for i, item in items {
carrier at a time, but may migrate between carriers via work
，推荐阅读搜狗输入法获取更多信息
5年过渡期里，总书记多次走进山野田间，为乡村特色产业的发展壮大指明方向：
For implementers, the locking model adds a fair amount of non-trivial internal bookkeeping. Every operation must check lock state, readers must be tracked, and the interplay between locks, cancellation, and error states creates a matrix of edge cases that must all be handled correctly.