Environment.Exit() deadlocks after context.GetCancellationToken()

[CodeCasterNL]

When code calls context.GetCancellationToken() to pass that token to a handler's logic and that logic (or other code outside caller's control) calls Environment.Exit(), the application deadlocks.

This is caused by CancelOnProcessTermination() subscribing to the CancellationHandlingAdded event.

Repro on version 2.0.0-beta4.22272.1:

using System.CommandLine;

var rootCommand = new RootCommand();

var testCommand = new Command("test", "Test command");

testCommand.SetHandler(async context =>
{
    await ExitAsync(context.GetCancellationToken());
});

rootCommand.AddCommand(testCommand);

await rootCommand.InvokeAsync(args);

static Task ExitAsync(CancellationToken cancellationToken)
{
    Console.WriteLine("Exiting...");

    // This hangs
    Environment.Exit(-1);

    // This is ignored
    return Task.CompletedTask;
}

If you comment out the Environment.Exit, the application exits successfully. When it's present, it indefinitely hangs there.

[adamsitnik]

Hi @CodeCasterNL

Thank you for a detailed bug report with a repo!

The bug has been fixed, most likely by #2044

static async Task Main(string[] args)
{
    var rootCommand = new RootCommand();

    var testCommand = new Command("test", "Test command");

    testCommand.SetAction((context, cancellationToken) => ExitAsync(cancellationToken));

    rootCommand.Subcommands.Add(testCommand);

    await rootCommand.Parse(args).InvokeAsync();

    static Task ExitAsync(CancellationToken cancellationToken)
    {
        Console.WriteLine("Exiting...");

        // This hangs
        Environment.Exit(-1);

        // This is ignored
        return Task.CompletedTask;
    }
}

In the next few weeks we are going to release a new nuget package to nuget.org.