Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!mucs!liv-cs!adh
From: adh@mva.cs.liv.ac.uk
Newsgroups: comp.unix.questions
Subject: Can a parent process determine its child's status ?
Message-ID: <5090.25e135aa@mva.cs.liv.ac.uk>
Date: 20 Feb 90 12:18:50 GMT
Organization: Computer Science CSMVAX, Liverpool University
Lines: 23

Does anyone know how a parent process can determine the status of one
of its children if it *hasn't* executed a wait ? It could arrange to 
catch a SIGCLD signal, but if the parent had several children it
wouldn't know which one had sent it the SIGCLD ... would it ?

My reason for asking is as follows: I need to write a program which
starts several children and reads from their respective stdout's via
pipes. The children are executing simultaneously, so the parent uses
non-blocking reads, polling each pipe to see if anything has arrived.
Unfortunately, a call to 'read' returns zero if the child hasn't
sent any new data *OR* if the child has terminated so the parent cannot
distinguish between EOF on a pipe and a pipe that temporarily has no
data in it.

Any advice and suggestions would be appreciated. 

Thanks

  David Harper
  University of Liverpool Computer Laboratory
  Liverpool, U.K.

  Preferred path for email replies: qq68@liverpool.ac.uk