[Haskell-cafe] Re[4]: Parallel combinator, performance advice

Bulat Ziganshin bulat.ziganshin at gmail.com
Tue Apr 7 11:58:24 EDT 2009

Hello Neil,

Tuesday, April 7, 2009, 7:47:17 PM, you wrote:

>> para = mapM_ forkIO

> I might try that tomorrow and see if it makes a difference to the
> performance. While the majority of computation is in system calls,
> quite a few of the threads open files etc, and having them all run in
> parallel would end up with way too many open handles etc.

if you have too much threads, you may replace forkIO with one more
QSem-enabled call:

semIO = unsafePerformIO$ newQSem 100

myForkIO = bracket_ (waitQSem semIO) (signalQSem semIO) . forkIO

this limit may be much higher than for System.Cmd.system

or you may go further and replace it with thread pool approach. the
main problem behind is raw calls to forkIO since these increases
amount of threads capable to call System.Cmd.system without any
control from us 

Best regards,
 Bulat                            mailto:Bulat.Ziganshin at gmail.com

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