Expert Python Programming - Third Edition

How Python deals with threads

Unlike some other languages, Python uses multiple kernel-level threads that can each run any of the interpreter-level threads. But the standard implementation of the CPython language comes with a major limitation that renders threads less usable in many contexts. All threads accessing Python objects are serialized by one global lock. This is done because much of the interpreter internal structures, as well as third-party C code, are not thread-safe and need to be protected.

This mechanism is called the Global Interpreter Lock (GIL), and its implementation details on Python/C API level were already discussed in the Releasing GIL section of Chapter 9, Python Extensions in Other Languages. The removal of GIL is ...