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Bug #29685 Destructor is called to late, unset do not work
Submitted: 2004-08-15 01:28 UTC Modified: 2004-08-15 16:09 UTC
From: sampw at hotmail dot com Assigned:
Status: Not a bug Package: Class/Object related
PHP Version: 5.* OS: *
Private report: No CVE-ID: None
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 [2004-08-15 01:28 UTC] sampw at hotmail dot com 
Description:
------------
Destructor is not called to late. If you use a singleton pattern unset does not work, because there exist a private static reference for the object.

Why is the destructor called so unreliable?

Is such a singleton pattern not possible in PHP?

Or must the static $instance be public, inorder to unset it manually? (Not a nice solution?!)

Reproduce code:
---------------
class Session { //Db Session (Singleton)

    static private $instance = false;

    private function __construct() { }

    public function __destruct() {
        $this->sessionWriteClose(); // e.G. store session data
    }

    static function instance() {
        if(!Session::$instance)
            Session::$instance = new Session();
        return Session::$instance;
    }
}

$OBJ_SESSION = Session::instance();
unset($OBJ_SESSION); // Does not work, because of the static private $instance

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 [2004-08-15 15:10 UTC] helly@php.net 
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

The dtor is called during shutdown. I don\'t see the slightest problem here.
 [2004-08-15 15:56 UTC] sampw at hotmail dot com 
The dtor is called during shutdown. Yes, but to late!
In other bug reports, you called it a feature to use unset at the end of a script inorder to get a reliable working destructor. Because otherwise functions like $this->sessionWriteClose();, which rely on other objects doesn't work reliable. That works fine, if you doesn't use a classical singleton implementation. Because here unset does not work (because there exist a private static reference inside the object!), which means that the destructor doesn't work correctly ($this->sessionWriteClose() works not!).

If you said that, that isn't a bug, I have to suggest that a classical singleton implementation with a reliable working destructor is not possible in php?? Sounds poor ...
 [2004-08-15 16:09 UTC] helly@php.net 
Well i must admit i haven't tried with sessions yet. They are closed during R-shutdown pahse and at least theoretically dtor's should be called kust before R-shutdown begins. If that is not the case we must either fix ext/session or something else. Until that is clear you need an explicitly shutdown function for your singleton (one that unsets the static member).
 
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