use strict; use warnings; use feature 'say';
use Time::HiRes qw/ time usleep /;
use MCE::Shared;

say sprintf '%-5s %-17s %-s', 'PID', 'Time', 'Action';

my $shared = MCE::Shared->condvar(0);
say sprintf '%s %.06f Init val: %s', $$, time, $shared->get;

my $pid = fork;

if ( $pid ) {
    for ( 0 .. 19 ) {
        say sprintf '%s %.06f write: %s', $$, time, $shared->incr;
        usleep 10000;
    }
} else {
    while (1) {
        usleep 50000;
        say sprintf '%s %.06f READ: %s', $$, time, $shared->get;
    }
}

__END__

##</code><code>##

$ perl shared.pl

PID   Time              Action
16648 1491411785.712927 Init val: 0
16648 1491411785.713604 write: 1
16648 1491411785.724157 write: 2
16648 1491411785.734731 write: 3
16648 1491411785.745270 write: 4
16648 1491411785.755807 write: 5
16650 1491411785.763780 READ: 5
16648 1491411785.766309 write: 6
16648 1491411785.776740 write: 7
16648 1491411785.787272 write: 8
16648 1491411785.797800 write: 9
16648 1491411785.808273 write: 10
16650 1491411785.814272 READ: 10
16648 1491411785.818806 write: 11
16648 1491411785.829300 write: 12
16648 1491411785.839957 write: 13
16648 1491411785.850539 write: 14
16648 1491411785.861082 write: 15
16650 1491411785.864522 READ: 15
16648 1491411785.871574 write: 16
16648 1491411785.882031 write: 17
16648 1491411785.892612 write: 18
16648 1491411785.903151 write: 19
16648 1491411785.913714 write: 20
16650 1491411785.914756 READ: 20