> For the complete documentation index, see [llms.txt](https://osl.mistium.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://osl.mistium.com/standard-library/concurrency.md).

# Concurrency and embedded languages

Packages for scripting, background threads, and synchronization.

* [testing](/standard-library/concurrency/testing.md) - Assertions for `osl test` files.
* [js](/standard-library/concurrency/js.md) - Run sandboxed JavaScript with hard resource limits.
* [lua](/standard-library/concurrency/lua.md) - Embed and run Lua scripts.
* [thread](/standard-library/concurrency/thread.md) - Background threads, parallel workers, racing, and message channels.
* [sync](/standard-library/concurrency/sync.md) - Named locks, scoped locking, one-time execution, and wait groups.