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From: keith@enmasse.UUCP (Keith Crews)
Newsgroups: net.unix-wizards
Subject: Re: System V and SIGCLD
Message-ID: <283@enmasse.UUCP>
Date: Fri, 9-May-86 10:45:30 EDT
Article-I.D.: enmasse.283
Posted: Fri May  9 10:45:30 1986
Date-Received: Sat, 10-May-86 23:58:45 EDT
References: <709@cheviot.uucp>
Reply-To: keith@enmasse.UUCP (Keith Crews)
Organization: EnMasse Computer Corp, Acton, MA
Lines: 20

In article <709@cheviot.uucp> lindsay@cheviot.newcastle.ac.uk (Lindsay F. Marshall) writes:
>The following code goes into an infinite loop on System V :-
>
>
>The problem is that resetting the SIGCLD trap inside the handler causes the
>signal to be raised again and the handler to be re-entered...... This
>is not documented in the manual page and seems to me to be a bug as if you
>do not reset the handler the system seems to set it to SIG_DFL, meaning that
>you will loose any SIGCLD signals between the handler's exit and your getting
>a chance to call signal again. Anyone have any thoughts, information etc. on
>this problem??

The signal is raised again because the child still exists.  To do what you want
you have to do a wait in the signal handler before resetting the signal.
This explaination is due to a fellow employee - any errors in conveying it
are no doubt due to me.  In my system V manual there is a discussion of
what happens to SIGCLD while the signal catcher is executing, but it
does not seem to imply this behavior.

		Keith Crews