C# TCP 服务器停止接收客户端消息，在服务重新启动时恢复

Question

我在使用 C# 编写的托管 Windows 服务中工作。它不断从通过 TCP/IP 连接的多个客户端接收消息。客户端基本上是一个路由器，用于接收温度计的消息并将其重新发送到服务器。服务器解析消息并将它们存储在 SQL Server 数据库中。

我面临的问题是某些客户端突然停止发送消息。但是，一旦服务重新启动，它们就会再次连接并继续发送。我没有客户端的代码，因为它是第三方设备，我很确定问题出在服务器上。

我设法通过实现一个计时器来减少问题，该计时器不断检查每个客户端是否仍处于连接状态(请参见下面的代码)。此外，我使用 socket.IOControl(IOControlCode.KeepAliveValues, ...) 方法向 Socket 添加了 Keep Alive 模式，但问题仍然存在。

我正在发布一些我认为相关的特定部分的代码。但是，如果需要更多片段来理解问题，请询问我，我将编辑帖子。删除了所有 try/catch block 以减少代码量。

我不想要一个完美的解决方案，只要任何指导，我将不胜感激。

private Socket _listener;
private ConcurrentDictionary<int, ConnectionState> _connections;

public TcpServer(TcpServiceProvider provider, int port)
{
    this._provider = provider;
    this._port = port;
    this._listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    this._connections = new ConcurrentDictionary<int, ConnectionState>();

    ConnectionReady = new AsyncCallback(ConnectionReady_Handler);
    AcceptConnection = new WaitCallback(AcceptConnection_Handler);
    ReceivedDataReady = new AsyncCallback(ReceivedDataReady_Handler);
}                

public bool Start()
{    
    this._listener.Bind(new IPEndPoint(IPAddress.Any, this._port));
    this._listener.Listen(10000);
    this._listener.BeginAccept(ConnectionReady, null);    
}

// Check every 5 minutes for clients that have not send any message in the past 30 minutes
// MSG_RESTART is a command that the devices accepts to restart
private void CheckForBrokenConnections()
{
    foreach (var entry in this._connections)
    {
        ConnectionState conn = entry.Value;

        if (conn.ReconnectAttemptCount > 3)
        {
            DropConnection(conn);
            continue;
        }

        if (!conn.Connected || (DateTime.Now - conn.LastResponse).TotalMinutes > 30)
        {
            byte[] message = HexStringToByteArray(MSG_RESTART);

            if (!conn.WaitingToRestart && conn.Write(message, 0, message.Length))
            {
                conn.WaitingToRestart = true;                    
            }
            else
            {
                DropConnection(conn);                
            }
        }
    }        
}


private void ConnectionReady_Handler(IAsyncResult ar)
{    
    lock (thisLock)
    {
        if (this._listener == null)
            return;

        ConnectionState connectionState = new ConnectionState();
        connectionState.Connection = this._listener.EndAccept(ar);

        connectionState.Server = this;
        connectionState.Provider = (TcpServiceProvider)this._provider.Clone();
        connectionState.Buffer = new byte[4];
        Util.SetKeepAlive(connectionState.Connection, KEEP_ALIVE_TIME, KEEP_ALIVE_TIME);
        int newID = (this._connections.Count == 0 ? 0 : this._connections.Max(x => x.Key)) + 1;
        connectionState.ID = newID;
        this._connections.TryAdd(newID, connectionState);

        ThreadPool.QueueUserWorkItem(AcceptConnection, connectionState);

        this._listener.BeginAccept(ConnectionReady, null);
    }
}

private void AcceptConnection_Handler(object state)
{    
    ConnectionState st = state as ConnectionState;
    st.Provider.OnAcceptConnection(st);

    if (st.Connection.Connected)
        st.Connection.BeginReceive(st.Buffer, 0, 0, SocketFlags.None, ReceivedDataReady, st);    
}

private void ReceivedDataReady_Handler(IAsyncResult result)
{
    ConnectionState connectionState = null;

    lock (thisLock)
    {
        connectionState = result.AsyncState as ConnectionState;
        connectionState.Connection.EndReceive(result);

        if (connectionState.Connection.Available == 0)
            return;

        // Here the message is parsed
        connectionState.Provider.OnReceiveData(connectionState);

        if (connectionState.Connection.Connected)
            connectionState.Connection.BeginReceive(connectionState.Buffer, 0, 0, SocketFlags.None, ReceivedDataReady, connectionState);
    }
}

internal void DropConnection(ConnectionState connectionState)
{
    lock (thisLock)
    {
        if (this._connections.Values.Contains(connectionState))
        {
            ConnectionState conn;
            this._connections.TryRemove(connectionState.ID, out conn);
        }

        if (connectionState.Connection != null && connectionState.Connection.Connected)
        {
            connectionState.Connection.Shutdown(SocketShutdown.Both);
            connectionState.Connection.Close();
        }
    }
}

Answer 1

我认为我看到的 2 件事...

• 如果这是您为多条消息保留的连接，当 connectionState.Connection.Available == 0 IIRC a 0 时，您可能不应该从 ReceivedDataReady_Handler 返回可以接收长度数据包。因此，如果连接仍然打开，您应该在离开处理程序之前调用 connectionState.Connection.BeginReceive( ... )。

• (我不太愿意把它放在这里，因为我不记得具体细节)有一个事件可以告诉你你的基础连接何时发生事情，包括错误和失败连接或关闭连接。对于我的生活，我不记得名字了......这可能比每隔几秒的计时器更有效。它还为您提供了一种断开卡在连接或关闭状态的连接的方法。