Detailed cas principle

The full name of CAS is Compare and Swap, which means compare and exchange. It is a lock-free atomic algorithm as well as an optimistic mechanism. CAS is mapped to the operating system as a CPU atomic instruction. The implementation method is based on the assembly instructions of the hardware platform. In Intel's CPU, the `cmpxchg` instruction is used, which means that CAS is implemented by hardware, thereby improving efficiency at the hardware level.