5

这个问题与In a non-blocking socket connect, select() always return 1非常相似(或几乎相同);但是,我似乎无法找到我的代码出现问题的地方。

我正在使用非阻塞套接字,并希望在将客户端连接到服务器时使用 select() 来检查超时/成功。问题是 select() 总是几乎立即返回 1,即使我什至没有运行服务器并且没有任何东西可以连接。提前感谢您的帮助,代码片段如下:

//Loop through the addrinfo structs and try to connect to the first one we can
for(p = serverinfo; p != NULL; p = p->ai_next) {
    if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) 
    {
        //We couldn't create the socket, try again
        perror("client: socket");
        continue;
    }

    //Set the socket to non-blocking
    int flags = fcntl(sockfd, F_GETFL, 0);
    fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);

    if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
        //The error was something other than non-block/in progress, try next addrinfo
        if(errno != EINPROGRESS) 
        {
            close(sockfd);
            perror("client: connect");
            continue;
        }

        fd_set write_fds;
        FD_ZERO(&write_fds);            //Zero out the file descriptor set
        FD_SET(sockfd, &write_fds);     //Set the current socket file descriptor into the set

        //We are going to use select to wait for the socket to connect
        struct timeval tv;              //Time value struct declaration
        tv.tv_sec = 5;                  //The second portion of the struct
        tv.tv_usec = 0;                 //The microsecond portion of the struct

        //DEBUG: This is ALWAYS 1
        int select_ret = select(sockfd + 1, NULL, &write_fds, NULL, &tv);
        cout << select_ret << endl;

        //Check return, -1 is error, 0 is timeout
        if(select_ret == -1 || select_ret == 0)
        {
            //We had an error connecting
            cout << "Error Connecting\n";
            close(sockfd);
            continue;
        }
    }

    //We successfully connected, break out of loop
    break;
}
4

2 回答 2

4

期望select() 返回什么?考虑到 select() 通常用于等待多个文件描述符 - 如果您连接两个,您将如何仅根据 select 的返回值知道哪个成功/失败?你不会,很明显。

这就是为什么 select() 只是告诉您哪些文件描述符以某种方式发生了变化,并且您应该独立确定那是什么。在 connect() 的情况下,您应该调用 getsockopt() 来检索连接尝试的结果。请参阅此答案,其中我解释了如何执行非阻塞连接()。

于 2012-07-01T22:34:57.383 回答
1

当以非阻塞模式连接并且 select() 指示连接是可写的时,您应该再次调用 connect()。这样做将返回 -1 并带有 errno == ECONNRESET 或其他任何内容。

于 2012-07-01T22:29:46.730 回答