PHP destructors with cycles

test1.txt

PHP 5.3.15 (cli) (Aug 24 2012 17:40:23) [Darwin]
>>> class Foo { public $x; function __destruct() { echo "destroy\n"; var_dump($this); } }
>>> $a = new Foo(); $b = new Foo(); $a->x = $b; $b->x = $a; unset($a); unset($b);
>>> gc_collect_cycles()
destroy
object(Foo)#2 (1) {
  ["x"]=>
  object(Foo)#1 (1) {
    ["x"]=>
    *RECURSION*
  }
}
destroy
object(Foo)#1 (1) {
  ["x"]=>
  object(Foo)#2 (1) {
    ["x"]=>
    *RECURSION*
  }
}

test2.txt

PHP 5.3.15 (cli) (Aug 24 2012 17:40:23) [Darwin]
>>>  class Foo { public $x; function __destruct() { echo "destroy\n"; var_dump($this); } }
>>> $a = new Foo(); $b = new Foo(); $c = new Foo()
>>> $a->x = $b; $b->x = $c; $c->x = $a
>>> unset($a); unset($b); unset($c)
>>> gc_collect_cycles()
destroy
object(Foo)#3 (1) {
  ["x"]=>
  object(Foo)#1 (1) {
    ["x"]=>
    object(Foo)#2 (1) {
      ["x"]=>
      *RECURSION*
    }
  }
}
destroy
object(Foo)#2 (1) {
  ["x"]=>
  object(Foo)#3 (1) {
    ["x"]=>
    object(Foo)#1 (1) {
      ["x"]=>
      *RECURSION*
    }
  }
}
destroy
object(Foo)#1 (1) {
  ["x"]=>
  object(Foo)#2 (1) {
    ["x"]=>
    object(Foo)#3 (1) {
      ["x"]=>
      *RECURSION*
    }
  }
}

test3.txt

PHP 5.3.15 (cli) (Aug 24 2012 17:40:23) [Darwin]
>>> class Foo { public $x; public $destroyed = false; function go() { var_dump($this->destroyed); } function __destruct() { echo "destroy\n"; var_dump($this); $this->destroyed = true; $this->x->go(); } }
>>> $a = new Foo(); $b = new Foo(); $a->x = $b; $b->x = $a; unset($a); unset($b);
>>> gc_collect_cycles()
destroy
object(Foo)#2 (2) {
  ["x"]=>
  object(Foo)#1 (2) {
    ["x"]=>
    *RECURSION*
    ["destroyed"]=>
    bool(false)
  }
  ["destroyed"]=>
  bool(false)
}
bool(false)
destroy
object(Foo)#1 (2) {
  ["x"]=>
  object(Foo)#2 (2) {
    ["x"]=>
    *RECURSION*
    ["destroyed"]=>
    bool(true)
  }
  ["destroyed"]=>
  bool(false)
}
bool(true)