How to use the Singleton design pattern - Page 2

roman · 10-30-2010, 12:13 PM

Hi,

I am trying to use singleton in my application. I believed singleton object can hold public variables to be used at any place of my code. But it does not work...
Thanks to anyone who can help me :)

PHP Code:


			


// singleton to keep errors
class Errors {
    
    private static $_instance;
    public $errorList;
    
    private function __construct () {
        $this->errorList = array();
    }
    
    public static function getInstance() {
        if (empty(self::$_instance))
            self::$_instance = new Errors ();
        return self::$_instance;
    }
    
    public function addError ($error) {
        $this->errorList[] = $error;
    }                
}

// when I use the singleton first time, it holds the public value of errorList
$err = Errors::getInstance();
$err->addError('some error');
print_r ($err->errorList);

// when I get the instance again, the errorList seems to have lost it's value ('some error')
$err = Errors::getInstance();
print_r ($err->errorList);

luisjba · 10-30-2010, 06:49 PM

Hi Roman,

Your code is OK, but you need to know some about the HTTP environment and how PHP works.

When the browser request to your resource (your script in this case), the vars and clases in PHP are initialized,and a thread in the server is open to attend your request. Until the thread is ended, all your vars and temporary memory in the server are cleaned, so if you try to access your var in the next request, your vars doesn't exist anymore because them ware cleaned for ending of the Thread of the previous request.

To keep your vars for global, you can implement MemCache, you need to install the Mem Cache server, it allows you to allocate primitive vars and objects, and then retrieve them any time in any request, by this way, you keep the state of your var globally for all users.

I hope that this was helpfully for you.

Regards

roman · 10-31-2010, 09:21 PM

Thanks for your answer, Luisjba,

I understand that all vars exist within one request.

What I meant was that the singleton lost it's public values WITHIN the same request, as I showed in the code... I called the singleton twice - one after other - and the second call its empty... I am trying to use singleton in various scopes (functions) and still I fail to use it even within the same scope - that's why I do strange thing to call it twice, just to demonstrate how weird they behave..

Regads,

Roman

jgetner · 11-02-2010, 05:16 AM

you shouldn't hijack this thread create a new thread witch would make it much easier for people to help you with your problem.

roman · 11-05-2010, 02:59 PM

Sorry, I am inexperienced forum user. Will do it.

mathewxiang · 06-11-2012, 09:26 AM

thanks for sharing this example about php singleton implement

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