Realmente no entiendo por quéawait yasync no mejore el rendimiento de mi código aquí como se supone que deben.

Aunque escéptico, pensé que el compilador debía reescribir mi método para que las descargas se hicieran en paralelo ... pero parece que eso no está sucediendo realmente.
(I hace darse cuenta de queawait yasync no cree hilos separados; sin embargo, el sistema operativo debería realizar las descargas en paralelo y volver a llamar mi código en el hilo original, ¿n)

Estoy usandoasync yawait incorrectamente? ¿Cuál es la forma correcta de usarlos?

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);
        }
    }
}

Salida

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??