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Clarified docs in std::sync::RwLock#153555

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Clarified docs in std::sync::RwLock#153555
asder8215 wants to merge 1 commit intorust-lang:mainfrom
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@asder8215 asder8215 commented Mar 8, 2026 •
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This addresses the issue with the std::sync::RwLock docs in #115338. It centers around the following lines:

An RwLock will allow any number of readers to acquire the lock as long as a writer is not holding the lock.

It's true that the RwLock in theory should allow any number of readers to acquire the lock when a writer is not holding it, but this may not be true in the implementation and could be os dependent. I decided to replace "any number of readers" to "multiple", so that it implies that more than 1 reader can acquire the lock, but you can't necessarily take away that this value is unbounded.

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@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Mar 8, 2026
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rustbot commented Mar 8, 2026

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@rustbot rustbot added the A-docs Area: Documentation for any part of the project, including the compiler, standard library, and tools label Mar 8, 2026
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Mark-Simulacrum commented Mar 9, 2026

Can we add a test that e.g. at least 2^32 read locks can be acquired and then document that? I've certainly written code (though not particularly cross-platform deployed code) that would benefit from a stronger guarantee here, and it seems like at least on tier 1 targets (for which we test in CI) we should be able to give a stronger guarantee than 'at least 2' :)

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asder8215 commented Mar 9, 2026

Can we add a test that e.g. at least 2^32 read locks can be acquired and then document that? I've certainly written code (though not particularly cross-platform deployed code) that would benefit from a stronger guarantee here, and it seems like at least on tier 1 targets (for which we test in CI) we should be able to give a stronger guarantee than 'at least 2' :)

I can do that for sure. Regarding the test, do you want me to add this in as a doctest within the RwLock::read() or within std/src/tests/sync/rwlock.rs? I think either way works.

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Mark-Simulacrum commented Mar 9, 2026

I don't think it should be a doc test, seems too noisy for the docs.

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A-docs Area: Documentation for any part of the project, including the compiler, standard library, and tools S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue.

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