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Children signalling to parents as they complete
Interprocess Communication example from a Well House Consultants training course
More on Interprocess Communication [link]

This example is described in the following article(s):
   • Children, zombies, and reaping processes - [link]

Source code: kidgoes Module: P223
# Children signalling to parents as they complete

use POSIX ":sys_wait_h";

sub kiddo {
        # You need to make sure the child is finished
        while (($kidval = waitpid(-1, &WNOHANG)) > 0) {
                 # do something with $kidval if you need
        }
        print "Signal Child in PID $$ - child reaped\n";
        # You should also re-arm the signal (if multiple children)
        $SIG{CHLD} = \&kiddo;
        }

# How to avoid cluttering process table with dead children (zombies)
# $SIG{CHLD} = 'IGNORE'; # easiest way if we don't need the signal
$SIG{CHLD} = \&kiddo; # If we need the signal - so must reap too

$parent = $$;
if (!($child = fork())) {

        # Child
        $child = $$;

        sleep 5;
        print "child done\n";
        exit();

}
print "Parent and child $parent $child\n";

# parent

sleep 10;

print "check email\n";
sleep 10;

print "parent done\n";

__END__

wizard:csr2 graham$ perl kidgoes
Parent and child 192 193
child done
Signal Child in PID 192 - child reaped
check email
parent done
wizard:csr2 graham$

Learn about this subject
This module and example are covered on our public Perl Extra course. If you have a group of three or more trainees who need to learn the subject, we can also arrange a private or on site course for you.

Books covering this topic
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Other Examples
This example comes from our "Interprocess Communication" training module. You'll find a description of the topic and some other closely related examples on the "Interprocess Communication" module index page.

Full description of the source code
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

Many other training modules are available for download (for limited use) from our download centre under an Open Training Notes License.

Other resources
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