取消令牌和線程不起作用

Question

我想取消一個線程，然后立即運行另一個線程。 這是我的代碼：

private void ResetMedia(object sender, RoutedEventArgs e)
{
        cancelWaveForm.Cancel(); // cancel the running thread
        cancelWaveForm.Token.WaitHandle.WaitOne(); // wait the end of the cancellation
        cancelWaveForm.Dispose();

        //some work

        cancelWaveForm = new CancellationTokenSource(); // creating a new cancellation token
        new Thread(() => WaveFormLoop(cancelWaveForm.Token)).Start(); // starting a new thread
}

當我調用此方法時，第一個線程不會停止，第二個線程開始運行...
但是，如果我跳過最后兩行，它將起作用：

private void ResetMedia(object sender, RoutedEventArgs e)
{
        cancelWaveForm.Cancel(); // cancel the running thread
        cancelWaveForm.Token.WaitHandle.WaitOne(); // wait the end of the cancellation
        cancelWaveForm.Dispose();

        //some work

        //cancelWaveForm = new CancellationTokenSource(); // creating a new cancellation token
        //new Thread(() => WaveFormLoop(cancelWaveForm.Token)).Start(); // starting a new thread
}

為什么不停止？

編輯1：

private void WaveFormLoop(CancellationToken cancelToken)
{
        try
        {
            cancelToken.ThrowIfCancellationRequested();
            //some stuff to draw a waveform
        }
        catch (OperationCanceledException) 
        {
            //Draw intitial Waveform
            ResetWaveForm();
        }
}

Answer 1

使用CancellationTokens稱為“合作取消”，因為代碼必須與取消動作合作。 您僅在函數啟動時檢查一次，如果取消在該檢查之后發生，則取消永遠不會發生。

基於函數的名稱，我假設其中存在某種循環。 您的函數需要看起來像這樣。

private void WaveFormLoop(CancellationToken cancelToken)
{
        try
        {
            while(someCondition) //Replace this with your real loop structure, I had to guess
            {
                cancelToken.ThrowIfCancellationRequested();
                //some stuff to draw a waveform
            }
        }
        catch (OperationCanceledException) 
        {
            //Draw intitial Waveform
            ResetWaveForm();
        }
}

現在，它檢查循環的每次迭代是否都發生取消。 如果循環主體需要很長時間才能處理，則您可能希望在循環內部進行多個調用。

private void WaveFormLoop(CancellationToken cancelToken)
{
        try
        {
            while(someCondition) //Replace this with your real loop structure, I had to guess
            {
                cancelToken.ThrowIfCancellationRequested();

                Thread.Sleep(1000); //Fake doing work

                cancelToken.ThrowIfCancellationRequested();

                Thread.Sleep(1000); //Fake doing more work
            }
        }
        catch (OperationCanceledException) 
        {
            //Draw intitial Waveform
            ResetWaveForm();
        }
}