parallel-io

It is often useful to be able to execute a number of IO actions in parallel, and then either gather the results back up, or report completion of the actions. This package is designed to support this scenario by providing a number of high-level combinators for enabling this parallelism without any hard work on your part. Features include:

• High level interface to powerful parallelism.
• Finer grained interface if you prefer to manage thread pools yourself.
• An effort is made to keep the number of unblocked threads running at exactly the number you request, to reduce contention for processor resources.
• No hidden exceptions on background threads!

import Control.Concurrent.ParallelIO
import qualified Control.Concurrent.ParallelIO.Local as Local

main = do
  -- Example with the global pool. You should call stopGlobalPool
  -- after the last use of a global parallelism combinator - the
  -- end of the main function is a fine place.
  parallel_ [putStrLn "Hello", putStrLn "World"]
  stopGlobalPool
  
  -- Example of an explicitly sized and passed pool. Use 2 threads.
  Local.withPool 2 $ \pool -> do
    Local.parallel_ pool [putStrLn "Goodbype", putStrLn "World"]

We can run this like so to get our parallel goodness:

$ ghc -package parallel-io -threaded Example.hs -o Example
$ ./Example +RTS -N2