C# 如果连接失败，总是重试 tcp 连接

Question

下面是我的代码，用于启动客户端到服务器的 tcp 连接：

Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

client.BeginConnect(remoteEP, new AsyncCallback(ConnectCallback), client);

连接回调：

    private void ConnectCallback(IAsyncResult ar)
    {
        try
        {
            // Retrieve the socket from the state object.  
            Socket client = (Socket)ar.AsyncState;

            // Complete the connection.  
            client.EndConnect(ar);
        }
        catch (Exception ex)
        {
            _logger.Info(ex.ToString());
        }
    }

但我的代码只在我的系统启动时连接一次。如果第一次尝试失败，我们如何重试连接？

如果连接总是失败，总是会重试？

也许每 30 秒重试一次？

Answer 1

client.BeginConnect(remoteEP, new AsyncCallback(ConnectCallback), client);

如果您想跟踪失败的尝试并保持良好的异步模式，我会传递一个状态对象：

class ConnectionState {
    Socket Client {get; set;}
    int FailedAttempts {get; set;} = 0;
}

然后传递：

client.BeginConnect(remoteEP, new AsyncCallback(ConnectCallback), new ConnectionState(){ .Client = client, FailedAttempts = 0});

在回调中：

private void ConnectCallback(IAsyncResult ar)
{
    ConnectionState state = (ConnectionState)ar.AsyncState;
    try
    {
        state.Client.EndConnect(ar);
    }
    catch (SocketException ex)
    {
        _logger.Info(ex.ToString());
        if( state.FailedAttempts < MAX_ATTEMPTS )
        {
            state.FailedAttempts += 1;
            state.Client.BeginConnect( remoteEP, new AsyncCallback(ConnectCallback), state );

            // you may also check the exception for what happened exactly.
            // There may be conditions where retrying does not make sense.
            // See SocketException.ErrorCode
        }
        else
        {
            // You may want to handle exceeding max tries.
            // - Notify User
            // - Maybe throw a custom exception
        }
    }
}

SocketException 错误代码参考：https://docs.microsoft.com/en-us/windows/desktop/winsock/windows-sockets-error-codes-2

为了设置基于时间的重试机制，我会创建某种“连接看门狗”：让计时器每 X 秒检查一次客户端字段。如果它为 null 并且连接启动尝试尚未运行，请启动一个。

---

不过，就我个人而言，我会尝试切换到TPL。但我认为这是一种替代方法，而不是您问题的直接答案。但我推荐它。