Actually, using a signal handler to reap children is problematic in Perl because Perl signal handlers aren't 100% reliable. Each time one is trigger, you have something like a 2% chance of corrupting Perl's internal structures. I think this may be fixed in a an upcoming version of Perl.

The safest way to reap children is shown under "perldoc -f waitpid" and closely matches the code in question. Perhaps Solaris doesn't define WNOHANG as 1? That seems unlikely, but that is all I've come up with so far.