Python多进程中，一个进程开启后并没有执行，也无法终止

Z时代
2024-02-13
分类：IT

from multiprocessing import Process
from multiprocessing import Queue 
import time
def write(q, urls):
    print("Process is writting...")
    for url in urls:
        q.put(url)
        print("put %s to queue..." % url)
        time.sleep(2)
def read(q):
    print("Process is reading...")
    while True:
        url = q.get(True)
        print("Get %s from queue" % url)
if __name__ == "__main__":
    q = Queue()
    # 父进程创建Queue，并传给各个子进程
    w1 = Process(target=write, args=(q,["url_1", "url_2", "url_3"]))
    w2 = Process(target=write, args=[q,["url_4", "url_5", "url_6"]])
    r = Process(target=read, args=(q,))
    w1.start()
    w2.start()
    r.start() 
    w1.join()
    w2.join()
    print(r.is_alive())  # True
    r.terminate()
    # 测试
    print(r.is_alive())  # True
    print(w1.is_alive())  # False
    print(w2.is_alive())  # False
    print("结束")

输出

Process is writting... put url_1 to queue... put url_2 to queue... put url_3 to queue... Process is writting... put url_4 to queue... put url_5 to queue... put url_6 to queue... True True False False

结束

从输出可以看出，进程r并没有执行read()，但是确是存活着，而且无法关闭

回答：

Process is writting... put url_1 to queue... Process is writting... put url_4 to queue... Process is reading... Get url_1 from queue Get url_4 from queue put url_2 to queue... Get url_2 from queue put url_5 to queue... Get url_5 from queue put url_3 to queue... Get url_3 from queue put url_6 to queue... Get url_6 from queue True True False False

End

为什么我每次运行都没有问题，你的机子是咋了，有其他不正常的地方吗？

    r.terminate()
    r.join()
    print(r.is_alive())  # now False
    print(w1.is_alive())  # False
    print(w2.is_alive())  # False    print("End")

不过让r进程结束可以这样实现，我查了下文档，terminate是给结束信号，并不保证马上停止，主进程也不会等待r结束再向下执行，需要使用join方法让主进程等待子进程r结束后再向下执行。

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