背景

以下服务器端代码用于启动长时间运行的任务,该任务将通过SignalR将更新发布到Web前端.我在前端放了一个按钮,我想根据用户的要求停止任务.

问题

当前端触发器的Stop方法时,tokenSource为null.我怀疑,这是因为它没有到达产生任务的ChartHub的同一个实例.

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;
    }
}
}

解决方法:

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

ConcurrentDictionary< IUserIdentity,CancellationTokenSource>.

那么,在这种情况下,用户一次只能启动一个进程.

该词典将存在于Hub之外的Singleton类中.您的集线器只是您单身人士中调用方法的代理.

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);
    }
}