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Date: -- (:)
From: Kuba Ober <ober.14@o...>
Subject: Re: [Caml-list] Re: thousands of CPU cores
On Thursday 10 July 2008, Gerd Stolpmann wrote:
> Am Donnerstag, den 10.07.2008, 21:02 +0000 schrieb Sylvain Le Gall:
> > On 10-07-2008, Gerd Stolpmann <info@gerd-stolpmann.de> wrote:
> > > Am Donnerstag, den 10.07.2008, 20:07 +0000 schrieb Sylvain Le Gall:
> > >> On 10-07-2008, Gerd Stolpmann <info@gerd-stolpmann.de> wrote:
> > >> > In Ocaml you can exploit multi-core currently only by using
> > >> > multi-processing parallel programs that communicate over message
> > >> > passing (and only on Unix). Actually, it's an excellent language for
> > >> > this style.
> > >>
> > >> Why only on Unix ?
> > >
> > > No fork() on Windows. And emulating its effects is hard.
> >
> > open_process + stdin/stdout should do the trick... at least i think so.
>
> After having ported godi to mingw I am not sure whether this works at
> all. The point is that you usually want to inherit OS resources to the
> child process (e.g. sockets). The CreateProcess Win32 call
> (http://msdn.microsoft.com/en-us/library/ms682425(VS.85).aspx) mentions
> that you can inherit handles, but I would be careful with the
> information given in MSDN. Often it works only as far as the presented
> examples. Windows isn't written for multi-processing, and its syscalls
> aren't as orthogonal as in Unix-type systems.

Windows syscalls are quite reasonable IMHO, if a tad undocumented. ReactOS
folk have done a great job of reimplementing most of them, and there isn't
anything mucho broken about those. In fact, I'd posit that Windows native
syscalls expose some functionality that's traditionally unavailable on unices
and requires hacks to achieve (usually via executable code injection). Just
look at what Wine folks had to do in order to emulate some win32 (not even
native!) API on Linux: a lot of hard work for what amounts to a single API
call. This of course works both ways, and on Windows, while a fork()
implementation is simple, it AFAIK requires a custom loader or some other
ingenuity to work.

> Furthermore, it looks like a pain in the ass - often you want to run
> some initialization code, and without fork() you have to run it as often
> as you start processes.

On Windows, there's the native API, which is then used by the win32 subsystem
and posix subsystems to do the job. Native API allows fork() implementations
mostly on par with what you get on Unices. MS has a posix subsystem on which
fork() performs in the same ballpark as fork() on linux, and make Cygwin's
fork() look bad like it deserves. About the only good thing about Cygwin's 
fork() is that it works on win9x.

> Also, Windows is just a bad platform for event-based programs, and you
> want to do it to some extent (e.g. for watching all your child
> processes). Only for socket handles there is a select() call. For all
> other types of handles you cannot find out in advance whether the
> operation would block or not.

This is misinformation at best, FUD at worst. I'm no Microsoft fanboy,
but the reality is quite opposite to what you claim. Windows has quite
robust asynchronous I/O support.

Cheers, Kuba