What is the underlying principle of CAS in Java?

CAS, short for Compare and Swap, is a concurrency control mechanism in Java that ensures atomic operations on shared variables by comparing the current value in memory with the expected value, and only performing the update if they match. It is an optimistic lock mechanism that eliminates the need for traditional mutual exclusion mechanisms like locks, reducing unnecessary thread blocking and waking operations. Underlying CAS is the use of hardware atomic instructions, such as the CMPXCHG instruction in the x86 architecture, to compare and update values atomically. In Java, CAS operations are implemented through a series of atomic operation methods provided by the Unsafe class.