#!/usr/local/perl_ithreads/bin/perl
use strict;
use warnings;
use threads;
use threads::shared;

my %h = ( a => 1, b => 2, c => 3 );
my @locking_keys = qw/ a b /;

my $guard:shared;

{
    lock( $guard ); ## Lock the guard

    ## do stuff with the hash

    cond_signal( $guard ); ## unlock the guard (atomic)
}