PHP Singleton：没有持有实例

Question

I'm just becoming dive into php after ages working in vb.net.

I wanna write a logger class that runs as singleon over my webapp, here the code:

class cLog{

private $data = NULL;


static private $instance = NULL;

static public function getInstance(){
    if(self::$instance == NULL){
        echo "empty!";
        self::$instance = new cLog();           
    }   
    return self::$instance;
}


private function __construct(){     
}   
private function __clone(){     
}



public function getData(){
    return self::getInstance()->data;
}

public function trace($o){
    self::getInstance()->data[] = $o;
}

}

What I expect is that, as i switch between pages of my application that make several calls to the cLog::trace() method, the data array increases and it's filled with all traces. But what I get is: everytime i run a page, the $instance is null so the object restarts (as you can see, I put an echo "empty!" line in the instance getter: it shows everytime)

I guess there's something I'm misunderstanding in the php application-lifecycle....

Here there's an usage example:

cLog::getInstance()->trace("hello world");
$logs = cLog::getInstance()->getData();

Thanks

Answer 1

PHP uses a "share nothing" architecture. This means (among other things) that nothing is shared between page loads. Unlike .NET, where the application is started on the first page hit and runs until stopped, just servicing requests as they come. In PHP, every time a page is requested the application is essentially compiled and run from scratch.