后台辅助角色报告繁忙，尽管已被取消且不再存在

当我取消并处置我的后台工作线程时，尽管它从 VS 线程列表中消失了，但它继续向我的应用程序报告忙碌，该应用程序正在等待它关闭。此外，我的 RunWorkerDone 事件从未引发。

调试显示代码已退出，没有我可以看到的进一步挂起执行。

如果我删除 .IsBusy 检查，VS 报告"此后台工作线程当前繁忙，无法同时运行多个任务"

我不明白为什么VS中不再列出的线程在关闭后继续运行。

     private void UpdateTimeLine()
        {
        txtb_timeline.Text = "Updating...";

        startTimelineUpdater.DoWork += new DoWorkEventHandler(startTimelineUpdater_DoWork);
        startTimelineUpdater.RunWorkerAsync("hometimeline");
        startTimelineUpdater.WorkerReportsProgress = true;
        startTimelineUpdater.ProgressChanged += new ProgressChangedEventHandler
                                             (startTimelineUpdater_ProgressChanged);
        startTimelineUpdater.WorkerSupportsCancellation = true;
    }

   void startTimelineUpdater_DoWork(object sender, DoWorkEventArgs e)
    {
        //begin the thread to maintain updates of SQL          
        beginRegUpdateTimeline.DoWork += new DoWorkEventHandler(beginRegUpdateTimeline_DoWork);
        beginRegUpdateTimeline.RunWorkerAsync();
        beginRegUpdateTimeline.WorkerSupportsCancellation = true;
        while (true)
        {
            List<string[]> sqlset;
            Xtweet getSQL = new Xtweet();
            if(e.Argument.ToString() == "hometimeline")
            {
                sqlset = getSQL.CollectLocalTimelineSql();
            }
            else
            {
                sqlset = getSQL.CollectLocalTimelineSql(Int64.Parse(e.Argument.ToString()));
            }
            int i = 0;
            while (i < 10)
            {
                foreach (var stringse in sqlset)
                {
                    StringBuilder sb = new StringBuilder();
                    sb.Append(stringse[0]);
                    sb.Append(": ");
                    sb.Append(stringse[1]);
                    sb.Append(" @ ");
                    sb.Append(stringse[2]);
                    sb.Append("'n");
                    BackgroundWorker bkgwk = sender as BackgroundWorker;
                    bkgwk.ReportProgress(0, sb.ToString());
                    Thread.Sleep(1000);
                    i++;
                    if(startTimelineUpdater.CancellationPending)
                    {
                        e.Cancel = true;
                        startTimelineUpdater.Dispose();
                        break;
                    }
                }
                if (e.Cancel == true)
                {
                    break;
                }
            }
            if (e.Cancel == true)
            {
                break;
            }
        }

    }
    /// <summary>
    /// Handles the DoWork event of the beginRegUpdateTimeline control.
    /// Updates the timeline sql on a regular basis
    /// </summary>
    /// <param name="sender">The source of the event.</param>
    /// <param name="e">The <see cref="System.ComponentModel.DoWorkEventArgs"/> instance containing the event data.</param>
    void beginRegUpdateTimeline_DoWork(object sender, DoWorkEventArgs e)
    {
        while (true)
        {
            //update time in seconds
            int secs = 10;
            Xtweet.PreSqlDataCollection(null,null);
            Thread.Sleep(secs*1000);
            if(beginRegUpdateTimeline.CancellationPending)
            {
                e.Cancel = true;
                beginRegUpdateTimeline.Dispose();
                break;
            }

        }

    }
    private void startTimelineUpdater_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        txtb_timeline.Text = e.UserState.ToString();
    }