[Haskell-cafe] Re: Thread pool in GHC

4 Aug 2005


      Dinh Tien Tuan Anh  writes:
...
Can thread pool be implemented in GHC ?
I have a program that is currently using about 12-15 threads (launch and 
kill for infinite times) and when running, especially after Ctrl-C, my 
computer got freezed up. And if i ran it several times, the "Stack 
overflows" occurs.
I made the following a while back. Maybe it's useful...

limitedThreadsWithChannelMapM :: Integer -> (a -> IO b) -> [a] -> IO [MVar b]
limitedThreadsWithChannelMapM lim ioaction x = do
    threadpoolcounter <- atomically ( newTVar 0 )
    mapM (throttledFork threadpoolcounter . ioaction) x
    where
        throttledFork poolcount io = do
            atomically ( do
                prev <- readTVar poolcount
                if prev >= lim then 
                    retry
                    else writeTVar poolcount (prev+1) )
            mvar <- newEmptyMVar
            forkIO(
                finally
                    (io >>= putMVar mvar)
                    (atomically ( readTVar poolcount >>= writeTVar poolcount .
(subtract 1) ) ) )
            return mvar
...
Cheers
TuanAnh
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[Haskell-cafe] Re: Thread pool in GHC

genneth