Eu realmente não entendo o porquêawait easync não melhore o desempenho do meu código aqui como eles deveriam.

Embora cético, pensei que o compilador deveria reescrever meu método para que os downloads fossem feitos em paralelo ... mas parece que isso não está realmente acontecend
(I Fa percebe queawait easync não crie threads separados; no entanto, o sistema operacional deve fazer os downloads em paralelo e retornar o meu código no thread original - não deveri)

Estou usandoasync eawait indevidamente? Qual é a maneira correta de usá-los?

Código

using System;
using System.Net;
using System.Threading;
using System.Threading.Tasks;

static class Program
{
    static int SumPageSizesSync(string[] uris)
    {
        int total = 0;
        var wc = new WebClient();
        foreach (var uri in uris)
        {
            total += wc.DownloadData(uri).Length;
            Console.WriteLine("Received synchronized data...");
        }
        return total;
    }

    static async Task<int> SumPageSizesAsync(string[] uris)
    {
        int total = 0;
        var wc = new WebClient();
        foreach (var uri in uris)
        {
            var data = await wc.DownloadDataTaskAsync(uri);
            Console.WriteLine("Received async'd CTP data...");
            total += data.Length;
        }
        return total;
    }

    static int SumPageSizesManual(string[] uris)
    {
        int total = 0;
        int remaining = 0;
        foreach (var uri in uris)
        {
            Interlocked.Increment(ref remaining);
            var wc = new WebClient();
            wc.DownloadDataCompleted += (s, e) =>
            {
                Console.WriteLine("Received manually async data...");
                Interlocked.Add(ref total, e.Result.Length);
                Interlocked.Decrement(ref remaining);
            };
            wc.DownloadDataAsync(new Uri(uri));
        }
        while (remaining > 0) { Thread.Sleep(25); }
        return total;
    }

    static void Main(string[] args)
    {
        var uris = new string[]
        {
            // Just found a slow site, to demonstrate the problem :)
            "http://www.europeanchamber.com.cn/view/home",
            "http://www.europeanchamber.com.cn/view/home",
            "http://www.europeanchamber.com.cn/view/home",
            "http://www.europeanchamber.com.cn/view/home",
            "http://www.europeanchamber.com.cn/view/home",
        };
        {
            var start = Environment.TickCount;
            SumPageSizesSync(uris);
            Console.WriteLine("Synchronous: {0} milliseconds", Environment.TickCount - start);
        }
        {
            var start = Environment.TickCount;
            SumPageSizesManual(uris);
            Console.WriteLine("Manual: {0} milliseconds", Environment.TickCount - start);
        }
        {
            var start = Environment.TickCount;
            SumPageSizesAsync(uris).Wait();
            Console.WriteLine("Async CTP: {0} milliseconds", Environment.TickCount - start);
        }
    }
}

Resultado

Received synchronized data...
Received synchronized data...
Received synchronized data...
Received synchronized data...
Received synchronized data...
Synchronous: 14336 milliseconds
Received manually async data...
Received manually async data...
Received manually async data...
Received manually async data...
Received manually async data...
Manual: 8627 milliseconds          // Almost twice as fast...
Received async'd CTP data...
Received async'd CTP data...
Received async'd CTP data...
Received async'd CTP data...
Received async'd CTP data...
Async CTP: 13073 milliseconds      // Why so slow??