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Multiprocessor support in OCaml
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Date: | 2007-04-22 (11:55) |
From: | Don Syme <Don.Syme@m...> |
Subject: | RE: [Caml-list] Multiprocessor support in OCaml |
Just to mention there is a way of getting multiple concurrently executing OCaml threads in a program, which I discovered a while back: you can statically link multiple independent copies of the OCaml runtime, each into its own DLL (on Windows). This allows multiple independent OCaml threads to run concurrently. I presume this technique works well enough for SMP up to 2-4 processors, though have never done any serious performance testing. The OCaml programs must not, of course, trade OCaml values, but can communicate in-process by other means (e.g. shared C memory or some other message passing technique). Regards, Don P.S. I've only used this technique on Windows. -----Original Message----- From: caml-list-bounces@yquem.inria.fr [mailto:caml-list-bounces@yquem.inria.fr] On Behalf Of Xavier Leroy Sent: 22 April 2007 11:30 To: Jason Ganetsky Cc: caml-list@yquem.inria.fr Subject: Re: [Caml-list] Multiprocessor support in OCaml > Anyway, I have recently written an OCaml thread pool implementation, on > top of the Thread and Event modules. I did this for the purpose of > exploiting an SMP system I have, and was a disappointed to read today > that OCaml doesn't support multiprocessor systems. You are correct that OCaml *threads* do not exploit multiprocessing. Basically, only one OCaml thread can run at a time. You can still get parallelism in several ways. First, external C libraries called from OCaml can run in parallel with OCaml code provided the OCaml/C interface for these libraries makes uses of the "blocking section" mechanism. Second, process-level parallelism works very well with programs written in message-passing style, using e.g. OcamlMPI or OCamlP3L. > I played around with it a little, and discovered that by liberally > calling Thread.yield, I do cajole my threads into running on multiple > processors. This is an illusion. Thread.yield gives more opportunities to the OS scheduler to reschedule a Caml thread on a different processor, but you're not gaining parallelism this way and you might actually lose performance (because of cache ping-pong effects and the like). - Xavier Leroy _______________________________________________ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs