Beispiel (mit STM)

main = do
  let steps = 10000
      threads = GHC.Conc.numCapabilities
  counter <- atomically $ newTVar 0
  ch <- newChan
  forM [ 1 ..  threads ] $ \ t -> forkIO $ do
    forM [ 1 .. steps ] $ \ s -> atomically $ do
        c <- readTVar counter
        writeTVar counter (c + 1)
    writeChan ch ()
  forM [ 1 .. threads ] $ \ s -> readChan ch
  c <- atomically $ readTVar counter
  putStrLn $ show c