C++ Memory Model 与 memory_order | C++

本章覆盖：happens-before；sequenced-before；synchronizes-with；memory ordering；`memory_order_seq_cst`；acquire；release；relaxed；acq_rel；fence 的高级定位；mutex 建立同步关系；初级代码默认先用 mutex / seq_cst，优化前必须证明正确。