Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!mcvax!goya!ai.mit.edu
From: tmb@ai.mit.edu (Thomas M. Breuel)
Newsgroups: comp.windows.x
Subject: unix System V
Message-ID: <8906021126.AA04281@wheat-chex.ai.mit.edu>
Date: 2 Jun 89 11:26:24 GMT
Sender: newsadm@goya.dit.upm.es
Lines: 30
To: velayos (M. del Mar Palazuelos)
In-Reply-To: velayos@bosco.dit.upm.es's message of 1 Jun 89 10:48:53 GMT
Status: RO


   From: velayos@bosco.dit.upm.es (M. del Mar Palazuelos)
   Newsgroups: comp.windows.x
   Date: 1 Jun 89 10:48:53 GMT
   Reply-To: velayos@bosco.dit.upm.es (M. del Mar Palazuelos)
   Organization: Dept. Ingenieria de Sistemas Telematicos, dit, upm, Madrid, Spain


   We are working with Compac 386 using X-window version 11 release III and unix
   system V of Interactive. 
   When we use AtAddInput over a pipe there is an error "select failed" with
   "ERRNO  =  ENO TTY".
   The select used is from libnet.a provided by X-windows, because in System V 
   there  is not select instruction.
   Can you help me?

You lose. System V doesn't have a general way of implementing a
select() function that works on all possible kinds of file descriptors
(there is no "real" non-blocking I/O, i.e., something that would let
you distinguish EOF from no-data-available, and there is no general
way of finding out how much data is available on a file descriptor).
In fact, I would strongly recommend not using the select() function in
any Xlib provided for System V systems because you don't know what or
how much they did implement.

A hack to get around this problem is to do a read() on the file
descriptor you are interested in and use an alarm() call to time out
after a second if there is no data. The granularity isn't great, but
it works well enough if you don't do it on more than one or two file
descriptors.