public function retry_incremental(\Exception $e = null, $output = null, $exp = 2, $unit = 'minutes') {
		if (self::$max_attempts > 0 AND $this->retry_attempt >= self::$max_attempts) {
			echo $output;
			throw $e;
		}

		$this->retry_attempt++;
		$this->schedule(pow($this->retry_attempt, $exp) . ' ' . $unit);
	}