OperationCanceledException Not Thrown without Config in Async Apps

[mpatkisson]

OperationCanceledException Not Thrown without Config in Async Apps

This documentation (published 02 AUG 25) on Learn implies that System.CommandLine will, without additional configuration, throw OperationCanceledException when CTRL+C is pressed allowing library consumers to gracefully handle any necessary cleanup or shutdown messaging.

Versions 2.0.0-beta5 and 2.0.0-beta6 both supported this behavior, but 2.0.0-beta7 and beyond break it.

Steps to reproduce

1. Clone and run https://github.com/mpatkisson/culbertson with .NET 9

   > git clone https://github.com/mpatkisson/culbertson.git
   > cd culbertson
   > dotnet run --project ./src/Culbertson

2. Once the project is running, press CTRL+C.

Expected Behavior

This routine should be handled when CTRL+C is pressed, thus printing these messages along with a slight delay for effect,

Termination requested. Cleaning up...
# 1 second delay
Cleanup complete. Exiting.

Actual Behavior

The program does exit when CTRL+C is pressed, but OperationCanceledException is never thrown, so cleanup messaging is not displayed.

Further Analysis

My guess is OperationCanceledException should be thrown in Beta 7 as it is in Betas 5 and 6. If this was a design decision, then apologies (but the docs / code commentary are confusing if so).

7bb08a6 was the latest commit supporting the expected behavior. 7bb08a6 was followed by 3132acb | Separate parse from invocation configurations (#2606) which had a lot of changes.

In the InvocationPipeline, this switch case creates a ProcessTerminationHandler only if InvocationConfiguration.ProcessTerminationTimeout is non-null. Before Beta7 a default value of 2s was being set on CommandLineConfiguration.ProcessTerminationTimeout like so

public TimeSpan? ProcessTerminationTimeout { get; set; } = TimeSpan.FromSeconds(2);

Commit 3132acb | Separate parse from invocation configurations (#2606) renamed CommandLineConfiguration to InvocationConfiguration and dropped the default setting which now looks like this.

/// <summary>
/// Enables signaling and handling of process termination (Ctrl+C, SIGINT, SIGTERM) via a <see cref="CancellationToken"/> 
/// that can be passed to a <see cref="CommandLineAction"/> during invocation.
/// If not provided, a default timeout of 2 seconds is enforced.
///                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/// </summary>
public TimeSpan? ProcessTerminationTimeout { get; set; }

Possible Fix

My sense is that the default value on InvocationConfiguration.ProcessTerminationTimeout got lost in the mix of 3132acb and is still not fixed in the latest.

Re-adding the default brings behavior around CTRL+C back in line with earlier versions and the Learn docs. I've tested this small change using this branch with success.

[mpatkisson]

Thanks, @adamsitnik for looking into this so quickly. I've tested the latest locally and all is well. Great product, BTW.