import System.IO

import Control.Concurrent

import Data.List

import Control.Monad

main = do

finished <- newEmptyMVar

input <- newMVar [1..30000]

ia <- newEmptyMVar

ib <- newEmptyMVar

ic <- newEmptyMVar

forkIO $ do x <- readMVar input

putMVar ia x

putMVar finished ()

forkIO $ do a <- readMVar ia

putMVar ib ( sum a )

putMVar finished ()

forkIO $ do a <- readMVar ia

putMVar ic ( reverse a )

putMVar finished ()

b <- readMVar ib

c <- readMVar ic

writeFile "somaEprod.txt" (show b ++ "\n")

appendFile "somaEprod.txt" (show c)

replicateM_ 3 (takeMVar finished)

Valeu

Mauricio

On Sun, Jul 1, 2012 at 12:24 AM, Felipe Almeida Lessa <felipe.lessa@gmail.com> wrote:

Your application is exiting before your forkIOs get a chance to
execute. Instead of

forkIO $ do
...
forkIO $ do
...
forkIO $ do
...

use something like

finished <- newEmptyMVar

forkIO $ do
...
putMVar finished ()

forkIO $ do
...
putMVar finished ()

forkIO $ do
...
putMVar finished ()

replicateM_ 3 (takeMVar finished)

Doing so will avoid your program to exit until all threads have finished.

Note that the code above is extremely fragile: doesn't handle
exceptions, you have to manually specify the number of threads that
you opened, etc. These are abstracted by some libraries on Hackage
that you may use later for Real World Code (TM).

Cheers, =)

--
Felipe.