Task -> CancellationToken (benchmarks)

Task_Action_continuation.cs

using System.Threading;
using System.Threading.Tasks;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.Runtime.CompilerServices;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            var bench = new Bench();
            var ct1 = bench.ContinueWith();
            var ct2 = bench.GetAwaiter();
#if !DEBUG
            BenchmarkRunner.Run<Bench>();
#endif
        }
    }
    //-------------------------------------------------------------------------
    [MemoryDiagnoser]
    public class Bench
    {
        private Task _task = Task.CompletedTask;

        [Benchmark(Baseline = true)]
        public CancellationToken ContinueWith() => _task.AsCancellationToken1();

        [Benchmark]
        public CancellationToken GetAwaiter() => _task.AsCancellationToken2();
    }
    //-------------------------------------------------------------------------
    public static class TaskExtensions
    {
        public static CancellationToken AsCancellationToken1(this Task task)
        {
            var cts = new CancellationTokenSource();
            task.ContinueWith((_, s) => (s as CancellationTokenSource).Cancel(), cts, CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);
            return cts.Token;
        }
        //---------------------------------------------------------------------
        public static CancellationToken AsCancellationToken2(this Task task)
        {
            var cts = new CancellationTokenSource();
            task.GetAwaiter().UnsafeOnCompleted(cts.Cancel);
            return cts.Token;
        }
    }
}

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.17134
Intel Core i7-7700HQ CPU 2.80GHz (Kaby Lake), 1 CPU, 8 logical and 4 physical cores
Frequency=2742192 Hz, Resolution=364.6718 ns, Timer=TSC
.NET Core SDK=2.1.300-rc1-008673
  [Host]     : .NET Core 2.1.0-rc1 (CoreCLR 4.6.26426.02, CoreFX 4.6.26426.04), 64bit RyuJIT
  DefaultJob : .NET Core 2.1.0-rc1 (CoreCLR 4.6.26426.02, CoreFX 4.6.26426.04), 64bit RyuJIT

Method	Mean	Error	StdDev	Scaled	ScaledSD	Gen 0	Allocated
ContinueWith	254.1 ns	1.136 ns	1.007 ns	1.00	0.00	0.0558	176 B
GetAwaiter	526.7 ns	10.417 ns	14.259 ns	2.07	0.06	0.0525	168 B