在 Python 中使用两个单独的线程打印偶数和奇数

Question

I have written a below code to print even and odd numbers using 2 separate threads in Python, but this code isn't working ( Program is not showing any output and expectation is to print numbers from 0-10 in sequence ). Any help in getting this debugged would be highly appreciated. Below is the code:

from threading import Thread
from threading import Event


even_available = Event()
odd_available = Event()

def print_even():
    global limit
    global exit_prog
    global number

    while not exit_prog and number <= limit:
        print(number)
        number = number + 1
        even_available.clear()

        odd_available.set()

def print_odd():
    global limit
    global exit_prog
    global number

    odd_available.wait()
    while not exit_prog and number <= limit:
        print(number)
        number = number+1
        odd_available.clear()
        even_available.set()

if __name__ == "__main__":

    limit = 10
    exit_prog = False
    number = 0

    t1 = Thread(target=print_even)
    t2 = Thread(target=print_odd)

    even_available.set()

    t1.start()
    t2.start()

    t1.join()
    t2.join()

Answer 1

Using multiprocessing makes the code a little cleaner. You also want to avoid global variables if you don't have to.

from multiprocessing import Process

def print_even(limit, exit_prog, number):
    while not exit_prog and number <= limit:
        if(number % 2 == 0):
            print(number)
        number = number + 1

def print_odd(limit, exit_prog, number):
    while not exit_prog and number <= limit:
        if(number % 2 == 1):
            print(number)
        number = number + 1

if __name__ == "__main__":

    limit = 10
    exit_prog = False
    number = 0

    t1 = Process(target=print_even, args=(limit, exit_prog, number))
    t1.start()
    t2 = Process(target=print_odd, args=(limit, exit_prog, number))
    t2.start()

    t1.join()
    t2.join()

Answer 2

You simply forgot to wait() for even_available / odd_available inside the while loop:

from threading import Thread
from threading import Event

even_available = Event()
odd_available = Event()

def print_even():
    global limit
    global exit_prog
    global number

    while not exit_prog and number < limit:
        even_available.wait()
        print('E', number)
        number = number + 1
        even_available.clear()
        odd_available.set()

def print_odd():
    global limit
    global exit_prog
    global number

    while not exit_prog and number < limit:
        odd_available.wait()
        print('O', number)
        number = number + 1
        odd_available.clear()
        even_available.set()

if __name__ == "__main__":

    limit = 10
    exit_prog = False
    number = 0

    t1 = Thread(target=print_even)
    t2 = Thread(target=print_odd)

    even_available.set()

    t1.start()
    t2.start()

    t1.join()
    t2.join()

Prints:

E 0
O 1
E 2
O 3
E 4
O 5
E 6
O 7
E 8
O 9
E 10