Python Multithreading and Multiprocessing Quiz (30 MCQs with Answers)

1. Which concurrent.futures function yields futures as they complete (any order)?

2. What will be the output of the following code

from multiprocessing import Process
count = 0

def inc():
    global count
    count += 1

p = Process(target=inc)
p.start(); p.join()
print(count)

3. What does the GIL (Global Interpreter Lock) in CPython primarily affect?

4. What does Barrier do in threading?

5. What happens if you call future.result(timeout=1) and it doesn’t finish in time?

6. What will be the output of the following code

from multiprocessing import Process
import time, os

def child():
    time.sleep(0.05)
    print("child")

p = Process(target=child)
p.daemon = True
p.start()
time.sleep(0.01)
print("parent")

7. What will be the output of the following code of Queue with worker thread

import threading, queue

q = queue.Queue()

def worker():
    while True:
        x = q.get()
        if x is None: break
        print(x * 2)
        q.task_done()

t = threading.Thread(target=worker)
t.start()
q.put(1); q.put(2)
q.put(None)
t.join(timeout=0.1)

8. Which best describes Condition in threading?

9. What is freeze_support() used for?

10. What will be the output of the following code

from multiprocessing import Process, Manager
import time

def add(lst, val, delay):
    time.sleep(delay)
    lst.append(val)

with Manager() as m:
    lst = m.list()
    p1 = Process(target=add, args=(lst, "A", 0.02))
    p2 = Process(target=add, args=(lst, "B", 0.01))
    p1.start(); p2.start()
    p1.join(); p2.join()
    print("".join(lst))

11. Which of the following is most accurate about I/O-bound tasks?

12. Which module provides a high-level thread pool in Python?

13. In multiprocessing, which statement is required on Windows/macOS to avoid infinite child spawning?

14. What will be the output of the following code

from multiprocessing import Process, Queue

def child(q):
    q.put("x")

q = Queue()
p = Process(target=child, args=(q,))
p.start(); p.join()
print(q.get())

15. Which call properly starts a thread?

16. In multiprocessing, the recommended object for passing large arrays efficiently between processes is:

17. What will be the output of the following code

import threading

def f(name):
    print(name)

t = threading.Thread(target=f, args=("T1",))
print("A")
t.start()
t.join()
print("Z")

18. How do processes typically share state safely?

19. What is a deadlock?

20. For CPU-bound tasks on CPython, which is generally better for parallelism?

21. What will be the output of the following code

import threading

lock = threading.RLock()

def critical():
    lock.acquire()
    lock.acquire()
    print("inside")
    lock.release()
    lock.release()

critical()
print("done")

22. Which is true about signal handling with threads in CPython?

23. Which method blocks until a thread finishes?

24. What does daemon=True mean for a process in multiprocessing?

25. Which is best for preventing a classic race condition on shared data among threads?