On Fri, Dec 19, 2008 at 9:27 AM, Paul Keir
module Main where
import Control.Concurrent
fibs = 0 : 1 : zipWith (+) fibs (tail fibs)
heavytask m = putMVar m (fibs !! 100000)
Oh, also, heavytask is not very heavy at all. It just writes the thunk (fibs !! 100000) into the MVar. Not a single number is added in this thread. You probably meant to have the thread evaluate its argument _before_ writing it to the variable: heavytask m = putMVar m $! (fibs !! 100000) (Or more transparently) heavytask m = let answer = fibs !! 100000 in answer `seq` putMVar m answer But as per my other comments, you will not see a speedup (in fact, you will probably see some slowdown as two threads compete to compute the same value). Luke
main = do ms <- sequence $ replicate 2 newEmptyMVar mapM_ (forkIO . heavytask) $ tail ms heavytask $ head ms ms' <- mapM takeMVar ms mapM_ print ms'
Regards, Paul _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe