public function kill($signal = SIGKILL)
    {
        if (!$this->getPid()) {
            throw new ResqueRuntimeException(
                'Cannot kill a process with out a pid set'
            );
        }

        //TODO: needs logger
        //$this->getLogger()->notice('Sending {signal} to process {pid}', array('signal'=>$signal, 'pid'=>$this->getPid()));

        // @todo Work out if I care to check the result, and if I did what to do about it... Exception?
        posix_kill($this->getPid(), $signal);

        $this->pid = null;

        return $this;
    }