c++ - 连接被拒绝后 connect() 长时间挂起

Question

我有一个小代理，应该不时连接到服务器 第一阶段它打开一个socket :

const char* hostname // e.g. "127.0.0.1"   
hostaddr = inet_addr(hostname);

    /* Ultra basic "connect to port 22 on localhost"
     * Your code is responsible for creating the socket establishing the
     * connection
     */ 
    sock = socket(AF_INET, SOCK_STREAM, 0);

    sin.sin_family = AF_INET;
    sin.sin_port = htons(22);
    sin.sin_addr.s_addr = hostaddr;
    if (connect(sock, (struct sockaddr*)(&sin),
                sizeof(struct sockaddr_in)) != 0) {
        fprintf(stderr, "failed to connect!\n");
        return -1;
    }

当 ip-address无效，连接似乎挂起很长时间 失败之前

查看man page提供有关该主题的一些数据，但不提供如何超越它

我的问题是为什么以及如何为其添加超时(或任何其他解决方案)

Answer 1

引自其中一个答案here

Put the socket into non-blocking mode until you've connected, and then put it back into blocking mode once the connection's established.