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Concurrency demos

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[[Category:Tutorials]]
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This page collects examples of concurrent and parallel programming in Haskell.
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[[Category:Code]]
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A large range of small demonstration programs for using concurrent and
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== Examples ==
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parallel Haskell are in the Haskell [http://darcs.haskell.org/testsuite/tests/ghc-regress/concurrent/should_run/ concurrency regression tests]. In particular, they show the use of <hask>MVars</hask> and <hask>forkIO</hask>.
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== A simple example of parallelism in Haskell ==
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* [[/Zeta |Riemann's Zeta function approximation]]
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* [[/Graceful exit|Signal that you want to gracefully exit another thread]]
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* [[/Two reader threads|Passing messages across a single chan to two readers]]
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* [[Implement a chat server|Chat server - using a single channel for a variable number of readers]]
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* [[/Simple producer and consumer|Passing IO events lazily from a producer to a consumer thread]]
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This little piece of code computes an approximation of Riemann's zeta function, balancing the work to be done between N threads.
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== More examples ==
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<haskell>
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A large range of small demonstration programs for using concurrent and
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import Control.Concurrent
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parallel Haskell are in the Haskell [http://darcs.haskell.org/testsuite/tests/ghc-regress/concurrent/should_run/ concurrency regression tests]. In particular, they show the use of <hask>MVars</hask> and <hask>forkIO</hask>.
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import Control.Concurrent.MVar
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import Control.Monad
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import Data.Complex
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import System.Environment
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zetaRange :: (Floating (Complex a), RealFloat a, Integral b) => Complex a -> (b, b) -> Complex a
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== Proposed updates ==
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zetaRange s (x,y) = sum [ (fromIntegral n :+ 0) ** (-s) | n <- [x..y] ]
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cut :: (Integral a) => (a, a) -> a -> [(a, a)]
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The base 3.0.3.1 package's Control.Concurrent.QSem and QSemN are not exception safe. The [[SafeConcurrent]] has the proposed replacement code.
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cut (x,y) n =
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(x, x + mine - 1) : cut' (x + mine) size (y - mine)
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where
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(size, modulo) = y `divMod` n
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mine = size + modulo
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cut' _ _ 0 = []
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== Other examples ==
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cut' x' size' n' = (x', x' + size' - 1) : cut' (x' + size') size' (n' - size')
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* [[/Haskell-Javascript concurrency|Haskell -> Javascript: Pseudo-concurrent threads in web browser]]
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getParams :: IO (Int, Int, Complex Double)
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[[Category:Parallel]]
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getParams = do
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[[Category:Tutorials]]
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argv <- getArgs
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[[Category:Code]]
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case argv of
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(t:n:s:[]) -> return (read t, read n, read s)
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_ -> error "usage: zeta <nthreads> <boundary> <s>"
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main :: IO ()
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main = do
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(t, n, s) <- getParams
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childs <- zipWithM thread (repeat s) (cut (1, n) t)
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results <- mapM takeMVar childs
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print $ sum results
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where
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thread s range = do
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putStrLn $ "Starting thread for range " ++ show range
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mvar <- newEmptyMVar
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forkIO (putMVar mvar (zetaRange s range))
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return mvar
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</haskell>
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Current revision

This page collects examples of concurrent and parallel programming in Haskell.

Contents

1 Examples

2 More examples

A large range of small demonstration programs for using concurrent and

parallel Haskell are in the Haskell concurrency regression tests. In particular, they show the use of
MVars
and
forkIO
.

3 Proposed updates

The base 3.0.3.1 package's Control.Concurrent.QSem and QSemN are not exception safe. The SafeConcurrent has the proposed replacement code.

4 Other examples

Retrieved from "http://www.haskell.org/haskellwiki/Concurrency_demos"

Categories: Parallel | Tutorials | Code