Clippy lint · Restriction · checked with Clippy 0.1.99

clippy::rc_mutex: Checks for Rc<Mutex<T>>

What it meansChecks for Rc<Mutex<T>>. It is in the restriction group and off by default.

Does it matter?

Rc is used in single thread and Mutex is used in multi thread. Consider using Rc<RefCell<T>> in single thread or Arc<Mutex<T>> in multi thread.

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. Change the code by hand:

Flagged

use std::rc::Rc;
use std::sync::Mutex;
fn foo(interned: Rc<Mutex<i32>>) { ... }

Write this instead

use std::rc::Rc;
use std::cell::RefCell
fn foo(interned: Rc<RefCell<i32>>) { ... }

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]
rc_mutex = "warn"

In code

#![warn(clippy::rc_mutex)]

One run

cargo clippy -- -W clippy::rc-mutex

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.

Settings in clippy.toml

avoid-breaking-exported-api: Suppress lints whenever the suggested change would cause breakage for other crates.

Restrictiongroup

allowdefault level

nofixed by cargo clippy --fix

1.55.0added in Rust

Clippy's own documentation

What it does

Checks for Rc<Mutex<T>>.

Why restrict this?

Rc is used in single thread and Mutex is used in multi thread. Consider using Rc<RefCell<T>> in single thread or Arc<Mutex<T>> in multi thread.

Known problems

Sometimes combining generic types can lead to the requirement that a type use Rc in conjunction with Mutex. We must consider those cases false positives, but alas they are quite hard to rule out. Luckily they are also rare.

Example

use std::rc::Rc;
use std::sync::Mutex;
fn foo(interned: Rc<Mutex<i32>>) { ... }

Better:

use std::rc::Rc;
use std::cell::RefCell
fn foo(interned: Rc<RefCell<i32>>) { ... }

Configuration

avoid-breaking-exported-api: Suppress lints whenever the suggested change would cause breakage for other crates.

(default: true)

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

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