PHP and the story of reference counting

Today I want to talk about a very specific situation, where PHP’s reference management simply fails. Imagine the follow piece of code (I’ve stripped some of the method bodies to simplify the example):

class Connection {    public function connect();    public function disconnect();    public function __destruct() {      $this->disconnect();    }  }  class MySpecialConnectionAggregator {    private $oConnection;    public function __construct() {      $this->oConnection = new Connection();      $this->oConnection->connect();  }

We have a class called „Connection“ and a aggregator for that class named „MySpecialConnectionAggregator“.
I would have expected, that a call of unset() on the MySpecialConnectionAggregator removes the instance of MySpecialConnectionAggregator and the encapsulated instance of Connection from the userland calling the __destruct() method of the Connection

What do you think? *Beeeep* … Wrong 😉 It is NOT removed and remains as a dead reference in the memory.

You have to implement something like this:

// ... we are in class MySpecialConnectionAggregator  public function __destruct() {    unset($this->oConnection);  }

We have a class called „Connection“ and a aggregator for that class named „MySpecialConnectionAggregator„.
I would have expected, that a call of unset() on the MySpecialConnectionAggregator removes the instance of MySpecialConnectionAggregator and the encapsulated instance of Connection from the userland calling the __destruct() method of the Connection

What do you think? *Beeeep* … Wrong 😉 It is NOT removed and remains as a dead reference in the memory.

You have to implement something like this:

// ... we are in class MySpecialConnectionAggregator  public function __destruct() {    unset($this->oConnection);  }

By the way: This is „fixed“ in PHP 5.3 and up, as the garbage collection of 5.3 works better than in 5.x.