Python Pipe Hang

Question

main0不会挂起但main1挂起。为什么？？？我认为将这个东西包装成一个类应该是无害的......

子进程应该只是将收到的消息发送回主进程。

Python3代码：

from multiprocessing import Process, Pipe
def child(conn):
    print("child started")
    while True:
        msg = conn.recv()
        if msg == "quit":
            break
        print("child recv:"+msg)
        print("child sending:" + msg)
        conn.send(msg)
    conn.close()
    print("child ended")


def main0():
    parent_conn, child_conn = Pipe()
    p = Process(target=child, args=(child_conn,))
    p.start()
    parent_conn.send("ping")
    print(parent_conn.recv())
    parent_conn.send("quit")
    print("#parent ended#")
    p.join()


class Parent(object):
    def __init__(self):
        self.parent_conn = None
        self.child_conn = None
        self.p = None

    def start(self):
        self.parent_conn, self.child_conn = Pipe()
        self.p = Process(target=child, args=(self.child_conn,))
        self.p.start() # <--- i initially missed this line
        print("started")

    def send(self, msg):
        print("try to send: " + msg)
        self.parent_conn.send(msg)
        return self.parent_conn.recv()

    def close(self):
        self.parent_conn.send("quit")
        self.p.join()


def main1():
    a = Parent()
    a.start()
    print(a.send("ping"))
    print(a.send("quit"))
    a.close()


if __name__ == '__main__':
    main0()  # doesn't hang
    main1()  # hangs.

输出：

~~~ main 0 ~~~
child started
child recv:ping
child sending:ping
ping
#parent ended#
child ended

~~~ main 1 ~~~
started <Process(Process-1, started)>
try to send: ping
waiting to recv
child started
child recv:ping
child sending:ping
ping
try to send: quit
waiting to recv
child ended
*still hangs ... after adding self.p.start()*

Answer 1

我在start方法中错过了self.p.start()行。

向儿童发送quit消息也不会返回任何消息。 正确的main1()应为：

def main1():
    a = Parent()
    a.start()
    print(a.send("ping"))
    a.close()

然后这是固定的。