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Add back Send and Sync impls on ChunksMut iterators #100023

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Aug 3, 2022
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Add back Send and Sync impls on ChunksMut iterators #100023

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24 changes: 24 additions & 0 deletions library/core/src/slice/iter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1788,6 +1788,12 @@ unsafe impl<'a, T> TrustedRandomAccessNoCoerce for ChunksMut<'a, T> {
const MAY_HAVE_SIDE_EFFECT: bool = false;
}

#[stable(feature = "rust1", since = "1.0.0")]
unsafe impl<T> Send for ChunksMut<'_, T> where T: Send {}

#[stable(feature = "rust1", since = "1.0.0")]
unsafe impl<T> Sync for ChunksMut<'_, T> where T: Sync {}

/// An iterator over a slice in (non-overlapping) chunks (`chunk_size` elements at a
/// time), starting at the beginning of the slice.
///
Expand Down Expand Up @@ -2114,6 +2120,12 @@ unsafe impl<'a, T> TrustedRandomAccessNoCoerce for ChunksExactMut<'a, T> {
const MAY_HAVE_SIDE_EFFECT: bool = false;
}

#[stable(feature = "chunks_exact", since = "1.31.0")]
unsafe impl<T> Send for ChunksExactMut<'_, T> where T: Send {}
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@danielhenrymantilla danielhenrymantilla Aug 3, 2022 •
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Debatable nit, but pointing it out just for consideration:

Suggested change
unsafe impl<T> Send for ChunksExactMut<'_, T> where T: Send {}
unsafe impl<'r, T> Send for ChunksExactMut<'r, T> where &'r mut [T]: Send {}

(this makes it "easier" to understand the causality relation, imho)

  • and so on for the others


#[stable(feature = "chunks_exact", since = "1.31.0")]
unsafe impl<T> Sync for ChunksExactMut<'_, T> where T: Sync {}

/// A windowed iterator over a slice in overlapping chunks (`N` elements at a
/// time), starting at the beginning of the slice
///
Expand Down Expand Up @@ -2835,6 +2847,12 @@ unsafe impl<'a, T> TrustedRandomAccessNoCoerce for RChunksMut<'a, T> {
const MAY_HAVE_SIDE_EFFECT: bool = false;
}

#[stable(feature = "rchunks", since = "1.31.0")]
unsafe impl<T> Send for RChunksMut<'_, T> where T: Send {}

#[stable(feature = "rchunks", since = "1.31.0")]
unsafe impl<T> Sync for RChunksMut<'_, T> where T: Sync {}

/// An iterator over a slice in (non-overlapping) chunks (`chunk_size` elements at a
/// time), starting at the end of the slice.
///
Expand Down Expand Up @@ -3168,6 +3186,12 @@ unsafe impl<'a, T> TrustedRandomAccessNoCoerce for RChunksExactMut<'a, T> {
const MAY_HAVE_SIDE_EFFECT: bool = false;
}

#[stable(feature = "rchunks", since = "1.31.0")]
unsafe impl<T> Send for RChunksExactMut<'_, T> where T: Send {}

#[stable(feature = "rchunks", since = "1.31.0")]
unsafe impl<T> Sync for RChunksExactMut<'_, T> where T: Sync {}

#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
unsafe impl<'a, T> TrustedRandomAccess for Iter<'a, T> {}
Expand Down
21 changes: 21 additions & 0 deletions library/core/tests/slice.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1191,6 +1191,27 @@ fn test_rchunks_exact_mut_zip() {
assert_eq!(v1, [0, 16, 17, 22, 23]);
}

#[test]
fn chunks_mut_are_send_and_sync() {
use std::cell::Cell;
use std::slice::{ChunksExactMut, ChunksMut, RChunksExactMut, RChunksMut};
use std::sync::MutexGuard;

#[allow(unused)]
fn assert_send_and_sync()
where
ChunksMut<'static, Cell<i32>>: Send,
ChunksMut<'static, MutexGuard<'static, u32>>: Sync,
ChunksExactMut<'static, Cell<i32>>: Send,
ChunksExactMut<'static, MutexGuard<'static, u32>>: Sync,
RChunksMut<'static, Cell<i32>>: Send,
RChunksMut<'static, MutexGuard<'static, u32>>: Sync,
RChunksExactMut<'static, Cell<i32>>: Send,
RChunksExactMut<'static, MutexGuard<'static, u32>>: Sync,
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@RalfJung RalfJung Aug 3, 2022 •
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Is that a reliable test? Don't we allow false where clauses that can never be satisfied (or might allow such things in the future)?

IMO the test should also call this function, to ensure its where clauses can actually be satisfied. An unused function with precondition False proves nothing.

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@danielhenrymantilla danielhenrymantilla Aug 3, 2022 •
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Yeah, we need an instantiation of it (not necessarily a call), à là:

let _ = assert_send_and_sync;

I guess a #[deny(trivial_bounds)] could do the job as well, since even with feature(trivial_bounds) at least that lint gets fired

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I may have time to address this in a follow-up tomorrow. I didn't want to delay this PR, and I don't have any spare time for this in the near future.

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#100112

{
}
}

#[test]
fn test_windows_count() {
let v: &[i32] = &[0, 1, 2, 3, 4, 5];
Expand Down