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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>. | | 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 ==
| | [http://haskell.org/haskellwiki/GHC/Concurrency/Zeta Riemann's Zeta function approximation] |
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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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| <haskell>
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| import Control.Concurrent
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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 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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| cut (x,y) n = (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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| cut' x' size' n' = (x', x' + size' - 1) : cut' (x' + size') size' (n' - size')
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| getParams :: IO (Int, Int, Complex Double)
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| getParams = do
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| argv <- getArgs
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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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Revision as of 15:22, 28 November 2006
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.
Riemann's Zeta function approximation