gistfile1.php

<?php 
/* class SingletonSample {...} */ 
?>

<?php
    /**
     * get instance
     */
    $instance1 = SingletonSample::getInstance();
    sleep(3);
    $instance2 = SingletonSample::getInstance();
    echo '<hr>';
    /**
     * compare two ids.
     */
    echo 'instance ID : ' . $instance1->getID() . '<br>';
    echo '$instance1->getID() === $instance2->getID() : ' . ($instance1->getID() === $instance2->getID() ? 'true' : 'false');
    echo '<hr>';
    
    /**
     * compare two instances.
     */
    echo '$instance1 === $instance2 : ' . ($instance1 === $instance2 ? 'true' : 'false');
    echo '<hr>';

    /**
     * confirm that you can not clone the instance.
     * you get RuntimeExpection error.
     */
    $instance1_clone = clone $instance1;
    
    /**
     * also you can not use 'new instance',
     * get fatal error.
     **/
    $instance_new = new SingletonSample;