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Atomic compare exchange shouldn't require the failure ordering to be as strong as the success ordering #97418

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m-ou-se opened this issue May 26, 2022 · 2 comments
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Atomic compare exchange shouldn't require the failure ordering to be as strong as the success ordering #97418

m-ou-se opened this issue May 26, 2022 · 2 comments
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A-concurrency Area: Concurrency A-intrinsics Area: Intrinsics T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

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@m-ou-se
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m-ou-se commented May 26, 2022

Right now, Rust does not support compare_exchange(a, b, Acquire, Release): we require the success ordering to be at least as strong as the failure ordering, which means we must upgrade the success ordering to AcqRel in this example.

C++ proposal P0418r2 argues this is unnecessary.

The restriction has been removed in C++17. We should consider doing the same in Rust.
@m-ou-se m-ou-se added A-concurrency Area: Concurrency T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. A-intrinsics Area: Intrinsics labels May 26, 2022
@tmiasko
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tmiasko commented May 26, 2022

Duplicate of #68464.

@m-ou-se
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m-ou-se commented May 26, 2022

Oh, thanks!

@m-ou-se m-ou-se closed this as completed May 26, 2022
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A-concurrency Area: Concurrency A-intrinsics Area: Intrinsics T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.
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