http://www.perlmonks.org?node_id=959364

rovf has asked for the wisdom of the Perl Monks concerning the following question:

My program (running on Solaris and Linux only, no Windows compatibility needed) is designed to start child processes and "monitor" them in the following way:
  1. If all the child processes exited, the parent also should terminate
  2. If the parent process detects a certain condition, it should kill all childs and terminate
My first approach for the parent (which was flawed) went like this: It was the last item, which did not work: The parent did not notice when I child exited. Inspecting the processes, I found that the exited child was marked as defunct, but still present in the process table. I guess that this is the reason why kill(0,...) still pretended that it could send the signal. Am I right so far?

I then thought that maybe the child could not deliver its SIGCHLD on exiting, so I added the following line to my program, prior to creating the first child process:

$SIG{CHLD}='IGNORE';
Indeed, my program now terminates immediately, when all its childs exit. Now I wonder: Why do I have to set this explicitly? What is the "default" interrupt handler for SIGCHLD?

And finally, I would like to ask you whether my approach to handling the child processes, is reasonable, or whether it maybe has other pitfalls, which I just don't see yet.
-- 
Ronald Fischer <ynnor@mm.st>