[Yhc] Concurrent Yhc

Tom Shackell shackell at cs.york.ac.uk
Fri Mar 3 12:32:47 EST 2006

Hello everyone,

Concurrent GHC, so for example the following is a concurrent Yhc program:

module Fair where

import Control.Concurrent
import Control.Concurrent.MVar

consumer :: MVar () -> Char -> IO ()
consumer mv c = do _ <- takeMVar mv
                    putChar c
                    consumer mv c

producer :: MVar () -> Int -> IO ()
producer mv 0 = return ()
producer mv n = do putMVar mv ()
                    producer mv (n-1)

main :: IO ()
main = do mv <- newEmptyMVar
           _ <- forkIO (consumer mv 'A')
           _ <- forkIO (consumer mv 'B')
           _ <- forkIO (consumer mv 'C')
           producer mv 1000
           putStrLn ""

Currently only


are implemented, however all the rest can easily be written in Haskell 
in terms of MVars.

Because the introduction of concurrency has changed the way stacks work 
for *all* of Yhc it is possible some bugs have been introduced. The 
concurrent yhc implementation passes all the unit tests that the single 
threaded yhc passed, but of course unit tests don't cover all cases.
If you find your previously working single threaded programs are now 
breaking please submit a BUG REPORT to the list :-)

Also concurrency support is still new and relatively untested so you 
might find some concurrent programs that segfault/crash/lock up/etc. ALL 

NOTE: the Windows release for concurrency isn't quite ready but it 
should be quite soon (thanks Neil for handling this).

Anyway, enjoy :-)


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