# Concurrency demos

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A large range of small demonstration programs for using concurrent and | A large range of small demonstration programs for using concurrent and | ||

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>. | ||

+ | |||

+ | == A simple example of parallelism in Haskell == | ||

+ | |||

+ | <haskell> | ||

+ | module Main where | ||

+ | |||

+ | import Control.Concurrent | ||

+ | import Control.Concurrent.MVar | ||

+ | import Control.Monad | ||

+ | import Data.Complex | ||

+ | import System.Environment | ||

+ | |||

+ | zetaRange :: (Floating (Complex a), RealFloat a, Integral b) => | ||

+ | Complex a -> (b, b) -> Complex a | ||

+ | zetaRange s (x,y) = sum [ (fromIntegral n :+ 0) ** (-s) | n <- [x..y] ] | ||

+ | |||

+ | cut :: (Integral a) => (a, a) -> a -> [(a, a)] | ||

+ | cut (x,y) n = | ||

+ | (x, x + mine - 1) : cut' (x + mine) size (y - mine) | ||

+ | where | ||

+ | (size, modulo) = y `divMod` n | ||

+ | mine = size + modulo | ||

+ | |||

+ | cut' _ _ 0 = [] | ||

+ | cut' x' size' n' = (x', x' + size' - 1) : cut' (x' + size') size' (n' - size') | ||

+ | |||

+ | getParams :: IO (Int, Int, Complex Double) | ||

+ | getParams = do | ||

+ | argv <- getArgs | ||

+ | case argv of | ||

+ | (t:n:s:[]) -> return (read t, read n, read s) | ||

+ | _ -> error "usage: zeta <nthreads> <boundary> <s>" | ||

+ | |||

+ | main :: IO () | ||

+ | main = do | ||

+ | (t, n, s) <- getParams | ||

+ | childs <- zipWithM thread (repeat s) (cut (1, n) t) | ||

+ | results <- mapM takeMVar childs | ||

+ | print $ sum results | ||

+ | where | ||

+ | thread s range = do | ||

+ | putStrLn $ "Starting thread for range " ++ show range | ||

+ | mvar <- newEmptyMVar | ||

+ | forkIO (putMVar mvar (zetaRange s range)) | ||

+ | return mvar | ||

+ | </haskell> |

## Revision as of 13:44, 28 November 2006

A large range of small demonstration programs for using concurrent and

MVars

forkIO

## A simple example of parallelism in Haskell

module Main where import Control.Concurrent import Control.Concurrent.MVar import Control.Monad import Data.Complex import System.Environment zetaRange :: (Floating (Complex a), RealFloat a, Integral b) => Complex a -> (b, b) -> Complex a zetaRange s (x,y) = sum [ (fromIntegral n :+ 0) ** (-s) | n <- [x..y] ] cut :: (Integral a) => (a, a) -> a -> [(a, a)] cut (x,y) n = (x, x + mine - 1) : cut' (x + mine) size (y - mine) where (size, modulo) = y `divMod` n mine = size + modulo cut' _ _ 0 = [] cut' x' size' n' = (x', x' + size' - 1) : cut' (x' + size') size' (n' - size') getParams :: IO (Int, Int, Complex Double) getParams = do argv <- getArgs case argv of (t:n:s:[]) -> return (read t, read n, read s) _ -> error "usage: zeta <nthreads> <boundary> <s>" main :: IO () main = do (t, n, s) <- getParams childs <- zipWithM thread (repeat s) (cut (1, n) t) results <- mapM takeMVar childs print $ sum results where thread s range = do putStrLn $ "Starting thread for range " ++ show range mvar <- newEmptyMVar forkIO (putMVar mvar (zetaRange s range)) return mvar