# ch14/example2.py

import threading
import random
import time

def update():
    global counter

    with count_lock:
        current_counter = counter # reading in shared resource
        time.sleep(random.randint(0, 1)) # simulating heavy calculations
        counter = current_counter + 1

counter = 0
count_lock = threading.Lock()

threads = [threading.Thread(target=update) for i in range(20)]

for thread in threads:
    thread.start()
for thread in threads:
    thread.join()

print(f'Final counter: {counter}.')
print('Finished.')