Path: utzoo!attcan!uunet!munnari.oz.au!bruce!labtam!timr
From: timr@labtam.oz (Tim Roper)
Newsgroups: comp.windows.x
Subject: Re: XDMCP/-query option to MIT sample servers
Summary: is non SYSV version really reliable?
Message-ID: <4783@labtam.oz>
Date: 13 Jun 90 16:24:39 GMT
References: <9006061659.AA05569@xenon.lcs.mit.edu>
Organization: Labtam Limited., Melbourne, Australia
Lines: 22

In <9006061659.AA05569@xenon.lcs.mit.edu> keith@EXPO.LCS.MIT.EDU (Keith Packard) writes:
> ...
>xdm does not support XDMCP when running on SYSV machines.  The lack of reliable
>signal handling in a SYSV environment would make this quite difficult to
>implement.  The problem revolves around listening for UDP packets on a socket
>and also waiting for child process termination.

>The server is working fine in your case, the display manager is simply not
>listening for the packets.

Even with System V.3 reliable signals and poll() the lack of a
non-blocking wait() and the lack of a mask-driven form of sighold()
will make WaitForSomething/WaitForChild ugly (ie. no equivalent of wait3
or sigsetmask).

However I wonder whether the non-SYSV version is 100% reliable.  For
example, if a SIGHUP or SIGCHLD arrives just before calling select() in
WaitForSomething() won't the rescan or dead child processing be delayed
until the select() happens to be woken by another signal or an arriving
XDMCP request?

-Tim.