_sending Whether we are currently sending sync items.
	 */
	public static function set_is_sending( $is_sending ) {
		self::$is_sending = $is_sending;
	}

	/**
	 * Whether should send from the queue
	 *
	 * @access public
	 * @static
	 *
	 * @param string $queue_id The queue identifier.
	 *
	 * @return boolean Whether sync is enabled.
	 */
	public static function is_sender_enabled( $queue_id ) {
		return (bool) self::get_setting( $queue_id . '_sender_enabled' );
	}

	/**
	 * Whether checksums are enabled.
	 *
	 * @access public
	 * @static
	 *
	 * @return boolean Whether sync is enabled.
	 */
	public static function is_checksum_enabled() {
		return ! (bool) self::get_setting( 'checksum_disable' );
	}

}