PERL Beginners - When does a process become defunct

Author

When does a process become defunct

Ramprasad A Padmanabhan

2005-03-28, 8:55 am

Hi all,
I am writing a daemon in perl , where the parent just forks on some
requests and the children take over. But I found many child processes
becoming defunct. I am not sure why. I am catching SIG_CHLD alright.

To reproduce the problem I have just written a skeleton of my script.
The parent process just forks 20 child processes which just sleep and
exit after some random seconds. When I run this too I find some defunct
processes, the problem is I do not get defunct processes everytime. So
this behaviour is not reproducible ( at least with my script :-) )

I am using perl 5.83 on linux ( fedora-3)

Can someone help me out avoiding these zombies

Thanks
Ram

------------------------------------ MY SCRIPT HERE ---------
use strict;
$GLOBAL::NUM_CH =0;
$|=1;
$SIG{CHLD}=\&count_ch;

foreach(1..20){
unless(fork()){
sleep int(rand(20));
exit 0;
}
print "No of children running now " . ++$GLOBAL::NUM_CH . "\n";
sleep 2;
}

foreach (1..100){
print "PARENT CHECK LOOP: No of children running now " .
$GLOBAL::NUM_CH . "\n";
exit(0) unless($GLOBAL::NUM_CH);
sleep 5;
}

print "Oops : Something went wrong Not all children have quit\n";

sub count_ch {
print "1 CHILD QUIT: No of children running now " . --$GLOBAL::NUM_CH
.. "\n";
wait();
}

--------------------------------- END OF SCRIPT --------

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Steven Schubiger

2005-03-28, 8:55 am

On 28 Mar, Rampra

A Padmanabhan wrote:

> I am writing a daemon in perl , where the parent just forks on some
> requests and the children take over. But I found many child processes
> becoming defunct.

> wait();

perldoc -f waitpid

--
The trouble with having an open mind, of course,
is that people will insist on coming along and trying to put things in it.
-- Terry Pratchett

John W. Krahn

2005-03-28, 8:55 am

Rampra

A Padmanabhan wrote:
> Hi all,

Hello,

> I am writing a daemon in perl ,

perldoc -q daemon

Also the sections "Complete Dissociation of Child from Parent" and
"Handling the SIGHUP Signal in Daemons" in:

perldoc perlipc

A description of daemons:

http://www.enderunix.org/docs/eng/daemon.php

And the definitive reference on daemons is this book:

http://www.aw-bc.com/catalog/academ...1563177,00.html

John
--
use Perl;
program
fulfillment

Ramprasad A Padmanabhan

2005-03-28, 8:55 am

On Mon, 2005-03-28 at 14:35, Steven Schubiger wrote:
> On 28 Mar, Rampra

A Padmanabhan wrote:
>
>
>
> perldoc -f waitpid

I was not very clear on usefulness of waitpid()
>From what I understand , I will have to do a waitpid for every fork I
do.
Can you show me how I could use waitpid() in my script ( non blocking )

Thanks
Ram

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