arbitrary-task-like.cs

using System;
using System.Diagnostics;
using System.Threading.Tasks;

class C
{
    static void Main()
    {
        MainAsync().GetAwaiter().GetResult();
    }

    static async Task MainAsync()
    {
        const int iters = 100000000;
        // Warmup
        int sum = await Warmup();

        var sw = Stopwatch.StartNew();

        sw.Restart();
        for (var i = 0; i < iters; i++)
        {
            sum += await g(0);
        }
        sw.Stop();
        Console.WriteLine($"ValueTask    Await    Async {sw.Elapsed.TotalMilliseconds}ms");

        sw.Restart();
        for (var i = 0; i < iters; i++)
        {
            var v = g(0);
            if (v.IsCompletedSuccessfully)
            {
                sum += v.Result;
            }
            else
            {
                sum += await v;
            }
        }
        sw.Stop();
        Console.WriteLine($"ValueTask No-Await    Async {sw.Elapsed.TotalMilliseconds}ms");

        sw.Restart();
        for (var i = 0; i < iters; i++)
        {
            sum += await g1(0);
        }
        sw.Stop();
        Console.WriteLine($"ValueTask    Await No-Async {sw.Elapsed.TotalMilliseconds}ms");

        sw.Restart();
        for (var i = 0; i < iters; i++)
        {
            var v = g1(0);
            if (v.IsCompletedSuccessfully)
            {
                sum += v.Result;
            }
            else
            {
                sum += await v;
            }
        }
        sw.Stop();
        Console.WriteLine($"ValueTask No-Await No-Async {sw.Elapsed.TotalMilliseconds}ms");

        sw.Restart();
        for (var i = 0; i < iters; i++)
        {
            sum += await t(0);
        }
        sw.Stop();
        Console.WriteLine($"     Task    Await    Async {sw.Elapsed.TotalMilliseconds}ms");
    }

    private static async Task<int> Warmup()
    {
        var sum = 0;
        for (var i = 0; i < 10; i++)
        {
            sum += await g(0);
            var v = g(0);
            if (v.IsCompletedSuccessfully)
            {
                sum += v.Result;
            }
            else
            {
                sum += await v;
            }
            sum += await g1(0);
            v = g1(0);
            if (v.IsCompletedSuccessfully)
            {
                sum += v.Result;
            }
            else
            {
                sum += await v;
            }
            sum += await t(0);
        }

        return sum;
    }

    static async ValueTask<int> g(int delay)
    {
        if (delay > 0)
        {
            await Task.Delay(delay);
        }
        return delay;
    }


    static ValueTask<int> g1(int delay)
    {
        if (delay > 0)
        {
            return t(delay);
        }
        return delay;
    }

    static async Task<int> t(int delay)
    {
        if (delay > 0)
        {
            await Task.Delay(delay);
        }
        return delay;
    }
}