RE: [PATCH] compat: Add another rudimentary poll() emulation

From: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Date: May 27, 2010, 15:17 UTC
Message-ID: <A612847CFE53224C91B23E3A5B48BAC74483678383@xmail3.se.axis.com>
In-Reply-To: <AANLkTin8MTa5zUhqh3dOfNN0nmI2kAeiqNreYn7TZnf1@mail.gmail.com>

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> -----Original Message-----
> From: git-owner@vger.kernel.org [mailto:git-owner@vger.kernel.org] On
> Behalf Of Erik Faye-Lund
> Sent: den 27 maj 2010 16:44
> To: Marko Kreen
> Cc: Jonathan Nieder; Jonathan Callen; git@vger.kernel.org;
> mduft@gentoo.org; Sverre Rabbelier; Michael J Gruber; Johannes Sixt;
> msysGit
> Subject: Re: [PATCH] compat: Add another rudimentary poll() emulation
> 
> On Thu, May 27, 2010 at 4:32 PM, Marko Kreen <markokr@gmail.com> wrote:

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> > Ah, ok.  I though this is the nfds for select().  In this case it can
> > still fail, as nfds=1 for poll() can still go over FD_SETSIZE for
> > select() if the fd value is big enough.  On non-windows, that is.
> 
> I don't quite get where one would get a fd that's value is FD_SETSIZE
> or above from. I mean, FD_SETSIZE would have to be the maximum value
> of a file descriptor, or else you risk open() or socket() returning
> file descriptors that cannot be select()'ed. Which would just be
> insane, no?
> 
> --
> Erik "kusma" Faye-Lund

That is exactly how e.g. Linux works. If your application can have more than 1024 file descriptors open simultaneously, you are restricted to use poll() as you risk having a file descriptor with a value >= 1024. And using FD_SET() with a file descriptor >= 1024 will trash memory...

//Peter