unset and __destruct

Gibou · 05-03-2008, 07:27 PM

Hi !

I'm used to unset my local variables but I'm wondering if it is really useful.

For instance, in this case:

PHP Code:


			
<?php
function toto()
{
  $myVar=5;
  [...] // some treatments
  unset($myVar);
}
?>

Is the local variable $myVar automatically free when we leave the function toto or is it really useful to unset it ?
Must I just unset the variables instancied by the "new" operator ?

Second question:

I don't know if what I put in my __destruct methods is good.
Indeed, my typical __destruct method is

PHP Code:


			
public function __destruct()
{
  foreach(get_object_vars($this) as $k=>$v)
    unset($this->$k);
}

and then, my __destruct() call on an object $foo is automatically followed by unset($foo);

In fact, I don't know the exact behavior of php when it leaves a method and when it has finished to parse my pages.

What do you advise ?

Thank you, have a nice evening !

delayedinsanity · 05-03-2008, 07:51 PM

I may be wrong about this, but I'm pretty sure unset()ing the object will destroy all the variables ($this) contained within that object without the need of explicitly doing so in the __destruct() method.

I also read a note in the manual stating that when if you are planning to destroy an object before the end of the script (ie, half way through, right after using it, etc), that you may want to call __destruct yourself. Otherwise PHP will wait until the end of the script before calling the method and you won't be gaining any resources along the way.
-m

Gibou · 05-03-2008, 08:02 PM

Quote:

Originally Posted by delayedinsanity

I may be wrong about this, but I'm pretty sure unset()ing the object will destroy all the variables ($this) contained within that object without the need of explicitly doing so in the __destruct() method.

mmmm, I don't think so.
I think it's the same way as the C or C++ dynamic allocation.

The object is the link between the user and the allocated memory used by dynamic attributes of the class instancied by the object. (Excuse if I'm not clear, I do my best in english

).

In C++, If I have an object foo and an attribute foo->bar which is itself another object of another class, if I do delete(foo) so bar is lost and I will never be able to free it.

I think it's the same in php, even if allocation and types are dynamic but I don't know how/where to verify it properly.

delayedinsanity · 05-03-2008, 08:06 PM

Ah, well you may be right about that. I hardly ever worry about unset()ing much except $_SESSION variables myself. Most of my pages load in less than 0.003 of a second anyways, and that's including my controllers which load multiple objects and do various database calls on top of that. I haven't seen the need, but I'm not suggesting it's not sloppy. I've only been at this for a little while.

-m

freenity · 05-03-2008, 11:50 PM

php has a garbage collector, that cleans the variables automatically when they are not referenced or used anymore

freenity · 05-03-2008, 11:54 PM

You can use something like this to tset it:

PHP Code:


			
<?php

class A
{
    public $var = array();

    public function __construct()
    {
        for ($i=0;$i<10;$i++) {
            $this->var[] = new B();
        }
    }
}


class B
{
    public $varb = array();

    public function __construct()
    {
        for ($i=0;$i<10000;$i++) {
            $this->var[] = rand();
        }
    }
}


echo "Just after load ".intval(memory_get_usage()/(1024*1024))."MB \n";
$a = new A();
echo "After creating A() ".intval(memory_get_usage()/(1024*1024))."MB \n";
unset($a);
echo "After destroying A() ".intval(memory_get_usage()/(1024*1024))."MB \n";