Thanks Luke, and everyone else. Ok, back to the drawing board. Paul
From: Luke Palmer [mailto:lrpal...@gmail.com] Sent: 19 December 2008 16:44 To: Paul Keir Cc: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] forkIO on multicore[MESSAGE NOT SCANNED] On Fri, Dec 19, 2008 at 9:27 AM, Paul Keir <pk...@dcs.gla.ac.uk> wrote: 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
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