How to get out from a TCP blocking connect() call?

Question

    int tcp_sock = ::socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);    

    struct sockaddr_in remoteaddr;
    struct sockaddr_in localAddr;
    short local_port = 22222;
    short remote_port = 33333;

    // local addr
    localAddr.sin_family      = AF_INET;
    localAddr.sin_port        = htons(local_port);
    localAddr.sin_addr.s_addr = 0xC0A80AA5; // we don't give a shit
    int addrLen = sizeof(struct sockaddr_in);

    //Now bind TCP to local addr
    int result = bind(tcp_sock,(struct sockaddr*)&localAddr,addrLen);
    if (result < 0)
    {
        perror("\nbind failed");
        close(tcp_sock);
        return -1;
    }

    result = connect(tcp_sock, (struct sockaddr*)&remoteaddr, sizeof(struct sockaddr_in));
    printf("\nConnect returned %d, error no: %d", result, errno);

Here the connect() call fails after a long time. Is there any way that I can make connect function return after a time of my choice? I tried calling close() from another thread but this doesn't change anything.

Answer 1

Put the socket into non-blocking mode before calling connect(), then you can use select() to specify a timeout. select() will tell you whether the connection succeeds or times out. If successful, you can put the socket back into blocking mode, if you want. If failed/timeout, close the socket instead.

int tcp_sock = ::socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);    

...

int flags = fcntl(tcp_sock, F_GETFL, 0);
fcntl(tcp_sock, F_SETFL, flags | O_NONBLOCK);

int errCode = 0;

result = connect(tcp_sock, ...);
if (result < 0)
{
    errCode = errno;

    if (errCode == EINPROGRESS)
    {
        fd_set wfd;
        FD_ZERO(&wfd);
        FD_SET(tcp_sock, &wfd);

        struct timeval timeout;
        timeout.tv_sec = ...;
        timeout.tv_usec = ...;

        result = select(tcp_sock+1, NULL, &wfd, NULL, &timeout);
        if (result > 0)
        {
            socklen_t len = sizeof(errCode);
            result = getsockopt(tcp_sock, SOL_SOCKET, SO_ERROR, &errCode, &len);
            if (result < 0)
                errCode = errno;
            else
                result = (errCode == 0) ? 0 : -1;
        }
        else if (result == 0)
        {
            errCode = ETIMEDOUT;
            result = -1;
        }
        else
        {
            errCode = errno;
        }
    }
}

if (result == 0)
{
    // connected
    fcntl(tcp_sock, F_SETFL, flags);
    ...
}
else
{
    // error, use errCode as needed
    ...
}