Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mandrill!gatech!bbn!milliken@bbn.com
From: milliken@bbn.com (Walter Milliken)
Newsgroups: comp.windows.x
Subject: X11 and multiple processes
Summary: Does X work with multiprocessor programs?
Message-ID: <25516@bbn.COM>
Date: 8 Jun 88 18:20:01 GMT
Sender: news@bbn.COM
Reply-To: milliken@bbn.com (Walter Milliken)
Organization: BBN Advanced Computers, Inc.
Lines: 37

I was hoping one of the X gurus out there might be able to help me
with a possible problem:

I have a (hypothetical) program which consists of many (possibly a
hundred or more) Unix processes.  Each of these processes would like
to do output to the X server.  All are children of a single process.
I can see two possible ways of handling this:

1) The original process calls XOpenDisplay and lets all the children
inherit the socket to the X server.

I'm not familiar with the protocol, the server, or the Xlib
implementations, but I can see that with some design choices, there
might be a problem.  If, for example, state is kept by both the server
and client on a per-connection basis, the client-side info would get
out of sync in the various processes.

2) Each child calls XOpenDisplay itself, and uses its own private
socket to communicate with the server.  Since X identifiers are
unique to the server, there's no problem with passing IDs around among
the various processes, and presumably, they could all write to the
same window.

The problem here is that this approach uses *lots* of sockets, which
may be a resource problem in the Unix implementation, and could also
cause problems if the server keeps per-connection data without
expecting someone to come along with *hundreds* of connections.  Can
the server run out of file descriptors in this case?


In case you're wondering, the system in question is a parallel
processor with up to 128 processors (the Butterfly GP1000).  Users
often run programs with one process per processor, all cooperating
on the same computation.  I'd like to have a workable strategy for
handling X output from such programs.  Any suggestions?

---Walter