sub get_lock
{
  open(SEM, ">$semaphore_file") || die "Cannot create semaphore: $!";
  flock(SEM, LOCK_EX) || die "Lock failed: $!";
}
sub release_lock
{
  close(SEM);
}
$semaphore_file="semfile";
get_lock();
#Do something here
release_lock;