总结
Multi level: 从"控制范围"来进行对比
简单概括来说:
1、sequential consistent ordering: 所有的thread看到的modification order是一致的
2、使用release-acquire、release-acquire实现的happens-before而构建起的modification order，仅限于参与的thread看到的modification order是一致的
下面总结对memory order的控制范围
| Ordering | 范围 |
|---|---|
| Relaxed | 不控制，因此范围为0 |
| Release-consume | 对存在data dependency的shared data的memory order进行控制 |
| Release-acquire | 不考虑data dependency关系，直接画两条线，不允许越界 |
| Sequentially consistent | 全局 |
Implementation
都会涉及strong、weak ordered memory CPU。
Acquire release memory order VS sequential consistency
基于producer-consumer来进行分析
multiple-producer-multiple-consumer需要sequential consistency
acquire release 能否实现multiple-producer-multiple-consumer？