Python: GIL (Global Interpreter Lock)

Rahul S
2 min readSep 27

The Global Interpreter Lock is a mutex (short for mutual exclusion) that protects access to Python objects, preventing multiple threads from executing Python bytecodes in parallel. It is built deep into the Python system and it is not possible at the moment to get rid of it.

In simpler terms, it ensures that only one thread can execute Python code at a time, even on multi-core processors. This can have performance implications, especially in CPU-bound multi-threaded Python programs.

It makes threading not truly concurrent. It locks the interpreter, and even though it looks like we are working with threads, they are not executed at the same time, resulting in performance losses.

Here are some ways to work around the GIL in Python:

  1. **Use Multiprocessing**: One of the most common ways to bypass the GIL is to use the `multiprocessing` module instead of the `threading` module.

`multiprocessing` allows you to create multiple processes, each with its own Python interpreter and memory space, which can run concurrently. This enables true parallelism, as each process operates independently of the GIL.

2. **Use Native Extensions**: You can write CPU-bound code in languages like C or C++ and create Python extensions (using CPython’s C-API or tools like Cython) to perform the CPU-intensive tasks. Since these extensions don’t run Python bytecode, they are not affected by the GIL.

3. **Use Python’s asyncio**: For I/O-bound tasks, you can use Python’s asyncio library to write asynchronous code. The GIL is released during I/O operations, so asynchronous code can achieve concurrency efficiently by not blocking the CPU-bound threads.

4. **Use Separate Processes or Subprocesses**: If your application architecture allows it, you can use separate processes or subprocesses instead of threads to parallelize tasks. This is similar to the multiprocessing approach but with more control over the process management.

6. **Optimize with GIL-Aware Libraries**: Some libraries are optimized to work efficiently within the GIL constraints. For example, NumPy operations often release the GIL, allowing for some level of parallelism when working with large arrays.

7. G: Instead of creating threads manually, you can utilize thread pool libraries like `concurrent.futures.ThreadPoolExecutor` or `multiprocessing.pool.ThreadPool`. These manage a pool of worker threads and can help mitigate the GIL’s impact.

It’s important to note that the GIL is a fundamental part of CPython, the most widely used Python implementation. While these workarounds can help improve concurrency in your Python programs, they come with their own trade-offs and complexities. The choice of approach should depend on your specific use case, as well as your application’s requirements and constraints.

Rahul S

LLM, NLP, Statistics, MLOps | Senior AI Consultant | IIT Roorkee | Connect: []