use v5.12;
use warnings;
#use Data::Dump;
use Fcntl qw(:flock);
use Time::HiRes qw/time sleep/;

$|=1;



my $lock_path = "./LOCK_DEMO";
my $wait      = 10;


# ------- traditional way test for existence
say "First One !?!" if ! -e $lock_path;

# NB: This fails sometimes because of race condition


# ------ Open
open my $fh, ">", $lock_path  or die "Can't open $lock_path: $!";


# ------ Lock File
say "Wait for Access";
flock($fh, LOCK_EX) or die "Cannot lock $lock_path - $!";



# ------ Unrivaled Actions
say "There can be only one HIGHLANDER!";
for (1..$wait) {
    say $_;
    sleep 1;
}
say "I'm done";


# ------ Release Lock
say "Un-Locking";
flock($fh, LOCK_UN) or die "Cannot unlock $lock_path - $!";



# ============ The last one has to switch off the light

# ------ allow concurrent lock
sleep 0.01;


# ----- Test Non-Blocking Lock
say "Try Lock without waiting";
my $can_lock = flock($fh, LOCK_EX | LOCK_NB);


# ------ Close
close $fh;


# ----- Last script cleans up LOCK-File for next demo
if ($can_lock) {
    say "LAST ONE!!!";
    say "delete $lock_path";
    unlink $lock_path  or die "Cannot delete $lock_path - $!";
} else {
    say "not last one"
}


# ----- Keep cmd window open for a while
for (1..20) {
    print ".";
    sleep 1;
}
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