How to undo any current concurrent .ForEach and start fresh

Functionally has a long list of words related to ListView. Use TextBox for characters to filter the list of words.

With any new char, you need to undo any background processing filter. Then wait 1 second (DispatcherTimer) to start a new background parallel filter.

Do you help work with BackGroundWorker, but you can’t translate the undo-processing part to Parallel. Basically, you need "if (backgroundWorkerFTSfilter.IsBusy) backgroundWorkerFTSfilter.CancelAsync ();" in parallel mode. If I go about it wrong, please let me know.

private List<FTSword> fTSwordsFiltered = new List<FTSword>();
CancellationTokenSource ftsCts = new CancellationTokenSource();
ParallelOptions ftspo = new ParallelOptions();
// in ctor ftspo.CancellationToken = ftsCts.Token;

public List<FTSword> FTSwordsFiltered  // ListView bound to
{
    get { return fTSwordsFiltered; }
    set
    {
        if (fTSwordsFiltered == value) return;
        fTSwordsFiltered = value;
        NotifyPropertyChanged("FTSwordsFiltered");
    }
}
public string FTSwordFilter            // TextBox bound to
{
    get { return fTSwordFilter; }
    set
    {
        if (value == fTSwordFilter) return;

        fTSwordFilter = value;
        NotifyPropertyChanged("FTSwordFilter");

        // cancel any filter currently processing
        ftsCts.Cancel();   // fts filter              
        // with BackgroundWorker this was able to cancel               
        // if (backgroundWorkerFTSfilter.IsBusy) backgroundWorkerFTSfilter.CancelAsync();

        dispatcherTimerFTSfilter.Stop();
        // wait 1 second and apply filter in background
        dispatcherTimerFTSfilter.Start();
    }
}
private void dispatcherTimerFTSfilter_Tick(object sender, EventArgs e)
{
    dispatcherTimerFTSfilter.Stop();
    List<FTSword> ftsWords = new List<FTSword>();
    //ftsCts = new CancellationTokenSource();  with these two it never cancels
    //ftspo.CancellationToken = ftsCts.Token;
    if (!(string.IsNullOrEmpty(FTSwordFilter)))
    {
        Task.Factory.StartNew(() =>
        {

            try
            {
                Parallel.ForEach(FTSwords, ftspo, ftsw =>
                {
                    if (ftsw.WordStem.StartsWith(FTSwordFilter))
                    {
                        ftsWords.Add(ftsw);
                    }
                    ftspo.CancellationToken.ThrowIfCancellationRequested();
                });
                Thread.Sleep(1000);   // so the next key stoke has time
                FTSwordsFiltered = (List<FTSword>)ftsWords;
            }
            catch (OperationCanceledException ei)
            {
                // problem is that it is always cancelled from the cancel request before DispatchTimer
                Debug.WriteLine(ei.Message);
            }
            Debug.WriteLine(ftsWords.Count.ToString() + "parallel ");
        });           
    }
}

A response from Irman led me to this

    if (!(string.IsNullOrEmpty(FTSwordFilter)))
    {
        string startWorkFilter = FTSwordFilter;
        Task.Factory.StartNew(() =>
        {
            try
            {
                fTSwordsFilteredCancel = false;
                Parallel.ForEach(FTSwords, ftspo, (ftsw, loopstate) =>
                {
                    if (ftsw.WordStem.StartsWith(startWorkFilter))
                    {
                        ftsWords.Add(ftsw);
                    }
                    // Thread.Sleep(1);
                    if (fTSwordsFilteredCancel)
                    {
                        loopstate.Break();
                    }
                });
                Debug.WriteLine("fTSwordsFilteredCancel " + fTSwordsFilteredCancel.ToString());
                FTSwordsFiltered = (List<FTSword>)ftsWords;
                Debug.WriteLine(ftsWords.Count.ToString() + " parallel " + startWorkFilter);                       
            }
            catch (OperationCanceledException ei)
            {
                Debug.WriteLine(ei.Message);
            }
        });
    }

, ​​ . get ( ​​1 ). . 800 000 1/10 .

public IEnumerable<FTSword> FTSwordsFiltered
{
    get 
    { 
        if(string.IsNullOrEmpty(FTSwordFilter) || FTSwordFilter == "*") return FTSwords; 
        return FTSwords.AsParallel().Where(ftsWrd => ftsWrd.WordStem.StartsWith(FTSwordFilter));
    }