locker.py

import threading

barrier = threading.Barrier(2)

main.py

import threading
import sys

import time
import locker

def worker1():
    import mod1
    print(f"Worker 1: {mod1.val}")
  
  
def worker2():
    import sys
    mod1 = sys.modules.get('mod1', None)
    if mod1 is None:
        import mod1
        print("Worker 2: No problems")
    else:
        print(f"Worker 2: {mod1.val}")

threading.Thread(target=worker1).start()
threading.Thread(target=worker2).start()
time.sleep(0.1)
locker.barrier.wait()

mod1.py

import locker

locker.barrier.wait()
val = "Forbidden variable"