运行两个简单的进程

使用多个进程的一个简单示例是两个单独执行的进程（worker）。在以下示例中，启动了两个进程：

• countUp() 每秒计数 1 次。
• countDown() 每秒计数 1 次。

import multiprocessing
import time
from random import randint

def countUp():
    i = 0
    while i <= 3:
        print('Up:\t{}'.format(i))
        time.sleep(randint(1, 3)) # sleep 1, 2 or 3 seconds
        i += 1

def countDown():
    i = 3
    while i >= 0:
        print('Down:\t{}'.format(i))
        time.sleep(randint(1, 3)) # sleep 1, 2 or 3 seconds
        i -= 1

if __name__ == '__main__':
    # Initiate the workers.
    workerUp = multiprocessing.Process(target=countUp)
    workerDown = multiprocessing.Process(target=countDown)
    
    # Start the workers.
    workerUp.start()
    workerDown.start()

    # Join the workers. This will block in the main (parent) process
    # until the workers are complete.
    workerUp.join()
    workerDown.join()

输出如下：

Up:    0
Down:    3
Up:    1
Up:    2
Down:    2
Up:    3
Down:    1
Down:    0