using System;

using System.Diagnostics;

using System.Linq;

using System.Collections.Generic;

using System.Threading.Tasks;

​

namespace Example

{

    public static class ExtensionMethods

    {

        static public async Task<List<T>> ToListAsync<T>(this IEnumerable<Task<T>> This)

        {

            var tasks = This.ToList();     //Force LINQ to iterate and create all the tasks. Tasks always start when created.

            var results = new List<T>();   //Create a list to hold the results (not the tasks)

            foreach (var item in tasks)

            {

                results.Add(await item);   //Await the result for each task and add to results list

            }

            return results;

        }

    }

​

​

​

​

    public class Program

    {

        private const int MillisecondsPerTask = 50;

        private const int TasksPerTest = 10;

        private const int TestIterations = 3;

        public static object DoSomethingExpensive(int id)

        {

            Console.WriteLine("Handling task {0} synchronously", id);

            System.Threading.Thread.Sleep(MillisecondsPerTask);

            Console.WriteLine("Done handling task {0} synchronously", id);

            return null;

        }

​

        public static async Task<object> DoSomethingExpensiveAsync(int id)

        {

            Console.WriteLine("Handling task {0} asynchronously", id);

            await Task.Delay(MillisecondsPerTask);

            Console.WriteLine("Done handling task {0} asynchronously", id);

            return null;

        }

​

        public static void TestBlocking()

        {

            var pages = Enumerable.Range(0, TasksPerTest).Select

                ( 

                    n => DoSomethingExpensive(n) 

                )

                .ToList();

        }

​

        public static async Task TestAsync()

        {

            var pages = await Enumerable.Range(0, TasksPerTest).Select

                ( 

                    async n => await DoSomethingExpensiveAsync(n) 

                )

                .ToListAsync();

        }

        public static async Task MainAsync()

        {

            //Run them once to prime any buffers or paging

            TestBlocking();

            await TestAsync();

​

            //Test and take timings

            for (int i = 0; i < TestIterations; i++)

            {

                var sw1 = new Stopwatch();

                sw1.Start();

                TestBlocking();

                sw1.Stop();

​

                var sw2 = new Stopwatch();

                sw2.Start();

                await TestAsync();

                sw2.Stop();

                Console.WriteLine("Sync:  {0:0000} milliseconds\r\nAsync: {1:0000} milliseconds", sw1.ElapsedMilliseconds, sw2.ElapsedMilliseconds);

            }

        }

​

        public static void Main()

        {

            MainAsync().GetAwaiter().GetResult();

        }

    }

}