> For example, in CPython multiple threads can append to a list without a lock or insert items into a dict without a lock, and the data structure will never bec

> For example, in CPython multiple threads can append to a list without a lock or insert items into a dict without a lock, and the data structure will never become corrupted. How is this achieved? > Though it is worth pointing out that Java has a well-defined memory model, and Python doesn't. Wouldn't you have to at least issue an mfence when a thread enters / exists the GIL?