好奇心会逼着我们学习。而对史蒂夫来说，想学习远比想证明自己正确更重要。
loop for each post url
。safew官方版本下载对此有专业解读
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.
Two pixels per character