Clippy lint · Suspicious · checked with Clippy 0.1.99

clippy::empty_loop: empty `loop {}` wastes CPU cycles

What it meansChecks for empty loop expressions. It is in the suspicious group and warns by default.

What you see

warning: empty `loop {}` wastes CPU cycles
 --> main.rs:3:1
  |
3 | loop {}
  | ^^^^^^^
  |
  = help: you should either use `panic!()` or add `std::thread::sleep(..);` to the loop body
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#empty_loop
  = note: `#[warn(clippy::empty_loop)]` on by default

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

These busy loops burn CPU cycles without doing anything. It is almost always a better idea to panic! than to have a busy loop. If panicking isn’t possible, think of the environment and either: block on something sleep the thread for some microseconds yield or pause the thread For std targets, this can be done with std::thread::sleep or std::thread::yield_now. For no_std targets, doing this is more complicated, especially because #[panic_handler]s can’t panic. To stop/pause the thread, you will probably need to invoke some target-specific intrinsic. Examples include: x86_64::instructions::hlt cortex_m::asm::wfi

Code that is most likely wrong or useless. Warns by default.

How to fix it

Clippy does not fix this one automatically. Change the code by hand:

Flagged

loop {}

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

On one item

#[allow(clippy::empty_loop)]
fn my_function() { /* ... */ }

Whole crate (Cargo.toml)

[lints.clippy]
empty_loop = "allow"

One run

cargo clippy -- -A clippy::empty-loop

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.

Suspiciousgroup

warndefault level

nofixed by cargo clippy --fix

pre 1.29.0added in Rust

Clippy's own documentation

What it does

Checks for empty loop expressions.

Why is this bad?

These busy loops burn CPU cycles without doing anything. It is almost always a better idea to panic! than to have a busy loop.

If panicking isn’t possible, think of the environment and either:

block on something
sleep the thread for some microseconds
yield or pause the thread

For std targets, this can be done with std::thread::sleep or std::thread::yield_now.

For no_std targets, doing this is more complicated, especially because #[panic_handler]s can’t panic. To stop/pause the thread, you will probably need to invoke some target-specific intrinsic. Examples include:

Example

loop {}

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

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