Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!usc!bloom-beacon!athena.mit.edu!jik
From: jik@athena.mit.edu (Jonathan I. Kamens)
Newsgroups: comp.unix.questions
Subject: Re: Need help spawning a child
Keywords: Signals, Zombies
Message-ID: <12244@bloom-beacon.MIT.EDU>
Date: 27 Jun 89 03:58:04 GMT
References: <1661@apt.UUCP> <873@cbnewsl.ATT.COM> <12131@bloom-beacon.MIT.EDU> <14972@pasteur.Berkeley.EDU>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: jik@athena.mit.edu (Jonathan I. Kamens)
Distribution: usa
Organization: Massachusetts Institute of Technology
Lines: 31

In article <14972@pasteur.Berkeley.EDU> gar@cory.Berkeley.EDU.UUCP (Gary D.
Wong) writes:

>My problem is, that to prevent a zombie process, I have to ignore
>SIGCLD with sigignore(SIGCLD), and my parent process does not wake
>up.  Is there any other way to prevent a zombie other than by
>ignoring SIGCLD?

I've posted this already; you should read the whole message chain
before asking a question that has already been answered.  Using
sigignore(SIGCLD) to get rid of zombie processes is unportable, and
will only work on SysV-based systems.  The portable way to get rid of
zombie processes is to establish a signal handler for the SIGCLD
signal, and to do wait(0) in that signal handler.  The wait(0) call
cleans up exited child processes and "allows" them to exit.

>Also, does anyone know what will happen to my sleeping process after
>the signal handling call? Will it go back to sleep, or continue as if
>it were given the alarm signal? What would be the effect of having
>the signal handler send the alarm signal to the process?

If a call to sleep() is interrupted by a signal for which a signal
handler has been established, then the sleep() will resume where it
left off after the signal handler exits.  I am fairly sure this will
happen on all architectures; I just tested it on BSD, so I know it
will happen there.

Jonathan Kamens			              USnail:
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