
/// Reorders the input items `Ok((index, item))` according to the index number and returns `item`.
///
/// It can be combined with [try_enumerate](crate::try_stream::TryStreamExt::try_enumerate) and
/// unordered parallel tasks.
///
/// If an `Err` item is received, it stops receiving future items and flushes buffered values,
/// and sends the `Err` in the end.
///
/// ```rust
/// # par_stream::rt::block_on_executor(async move {
/// use futures::prelude::*;
/// use par_stream::prelude::*;
///
/// let result: Result<Vec<_>, _> = stream::iter(0..100)
/// .map(|val| if val < 50 { Ok(val) } else { Err(val) })
/// // add index number
/// .try_enumerate()
/// // double the values in parallel
/// .try_par_then_unordered(None, move |(index, value)| {
/// // the closure is sent to parallel worker
/// async move { Ok((index, value * 2)) }
/// })
/// // add values by one in parallel
/// .try_par_then_unordered(None, move |(index, value)| {
/// // the closure is sent to parallel worker
/// async move {
/// let new_val = value + 1;
/// if new_val < 50 {
/// Ok((index, new_val))
/// } else {
/// Err(value)
/// }
/// }
/// })
/// // reorder the values according to index number
/// .try_reorder_enumerated()
/// .try_collect()
/// .await;
/// # })
/// ```
fn try_reorder_enumerated(self) -> TryReorderEnumerated<Self, Self::Ok, Self::Error>;
}
impl<S, T, E> TryIndexStreamExt for S
where
S: Stream<Item = Result<(usize, T), E>>,
{
type Ok = T;
type Error = E;
fn try_reorder_enumerated(self) -> TryReorderEnumerated<Self, T, E> {
TryReorderEnumerated {
stream: self,
commit: 0,
pending_error: None,
is_terminated: false,
buffer: HashMap::new(),
_phantom: PhantomData,
}
}
}
// try_reorder_enumerated
pub use try_reorder_enumerated::*;
mod try_reorder_enumerated {
use super::*;
/// Stream for the [try_reorder_enumerated()](TryIndexStreamExt::try_reorder_enumerated) method.
#[derive(Derivative)]
#[derivative(Debug)]
#[pin_project]
pub struct TryReorderEnumerated<S, T, E>
where
S: ?Sized,
{
pub(super) commit: usize,
pub(super) is_terminated: bool,
pub(super) pending_error: Option<E>,
pub(super) buffer: HashMap<usize, T>,
pub(super) _phantom: PhantomData<E>,
#[pin]
#[derivative(Debug = "ignore")]
pub(super) stream: S,
}
impl<S, T, E> Stream for TryReorderEnumerated<S, T, E>
where
S: Stream<Item = Result<(usize, T), E>>,
{
type Item = Result<T, E>;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
let mut this = self.project();
Ready(loop {
if *this.is_terminated {
break None;
} else if let Some(err) = this.pending_error.take() {
if let Some(item) = this.buffer.remove(this.commit) {
*this.pending_error = Some(err);
*this.commit += 1;
break Some(Ok(item));
} else {
*this.is_terminated = true;
break Some(Err(err));
}
} else if let Some(item) = this.buffer.remove(this.commit) {
*this.commit += 1;
break Some(Ok(item));
} else {
match ready!(Pin::new(&mut this.stream).poll_next(cx)) {
Some(Ok((index, item))) => match (*this.commit).cmp(&index) {
Less => {
let prev = this.buffer.insert(index, item);
assert!(
prev.is_none(),
"the index number {} appears more than once",
index
);
}
Equal => {
*this.commit += 1;
break Some(Ok(item));
}
Greater => {
panic!("the index number {} appears more than once", index);
}
},
Some(Err(err)) => {
*this.pending_error = Some(err);
}
None => {
assert!(
this.buffer.is_empty(),
"the item for index number {} is missing",
this.commit
);
break None;
}
}
}
})
}
}
impl<S, T, E> FusedStream for TryReorderEnumerated<S, T, E>
where
Self: Stream,
{
fn is_terminated(&self) -> bool {
self.is_terminated
}
}
}