https://github.com/statusfailed/machines-io

https://github.com/statusfailed/machines-io

Last synced: 12 months ago
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• Host: GitHub
• URL: https://github.com/statusfailed/machines-io
• Owner: statusfailed
• License: mit
• Created: 2015-04-26T18:42:31.000Z (almost 11 years ago)
• Default Branch: master
• Last Pushed: 2018-01-30T23:07:40.000Z (about 8 years ago)
• Last Synced: 2025-01-31T08:18:58.369Z (about 1 year ago)
• Language: Haskell
• Size: 6.84 KB
• Stars: 2
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
# Concurrency utilities for `machines`

NOTE: this is mostly an experiment. I advise against using it!

# What is it for?

Simple use case: if you have two sources of data (say sockets),

and you want to do a blocking read on both, and merge the events

Example code below. Note this will finish by crashing, because

there are no more processes writing to the `Chan`.

    {-# LANGUAGE RankNTypes #-}

    module Main where

    import Data.Machine

    import Data.Machine.IO.Concurrent

    import Control.Monad.IO.Class

    import Control.Concurrent (newChan, forkIO, threadDelay)

    -- | Yield elements from a list with a specified delay in microseconds between each.

    slowSource :: MonadIO m => Int -> [a] -> ProcessT m () a

    slowSource t xs = construct $ go xs

      where

        go [] = return ()

        go (x:xs) = do

          liftIO $ threadDelay t -- wait 1 second

          yield x

          go xs

    main = do

      c <- newChan

      t1 <- forkIO id (runT_ $ slowSource 500000  [1..4] ~> toChan c)

      t2 <- forkIO id (runT_ $ slowSource 1000000 [1..4] ~> toChan c)

      runT_ $ fromChan c ~> autoM print

      print "done"

Running it:

    *Main> main

    1

    2

    1

    3

    4

    2

    3

    4

    *** Exception: thread blocked indefinitely in an MVar operation