Unity+SignalR场景下HttpRequestException导致HoloLens帧率骤降问题

问题场景 #

使用ASP.NET Core Web API服务器 + Unity/HoloLens客户端，正常连接运行无异常。测试断开重连流程：启动服务器→客户端连接→关闭服务器。断开后WithAutomaticReconnect定义的逻辑触发，随后连接关闭；在Closed方法中调用自定义Action触发Restart操作，此时StartAsync抛出HttpRequestException（符合预期，因服务器离线），但HoloLens应用帧率从60FPS骤降至10FPS，持续约20秒后恢复。

错误信息 #

Default: ⨯[SignalRClient]: System.Net.Http.HttpRequestException: An error occurred while sending the request
System.Net.WebException: Error: ConnectFailure (No connection could be established because the target computer refused to connect.

UnityEngine.DebugLogHandler:LogFormat (UnityEngine.LogType,UnityEngine.Object,string,object[])
MyLogHandler:LogFormat (UnityEngine.LogType,UnityEngine.Object,string,object[]) (at Assets/Scripts/Logging/MyLogHandler.cs:29)
UnityEngine.Logger:LogError (string,object)
MyApp.Logging.MyLogger:DoLog (MyApp.Logging.DebugMode,System.Action`2<string, object>,string,object,object[]) (at Assets/Scripts/Logging/MyLogger.cs:66)
MyApp.Logging.MyLogger:LogError (MyApp.Logging.DebugMode,object,object[]) (at Assets/Scripts/Logging/MyLogger.cs:33)
SignalRClient/<StartConnection>d__4:MoveNext () (at Assets/Scripts/Clients/SignalRClient.cs:78)
System.Runtime.CompilerServices.AsyncTaskMethodBuilder:SetException (System.Exception)
Microsoft.AspNetCore.SignalR.Client.HubConnection/<StartAsync>d__48:MoveNext ()
System.Runtime.CompilerServices.AsyncTaskMethodBuilder:SetException (System.Exception)
Microsoft.AspNetCore.SignalR.Client.HubConnection/<StartAsyncInner>d__49:MoveNext ()
System.Runtime.CompilerServices.AsyncTaskMethodBuilder:SetException (System.Exception)
Microsoft.AspNetCore.SignalR.Client.HubConnection/<StartAsyncCore>d__58:MoveNext ()
System.Runtime.CompilerServices.AsyncValueTaskMethodBuilder`1<Microsoft.AspNetCore.Connections.ConnectionContext>:SetException (System.Exception)
Microsoft.AspNetCore.Http.Connections.Client.HttpConnectionFactory/d__3:MoveNext ()
System.Runtime.CompilerServices.AsyncTaskMethodBuilder:SetException (System.Exception)
Microsoft.AspNetCore.Http.Connections.Client.HttpConnection/ d__40:MoveNext ()
System.Runtime.CompilerServices.AsyncTaskMethodBuilder:SetException (System.Exception)
Microsoft.AspNetCore.Http.Connections.Client.HttpConnection/d__41:MoveNext ()
System.Runtime.CompilerServices.AsyncTaskMethodBuilder:SetException (System.Exception)
Microsoft.AspNetCore.Http.Connections.Client.HttpConnection/d__44:MoveNext ()
System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<Microsoft.AspNetCore.Http.Connections.NegotiationResponse>:SetException (System.Exception)
Microsoft.AspNetCore.Http.Connections.Client.HttpConnection/<GetNegotiationResponseAsync>d__52:MoveNext ()
System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<Microsoft.AspNetCore.Http.Connections.NegotiationResponse>:SetException (System.Exception)
Microsoft.AspNetCore.Http.Connections.Client.HttpConnection/d__45:MoveNext ()
System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<System.Net.Http.HttpResponseMessage>:SetException (System.Exception)
Microsoft.AspNetCore.Http.Connections.Client.Internal.LoggingHttpMessageHandler/<SendAsync>d__2:MoveNext ()
System.Runtime.CompilerServices.AsyncTaskMethodBuilder`1<System.Net.Http.HttpResponseMessage>:SetException (System.Exception)
Microsoft.AspNetCore.Http.Connections.Client.Internal.AccessTokenHttpMessageHandler/d__3:MoveNext ()
System.Threading.Tasks.TaskFactory`1<System.Net.WebResponse>:FromAsyncCoreLogic (System.IAsyncR

代码实现 #

public class SignalRClient
{
    private Action _connectionClosed;

    public SignalRClient()
    {
        _connectionClosed += Restart;

        _hubConnection = new HubConnectionBuilder()
            .WithUrl(ConfigModel.Config.MyUri + "/hmdHub")
            .WithAutomaticReconnect(new[]{ TimeSpan.FromSeconds(5) })
            .Build();

        _hubConnection.Reconnecting += Reconnecting;
        _hubConnection.Reconnected += Reconnected;
        _hubConnection.Closed += Closed;
    }

    public async void Start()
    {
        ConfigureConnection();
        _ = await StartConnection();
    }

    public async void Restart()
        => _ = await StartConnection();

    public async Task Dispose()
    {
        _connectionClosed -= Restart;

        _hubConnection.Reconnecting -= Reconnecting;
        _hubConnection.Reconnected -= Reconnected;
        _hubConnection.Closed -= Closed;

        await _hubConnection.StopAsync();
        await _hubConnection.DisposeAsync();
    }

    private void ConfigureConnection()
    {
        _hubConnection.On<Alarm>("CreateAlarm", (alarmObject) =>
        {
            MyLogger.Log(DebugMode.Default, "SignalRClient>CreateAlarm", $"Got new alarm with id: {alarmObject.Id} with message: {alarmObject.Message}");
        });
    }

    private async Task<bool> StartConnection()
    {
        _tokenSource = new CancellationTokenSource();

        while (true)
        {
            try
            {
                await _hubConnection.StartAsync(_tokenSource.Token);
                MyLogger.LogSuccess(DebugMode.Default, this, "Connected to SignalR-Hub");
                return true;
            }
            catch when (_tokenSource.IsCancellationRequested)
            {
                return false;
            }
            catch(Exception ex)
            {
                MyLogger.LogError(DebugMode.Default, this, ex.ToString());
                await Task.Delay(5000);
            }
        }
    }

    private Task Reconnecting(Exception arg)
    {
        MyLogger.Log(DebugMode.Default, this, "Attempting to reconnect...");
        return Task.CompletedTask;
    }

    private Task Reconnected(string arg)
    {
        MyLogger.LogSuccess(DebugMode.Default, this, "Connection restored.");
        return Task.CompletedTask;
    }

    private Task Closed(Exception arg)
    {
        MyLogger.LogWarning(DebugMode.Default, this, "Connection closed.");
        _connectionClosed?.Invoke();
        return Task.CompletedTask;
    }

    private HubConnection _hubConnection;
    private CancellationTokenSource _tokenSource;
}

原因分析 #

1. 双重重连逻辑冲突：同时启用了SignalR内置的WithAutomaticReconnect和手动触发的Restart重连循环，两个独立的重连任务同时发起网络请求，占用HoloLens有限的CPU和网络资源，引发帧率下降。
2. async void滥用：Start和Restart使用async void，导致异步任务脱离Unity上下文管理，异常无法被正确捕获，还可能造成主线程调度混乱。
3. 日志输出过载：每次连接失败都会打印完整的异常堆栈，高频日志输出占用大量CPU资源，进一步拖慢帧率。

解决方案 #

1. 移除重复重连逻辑 #

保留SignalR内置的WithAutomaticReconnect即可，它会自动处理断开后的重连流程，无需手动触发：

public SignalRClient()
{
    // 移除手动重连绑定
    // _connectionClosed += Restart;

    _hubConnection = new HubConnectionBuilder()
        .WithUrl(ConfigModel.Config.MyUri + "/hmdHub")
        .WithAutomaticReconnect(new[]{ TimeSpan.FromSeconds(5) })
        .Build();

    _hubConnection.Reconnecting += Reconnecting;
    _hubConnection.Reconnected += Reconnected;
    _hubConnection.Closed += Closed;
}

private Task Closed(Exception arg)
{
    MyLogger.LogWarning(DebugMode.Default, this, "Connection closed.");
    // 移除手动重连触发
    // _connectionClosed?.Invoke();
    return Task.CompletedTask;
}

2. 替换async void为async Task #

Unity中异步方法应使用async Task，避免上下文丢失和异常无法处理：

public async Task Start()
{
    ConfigureConnection();
    await StartConnection();
}

// 若需手动重启，同步修改为async Task
public async Task Restart()
    => await StartConnection();

调用时在Unity异步上下文执行：

// 在MonoBehaviour脚本中
private async void Start()
{
    await _signalRClient.Start();
}

3. 优化日志输出 #

简化错误日志，避免每次失败都打印完整堆栈：

catch(Exception ex)
{
    MyLogger.LogError(DebugMode.Default, this, $"连接失败，5秒后重试：{ex.Message}");
    await Task.Delay(5000);
}

4. 确保重连循环唯一性 #

若坚持使用手动重连，必须移除SignalR内置重连，避免双重任务：

_hubConnection = new HubConnectionBuilder()
    .WithUrl(ConfigModel.Config.MyUri + "/hmdHub")
    // 移除内置重连
    // .WithAutomaticReconnect(new[]{ TimeSpan.FromSeconds(5) })
    .Build();

内容的提问来源于stack exchange，提问作者Perazim