Understanding Python's Global Interpreter Lock (GIL)

Posted by Afsal on 05-Apr-2024

Hi Pythonistas!

In the previous 2 posts we have mentioned about GIL. Some of us wonder what is it ?. Today we are going to learn about GIL.

What is GIL

The Global Interpreter Lock is a mutex (or a lock) that protects access to Python objects, preventing multiple native threads from executing Python bytecodes simultaneously. In simpler terms, it ensures that only one thread executes Python bytecode at a time, even on multi-core systems.

Why does Python have the GIL?

Python's GIL was implemented to simplify memory management and to make it easier to integrate with existing C libraries, such as those for manipulating images, audio, and video. Without the GIL, managing Python's memory across multiple threads could lead to complex and error-prone code, potentially introducing bugs that are hard to track down.

Implications of the GIL

Limited Multithreading Performance: Because only one thread can execute Python bytecode at a time, multithreading in Python doesn't always lead to performance improvements, especially in CPU-bound tasks. This limitation primarily affects CPU-bound applications but has less impact on I/O-bound applications, where threads spend most of their time waiting for I/O operations to complete.

Concurrency vs. Parallelism: While Python excels in handling concurrent tasks, thanks to libraries like asyncio, multiprocessing is often preferred over multithreading for achieving parallelism. By utilizing multiple processes instead of threads, Python can bypass the GIL and fully utilize multiple CPU cores, improving performance for CPU-bound tasks.

Compatibility with C Extensions: Many Python libraries and frameworks, particularly those with C extensions, rely on the GIL for thread safety. Removing the GIL would require significant changes to these libraries, potentially breaking backward compatibility with existing codebases.


Understanding the Global Interpreter Lock is crucial for Python developers aiming to write efficient and scalable applications. While the GIL imposes limitations on multithreading performance, Python's rich ecosystem of libraries and tools offers various alternatives for achieving concurrency and parallelism, ensuring that developers can still build high-performance applications in Python.

If you need more about GIL see this video

I hope you have learned something from this post please share your valuable suggestions with afsal@parseltongue.co.in