Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::mutex_atomic: Checks for usage of Mutex<X> where an atomic will do

What it meansChecks for usage of Mutex<X> where an atomic will do. It is in the restriction group and off by default.

Does it matter?

Using a mutex just to make access to a plain bool or reference sequential is shooting flies with cannons. std::sync::atomic::AtomicBool and std::sync::atomic::AtomicPtr are leaner and faster. On the other hand, Mutexes are, in general, easier to verify correctness. An atomic does not behave the same as an equivalent mutex. See this issue’s commentary for more details.

Lints that forbid language features for specific codebases (no unwrap, no indexing...). Off by default; pick them one by one, never the whole group.

How to fix it

Clippy does not fix this one automatically (its suggestion may change behaviour, so it only shows it). Change the code by hand:

Flagged

let x = Mutex::new(&y);

Write this instead

let x = AtomicBool::new(y);

Turn it off, or on

It is off by default. To use it, set it to warn or deny:

Whole crate (Cargo.toml)

[lints.clippy]
mutex_atomic = "warn"

In code

#![warn(clippy::mutex_atomic)]

One run

cargo clippy -- -W clippy::mutex-atomic

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.

Restrictiongroup

allowdefault level

nofixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Checks for usage of Mutex<X> where an atomic will do.

Why restrict this?

Using a mutex just to make access to a plain bool or reference sequential is shooting flies with cannons. std::sync::atomic::AtomicBool and std::sync::atomic::AtomicPtr are leaner and faster.

On the other hand, Mutexes are, in general, easier to verify correctness. An atomic does not behave the same as an equivalent mutex. See this issue’s commentary for more details.

Known problems

This lint cannot detect if the mutex is actually used for waiting before a critical section.
This lint has a false positive that warns without considering the case where Mutex is used together with Condvar.

Example

let x = Mutex::new(&y);

Use instead:

let x = AtomicBool::new(y);

From the Clippy lint list (0.1.99), part of the Rust project, MIT or Apache-2.0. Official entry.

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