1 unstable release

0.1.0 Jan 14, 2024

#465 in Concurrency

MIT license

5.5K SLoC


Testing for concurrent code.


Add this to your Cargo.toml:

fenic = "0.7"

Next, create a test file and add a test:

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

fn buggy_concurrent_inc() {
    fenic::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 fenic" cargo test --test buggy_concurrent_inc --release

Unsupported features

Loom currently does not implement the full C11 memory model. Here is the (incomplete) list of unsupported features.

  • SeqCst accesses (e.g. load, store, ..): They are are regarded as AcqRel. That is, they impose weaker synchronization, causing Loom to generate false alarms (not complete). See #180 for example. On the other hand, fence(SeqCst) is supported.
  • Load buffering behavior: Loom does not explore some executions that are possible in the C11 memory model. That is, there can be a bug in the checked code even if Loom says there is no bug (not sound). See the load_buffering test case in tests/litmus.rs.


This project is licensed under the MIT license.


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


~424K SLoC