first try on try2.

                     , random

  default-language:    Haskell2010

executable try2

  main-is:             try2.hs

  ghc-options:         -threaded -rtsopts -with-rtsopts=-N

  build-depends:       base

                     , random

  default-language:    Haskell2010

source-repository head

  type:     git

  location: https://github.com/sylecn/queue-base-threading

import Control.Monad

import Control.Concurrent.MVar

import Control.Concurrent

import Text.Printf

import System.Random

fuzz :: IO ()

fuzz = do

  seconds <- (getStdRandom random :: IO Double)

  threadDelay $ round (realToFrac (1000000 * seconds))

counterManager :: MVar Integer -> Chan Integer -> Chan [String] -> IO ()

counterManager counter counterCh printerCh = forever $ do

  fuzz

  incrementBy <- readChan counterCh

  fuzz

  newCount <- modifyMVar counter (\i -> return (i + 1, i + 1))

  fuzz

  writeChan printerCh [printf "The count is %d" newCount,

                       "---------------"]

  fuzz

printerManager :: Chan [String] -> IO ()

printerManager ch = forever $ do

  fuzz

  rows <- readChan ch

  fuzz

  mapM_ putStrLn rows

  fuzz

main :: IO ()

main = do

  counter <- newMVar 0

  counterCh <- newChan

  printerCh <- newChan

  forkIO $ counterManager counter counterCh printerCh

  forkIO $ printerManager printerCh

  writeChan printerCh ["Starting up"]

  replicateM_ 10 (writeChan counterCh 1)

  -- join counterCh

  writeChan printerCh ["Finishing up"]

  -- join printerCh

  -- done

  threadDelay $ 20 * 1000000