NewDivide new a divide.

NewMulti new a Multi with num.

OptPage set page.

OptPageSize set page size.

OptTotal set total.

Safe mode, recover the panic, prevent crash the server.

Divide 分批操作，使用场景为：需要获取下游全量数据，而下游必传分页参数 multi 并发方法，用于并发请求 page 当前分页，默认为1 pageSize 页面大小，默认为100.

Multi allows start num of goroutines and save err msg.

WaitGroup contains sync.WaitGroup.