use strict;
use warnings;
use threads;
use feature 'say' ;
use Fcntl qw(:flock);
open(FILE, ">>/tmp/test.txt");

for(0..9) {
    threads->new(\&worker, $_);
}

$_->join for threads->list;

sub worker {
    my $x = shift;
    my $locked;
    $locked = flock(FILE, LOCK_EX|LOCK_NB );
    if( $locked ) {
        say "$x: lock acquired";
        sleep 4;
    } else {
        say "$x: cannot acquire lock";
    }
    flock( FILE, LOCK_UN );
    print "$x: lock released\n";
    return;
}

##</code><code>##

0: lock acquired
1: lock acquired
2: lock acquired
3: lock acquired
4: lock acquired
5: lock acquired
6: lock acquired
7: lock acquired
8: lock acquired
9: lock acquired
0: lock released
1: lock released
2: lock released
3: lock released
4: lock released
5: lock released
6: lock released
7: lock released
8: lock released
9: lock released