客戶端調用函數時的 c# .NET Core SignalR 異常（並非總是發生）

Question

我有以下服務器SignalR集線器：

 public class AlertHub : Hub
    {
        static ConcurrentDictionary<string, string> _users = new ConcurrentDictionary<string, string>();

        public Task SendMessage(string user, string message)
        {
            return Clients.All.SendAsync("BroadcastMessage", user, message);
        }

        public Task SendMessageToUser(string userUid, string user, string message, string totalMessages)
        {
            var clientId = _users.FirstOrDefault(x => x.Value == userUid).Key;
            return Clients.Client(clientId).SendAsync("BroadcastMessage", user, message, totalMessages);
        }

        public static void ClearState()
        {
            _users.Clear();
        }

        public override Task OnConnectedAsync()
        {
            _users.TryAdd(Context.ConnectionId, Context.ConnectionId);

            return base.OnConnectedAsync();
        }

        public override Task OnDisconnectedAsync(Exception exception)
        {
            string userUid;
            _users.TryRemove(Context.ConnectionId, out userUid);

            return base.OnDisconnectedAsync(exception);
        }

        public void SetUserUid(string userUid)
        {
            _users[Context.ConnectionId] = userUid;
        }
    }

在我的客戶端上await _signalRConnection.StartAsync(); 我將userUid設置為我的_users字典：

//Send user name for this client, so we won't need to send it with every message
                await _signalRConnection.InvokeAsync("SetUserUid", this.State.UserUID);

這工作完美，也不例外。

然后在我的客戶端上，當我嘗試發送消息時，我執行以下操作：（這通常有效，異常​​是間歇性的）

await _signalRConnection.InvokeAsync("SendMessageToUser", model.UserUid.ToString().ToLower(), this.State.UserName, $"{model.UserName} has sent you a message.", countMessagesString);

這通常有效，但有時它開始崩潰，在服務器中顯示以下錯誤：

Microsoft.AspNetCore.SignalR.Internal.DefaultHubDispatcher.? [?] - MESSAGE: Failed to invoke hub method 'SendMessageToUser'.
 System.ArgumentNullException: Value cannot be null. (Parameter 'connectionId')

那是因為當嘗試獲取 clientId 時，它在此處返回 null：

 var clientId = _users.FirstOrDefault(x => x.Value == userUid).Key; <-- HERE
return Clients.Client(clientId).SendAsync("BroadcastMessage", user, message, totalMessages);

所以我不知道為什么_users字典有時沒有密鑰。 這很奇怪。

關於如何挖掘或解決它的任何線索？

** 更新 **

這就是我所做的：

  public class AlertHubDictionary
    {
        static ConcurrentDictionary<string, string> _users;

        public AlertHubDictionary()
        {
            _users = new ConcurrentDictionary<string, string>();
        }

        public ConcurrentDictionary<string, string> UsersDictionary { get { return _users; } }

        public void ClearUsersDictionary()
        {
            _users.Clear();
        }
    }

然后這個類注冊為 Singleton DI：

   services.AddSingleton<AlertHubDictionary>();

最后對 Hub 類進行替換：

public class AlertHub : Hub
    {
        private readonly ILogger<AlertHub> _logger;
        private AlertHubDictionary _hubDictionary;
        static ConcurrentDictionary<string, string> _users = new ConcurrentDictionary<string, string>();

        public AlertHub(ILogger<AlertHub> logger, AlertHubDictionary hubDictionary)
        {
            _logger = logger;
            _hubDictionary = hubDictionary;
        }
        public Task SendMessage(string user, string message)
        {
            //Clients.Client("").SendAsync("BroadcastMessage", user, message);
            return Clients.All.SendAsync("BroadcastMessage", user, message);
        }

        public Task SendMessageToUser(string userUid, string user, string message, string totalMessages)
        {
            //var clientId = _users.FirstOrDefault(x => x.Value == userUid).Key;
            var clientId = _hubDictionary.UsersDictionary.FirstOrDefault(x => x.Value == userUid).Key;

            using (var scope = _logger.BeginScope("SCOPED_VALUE"))
            {
                _logger.LogInformation($"Send message to userUid {userUid} - {user} with clientId {clientId}.");

            }


            if (clientId == null)
            {
                // the user is not connected
                return Task.FromResult(0);
            }
            else
            {

                return Clients.Client(clientId).SendAsync("BroadcastMessage", user, message, totalMessages);
            }
        }

        public void ClearState()
        {
            _hubDictionary.ClearUsersDictionary();
            //_users.Clear();

            using (var scope = _logger.BeginScope("SCOPED_VALUE"))
            {
                _logger.LogInformation("_users cleared");

            }

        }

        public override Task OnConnectedAsync()
        {
            _hubDictionary.UsersDictionary.TryAdd(Context.ConnectionId, Context.ConnectionId);
            //_users.TryAdd(Context.ConnectionId, Context.ConnectionId);

            using (var scope = _logger.BeginScope("SCOPED_VALUE"))
            {
                _logger.LogInformation($"ConnectionId {Context.ConnectionId} connected.");

            }

            return base.OnConnectedAsync();
        }

        public override Task OnDisconnectedAsync(Exception exception)
        {
            string userUid;
            _hubDictionary.UsersDictionary.TryRemove(Context.ConnectionId, out userUid);

            using (var scope = _logger.BeginScope("SCOPED_VALUE"))
            {
                _logger.LogInformation($"UserUid {userUid} disconnected.");

            }


            return base.OnDisconnectedAsync(exception);
        }

        public void SetUserUid(string userUid)
        {
            _hubDictionary.UsersDictionary[Context.ConnectionId] = userUid;

            using (var scope = _logger.BeginScope("SCOPED_VALUE"))
            {
                _logger.LogInformation($"Connection {Context.ConnectionId} linked to userUid {userUid}");

            }

            //ClientNameChanged?.Invoke(Context.ConnectionId, userName);
        }
    }

Answer 1

根據您捕獲用戶 ID 的方式，您似乎試圖將 SignalR 集線器視為單例。 根據 Microsoft 的文檔，集線器是一個瞬態類：

https://docs.microsoft.com/en-us/aspnet/core/signalr/hubs?view=aspnetcore-3.1#create-and-use-hubs

集線器是暫時的：

不要將狀態存儲在集線器類的屬性中。 每個集線器方法調用都在新的集線器實例上執行。

因此，如果您想保留已注冊用戶 ID 的共享實例，您可能應該將其作為一個單獨的類進行管理，該類注冊為單例並注入到您的集線器類中，以便可以獨立於集線器來維護狀態。