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feat: Remove MaybeDone for tuple::join (without additional deps) #84

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feat: Remove MaybeDone for tuple::join (without additional deps) #84

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93 changes: 66 additions & 27 deletions src/future/join/tuple.rs
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Original file line number Diff line number Diff line change
@@ -1,16 +1,30 @@
use super::Join as JoinTrait;
use crate::utils::MaybeDone;
use crate::utils::PollState;

use core::fmt::{self, Debug};
use core::future::{Future, IntoFuture};
use core::mem::MaybeUninit;
use core::pin::Pin;
use core::task::{Context, Poll};

use pin_project::pin_project;

macro_rules! impl_merge_tuple {
($StructName:ident $($F:ident)*) => {
/// Waits for two similarly-typed futures to complete.
($mod_name:ident :: $StructName:ident $($F:ident)*) => {
mod $mod_name {
#[allow(unused_imports)] // Len == 0
use super::*;

pub(super) struct Outputs<$($F: Future),*> {
$(pub(super) $F: MaybeUninit<$F::Output>),*
}

pub(super) struct States {
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you could use PollStates here

I can run a comparison with the main, my branch, and ours after that :)

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but here's the current results

>> critcmp main patch84 -f tuple::join
group             patch84                                   main
-----             -------                                   ----
tuple::join 10    1.00    213.1±0.96ns        ? ?/sec    1.12    239.5±0.56ns        ? ?/sec

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PollStates is not no_std since it uses Box, we probably want a static version for tuples and small arrays to avoid lots of small branches

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We have a no_std version of PollStates now: utils::PollArray.

$(pub(super) $F: PollState),*
}
}

/// Waits for similarly-typed futures to complete.
///
/// This `struct` is created by the [`join`] method on the [`Join`] trait. See
/// its documentation for more.
Expand All @@ -21,8 +35,10 @@ macro_rules! impl_merge_tuple {
#[must_use = "futures do nothing unless you `.await` or poll them"]
#[allow(non_snake_case)]
pub struct $StructName<$($F: Future),*> {
done: bool,
$(#[pin] $F: MaybeDone<$F>,)*
completed: usize,
$(#[pin] $F: $F,)*
outputs: $mod_name::Outputs<$($F),*>,
states: $mod_name::States,
}

impl<$($F),*> Debug for $StructName<$($F),*>
Expand All @@ -46,17 +62,38 @@ macro_rules! impl_merge_tuple {
fn poll(
self: Pin<&mut Self>, cx: &mut Context<'_>
) -> Poll<Self::Output> {
let mut all_done = true;
const LEN: usize = {
// This will disappear after compilation, leaving only the usize constant but
// we need it to indicate a type for the slice content (for empty slices).
const ARRAY: &[&str] = &[$(stringify!($F)),*];
ARRAY.len()
};

let mut this = self.project();
assert!(!*this.done, "Futures must not be polled after completing");

$(all_done &= this.$F.as_mut().poll(cx).is_ready();)*
assert_ne!(*this.completed, LEN + 1, "Futures must not be polled after completing");

if all_done {
*this.done = true;
Poll::Ready(($(this.$F.take().unwrap()),*))
} else {
$(
if this.states.$F.is_pending() {
if let Poll::Ready(value) = this.$F.poll(cx) {
this.outputs.$F.write(value);
this.states.$F = PollState::Done;
*this.completed += 1;
}
}
)*

if *this.completed < LEN {
Poll::Pending
} else {
*this.completed += 1; // That way the 0-len case can be awaited once without problems
Poll::Ready(( $({
let mut out = MaybeUninit::uninit();
core::mem::swap(&mut this.outputs.$F, &mut out);
// Safety: we have reached `this.completed == LEN` so all futures have
// been successfully polled and the output written to `this.output`.
unsafe { out.assume_init() }
}),* ))
}
}
}
Expand All @@ -72,27 +109,29 @@ macro_rules! impl_merge_tuple {
fn join(self) -> Self::Future {
let ($($F,)*): ($($F,)*) = self;
$StructName {
done: false,
$($F: MaybeDone::new($F.into_future())),*
completed: 0,
$($F: $F.into_future(),)*
outputs: $mod_name::Outputs { $($F: MaybeUninit::uninit()),* },
states: $mod_name::States { $($F: PollState::default()),* },
}
}
}
};
}

impl_merge_tuple! { Join0 }
impl_merge_tuple! { Join1 A }
impl_merge_tuple! { Join2 A B }
impl_merge_tuple! { Join3 A B C }
impl_merge_tuple! { Join4 A B C D }
impl_merge_tuple! { Join5 A B C D E }
impl_merge_tuple! { Join6 A B C D E F }
impl_merge_tuple! { Join7 A B C D E F G }
impl_merge_tuple! { Join8 A B C D E F G H }
impl_merge_tuple! { Join9 A B C D E F G H I }
impl_merge_tuple! { Join10 A B C D E F G H I J }
impl_merge_tuple! { Join11 A B C D E F G H I J K }
impl_merge_tuple! { Join12 A B C D E F G H I J K L }
impl_merge_tuple! { join_0 :: Join0 }
impl_merge_tuple! { join_1 :: Join1 A }
impl_merge_tuple! { join_2 :: Join2 A B }
impl_merge_tuple! { join_3 :: Join3 A B C }
impl_merge_tuple! { join_4 :: Join4 A B C D }
impl_merge_tuple! { join_5 :: Join5 A B C D E }
impl_merge_tuple! { join_6 :: Join6 A B C D E F }
impl_merge_tuple! { join_7 :: Join7 A B C D E F G }
impl_merge_tuple! { join_8 :: Join8 A B C D E F G H }
impl_merge_tuple! { join_9 :: Join9 A B C D E F G H I }
impl_merge_tuple! { join_10 :: Join10 A B C D E F G H I J }
impl_merge_tuple! { join_11 :: Join11 A B C D E F G H I J K }
impl_merge_tuple! { join_12 :: Join12 A B C D E F G H I J K L }

#[cfg(test)]
mod test {
Expand Down