The concurrent-extra package offers among other things the following selection of synchronisation primitives: Broadcast: Wake multiple threads by broadcasting a value. Event: Wake multiple threads by signalling an event. Lock: Enforce exclusive access to a resource. Also known as a binary semaphore or mutex. The package additionally provides an alternative that works in the STM monad. RLock: A lock which can be acquired multiple times by the same thread. Also known as a reentrant mutex. ReadWriteLock: Multiple-reader, single-writer locks. Used to protect shared resources which may be concurrently read, but only sequentially written. ReadWriteVar: Concurrent read, sequential write variables. Please consult the API documentation of the individual modules for more detailed information. This package was inspired by the concurrency libraries of Java and Python.