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mention Arc::make_mut alongside Mutex #138322

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lolbinarycat opened this issue Mar 10, 2025 · 1 comment · Fixed by #138341
Closed

mention Arc::make_mut alongside Mutex #138322

lolbinarycat opened this issue Mar 10, 2025 · 1 comment · Fixed by #138341
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@xizheyin
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A-docs Area: Documentation for any part of the project, including the compiler, standard library, and tools needs-triage This issue may need triage. Remove it if it has been sufficiently triaged.

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@lolbinarycat
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lolbinarycat commented Mar 10, 2025 •
edited by rustbot
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https://doc.rust-lang.org/stable/std/sync/struct.Arc.html

Summary

The prose here mentions how Arc does not provide interior mutability, but in many cases you don't actually need shared interior mutability, just the ability to effeciently mutate something that happens to be in an Arc.

Seeing how many people who are new to rust gravitate towards Arc<Mutex<T>> to avoid dealing with references, it would probably be good to mention copy-on-write semantics as an alternative.
@lolbinarycat lolbinarycat added the A-docs Area: Documentation for any part of the project, including the compiler, standard library, and tools label Mar 10, 2025
@rustbot rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Mar 10, 2025
@xizheyin
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Shared interior mutability, i.e. Arc<Mutex<T>> can cause performance degradation, I can try this. I made this mistake once.

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@xizheyin xizheyin mentioned this issue Mar 11, 2025
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@bors bors closed this as completed in 625278b Mar 17, 2025
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Mar 17, 2025
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Unrolled build for rust-lang#138341
b04b807 
Rollup merge of rust-lang#138341 - xizheyin:issue-138322, r=joboet

std: Mention clone-on-write mutation in Arc<T>

Fixes rust-lang#138322

r? libs
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std: Mention clone-on-write mutation in Arc<T> xizheyin/rust
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