Why doesn't my timer thread run in python?

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?

Tim Peters · Accepted Answer · 2020-07-23 16:08:45Z

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 :-)

answered Jul 23, 2020 at 16:08

Tim Peters

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1 Comment

Jackson Over a year ago

Thank you so much!

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