I had thought about waitpid with NO_WAIT (I have used a similar solution in a different application), but I was interested in get it to run by using kill 0. Actually, this seems to work so far, only that I didn't understand, why I had to 'IGNORE' SIGCHLD explicitly. Actually, I got the idea to use kill instead of waitpid from an example at perlipc:

Another interesting signal to send is signal number zero. This doesn't actually affect a child process, but instead checks whether it's alive or has changed its UID.

    unless (kill 0 => $kid_pid) {
        warn "something wicked happened to $kid_pid";
    }
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This seemed to be an attractive and easy solution - that's why I wanted to try it out.