c# - 取消由 ASP.NET 启动的任务

Question

背景

以下服务器端代码用于启动一个长时间运行的任务，该任务将通过 SignalR 将更新发布到 Web 前端。我在前端放置了一个按钮，然后我想根据用户的请求停止任务。

问题

当前端触发Stop方法时，tokenSource为空。我怀疑，这是因为它没有到达生成任务的 ChartHub 的同一个实例。

代码

using System;
...
using System.Security.Principal;

namespace dvvWeb.Hubs
{
public class ChartHub : Hub
{
    CancellationTokenSource tokenSource;
    CancellationToken ct;
    public void Start(string serverName, string dbName, string numberOfPoints, string pollingFrequency)
    {
        ConfigModel config = new ConfigModel();

        tokenSource = new CancellationTokenSource();
        ct = tokenSource.Token;

        config.Servername = HttpUtility.UrlDecode(serverName);
        config.DbName = HttpUtility.UrlDecode(dbName);
        config.Preferences.NumberOfPoints = int.Parse(numberOfPoints);
        config.Preferences.PollingFrequency = int.Parse(pollingFrequency);

        dvvGraphingModel graphingModel = new dvvGraphingModel();

        dvvGraphingHelper graphingHelper = new dvvGraphingHelper(graphingModel, config.Servername, config.DbName);

        graphingModel = graphingHelper.Tick(config.Preferences);

        var identity = WindowsIdentity.GetCurrent();

        Task.Run(() => workItemAsync(ct, graphingModel, graphingHelper, config, identity));
    }

    public void Stop()
    {
        tokenSource.Cancel();
    }


    private async Task<CancellationToken> workItemAsync(CancellationToken ct, dvvGraphingModel graphingModel, dvvGraphingHelper graphingHelper, ConfigModel configModel, WindowsIdentity identity)
    {
        await addDataAsync(ct, graphingModel, graphingHelper, configModel, identity);
        return ct;
    }

    private async Task<CancellationToken> addDataAsync(CancellationToken ct, dvvGraphingModel graphingModel, dvvGraphingHelper graphingHelper, ConfigModel configModel, WindowsIdentity identity)
    {

        try
        {
            while(!ct.IsCancellationRequested)
            {
                identity.Impersonate();
                Clients.Caller.addPointToChart(JsonConvert.SerializeObject(graphingModel));
                System.Threading.Thread.Sleep(configModel.Preferences.PollingFrequency * 1000);
                graphingModel = graphingHelper.Tick(configModel.Preferences);

            }
        }
        catch (TaskCanceledException tce)
        {
            Trace.TraceError("Caught TaskCanceledException - signaled cancellation " + tce.Message);
        }
        return ct;
    }
}
}

Answer 1

我会创建一个 ConcurrentDictionary<string, CancellationTokenSource>其中“string”是用户名/id 或者可能是

ConcurrentDictionary<IUserIdentity, CancellationTokenSource> .

嗯，这是在用户一次只能启动一个进程的情况下。

该字典将存在于 Hub 之外的单例类中。您的集线器将只是调用单例中方法的代理。

YourSingleton.Instance.Start(userId, serverName, dbName, numberOfPoints, pollingFrequency);

和

YourSingleton.Instance.Stop(userId);

然后，你可以这样做:

public void Stop(string userId)
{
    CancellationTokenSource tokenSource;
    if(dictionary.TryGetValue(userId, out tokenSource))
    {
        tokenSource.Cancel();
        dictionary.TryRemove(userId out tokenSource);
    }
}