$SIG{CHLD} = \&waitforchildren;

# reaper:

sub waitforchildren {
    my $cpid;
    while ( ($cpid = waitpid(-1, &WNOHANG)) > 0 ) {
          $TrappedPIDs{$cpid} = WEXITSTATUS($?) if WIFEXITED($?);
    }
}

# processing routine

...
foreach $pid ( keys(%TrappedPIDs) ) {

    # check return code for pid and do something

}