ID: 40968
Comment by: smlerman at gmail dot com
Reported By: oriol dot gual at gmail dot com
Status: Open
Bug Type: Session related
Operating System: Windows XP SP2
PHP Version: 5.2.1
New Comment:
The only thing that can guarantee only one instance of your class
existing is that Singleton::$instance is the only place you store an
instance and getInstance() is the only way to retrieve an instance. Once
you create a second place that an instance can be stored, such as
storing an instance somewhere else (in the session data) and destroying
the instance in the static property (which happens when the script
ends), you create a second way to retrieve an entirely different
instance. In general, there's no 100% guaranteed way to ensure that only
one instance of a given class can ever exist.
Previous Comments:
------------------------------------------------------------------------
[2007-04-01 01:42:08] b dot fore at mail dot com
That's a gross abuse of ext/session dude.
------------------------------------------------------------------------
[2007-03-31 16:54:52] oriol dot gual at gmail dot com
Description:
------------
When storing an object of a singleton class in the session, you can
have more than one instance of that class in other subsequent
executions.
Reproduce code:
---------------
class Singleton {
private static $instance;
private function __construct() {}
final public static function getInstance()
{
if (!isset(Singleton::$instance))
{
Singleton::$instance = &new Singleton;
}
return Singleton::$instance;
}
}
session_start();
if(!isset($_SESSION['singleton'])) $_SESSION['singleton'] =
Singleton::getInstance();
$test = Singleton::getInstance();
$anotherTest = Singleton::getInstance();
var_dump(Singleton::getInstance() === $test);
var_dump(Singleton::getInstance() === $anotherTest);
var_dump($test === $anotherTest);
var_dump(Singleton::getInstance() === $_SESSION['singleton']);
var_dump($test === $_SESSION['singleton']);
var_dump($anotherTest === $_SESSION['singleton']);
session_write_close();
Expected result:
----------------
Session not started (first execution)
bool(true)
bool(true)
bool(true)
bool(true)
bool(true)
bool(true)
Subsequent executions
bool(true)
bool(true)
bool(true)
bool(true)
bool(true)
bool(true)
Actual result:
--------------
Session not started (first execution it's OK)
bool(true)
bool(true)
bool(true)
bool(true)
bool(true)
bool(true)
Subsequent executions (fails, multiple instances)
bool(true)
bool(true)
bool(true)
bool(false)
bool(false)
bool(false)
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/?id=40968&edit=1
