Lock-free data structures tend to use the compare-and-swap atomic operation as a primitive: https://en.wikipedia.org/wiki/Compare-and-swap https://en.wikipedia.

Lock-free data structures tend to use the compare-and-swap atomic operation as a primitive: https://en.wikipedia.org/wiki/Compare-and-swap https://en.wikipedia.org/wiki/Compare-and-swap You provide three values to a CAS operation: the memory address you want to change, the value you expect to be there and the new value you want to be there. If the expected value is not what is at that memory address, the CAS fails; presumably, the expected value is not there because another thread's CAS succeeded before you. You now need to do try again (and maybe do some more work before doing so). You can see this in Section 3.3, "The insert operation": https://arxiv.org/abs/1909.02852 https://arxiv.org/abs/1909.02852 I think this answers your question: algorithms for data structures like this one use primitives like CAS to ensure that the data structure remains valid even when multiple threads are modifying it, and all without mutual exclusion mechanisms likes locks and mutexes.