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https://github.com/awslabs/shuttle

Shuttle is a library for testing concurrent Rust code
https://github.com/awslabs/shuttle

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Shuttle is a library for testing concurrent Rust code

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# Shuttle



[![crates.io](https://img.shields.io/crates/v/shuttle.svg)](https://crates.io/crates/shuttle)

[![docs.rs](https://docs.rs/shuttle/badge.svg)](https://docs.rs/shuttle)

[![Tests](https://github.com/awslabs/shuttle/actions/workflows/tests.yml/badge.svg)](https://github.com/awslabs/shuttle/actions/workflows/tests.yml)



Shuttle is a library for testing concurrent Rust code. It is an implementation of a number of

*randomized concurrency testing* techniques, including

[A Randomized Scheduler with Probabilistic Guarantees of Finding Bugs](https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/asplos277-pct.pdf).



## Getting started



Consider this simple piece of concurrent code:



```rust

use std::sync::{Arc, Mutex};

use std::thread;



let lock = Arc::new(Mutex::new(0u64));

let lock2 = lock.clone();



thread::spawn(move || {

    *lock.lock().unwrap() = 1;

});



assert_eq!(0, *lock2.lock().unwrap());

```



There is an obvious race condition here: if the spawned thread runs before the assertion, the

assertion will fail. But writing a unit test that finds this execution is tricky. We could run

the test many times and try to "get lucky" by finding a failing execution, but that's not a very

reliable testing approach. Even if the test does fail, it will be difficult to debug: we won't

be able to easily catch the failure in a debugger, and every time we make a change, we will need

to run the test many times to decide whether we fixed the issue.



### Randomly testing concurrent code with Shuttle



Shuttle avoids this issue by controlling the scheduling of each thread in the program, and

scheduling those threads *randomly*. By controlling the scheduling, Shuttle allows us to

reproduce failing tests deterministically. By using random scheduling, with appropriate

heuristics, Shuttle can still catch most (non-adversarial) concurrency bugs even though it is

not an exhaustive checker.



A Shuttle version of the above test just wraps the test body in a call to Shuttle's

`check_random` function, and replaces the concurrency-related imports from `std` with imports

from `shuttle`:



```rust

use shuttle::sync::{Arc, Mutex};

use shuttle::thread;



shuttle::check_random(|| {

    let lock = Arc::new(Mutex::new(0u64));

    let lock2 = lock.clone();



    thread::spawn(move || {

        *lock.lock().unwrap() = 1;

    });



    assert_eq!(0, *lock2.lock().unwrap());

}, 100);

```



This test detects the assertion failure with extremely high probability (over 99.9999%).



Shuttle is inspired by the [Loom](https://github.com/tokio-rs/loom) library for

testing concurrent Rust code.  Shuttle focuses on randomized testing, rather

than the exhaustive testing that Loom offers. This is a soundness—scalability

trade-off: Shuttle is not sound (a passing Shuttle test does not prove the code

is correct), but it scales to much larger test cases than Loom. Empirically,

randomized testing is successful at finding most concurrency bugs, which tend

not to be adversarial.

## License



This project is licensed under the Apache-2.0 License.



## Security



See [CONTRIBUTING](CONTRIBUTING.md#security-issue-notifications) for more information.