loom 0.4.1

Permutation testing for concurrent code


Loom is a testing tool for concurrent Rust code. It runs a test many times, permuting the possible concurrent executions of that test under the [C11 memory model]. It uses [state reduction techniques][cdschecker] to avoid combinatorial explosion.

Crates.io [Documentation][docs] Build Status

docs [spec]: https://en.cppreference.com/w/cpp/atomic/memory_order [cdschecker]: http://demsky.eecs.uci.edu/publications/c11modelcheck.pdf


The [loom documentation][docs] has significantly more documentation on how to use loom. But if you just want a jump-start, first add this to your Cargo.toml.

loom = "0.4"

Next, create a test file and add a test:

use loom::sync::Arc;
use loom::sync::atomic::AtomicUsize;
use loom::sync::atomic::Ordering::{Acquire, Release, Relaxed};
use loom::thread;

fn buggy_concurrent_inc() {
    loom::model(|| {
        let num = Arc::new(AtomicUsize::new(0));

        let ths: Vec<_> = (0..2)
            .map(|_| {
                let num = num.clone();
                thread::spawn(move || {
                    let curr = num.load(Acquire);
                    num.store(curr + 1, Release);

        for th in ths {

        assert_eq!(2, num.load(Relaxed));

Then, run the test with

RUSTFLAGS="--cfg loom" cargo test --test buggy_concurrent_inc --release


This project is licensed under the MIT license.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in loom by you, shall be licensed as MIT, without any additional terms or conditions.