(PECL gearman >= 0.5.0)
GearmanClient::echo — Send data to all job servers to see if they echo it back [deprecated]
$workload): boolThe GearmanClient::echo() method is deprecated as of pecl/gearman 1.0.0. Use GearmanClient::ping().
workloadSome arbitrary serialized data to be echo back
成功时返回 true， 或者在失败时返回 false。