Resettable CTSs using InterlockedState

AutoResetCancellationTokenSource.cs

using System.Threading;

/// <summary>
/// A <see cref="CancellationTokenSource"/> that resets itself to uncanceled after <see cref="Cancel"/> is called.
/// </summary>
public sealed class AutoResetCancellationTokenSource
{
	/// <summary>
	/// Cancels any tokens previously returned from <see cref="Token"/>, and resets this instance to an uncancelled state.
	/// </summary>
	public void Cancel()
	{
		var (oldState, _) = InterlockedState.Transform(ref _cts, state => null);
		oldState?.Cancel();
	}

	/// <summary>
	/// Returns the current <see cref="CancellationToken"/>.
	/// </summary>
	public CancellationToken Token
	{
		get
		{
			var (_, newState) = InterlockedState.Transform(ref _cts, state => state switch
			{
				null => new CancellationTokenSource(),
				not null => state,
			});
			return newState!.Token;
		}
	}

	/// <summary>
	/// Either <c>null</c> or a <see cref="CancellationTokenSource"/> instance that is not canceled.
	/// </summary>
	private CancellationTokenSource? _cts;
}

ManualResetCancellationTokenSource.cs

using System.Threading;

/// <summary>
/// A <see cref="CancellationTokenSource"/> that stays canceled until <see cref="Reset"/> is called.
/// </summary>
public sealed class ManualResetCancellationTokenSource
{
	/// <inheritdoc cref="CancellationTokenSource.IsCancellationRequested"/>
	public bool IsCancellationRequested
	{
		get
		{
			var state = InterlockedState.Read(ref _cts);
			if (state == null)
				return false;
			return state.IsCancellationRequested;
		}
	}

	/// <summary>
	/// Returns the current <see cref="CancellationToken"/>.
	/// </summary>
	public CancellationToken Token
	{
		get
		{
			var (_, newState) = InterlockedState.Transform(ref _cts, state => state switch
			{
				null => new CancellationTokenSource(),
				not null => state,
			});
			return newState!.Token;
		}
	}

	/// <summary>
	/// Cancels any tokens previously returned from <see cref="Token"/>.
	/// </summary>
	public void Cancel()
	{
		var (_, newState) = InterlockedState.Transform(ref _cts, state => state switch
		{
			null => new CancellationTokenSource(),
			not null => state,
		});
		newState!.Cancel();
	}

	/// <summary>
	/// Resets this instance to an uncancelled state.
	/// </summary>
	public void Reset()
	{
		InterlockedState.Transform(ref _cts, state => state switch
		{
			{ IsCancellationRequested: true } => null,
			{ IsCancellationRequested: false } => state,
			null => null,
		});
	}

	/// <summary>
	/// If <c>null</c>, this instance is not canceled. If not <c>null</c>, the <see cref="CancellationTokenSource"/> may or may not be canceled.
	/// </summary>
	private CancellationTokenSource? _cts;
}