use POSIX;

$SIG = 10; $SIGNAME = "USR1";
#$SIG = 50; $SIGNAME = "NUM50";

$SIG{$SIGNAME} = sub { $got++ };
sigaction($SIG, undef, my $act=bless({}, "POSIX::SigAction"));
$act->{FLAGS} |= &POSIX::SA_RESTART;
sigaction($SIG, $act);

my $parent_pid = $$;
die "can't fork\n" unless defined(my $chield_pid = fork());
unless ($chield_pid) {
    select(undef,undef,undef, 0.1), kill($SIG, $parent_pid) while 1;
}

my $n = sysread \*STDIN, my $buf, 1;
printf "got=%d n=%s err=%s\n", $got, defined($n) ? $n : "undef", $!;

kill 9, $chield_pid;