c++ - 在非阻塞套接字中选择函数

Question

我正在构建一个在线游戏客户端，当我尝试连接到离线服务器时，我的客户端卡住了，所以我想使用适合游戏的非阻塞套接字，因为在连接到服务器时还需要​​完成其他任务.

当使用非阻塞套接字时，connect 函数总是返回相同的值，不管结果如何，所以这里的人推荐使用 select 函数来查找结果连接请求。

(连接前设置非阻塞套接字)

u_long iMode=1;
ioctlsocket(hSocket,FIONBIO,&iMode);

---

(设置套接字集)

FD_ZERO(&Write);
FD_ZERO(&Err);
FD_SET(hSocket, &Write);
FD_SET(hSocket, &Err);

---

TIMEVAL Timeout;

int TimeoutSec = 10; // timeout after 10 seconds
Timeout.tv_sec = TimeoutSec;
Timeout.tv_usec = 0;
int iResult = select(0,     //ignored
                     NULL,      //read
                     &(client.Write),    //Write Check
                     &(client.Err),      //Error Check
                     &Timeout);

if(iResult)
{
}
else
{
    message_login("Error","Can't connect to the server");
}

select 函数总是返回 -1，为什么？

Answer 1

当 select() 返回 -1 (SOCKET_ERROR) 时，使用 WSAGetLastError() 找出失败的原因。

如果套接字在 select() 退出时设置的 Err 中，使用 getsockopt(SOL_SOCKET, SO_ERROR) 检索套接字错误告诉您为什么 connect() 失败的代码。

if(iResult) 对任何非零值(包括 -1)的计算结果为真。您需要改用 if(iResult > 0)，因为 iResult 将报告在 any fd_set 中发出信号的套接字数量，0 表示超时，-1 表示失败。

尝试更像这样的东西:

u_long iMode = 1;
if (ioctlsocket(hSocket, FIONBIO, &iMode) == SOCKET_ERROR)
{
    int errCode = WSAGetLastError();
    // use errCode as needed...
    message_login("Error", "Can't set socket to non-blocking, error: ..."); // however you supply a variable value to your message...
}

if (connect(client.hSocket, ...) == SOCKET_ERROR)
{
    int errCode = WSAGetLastError();
    if (errCode != WSAEWOULDBLOCK)
    {
        // use errCode as needed...
        message_login("Error", "Can't connect to the server, error: ..."); // however you supply a variable value...
    }
    else
    {
        // only in this condition can you now use select() to wait for connect() to finish...
    }
}

TIMEVAL Timeout;

int TimeoutSec = 10; // timeout after 10 seconds
Timeout.tv_sec = TimeoutSec;
Timeout.tv_usec = 0;

int iResult = select(0,     //ignored
                     NULL,      //read
                     &(client.Write),    //Write Check
                     &(client.Err),      //Error Check
                     &Timeout);

if (iResult > 0)
{
    if (FD_ISSET(client.hSocket, &(client.Err)))
    {
        DWORD errCode = 0;
        int len = sizeof(errCode);
        if (getsockopt(client.hSocket, SOL_SOCKET, SO_ERROR, (char*)&errCode, &len) == 0)
        {
             // use errCode as needed...
             message_login("Error", "Can't connect to the server, error: ..."); // however you supply a variable value to your message...
        }
        else
            message_login("Error", "Can't connect to the server, unknown reason");
    }
    else
        message_login("Success", "Connected to the server");
}
else if (iResult == 0)
{
    message_login("Error", "Timeout connecting to the server");
}
else
{
    int errCode = WSAGetLastError();
    // use errCode as needed...
    message_login("Error", "Can't connect to the server, error: ..."); // however you supply a variable value to your message...
}