use File::NFSLock;
use Fcntl qw(LOCK_EX LOCK_NB);
my $file = "somefile";
if (my $lock = new File::NFSLock {
    file      => $file,
    lock_type => LOCK_EX|LOCK_NB,
    blocking_timeout   => 10,      # 10 sec
    stale_lock_timeout => 30 * 60, # 30 min
}) {
    open(FILE, "+<$file") || die $!;
    # or open it any way you like
    # ...
    $lock->unlock();
}else{
    die "I couldn't lock the file [$File::NFSLock::errstr]";
}