What is the purpose of the *Async methods in .Net Framework given the ability to run any method asynchronously using Task.Run?

Question

Short question:

Why did .Net Framework add a lot of *Async versions of method instead of developers just using Task.Run to run synchron

Answer 1

Let's do the realistic test: naturally asynchronous WebRequest.GetResponseAsync vs unnaturally synchronous WebRequest.GetResponse.

First, we extend the standard limits of the ThreadPool:

ThreadPool.SetMaxThreads(MAX_REQS * 2, MAX_REQS * 2);
ThreadPool.SetMinThreads(MAX_REQS, MAX_REQS);

Note I request the same number of workerThreads and completionPortThreads. Then we'll perform MAX_REQS = 200 parallel requests to bing.com, using each API.

The code (a standalone console app):

using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using System.Linq;
using System.Collections.Generic;
using System.Net;

namespace Console_21690385
{
    class Program
    {
        const int MAX_REQS = 200;

        // implement GetStringAsync
        static async Task GetStringAsync(string url)
        {
            using (var response = await WebRequest.Create(url).GetResponseAsync())
            using (var stream = response.GetResponseStream())
            using (var reader = new System.IO.StreamReader(stream))
            {
                return await reader.ReadToEndAsync();
            }
        }

        // test using GetStringAsync
        static async Task TestWithGetStringAsync()
        {
            var tasks = Enumerable.Range(1, MAX_REQS).Select((i) =>
                GetStringAsync("http://www.bing.com/search?q=item1=" + i));

            Console.WriteLine("Threads before completion: " + Process.GetCurrentProcess().Threads.Count);

            await Task.WhenAll(tasks);

            Console.WriteLine("Threads after completion: " + Process.GetCurrentProcess().Threads.Count);
        }

        // implement GetStringSync
        static string GetStringSync(string url)
        {
            using (var response = WebRequest.Create(url).GetResponse())
            using (var stream = response.GetResponseStream())
            using (var reader = new System.IO.StreamReader(stream))
            {
                return reader.ReadToEnd();
            }
        }

        // test using GetStringSync
        static async Task TestWithGetStringSync()
        {
            var tasks = Enumerable.Range(1, MAX_REQS).Select((i) =>
                Task.Factory.StartNew(
                    () => GetStringSync("http://www.bing.com/search?q=item1=" + i),
                    CancellationToken.None, TaskCreationOptions.PreferFairness, TaskScheduler.Default));

            Console.WriteLine("Threads before completion: " + Process.GetCurrentProcess().Threads.Count);

            await Task.WhenAll(tasks);

            Console.WriteLine("Threads after completion: " + Process.GetCurrentProcess().Threads.Count);
        }

        // run either of the tests
        static void RunTest(Func runTest)
        {
            Console.WriteLine("Threads at start: " + Process.GetCurrentProcess().Threads.Count);

            var stopWatch = new Stopwatch();
            stopWatch.Start();

            var testTask = runTest();

            while (!testTask.IsCompleted)
            {
                Console.WriteLine("Currently threads: " + Process.GetCurrentProcess().Threads.Count);
                Thread.Sleep(1000);
            }
            Console.WriteLine("Threads at end: " + Process.GetCurrentProcess().Threads.Count + ", time: " + stopWatch.Elapsed);

            testTask.Wait();
        }

        static void Main(string[] args)
        {
            ThreadPool.SetMaxThreads(MAX_REQS * 2, MAX_REQS * 2);
            ThreadPool.SetMinThreads(MAX_REQS, MAX_REQS);

            Console.WriteLine("Testing using GetStringAsync");
            RunTest(TestWithGetStringAsync);
            Console.ReadLine();

            Console.WriteLine("Testing using GetStringSync");
            RunTest(TestWithGetStringSync);
            Console.ReadLine();
        }
    }
}

Output:

Testing using GetStringAsync
Threads at start: 3
Threads before completion: 3
Currently threads: 25
Currently threads: 84
Currently threads: 83
Currently threads: 83
Currently threads: 83
Currently threads: 83
Currently threads: 83
Currently threads: 84
Currently threads: 83
Currently threads: 83
Currently threads: 84
Currently threads: 84
Currently threads: 84
Currently threads: 83
Currently threads: 83
Currently threads: 84
Currently threads: 83
Currently threads: 82
Currently threads: 82
Currently threads: 82
Currently threads: 83
Currently threads: 25
Currently threads: 25
Currently threads: 26
Currently threads: 25
Currently threads: 25
Currently threads: 25
Currently threads: 23
Currently threads: 23
Currently threads: 24
Currently threads: 20
Currently threads: 20
Currently threads: 19
Currently threads: 19
Currently threads: 19
Currently threads: 19
Currently threads: 18
Currently threads: 19
Currently threads: 19
Currently threads: 19
Currently threads: 18
Currently threads: 18
Currently threads: 18
Currently threads: 19
Currently threads: 19
Currently threads: 18
Currently threads: 19
Currently threads: 19
Currently threads: 18
Currently threads: 18
Currently threads: 17
Threads after completion: 17
Threads at end: 17, time: 00:00:51.2605879

Testing using GetStringSync
Threads at start: 15
Threads before completion: 15
Currently threads: 55
Currently threads: 213
Currently threads: 213
Currently threads: 213
Currently threads: 213
Currently threads: 213
Currently threads: 213
Currently threads: 213
Currently threads: 213
Currently threads: 212
Currently threads: 210
Currently threads: 210
Currently threads: 210
Currently threads: 210
Currently threads: 210
Currently threads: 210
Currently threads: 210
Currently threads: 210
Currently threads: 210
Currently threads: 210
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 209
Currently threads: 205
Currently threads: 201
Currently threads: 196
Currently threads: 190
Currently threads: 186
Currently threads: 182
Threads after completion: 178
Threads at end: 173, time: 00:00:47.2603652

The result:

Both tests takes about 50 seconds to complete, but GetStringAsync peaks at 83 threads, while GetStringSync does at 213. The higher the MAX_REQS figure goes, the more threads are wasted by the blocking WebRequest.GetResponse API.

@Ark-kun, I hope you see the point now.