CreateAsynCancellationToken.cs

// http://stackoverflow.com/q/31495411/1768303
// use: await Task.Delay(5000, token.CreateAsynCancellationToken());

public static CancellationToken CreateAsynCancellationToken(this CancellationToken @this)
{
	var cts = new CancellationTokenSource();
	var reg = default(CancellationTokenRegistration);
	reg = @this.Register(() =>
	{
		ThreadPool.QueueUserWorkItem(_ =>
		{
			try
			{
				cts.Cancel();
			}
			finally
			{
				reg.Dispose();
			}
		});
	}, useSynchronizationContext: false);
	return cts.Token;
}