Cleary, Stephen

Cancellation

Sourced from . Notes

1. ✅ Overview: cooperative cancellation; the 90% case; the cancellation contract; exceptions to the “90% case”
2. ✅ Requesting Cancellation: CancellationTokenSource; timeouts; manual cancellation; cancelling and disposing
3. ✅ Detecting Cancellation: responding to cancellation; TaskCanceledException; OperationCanceledException.CancellationToken
4. ✅ Polling: how to poll; how not to poll; when to poll
5. ✅ Registration: how to register; a race condition; cleanup is important; synchronous cancellation callbacks
6. ✅ Linking: linked cancellation tokens; use cases; don’t use OperationCanceledException.CancellationToken

References

1. Cancellation, Part 1: Overview. Stephen Cleary. blog.stephencleary.com . Accessed Sep 22, 2026.

Overview

Cancellation is cooperative. One part of the code politely notifies the other code that it’d like it to please stop. The responding code may immediately stop, or continue until it reaches a valid stopping point, or ignore the cancellation request entirely.

Most code has the form:

async Task DoSomethingAsync(int data, CancellationToken cancellationToken)
{
  var intermediateValue = await DoFirstStepAsync(data, cancellationToken);
  await DoSecondStepAsync(intermediateValue, cancellationToken);
}

… where the CancellationToken is passed down to whatever APIs you call.

By convention, the CancellationToken is the last in the method signature: