WCF 双工 TCP 通信错误

Question

我有一个示例服务来测试 WCF net.tcp 通信。这是一个非常简单的服务，它所做的只是为客户端订阅服务，然后调用回调 channel 来通知所有连接的客户端有关广播消息的信息。该服务托管在 IIS 7.5 中。

这是服务代码和测试客户端来测试它。

[ServiceContract(CallbackContract = typeof(ISampleServiceCallBack), SessionMode = SessionMode.Required)]
public interface ISampleCuratioService
{
    [OperationContract(IsOneWay = true)]
    void SubcribeToService(string sub);

    [OperationContract]
    string GetData(int value);

    [OperationContract(IsOneWay = true)]
    void Broadcast(string message);
}

public interface ISampleServiceCallBack
{
    [OperationContract(IsOneWay = true)]
    void NotifyClient(string message);
}

这是服务实现:

[ServiceBehavior(Name = "CuratioCSMService", InstanceContextMode = InstanceContextMode.PerSession)]
public class Service1 : ISampleCuratioService
{
    private static List<ISampleServiceCallBack> JoinedClien = new List<ISampleServiceCallBack>();

    public void SubcribeToService(string sub)
    {
        var subscriber = OperationContext.Current.GetCallbackChannel<ISampleServiceCallBack>();
        if (!JoinedClien.Contains(subscriber))
        {
            JoinedClien.Add(subscriber);
        }
    }

    public string GetData(int value)
    {
        return string.Format("You entered: {0}", value);
    }

    public void Broadcast(string message)
    {
        JoinedClien.ForEach(c => c.NotifyClient("message was received " + message));
    }
}

我无法理解运行它时的行为。第一个客户端运行后一切正常，但是当我关闭并打开测试客户端应用程序时，它会抛出异常通知 channel 不能用于通信，因为它处于故障状态。

这是示例测试客户端:

    static void Main(string[] args)
    {
        var callneckclient = new ServiceClientProxy();
        var client = new SampleCuratioServiceClient(new InstanceContext(callneckclient));
        client.SubcribeToService("me");
        Console.ReadLine();

        for (int i = 0; i < 15; i++)
        {
            Console.WriteLine(client.GetData(5));
            client.Broadcast("this is from client me");
        }
        client.Close();
        Console.Read();
    }

    public class ServiceClientProxy : ISampleCuratioServiceCallback, IDisposable
    {
        public void NotifyClient(string message)
        {
            Console.WriteLine(message);
        }

        public void Dispose()
        {
            GC.SuppressFinalize(this);
        }
    }

当我运行 5 个客户端时，情况变得更加糟糕。这些都不是发送或接收消息。

Answer 1

当客户调用SubcribeToService您将其操作上下文添加到名为 JoinedClien 的列表中.

当您调用 Broadcast在您的服务器中，您调用方法 NotifyClient在曾经连接过的每个客户端的所有收集的操作上下文上。

问题是，断开连接的客户端不会从您的 JoinedClien 中删除。列表。
当您尝试在断开连接的操作上下文上调用操作方法时，您会得到 channel 处于故障状态错误。

要解决此问题，您应该订阅 Channel_Closed和 Channel_Faulted事件，还 catch CommunicationException当回调您的客户端并删除故障客户端的操作上下文时:

public void Broadcast(string message)
{
    // copy list of clients
    List<OperationContext> clientsCopy = new List<OperationContext>();
    lock(JoinedClien) {
        clientsCopy.AddRange(JoinedClien);
    }

    // send message and collect faulted clients in separate list
    List<OperationContext> clientsToRemove = new List<OperationContext>();
    foreach (var c in JoinedClien) 
    { 
        try {
            c.NotifyClient("message was received " + message));
        }
        catch (CommunicationException ex) {
            clientsToRemove.Add(c);
        }
    }

    foreach (var c in clientsToRemove)
    {
        lock(JoinedClien) {
            if(JoinedClien.Contains(c))
                JoinedClien.Remove(c);
        }
    }
}

添加新客户端时，您也必须锁定该操作:

var subscriber = OperationContext.Current.GetCallbackChannel<ISampleServiceCallBack>();
lock(JoinedClien) 
{
    if (!JoinedClien.Contains(subscriber))
    {
        JoinedClien.Add(subscriber);
    }
}