$ diff ex1.pl ex2.pl 
2a3
> use MCE::Shared;
4c5
< my $string = "First value";
---
> tie my $string, "MCE::Shared", "First value";

##</code><code>##

use strict;
use warnings;
use MCE::Shared;

my $string = MCE::Shared->scalar("First value");

sub do_subroutine
{
    print "I am the subroutine and my PID is $$\n";
    $string->set("Second value");
}

print "I am the invoking process and my PID is $$\n";
print "The value of \$string is ", $string->get(), "\n";

unless (fork)
{
    do_subroutine ();
    exit;
}

my $waited_pid = wait;

print "The PID of the child upon whom I waited was $waited_pid\n";
print "The value of \$string is ", $string->get(), "\n";

__END__

I am the invoking process and my PID is 22725
The value of $string is First value
I am the subroutine and my PID is 22727
The PID of the child upon whom I waited was 22727
The value of $string is Second value

##</code><code>##

use strict;
use warnings;
use MCE::Shared;

package My::String;

sub new {
    my ($class, $string) = @_; 
    return bless \$string, $class;
}

sub set {
    my ($self) = @_;
    $$self = $_[1];
    return 1;
}

sub get {
    my ($self) = @_;
    return $$self;
}

package main;

my $string = MCE::Shared->share(
    { module => "My::String" }, "First value"
);

sub do_subroutine
{
    print "I am the subroutine and my PID is $$\n";
    $string->set("Second value");
}

print "I am the invoking process and my PID is $$\n";
print "The value of \$string is ", $string->get(), "\n";

unless (fork)
{
    do_subroutine ();
    exit;
}

my $waited_pid = wait;

print "The PID of the child upon whom I waited was $waited_pid\n";
print "The value of \$string is ", $string->get(), "\n";


__END__

I am the invoking process and my PID is 22978
The value of $string is First value
I am the subroutine and my PID is 22980
The PID of the child upon whom I waited was 22980
The value of $string is Second value

##</code><code>##

use strict;
use warnings;
use MCE::Shared;

package My::String;

sub new
{
    my ($class) = @_; 
    my $string = MCE::Shared->scalar($_[1]);
    return bless [ $string ], $class;
}

sub set
{
    my ($self) = @_;
    $self->[0]->set($_[1]);
    return 1;
}

sub get
{
    my ($self) = @_;
    return $self->[0]->get();
}

package main;

my $string = My::String->new("First value");

sub do_subroutine
{
    print "I am the subroutine and my PID is $$\n";
    $string->set("Second value");
}

print "I am the invoking process and my PID is $$\n";
print "The value of \$string is ", $string->get(), "\n";

unless (fork)
{
    do_subroutine ();
    exit;
}

my $waited_pid = wait;

print "The PID of the child upon whom I waited was $waited_pid\n";
print "The value of \$string is ", $string->get(), "\n";

__END__

I am the invoking process and my PID is 23089
The value of $string is First value
I am the subroutine and my PID is 23091
The PID of the child upon whom I waited was 23091
The value of $string is Second value