public function watch($path, $callback)
	{
		if (!is_callable($callback)) {
			return null;
		}
		
		if ($this->zookeeper->exists($path)) {
			if (!isset($this->callback[$path])) {
				$this->callback[$path] = array();
			}
			if (!in_array($callback, $this->callback[$path])) {
				$this->callback[$path][] = $callback;
				return $this->zookeeper->get($path, array($this, 'watchCallback'));
			}
		}
	}