import threading
import time


foo = 0

def race_cond():
    flag = threading.Event()

    def mutator():
        flag.wait()
        foo += 1
        foo -= 1
    ts = [threading.Thread(target=mutator)
         for i in range(100000)]
    [t.start() for t in ts]
    flag.set()
    [t.join() for t in ts]

for i in range(100):
    print(f'Expect 0, actual: {foo}')