#!/usr/bin/perl
eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
        if $running_under_some_shell;
require 'sys/ipc.ph';
require 'sys/msg.ph';
$| = 1;
$mode = shift;
die "usage: ipcmsg {r|s}\n" unless $mode =~ /^[rs]$/;
$signal = ($mode eq "s");
$id = semget(0x1234, 1, ($signal ? 0 : &IPC_CREAT) | 0644);
die "Can't get semaphore: $!\n" unless defined($id);
print "semaphore id: $id\n";
if ($signal) {
        while (<STDIN>) {
                print "Signalling\n";
                unless (semop($id, pack("sss", 0, 1, 0))) {
                        die "Can't signal semaphore: $!\n";
                }
        }
}
else {
        $SIG{'INT'} = $SIG{'QUIT'} = "leave";
        for (;;) {
                unless (semop($id, pack("sss", 0, -1, 0))) {
                        die "Can't wait for semaphore: $!\n";
                }
                print "Unblocked\n";
        }
}
&leave;
sub leave {
        if (!$signal) {
                $x = semctl($id, 0, &IPC_RMID, 0);
                if (!defined($x) || $x < 0) {
                        die "Can't remove semaphore: $!\n";
                }
        }
        exit;
}