concurrency =========== A typeclass abstraction over much of Control.Concurrent (and some extras!). If you're looking for a general introduction to Haskell concurrency, you should check out the excellent [Parallel and Concurrent Programming in Haskell][parconc], by Simon Marlow. If you are already familiar with concurrent Haskell, just change all the imports from Control.Concurrent.* to Control.Concurrent.Classy.* and fix the type errors. A brief list of supported functionality: - Threads: both unbound and bound. - Getting and setting capablities. - Yielding and delaying. - Mutable state: STM, `MVar`, and `IORef`. - Atomic compare-and-swap for `IORef`. - Exceptions. - All of the data structures in Control.Concurrent.* and Control.Concurrent.STM.* have typeclass-abstracted equivalents. - A reimplementation of the [async][] package, providing a higher-level interface over threads, allowing users to conveniently run `MonadConc` operations asynchronously and wait for their results. This is quite a rich set of functionality, although it is not complete. If there is something else you need, file an issue! This used to be part of dejafu, but with the dejafu-0.4.0.0 release, it was split out into its own package. Why this and not something else? -------------------------------- - **Why not base:** like lifted-base, concurrency uses typeclasses to make function types more generic. This automatically eliminates calls to `lift` in many cases, resulting in clearer and simpler code. - **Why not lifted-base:** fundamentally, lifted-base is still using actual threads and actual mutable variables. When using a concurrency-specific typeclass, this isn't necessarily the case. The dejafu library provides non-IO-based implementations to allow testing concurrent programs. - **Why not IOSpec:** IOSpec provides many of the operations this library does, however it uses a free monad to do so, which has extra allocation overhead. Furthermore, it does not expose enough of the internals in order to accurately test real-execution semantics, such as relaxed memory. Contributing ------------ Bug reports, pull requests, and comments are very welcome! Feel free to contact me on GitHub, through IRC (#haskell on libera.chat), or email (mike@barrucadu.co.uk). [async]: https://hackage.haskell.org/package/async [parconc]: http://chimera.labs.oreilly.com/books/1230000000929