Fun with Futex Implementing an optimized lock in Linux requires some Operating System help. You can only get so far by doing everything in user-land. We are going to take a look how one can implement a simple spin lock in C (just like the spin lock in Go I implemented a while back) and then a slightly more elaborate lock using operating system’s primitives. The idea behind a mutex (mutual exclusion) is straightforward: we want some part of the code to be accessed only by a single thread at a time. If the resource a thread is trying to access (the critical zone) is already being accessed by something else: wait. The trick about implementing them is how you to do wait part!