What is GIL in Python and why do we need to know about it?

GIL (Global Interpreter Lock) is a mechanism in CPython that ensures only one thread executes Python bytecode at a time. This is done to simplify memory management and prevent issues with thread safety.

Why know about GIL:

• It limits the efficiency of multithreaded execution of CPU-bound tasks in Python, as threads cannot run in parallel on multiple cores.
• For tasks requiring parallelism, multiprocessing (processes) or external libraries that bypass GIL (e.g., numpy, implemented in C) are often used.

Example: if you run multiple threads for computations, they will work sequentially due to GIL, not in parallel.

import threading

def cpu_bound_task():
    count = 0
    for i in range(10**7):
        count += i

threads = []
for _ in range(4):
    t = threading.Thread(target=cpu_bound_task)
    t.start()
    threads.append(t)

for t in threads:
    t.join()

In this example, 4 threads will not provide a performance increase due to GIL.