multiple register() on CancellationToken

Question

I have a set of async methods that get called in a chain. Each method passes the CancellationToken it received from its parent caller to its child down the chain. When the originator cancels, everyone downstream is notified. Upon the cancel notification each method in the chain is responsible for its own mid completion cleanup. CancellationToken.Register() is perfect for this requirement but it can only register one delegate and I need each method to have its own cleanup delegate registered with this single token. Maybe I am not using the pattern correctly. How should I go about it achieving this? 

Answer 1

CancellationToken.Register() is perfect for this requirement but it can only register one delegate

Why do think so? Register() can certainly be called multiple times to register multiple delegates, there is nothing stopping you from doing that.

For example, take following code:

Dim cts = New CancellationTokenSource
Dim token  = cts.Token
token.Register(Sub() Console.WriteLine("first"))
token.Register(Sub() Console.WriteLine("second"))
cts.Cancel()

When I run it, it prints both “second” and “first” (in this order, not sure whether that's guaranteed).

Answer 2

Interesting, I didn't see that in the documentation. I assumed a second call would overwrite the first since there is no unregister. I should have tested my assumption.

Answer 3

Also, there is unregister. You can do that by Dispose()ing the returned CancellationTokenRegistration.