>From: Wolfgang Thaller <[EMAIL PROTECTED]>
>To: [EMAIL PROTECTED]
>CC: [EMAIL PROTECTED]
>Subject: Re: About Haskell Thread Model
>Date: Sat, 11 Oct 2003 22:58:04 +0200
>
>>I am a new learner of Haskell and I am interested in Haskell's
>>concurrent model. Can somebody give me a brief intro about
>>Haskell's
>>thread model, like how the use-level threads are mapped to kernel
>>thread
>>and what scheduling mechanism that Haskell uses, or point me to
>>some
>>links or documents that I can learn from.
>
>In the interpreter Hugs, all Haskell threads are run in one kernel
>thread. They are scheduled cooperatively; thread switches only take
>place when a function from the "Concurrent" module is called.
>
>In the currently released version of GHC, all Haskell threads are
>run in one kernel thread, too; however, thread switches can take
>place whenever memory is allocated --- and in Haskell, that means
>"almost always". The optimizer manages to compile a fibonacci
>function that doesn't allocate any memory, but in the real world,
>it's as good as real preemption.
>
>If you compile the bleeding-edge GHC from the CVS HEAD, you'll get
>something else; while "most" threads (those created using "forkIO")
>are still light-weight threads that are scheduled in just one kernel
>thread, you can also create threads that get their own operating
>system thread. This is solves all the problems that lightweight
>threads can have with foreign (i.e. non-Haskell) libraries.
>
>You should also note that no Haskell implementation currently
>supports SMP; even when multiple kernel threads are used, there is a
>mutual exclusion lock on the Haskell heap, so a multithreaded
>Haskell program will use only one CPU on an SMP system.
>
>I hope my answer was useful...
>
>Cheers,
>
>Wolfgang
>
>P.S.: If you want to do me a favour, you could tell your mail
>program not to send multipart or HTML messages to the list; they
>look terrible to people like me who get a daily digest from the
>mailing list.
>
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