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Multiprocessor support in OCaml
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Date: | 2007-04-22 (10:30) |
From: | Xavier Leroy <Xavier.Leroy@i...> |
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