ASP.NET SignalR Clients.All.ReceiveMessage无法向所有客户端同步发消息

AI 小北

2026-7-22

SignalR消息推送不一致问题

我实现了一个SignalR示例，功能是从第三方API获取最新更新，当API返回的LastUpdateDateTime属性时间戳发生变化时，控制器会向所有连接的客户端发送消息。控制器代码如下：

[Route("[controller]")]
public class ChatController : Controller
{
private readonly IHubContext<ChatHub, IChatClient> _chatHub;

List<Users> lstUsers = new List<Users>();

public ChatController(IHubContext<ChatHub, IChatClient> chatHub)
{
    _chatHub = chatHub;
}

public async Task<IActionResult> Index()
{
    return new ContentResult
    {
        Content = "Index Called",
        ContentType = "text/html"
    };
}


[HttpGet("StartSocket")]
public ContentResult StartSocket()
{
    System.Timers.Timer timer = new System.Timers.Timer(1000);
    timer.Elapsed += (sender, e) =>
    {
        timer.Stop();
        timer.Dispose();
        AppGlobal.SocketStarted = true;
        StartApiCalling();
    };
    timer.Start();

    return new ContentResult
    {
        Content = "Socket Started",
        ContentType = "text/html"
    };
}


[HttpGet("StopSocket")]
public ContentResult StopSocket()
{
    AppGlobal.SocketStarted = false;

    return new ContentResult
    {
        Content = "Socket Stopped",
        ContentType = "text/html"
    };
}

private async Task CallApiAsync(string apiUrl)
{
    Thread.Sleep(2000);
    while (AppGlobal.SocketStarted)
    {
        var client = new HttpClient();
        var response = await client.GetAsync(apiUrl);
        var content = await response.Content.ReadAsStringAsync();
        ProcessResponse(content);
        Thread.Sleep(50);
    }
}

private async Task StartApiCalling()
{
    var tasks = new List<Task>();
    var urls = new List<string> { "http://192.168.1.3/temp/api1", "http://192.168.1.3/temp/api2", "http://192.168.1.3/temp/api3" };

    //reponse of api1 is like : [{"Id":"1","Name":"Name1","LastUpdateDateTime":"2023-05-07 17:28:42.334618"}]
    //reponse of api2 is like : [{"Id":"2","Name":"Name2","LastUpdateDateTime":"2023-05-07 17:28:42.334618"}]
    //reponse of api3 is like : [{"Id":"3","Name":"Name3","LastUpdateDateTime":"2023-05-07 17:28:42.334618"}]

    foreach (var url in urls)
    {
        tasks.Add(Task.Run(async () =>
        {
            try
            {
                CallApiAsync(url);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }));
    }
}

private void ProcessResponse(string response)
{
    if (string.IsNullOrEmpty(response)) { return; }

    List<Users> lstData = new List<Users>();
    try { 
        lstData = JsonConvert.DeserializeObject<List<Users>>(response) ?? new List<Users>(); 
    }
    catch {
    }

    if (lstData != null && lstData.Count > 0)
    {
        foreach (var item in lstData)
        {
            var objUser = lstUsers.Where(x => x.Id == item.Id).FirstOrDefault();
            if (objUser == null)
            {
                objUser = new Users();
                objUser.DeepCopy(item);
                objUser.PropertyChanged += UserData_PropertyChanged;
                lstUsers.Add(objUser);
            }
            else
            {
                objUser.DeepCopy(item);
            }
        }
    }
}

private void UserData_PropertyChanged(object? sender, PropertyChangedEventArgs e)
{
    if (sender != null)
    {
        Users usrs = (Users)sender;
        if (e.PropertyName == nameof(usrs.LastUpdateDateTime))
        {
            SendUpdatedMessages(usrs.Name + " Changed - " + usrs.LastUpdateDateTime.ToString("dd/MMM/yyyy HH:mm:ss.fff"));
        }
    }
}

private async Task SendUpdatedMessages(string msg)
{
    ChatMessage message = new ChatMessage { Group = "RoomA", Message = msg, User = "user1" };
    await _chatHub.Clients.All.ReceiveMessage(message);
}

问题

当有2个客户端连接时，两者收到的消息数量不同。例如运行约1分钟后，一个客户端收到279条消息，另一个收到254条，直到调用StopSocket操作。预期所有客户端收到的消息数量基本一致（若无法完全相同也应接近），因为每次API调用的时间戳都会变化，若消息丢失会导致客户端无法保持同步更新。请指出我遗漏或错误的地方。

问题分析与修复建议

异步任务未正确等待，导致任务脱离跟踪
在StartApiCalling方法中，调用CallApiAsync(url)时未使用await，外层Task.Run的异步lambda也未等待该任务，会导致CallApiAsync的异步操作脱离系统跟踪，可能出现任务被意外终止、调度异常的情况，进而引发消息推送丢失。修复时需添加await：
```
try
{
    await CallApiAsync(url);
}
```
非线程安全集合引发数据不一致
lstUsers是普通List<Users>，多个后台任务会同时调用ProcessResponse修改该集合，而List<T>不支持并发读写，会导致元素查找失败、更新丢失等问题，最终造成消息推送缺失。解决方式有两种：
1. 使用线程安全集合ConcurrentDictionary<string, Users>（以用户Id为键）替代List<Users>；
2. 在操作lstUsers时添加锁：
```
private readonly object _usersLock = new object();

// ProcessResponse中操作集合的代码包裹在锁内
lock(_usersLock)
{
    var objUser = lstUsers.Where(x => x.Id == item.Id).FirstOrDefault();
    // 后续添加/更新逻辑
}
```
HttpClient实例重复创建耗尽资源
在CallApiAsync的循环中每次创建新HttpClient实例，会快速耗尽套接字资源，导致API请求失败，进而丢失消息。应复用HttpClient实例，比如通过控制器注入IHttpClientFactory来创建实例，或使用静态HttpClient。

异步推送任务未等待
UserData_PropertyChanged事件处理方法中调用SendUpdatedMessages(msg)时未使用await，会导致推送任务脱离上下文，可能在未完成推送时被中断，造成消息丢失。需将事件处理方法改为异步并等待推送：

private async void UserData_PropertyChanged(object? sender, PropertyChangedEventArgs e)
{
    if (sender != null)
    {
        Users usrs = (Users)sender;
        if (e.PropertyName == nameof(usrs.LastUpdateDateTime))
        {
            await SendUpdatedMessages(usrs.Name + " Changed - " + usrs.LastUpdateDateTime.ToString("dd/MMM/yyyy HH:mm:ss.fff"));
        }
    }
}

Thread.Sleep阻塞线程池线程
异步方法中使用Thread.Sleep会阻塞线程池线程，影响任务调度效率，可能导致API请求和消息推送延迟或丢失。应替换为await Task.Delay()，比如Thread.Sleep(2000)改为await Task.Delay(2000)，Thread.Sleep(50)改为await Task.Delay(50)。

内容的提问来源于stack exchange，提问作者Rohit

ASP.NET SignalR Clients.All.ReceiveMessage无法向所有客户端同步发消息

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