Date: Mon, 9 Nov 1998 10:42:58 -0800 (PST) From: Marc Slemko <marcs@znep.com> To: Nate Williams <nate@mt.sri.com> Cc: hackers@FreeBSD.ORG Subject: Re: Supporting more than FD_SETSIZE fd's Message-ID: <Pine.BSF.4.05.9811091037490.8174-100000@alive.znep.com> In-Reply-To: <199811091826.LAA05253@mt.sri.com>
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On Mon, 9 Nov 1998, Nate Williams wrote: > > > I need to support more than the default 255 FD's in an application (the > > > JDK for what it's worth). > ... > > > I looked through the code in Apache, and I don't see how it does this, > > > since I never saw any re-definition of FD_SETSIZE, or use of anything > > > other than fd_setsize. (Although, I did see mention of FD_SETSIZE quite > > > a bit in the comments.) > > > > Apache doesn't use select() on high numbered descriptors so it doesn't > > matter. > > How does it determine if there is data on those FD's w/out select? I It doesn't have to. > would think that if you have more than 255 active FD's (pretty common) > then you'd have a problem. One connection per process at any given time. High descriptor use in Apache only comes in with logfiles, eg. 10000 vhosts with two logfiles for each. > > FD_SETSIZE doesn't limit the number of descriptors, it just limits the > > highest descriptor you can pass to select(). > > Right, hence my question on how other applications deal with the > problem, since select doesn't have inherent limitation. > > > There are various possible workarounds: > > > > - use poll(). Only on 3.0 unfortunately. > > > > - on 3.0, FD_SETSIZE defaults to 1024. > > I'm on 2.2.* > > > - redefine FD_SETSIZE before including sys/types.h. This may seem to be a > > pain, but in most large projects you should have some common header files > > you can use for that anyway. This doesn't fix any libraries that you use > > though, which may use select() internally with a small FD_SETSIZE. > > No external libraries are used except for Motif. I'm not sure if it > uses Select, but I doubt it. In any case, I'm still defaulting to a A lot of X11 stuff will use select(). > larger limit, which is still not a great solution. If you need a generic ability to select() on descriptors above 256, the only real choice you have is to redefine FD_SETSIZE everywhere and hope no other libraries cause problems. Or insist that anyone building or using it changes the global FD_SETSIZE on their system and does a make world. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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