What internal mechanisms limit the execution of threads in the Python interpreter due to the GIL?

In Python, there is a mechanism called GIL (Global Interpreter Lock), which restricts the concurrent execution of interpreter bytecode in multiple threads. GIL is a global lock that allows only one thread to execute Python bytecode at any given time. This means that even if you have multiple threads, they cannot execute Python code in parallel and will switch back and forth.

GIL is implemented to simplify memory management and ensure object safety in CPython. Because of this, multithreaded Python programs do not gain performance improvements on multi-core processors when performing CPU-intensive tasks.

Example: if you have several threads performing calculations in Python, they will sequentially acquire control due to the GIL. To bypass this limitation, multithreading is often replaced with multiprocessing (the multiprocessing module) or C extensions that release the GIL during heavy operations.