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

[Brad Clow]

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 <brad at bjclow.org> 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

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