python - 如何让多处理运行？

Question

我试图让两个进程同时运行，而不是一次运行一个进程。我的代码如下。有人能告诉我出了什么问题吗？谢谢!

from multiprocessing import Process
from os import getpid
from random import randint
from time import time, sleep

def download_task(filename):
    print('Initiate downloading task, task No.[%d].' % getpid())
    print('Begin downloading %s...' % filename)
    time_to_download = randint(5, 10)
    sleep(time_to_download)
    print('Finished downloading %s! It took %d seconds' % (filename, time_to_download))

def main():
    start = time()
    p1 = Process(target=download_task, args=('Python: from beginer to lunatic.pdf',))
    p1.start()
    p2 = Process(target=download_task, args=('Peking Hot.avi',))
    p2.start()
    p1.join()
    p2.join()
    end = time()
    print('It took %.2f seconds in total.' % (end - start))

if __name__ == '__main__':
    main()

现在，这就是我所拥有的一切。

It took 0.14 seconds in total.

但是我应该得到这样的东西:

Start downloading Python: from beginer to lunatic.pdf...
Start downloading Peking Hot.avi...
Finished downloading Python: from beginer to lunatic.pdf! It took 5 seconds
Finished downloading Peking Hot.avi! It took 5 seconds
It took 5.00 seconds in total.

Answer 1

您应该刷新多处理位中的输出流。您可以通过将 flush=True 添加到打印语句、将 sys.stdout.flush() 添加到函数末尾、添加单个 print("",lush=True) 到函数末尾，或者在从命令行调用程序时指定 -u 参数 (python -u your_file_name.py)。后者以“unbuffered”模式运行python。其中任何一个都应该有效。