(PECL gearman >= 0.5.0)
GearmanClient::setWorkloadCallback — Set a callback for accepting incremental data updates
Sets a function to be called when a worker needs to send back data prior to job completion. A worker can do this when it needs to send updates, send partial results, or flush data during long running jobs. The callback should accept a single argument, a GearmanTask object.
callbackA function to call
成功时返回 TRUE， 或者在失败时返回 FALSE。