Concurrency demos
From HaskellWiki
(Difference between revisions)
| Line 40: | Line 40: | ||
childs <- zipWithM thread (repeat s) (cut (1, n) t) | childs <- zipWithM thread (repeat s) (cut (1, n) t) | ||
results <- mapM takeMVar childs | results <- mapM takeMVar childs | ||
| - | print | + | print (sum results) |
where | where | ||
thread s range = do | thread s range = do | ||
| - | putStrLn | + | putStrLn ("Starting thread for range " ++ show range) |
mvar <- newEmptyMVar | mvar <- newEmptyMVar | ||
forkIO (putMVar mvar (zetaRange s range)) | forkIO (putMVar mvar (zetaRange s range)) | ||
return mvar | return mvar | ||
</haskell> | </haskell> | ||
Revision as of 13:53, 28 November 2006
A large range of small demonstration programs for using concurrent and
MVars
forkIO
A simple example of parallelism in Haskell
This little piece of code computes an approximation of Riemann's zeta function, balancing the work to be done between N threads.
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
