php crash segfault

<?php

class LinkedList {
    // object Node representing the head of the list
    private $head;
    // object Node representing the tail of the list
    private $tail;

    public function __construct() {
        $this->head = new Node(null);
        $this->tail = new Node(null);

        $this->head->setNext($this->tail);
        $this->tail->setPrevious($this->head);
    }

    /**
     * Add node to the tail of the list
     * @param type $key
     * @param type $data
     * @return boolean
     */
    public function addTail($data) {
        $this->attach($this->tail->getPrevious(), new Node($data));
    }

    /**
     * Add node to the head of the list
     * @param type $key
     * @param type $data
     */
    public function addHead($data) {
        $this->attach($this->head, new Node($data));
    }

    /**
     * Removes a node
     * @param Node $node node to remove
     */
    public function remove($nodeToRemove) {
        $this->detach($nodeToRemove);
    }

    /**
     * Returns the number of elements in the linked list
     * @return int
     */
    public function count() {
        $count = 0;
        $p = $this->head->getNext();
        while ($p->getNext() != null) {
            $p = $p->getNext();
            $count++;
        }
        return $count;
    }

    /**
     * Adds a node after another
     * @param Node $prev the node after which we want to add (e.g. head, tail or another generic node)
     * @param Node $node the node to add
     */
    private function attach($prev, $node) {
        $node->setPrevious($prev);
        $node->setNext($prev->getNext());
        $node->getNext()->setPrevious($node);
        $node->getPrevious()->setNext($node);
    }

    /**
     * Removes a node from the list
     * @param Node $node the node to remove from the list
     */
    private function detach($node) {
        $node->getPrevious()->setNext($node->getNext());
        $node->getNext()->setPrevious($node->getPrevious());
    }

    public function __toString() {
        $r = 'LinkedList { ';
        $h = $this->head->getNext();
        while ($h->getNext() != null) {
            $r .= $h->getData() . ', ';
            $h = $h->getNext();
        }
        return $r . '}';
    }

}

/**
 * Class that represents a node in a doubly linked list
 */
class Node {
    private $data;
    // the next node
    private $next;
    // the previous node
    private $previous;

    /**
     * @param string $data the content of the node
     */
    public function __construct($data) {
        $this->data = $data;
    }

    /**
     * Sets a new value for the node data
     * @param string the new content of the node
     */
    public function setData($data) {
        $this->data = $data;
    }

    /**
     * Sets a node as the next node
     * @param Node $next the next node
     */
    public function setNext(Node $next) {
        $this->next = $next;
    }

    /**
     * Sets a node as the previous node
     * @param Node $previous the previous node
     */
    public function setPrevious(Node $previous) {
        $this->previous = $previous;
    }

    /**
     * Returns the node data
     * @return mixed the content of the node
     */
    public function getData() {
        return $this->data;
    }

    /**
     * Returns the next node
     * @return Node the next node of the node
     */
    public function getNext() {
        return $this->next;
    }

    /**
     * Returns the previous node
     * @return Node the previous node of the node
     */
    public function getPrevious() {
        return $this->previous;
    }

    public function __toString() {
        return "Node($this->data)";
    }

}

$foo = new LinkedList();
for ($i = 0; $i < 200000; ++$i) {
    // echo "putting $i\n";
    $foo->addTail($i);
}
echo "start counting", PHP_EOL;
echo "count: ",  $foo->count(), PHP_EOL;
// php crashes during the count()!