Overview Threads and locks are a software-defined formalization of the hardware underneath, and as such comprise the simplest possible concurrency model. It forms the basis of other concurrency abstractions built on top of it, so it’s important to understand in this regards. However, it’s difficult or impossible to build reliable, scalable systems directly on these primitives. While most every language has support for threads and locks, CPython remains special in its use of a global interpreter lock that prevents threads from concurrently accessing shared memory, because CPython’s memory management is not thread-safe.