Just to report back what I come up with (ideas stolen from Perl Cookbook and the Perl command reference)

use strict;
use warnings;
use IPC::Run;
use POSIX qw(:signal_h :errno_h :sys_wait_h);
use Config;

...

my $has_nonblocking = $Config{d_waitpid} eq "define" || $Config{d_wait
+4} eq "define";
if ($has_nonblocking) {
  $SIG{CHLD} = \&REAPER;
  sub REAPER {
    my $pid = waitpid(-1, &WNOHANG); # wait for any child, return PID 
+if state changed else return 0 if stopped or -1 if error
    if ($pid == -1) {
      # ignore
    }
    elsif ( &WIFEXITED($?) ) { # true if exited normally
      print "$pid exited.\n";
    }
    else { # must have been some stop signal or no change in state
      print "False alarm $pid.\n";
    }
    $SIG{CHLD} = \&REAPER;
  }

  my $pid = fork();
  defined $pid or die $!;

  unless ($pid) {
    my @args = ( ... );
    run \@args or die $?;
    exit;
  }

  my $kid;
  do {
    $kid = waitpid(-1, &WNOHANG);
  } while $kid > 0;
}

...

exit;
[download]

Please comment and give advice. Thank you.