Ctrl+C and CancellationToken

TLDR, How to enable

Enable the feature with appRunner.UseCancellationHandlers() or appRunner.UseDefaultMiddleware().

The problem space

Console applications should stop gracefully when the user enters Ctrl+C or Ctrl+Break. If your app is consuming the main thread the app will not exit right away.

Traditionally, this is solved with a following steps:

1. Create a CancellationTokenSource and make the cancellationTokenSource.Token available for the rest of the app to reference.
2. Subscribe to Console.CancelKeyPress and call cancellationTokenSource.Cancel() when triggered. cancellationToken.IsCancellationRequested will then return true.
3. Check cancellationToken.IsCancellationRequested in any looping code and pass the token to any libraries that check it. Instead of Thread.Sleep(...), use cancellationToken.WaitHandle.WaitOne(...) or Task.Delay(..., cancellationToken)

Cancellation middleware

When enabled, the framework will:

• set the CommandContext.AppConfig.CancellationToken with a new token.
• register a parameter resolver for CancellationToken
• cancel the token on
  • Console.CancelKepPress
  • AppDomain.CurrentDomain.ProcessExit
  • AppDomain.CurrentDomain.UnhandledException when UnhandledExceptionEventArgs.IsTerminating == true

The framework checks the cancellation token before every step in the pipeline.

Using the CancellationToken

The CancellationToken is easy to access in your commands thanks to parameter resolvers. Simply add a parameter to your command or interceptor method.

public void MigrateRecords(CancellationToken cancellationToken, List<int> ids)
{    
    foreach(int id in ids.TakeWhile(!cancellationToken.IsCancellationRequested))
    {
        MigrateRecord(id);
    }
}

Tip

Remember to pass the CancellationToken to all database, web and service requests that take one.