What is Python’s Global Interpreter Lock (GIL) and what problem does it create for CPU-bound multi-threaded programs?

Question

Python Developer — Hard

What is Python’s Global Interpreter Lock (GIL) and what problem does it create for CPU-bound multi-threaded programs?

Accepted Answer

The Global Interpreter Lock (GIL) in Python is a CPython-specific mutex that allows only one thread to execute Python bytecode at a time. This creates a problem for CPU-bound multi-threaded programs because threads cannot run in parallel on multiple cores, making them slower. The issue can be solved by using multiprocessing instead of threading.