任务取消不停止任务执行

我有一个Task，它查询一个活动目录并用结果填充一个列表。我已经设置了我的任务，以便可以取消它，但是，当调用取消时，任务会继续执行其工作。我知道任务已被取消，因为它返回并且打算在任务返回时执行的操作正在运行，但查询继续在后台运行，使用内存和处理能力。任务可以反复启动和"取消"，每次迭代任务都会运行并使用资源。如何使取消实际取消？

视图模型

private async Task RunQuery(QueryType queryType,
    string selectedItemDistinguishedName = null)
{
    StartTask();
    try
    {
        _activeDirectoryQuery = new ActiveDirectoryQuery(queryType,
            CurrentScope, selectedItemDistinguishedName);
        await _activeDirectoryQuery.Execute();
        Data = _activeDirectoryQuery.Data.ToDataTable().AsDataView();
        CurrentQueryType = queryType;
    }
    catch (ArgumentNullException)
    {
        ShowMessage(
            "No results of desired type found in selected context.");
    }
    catch (OutOfMemoryException)
    {
        ShowMessage("The selected query is too large to run.");
    }
    FinishTask();
}
private void CancelCommandExecute()
{
    _activeDirectoryQuery?.Cancel();
}

活动目录查询

public async Task Execute()
{
    _cancellationTokenSource = new CancellationTokenSource();
    var taskCompletionSource = new TaskCompletionSource<object>();
    _cancellationTokenSource.Token.Register(
        () => taskCompletionSource.TrySetCanceled());
    DataPreparer dataPreparer = null;
    var task = Task.Run(() =>
    {
        if (QueryTypeIsOu())
        {
            dataPreparer = SetUpOuDataPreparer();
        }
        else if (QueryTypeIsContextComputer())
        {
            dataPreparer = SetUpComputerDataPreparer();
        }
        else if (QueryTypeIsContextDirectReportOrUser())
        {
            dataPreparer = SetUpDirectReportOrUserDataPreparer();
        }
        else if (QueryTypeIsContextGroup())
        {
            dataPreparer = SetUpGroupDataPreparer();
        }
        Data = GetData(dataPreparer);
    },
    _cancellationTokenSource.Token);
    await Task.WhenAny(task, taskCompletionSource.Task);
}
public void Cancel()
{
    _cancellationTokenSource?.Cancel();
}

Cancel()由绑定到Button的Command调用。该任务可能需要几分钟才能执行，并且可能会消耗数百兆字节的 RAM。如果有帮助，我可以提供任何引用的方法或任何其他信息。

public async Task Execute()
{
    _cancellationTokenSource = new CancellationTokenSource();
    var taskCompletionSource = new TaskCompletionSource<object>();
    //Token registrations need to be disposed when done.
    using(_cancellationTokenSource.Token.Register(
        () => taskCompletionSource.TrySetCanceled()))
    {
        DataPreparer dataPreparer = null;
        var task = Task.Run(() =>
        {
            if (QueryTypeIsOu())
            {
                dataPreparer = SetUpOuDataPreparer(_cancellationTokenSource.Token);
            }
            else if (QueryTypeIsContextComputer())
            {
                dataPreparer = SetUpComputerDataPreparer(_cancellationTokenSource.Token);
            }
            else if (QueryTypeIsContextDirectReportOrUser())
            {
                dataPreparer = SetUpDirectReportOrUserDataPreparer(_cancellationTokenSource.Token);
            }
            else if (QueryTypeIsContextGroup())
            {
                dataPreparer = SetUpGroupDataPreparer(_cancellationTokenSource.Token);
            }
            Data = GetData(dataPreparer, _cancellationTokenSource.Token);
        },
        _cancellationTokenSource.Token);
        await Task.WhenAny(task, taskCompletionSource.Task);
   }
}