为什么我的计时器线程不在 python 中运行？

Question

I am making a simple project to learn about threading and this is my code:

import time
import threading

x = 0

def printfunction():
    while x == 0:
        print("process running")


def timer(delay):
    while True:
        time.sleep(delay)
        break
    x = 1
    return x

t1 = threading.Thread(target = timer,args=[3])
t2 = threading.Thread(target = printfunction)

t1.start()
t2.start()
t1.join()
t2.join()

It is supposed to just print out process running in the console for three seconds but it never stops printing. The console shows me no errors and I have tried shortening the time to see if I wasn't waiting long enough but it still doesn't work. Then I tried to delete the t1.join() and t2.join() but I still have no luck and the program continues running.

What am I doing wrong?

Answer 1

Add

global x

to the top of timer() . As is, because timer() assigns to x , x is considered to be local to timer() , and its x = 1 has no effect on the module-level variable also named x . The global x remains 0 forever, so the while x == 0: in printfunction() always succeeds. It really has nothing to do with threading:-)