ForkJoinWithAsyncAwait.cs

readonly HttpClient http = new HttpClient();

async Task<DownloadResult[]> DownloadUrlsAsync(string path) =>
    await Task.WhenAll(File.ReadLines(path).Select(DownloadAsync));

async Task<DownloadResult> DownloadAsync(string url)
{
    var time = Stopwatch.StartNew();

    try
    {
        return new DownloadResult
        {
            Url = url,
            Time = time.ElapsedMilliseconds,
            Success = true,
            SizeInBytes = (await http.GetByteArrayAsync(url)).Length
        };
    }
    catch (Exception x)
    {
        Console.WriteLine("error downloading {0}: {1}", url, x);
        return new DownloadResult
        {
            Url = url,
            Time = time.ElapsedMilliseconds,
        };
    }
}

class DownloadResult
{
    public string Url;
    public long Time;
    public bool Success;
    public int SizeInBytes;
}