CSocket的listen()函数的分析

这个Listen应该是为了实现server而做的，基本流程：
1. getaddr得到地址信息
2. socket建立socket
3. bind帮定到socket上
4. listen开始监听
5. 将socket交给thread去处理
code:

int CSocket::Listen(int family, int port /*=0*/)
{
    //node是一个socket的初始状态
    if (m_state != none)
        return EALREADY;

    if (port < 0 || port > 65535)
        return EINVAL;

#ifdef __WXMSW__ //这是windows下的代码
    if (!getaddrinfo)
    {
        m_fd = socket(AF_INET, SOCK_STREAM, 0);
        if (m_fd == -1)
            return ConvertMSWErrorCode(WSAGetLastError());

        SetNonblocking(m_fd);

        struct sockaddr_in addr = {0};
        addr.sin_family = AF_INET;
        addr.sin_port = htons(port);

        int res = bind(m_fd, (sockaddr *)&addr, sizeof(addr));
        if (res)
        {
            res = WSAGetLastError();
            closesocket(m_fd);
            m_fd = -1;

            return ConvertMSWErrorCode(res);
        }
    }
    else
#endif
    {
	//getaddrinfo用来获取一个地址信息，然后我们才能用它来创建socket
	//其中，hints用来制定你要获取什么类型的地址信息，如family, socket_type等
        struct addrinfo hints = {0};
        hints.ai_family = family;
        hints.ai_socktype = SOCK_STREAM;

	//PASSIVE表明我们要被动接受别人的连接请求，所谓我们在调用getaddrinfo时就不用
	//制定nodename
        hints.ai_flags = AI_PASSIVE; 
#ifdef AI_NUMERICSERV
        // Some systems like Windows or OS X don't know AI_NUMERICSERV.
        hints.ai_flags |= AI_NUMERICSERV;
#endif

	//我们只制定port，即对应了getaddrinfo的servicename
        char portstring[6];
        sprintf(portstring, "%d", port);

        struct addrinfo* addressList = 0;

	//得到的所有的地址信息都存在addrlessList指向的链表里面
        int res = getaddrinfo(0, portstring, &hints, &addressList);

        if (res)
        {
#ifdef __WXMSW__
            return ConvertMSWErrorCode(res);
#else
            return res;
#endif
        }

	//下面要用得到的地址去建立socket，然后帮定在该地址上，然后监听
	//只要有一个地址成功的建立了socket我们就不再创建其他的地址对应的socket了
        for (struct addrinfo* addr = addressList; addr; addr = addr->ai_next)
        {
            m_fd = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
#ifdef __WXMSW__
            res = ConvertMSWErrorCode(WSAGetLastError());
#else
            res = errno;
#endif
            if (m_fd == -1)
                continue;

            SetNonblocking(m_fd);

	    //帮定
            res = bind(m_fd, addr->ai_addr, addr->ai_addrlen);

	    //如果成功就跳出循环
            if (!res)
                break;
#ifdef __WXMSW__
            res = ConvertMSWErrorCode(WSAGetLastError());
            closesocket(m_fd);
#else
            res = errno;
            close(m_fd);
#endif
            m_fd = -1;
        }
        freeaddrinfo(addressList);
        if (m_fd == -1)
            return res;
    }

    //这里，我们就要开始监听了，我们的pending queue大小为一，表明最多只允许1个连接
    //请求处于pending状态，当我们调用accept后，才会将pending queue中的连接请求处理
    int res = listen(m_fd, 1);
    if (res)
    {
#ifdef __WXMSW__
        res = ConvertMSWErrorCode(res);
        closesocket(m_fd);
#else
        close(m_fd);
#endif
        m_fd = -1;
        return res;
    }

    m_state = listening;

    m_pSocketThread = new CSocketThread();
    m_pSocketThread->SetSocket(this);

    m_pSocketThread->m_waiting = WAIT_ACCEPT;

    //让一个线程去管理这个socket。start()函数会调用该thread的Entry()函数，即线程
    //的执行体
    m_pSocketThread->Start();

    return 0;
}