**************************************************************
object(Singleton)#1 (0) {
}
object(Singleton)#2 (0) {
}
object(Singleton)#2 (0) {
}
bool(false)
bool(false)
bool(true)


__CLASS__.self::$ncount;
Singleton2

__CLASS__.self::$ncount;
Singleton2

__CLASS__.self::$ncount;
Singleton2

unset
Singleton1

object(Singleton)#1 (0) {
}
**************************************************************


<?php
class Singleton 
{    
    private static $instance;
    // if max_instance is 1, we have a pure singleton
    private static $ncount = 0;
    const MAX_INSTANCE = 2; 
     
    private function __construct() {}
        
    private function __clone() {}
           
    public static function getInstance() 
    {
      if (self::$ncount < self::MAX_INSTANCE) {
         self::$instance = new Singleton;
         ++self::$ncount;
      }
     return self::$instance;
    }
                                  
    public function doAction() 
    {
      echo __CLASS__.self::$ncount;
    }

    public function __destruct() 
    {
      --self::$ncount;
    }
}
                                           
//usage
//Singleton::getInstance()->doAction();

$first = Singleton::getInstance();
// object(Singleton)#1 (0) { }

$second = Singleton::getInstance();
// object(Singleton)#2 (0) { }

$third =  Singleton::getInstance();
// object(Singleton)#2 (0) { }

echo "<pre>\n", str_repeat("*", 62), "\n";

var_dump($first);
var_dump($second);
var_dump($third);

var_dump($fist instanceof Singleton);
var_dump($first === $second); // false
var_dump($second === $third); // true

echo "\n\n__CLASS__.self::\$ncount;\n";
$first->doAction();
echo "\n\n__CLASS__.self::\$ncount;\n";
$second->doAction();
echo "\n\n__CLASS__.self::\$ncount;\n";
$third->doAction();
echo "\n\nunset\n";

unset($first, $second, $third);

$first = Singleton::getInstance();
$first->doAction();
echo "\n\n";
var_dump($first);
// object(Singleton)#1 (0) { }

echo str_repeat("*", 62)."</pre>";


if ('cli'===php_sapi_name() &&
    __FILE__===realpath(
    getcwd().DIRECTORY_SEPARATOR.$_SERVER['argv'][0]
  )) {
  // cli
  define (NEW_LINE, "\n");
  $is_cli = 1;
  } else {
  define (NEW_LINE, "<br/>");
  $is_cli = 0;
}

if (!$is_cli) {
  show_source(__FILE__);
  echo "</body></html>";
}

?>