取消任务后会发生什么？

Question

I was toying with Await/Async and CancellationTokens. My code works, but what happens to the Task when it's Cancelled? Is it still taking up resources or is it garbage collected or what?

Here is my code:

    private CancellationTokenSource _token = new CancellationTokenSource();

    public Form1()
    {
        InitializeComponent();
    }

    async Task<String> methodOne()
    {
        txtLog.AppendText("Pausing for 10 Seconds \n");
        var task = Task.Delay(10000, _token.Token);
        await task;
        return "HTML Returned. \n";

    }

    private async void button1_Click(object sender, EventArgs e)
    {
        try
        {
            var task1 = methodOne();
            await task1;
            txtLog.AppendText(task1.Result + "\n");
            txtLog.AppendText("All Done \n");
        }
        catch (OperationCanceledException oce)
        {
            txtLog.AppendText("Operation was cancelled");
        }
    }

    private void button2_Click(object sender, EventArgs e)
    {
        _token.Cancel();
    }

Answer 1

When a task is cancelled, it completes (in the cancelled state). It acts just like any other object in regards to garbage collection: if you have no references to it, it will be collected.

Note that although Task does implement IDisposable , you don't have to dispose it unless you're using the IAsyncResult.AsyncWaitHandle member .

Answer 2

A task can only be cancelled synchronously (meaning that it must ask "am I cancelled?"), so it's easy for the task to do cleanup (for example by using the using statement). All the resources it had allocated are then freed by the GC before or later (as always, we don't know when the GC will act, unless we do a GC.Collect(); GC.WaitForFinalizers(); )...