蟒蛇;(Python; Troubles controlling dead sockets through select)

 我有一些代码将连接到主机，除了监听传入的数据，直到客户端关闭或主机发送关闭语句。 为此我的代码运作良好。 
 
 但是，当主机在没有发送关闭语句的情况下死亡时，我的客户端会一直按预期继续侦听传入数据。 为了解决这个问题，我每隔foo秒就进行一次套接字超时，并开始检查连接是否存活。 从Python 套接字 howto我发现了这个： 
 
 
 
 选择的一个非常令人讨厌的问题：如果那些输入列表中的插座中的某个地方已经死了一个令人讨厌的死亡，那么选择将失败。 然后你需要遍历所有这些列表中的每一个该死的套接字并执行select（[sock]，[]，[]，0）直到找到坏的套接字。 超时0意味着它不会花费很长时间，但它很难看。 
 
 
    # Example code written for this question.
    from select import select
    from socket include socket, AF_INET, SOCK_STREAM

    socket = socket(AF_INET, SOCK_STREAM)
    socket.connect(('localhost', 12345))
    socklist = [socket,]
    attempts = 0

    def check_socklist(socks):
        for sock in socklist:
            (r, w, e) = select([sock,], [], [], 0)          

            ...
            ...
            ...

    while True:

        (r, w, e) = select(socklist, [], [], 60)

        for sock in r:      
            if sock is socket:
                msg = sock.recv(4096)
                if not msg:
                    attempts +=1
                    if attempts >= 10:
                        check_socket(socklist)
                    break
                else:
                    attempts = 0
                    print msg
 
 本文提出了三个问题。 
 
 
 
 我被教导要检查连接是否存活，必须写入套接字并查看响应是否返回。 如果没有，则必须假设连接已经死亡。 在文中它说要检查错误的连接，每个套接字一个，将它传递给select的第一个参数并将超时设置为零。 这将如何确认插座是否已经死？ 
 
 
 为什么不通过尝试写入套接字来测试套接字是死还是活？ 
 
 
 当连接处于活动状态并且已经死亡时，我在寻找什么？ 选择将立即超时，因此没有数据将证明什么。 
 
 
 我意识到像gevent ， asyncore和twisted这样的库可以帮助我解决这个问题，但是我选择这样做是为了更好地理解正在发生的事情，并且能够更好地控制我的源头。 

I have some code which will connect to a host and do nothing but listen for incoming data until either the client is shut down or the host send a close statement. For this my code works well.
 
However when the host dies without sending a close statement, my client keeps listening for incoming data forever as expected. To resolve this I made the socket timeout every foo seconds and start the process of checking if the connection is alive or not. From the Python socket howto I found this: 
 
 
 
One very nasty problem with select: if somewhere in those input lists of sockets is one which has died a nasty death, the select will fail. You then need to loop through every single damn socket in all those lists and do a select([sock],[],[],0) until you find the bad one. That timeout of 0 means it won’t take long, but it’s ugly.
 
 
    # Example code written for this question.
    from select import select
    from socket include socket, AF_INET, SOCK_STREAM

    socket = socket(AF_INET, SOCK_STREAM)
    socket.connect(('localhost', 12345))
    socklist = [socket,]
    attempts = 0

    def check_socklist(socks):
        for sock in socklist:
            (r, w, e) = select([sock,], [], [], 0)          

            ...
            ...
            ...

    while True:

        (r, w, e) = select(socklist, [], [], 60)

        for sock in r:      
            if sock is socket:
                msg = sock.recv(4096)
                if not msg:
                    attempts +=1
                    if attempts >= 10:
                        check_socket(socklist)
                    break
                else:
                    attempts = 0
                    print msg
 
This text creates three questions.
 
 
 
I was taught that to check if a connection is alive or not, one has to write to the socket and see if a response returns. If not, the connection has to be assumed it is dead. In the text it says that to check for bad connections, one single out each socket, pass it to select's first parameter and set the timeout to zero. How will this confirm that the socket is dead or not?
 
 
Why not test if the socket is dead or alive by trying to write to the socket instead?
 
 
What am I looking for when the connection is alive and when it is dead? Select will timeout at once, so having no data there will prove nothing. 
 
 
I realize there are libraries like gevent, asyncore and twisted that can help me with this, but I have chosen to do this my self to get a better understanding of what is happening and to get more control over the source my self.

原文：https://stackoverflow.com/questions/19795529