async { lock $LockVar; $LockVar = 'Haha'; sleep 3; print "Thread 1: $LockVar\n" };
    async { lock $LockVar; $LockVar = 'Hehe'; sleep 3; print "Thread 2: $LockVar\n" };

##</code><code>##

#!perl -w
use strict;
use 5.010;
use threads;
use threads::shared;

my $LockVar :shared;
$LockVar = 'default';

async { lock $LockVar; my $oldLockVar= $LockVar; $LockVar = 'Haha'; sleep 3; say "Thread 1: set var from $oldLockVar to $LockVar" };
async { lock $LockVar; my $oldLockVar= $LockVar; $LockVar = 'Hehe'; sleep 5; say "Thread 2: set var from $oldLockVar to $LockVar" };

my $TryToReadLockVar = threads->new(
    {'void' => 'void'},
    sub {
        my $count = 1;
        while( 1 ) {
            say "try to modify the Lock var {$count} time";
            $count += 1;
            lock($LockVar); # !!!
            say "Now setting LockVar";
            $LockVar = 'this lock var has been change';
            last;
        }
    },
);

$TryToReadLockVar->join();    
say "LockVar is now $LockVar";
__END__
try to modify the Lock var {1} time
Thread 1: set var from default to Haha
Thread 2: set var from Haha to Hehe
Now setting LockVar
LockVar is now this lock var has been change
Perl exited with active threads:
        0 running and unjoined
        2 finished and unjoined
        0 running and detached