Hi all, I'm seeing no performance increase with a simple coarse-grained 2-thread code using Control.Concurrent. I compile with:
hc conc.hs -o conc --make -threaded
and I run with
time ./conc +RTS -N2
But using either "-N1" or "-N2", the program runs in about 1.8secs. (I'd prefer a longer running thread task, but my fib function currently runs out of memory). Anyway, my program is below, and I'm using GHC version 6.8.2 on a 2-core Pentium D. Can anyone help? module Main where import Control.Concurrent fibs = 0 : 1 : zipWith (+) fibs (tail fibs) heavytask m = putMVar m (fibs !! 100000) main = do ms <- sequence $ replicate 2 newEmptyMVar mapM_ (forkIO . heavytask) $ tail ms heavytask $ head ms ms' <- mapM takeMVar ms mapM_ print ms' Regards, Paul