PHP静态类变量，继承和垃圾回收

I am having some memory problems with a script that uses objects set up with inherited static variables like this.

class a
{
    public static $a = "a";
}

class b extends a
{
    private $instanceVar = 'hey';
    private $otherVar = 'you';

    public function DoStuff()
    {
        echo self::$a;
    }
}

then code that uses the classes like this

while(condition)
{
    $obj = new b();
    $obj -> DoStuff();
    unset($obj);
}

My question is, will unsetting obj trigger garbage collection and the unsetting of its instance variables since it also holds a reference to the the inherited static variable?

unset in this code doesn't bring anything.

With and without it the object will be successfully collected when it's possible.

will unsetting obj trigger garbage collection

Not it won't. Garbage collector will be called automatically when it makes sense.

since it also holds a reference to the the inherited static variable

It doesn't. Objects don't hold references to a static properties.

If you care so much about GC and have PHP >= 5.3.0 have a look to gc_collect_cycles and garbage collection in general