CancellationToken UnRegister Action

Question

I have a token for various tasks and I need to better manage their cancellation, to be notified of a cancellation I can use:

token.Register(RegisterMethod);

How can I remove this "subscription"? Is there any way to "UnRegister"?

I thought about doing a workaround with TaskCompletionSource. But I do not know if it would work well. What is the best way to solve this approach?

will either of these 2 links help you http://social.msdn.microsoft.com/Forums/en-US/parallelextensions/thread/c2f614f6-c96c-4821-84cc-050b21aaee45 http://stackoverflow.com/questions/5299903/cancellationtokensource-cancelfalse — MethodMan, Dec 13 '12 at 16:52

score 89 · Accepted Answer · answered Dec 13 '12 at 19:01

89

CancellationToken.Register returns a CancellationTokenRegistration instance. If you call Dispose on that instance, your registration will be removed.

answered Dec 13 '12 at 19:01

Richard Deeming

29,830
10
79
151

2

had missed this, thank you. Although it would be nice if this could be done directly on token .. – J. Lennon Dec 13 '12 at 19:07

score 2 · Answer 2 · answered Jan 29 '21 at 16:03

You can safely dispose the entire CancellationTokenSource. Without worry about unregister callbacks.

Code: https://github.com/microsoft/referencesource/blob/master/mscorlib/system/threading/CancellationTokenSource.cs#L552

The Dispose() method of the CancellationTokenSource will call dispose on every registered callback you added into your Token via Token.Register(callBack).

score -6 · Answer 3 · edited Mar 23 '16 at 16:09

-6

There is no way to really undo a registration. While the dispose method will remove the callback the token still contains the information that there is a registration:

var cancellationTokenSource = new CancellationTokenSource();

basicTask = Task.Factory.StartNew(() => {
 for (;;) {
  var z = DateTime.Today.ToString();
 }
}, cancellationTokenSource.Token);

var basicTask2 = Task.Factory.StartNew(() => {
 for (;;) {
  var z = DateTime.Today.ToString();
 }
}, cancellationTokenSource.Token);

//var usingThisCodeWillResultInADeadlock = cancellationTokenSource.Token.Register(() => { });
//usingThisCodeWillResultInADeadlock.Dispose();
cancellationTokenSource.Cancel();
basicTask.Wait();

Disabling the comments will result in a deadlock.

edited Mar 23 '16 at 16:09

Frank van Wijk

3,234
20
41

answered Mar 23 '16 at 15:48

Benny Bürger

49
8

5

I am not sure what you wanted to show -- your `basicTask2` is unused, your `basicTask` has infinite loop inside, so no matter what you cannot stop it or cancel it, and you wait for that task which (by definition) never ends. Uncommenting those 2 lines does not change a thing. – greenoldman Oct 07 '16 at 10:36
1

You must be joking. Have you misread the question, or have you never looked what CancellationToken.Register returns? – quetzalcoatl Apr 23 '20 at 13:30

CancellationToken UnRegister Action

3 Answers3