import threading def job1(): global A, lock lock.acquire() for i in range(10): A += 1 print('job1', A) lock.release() def job2(): global A, lock lock.acquire() for i in range(10): A += 10 print('job2', A) lock.release() if __name__ == '__main__': lock = threading.Lock() A = 0 t1 = threading.Thread(target=job1) t2 = threading.Thread(target=job2) t1.start() t2.start() t1.join() t2.join()