Re: [Haskell-cafe] Re: Waiting for thread to finish

28 Nov 2007


      I was just watching top while executing this and noticed that it
really only used one core (I am using GHC 6.8.1 on a MacBook). Does
anyone know why?

On Nov 28, 2007 10:34 AM, Brad Clow  wrote:
...
If you would like to wait on multiple threads, you can use STM like so:
import Control.Concurrent
import Control.Concurrent.STM
import Control.Exception
main = do
  tc <- atomically $ newTVar 2
  run tc (print (last [1..100000000]))
  run tc (print (last [1..110000000]))
  print "Waiting...."
  atomically $ readTVar tc >>= \x -> if x == 0 then return () else retry
  print "OK."
  where
    run tc f = forkIO (f `finally` atomReplace (\x -> x - 1) tc)
atomReplace fn x = atomically $ readTVar x >>= writeTVar x . fn
Regards
brad

-- 
www.scoodi.com
Recycle is good: Reuse is better