FeedReader: 並列処理の実装に挑戦(失敗!)

FeedReader.cs

public async Task<IList<FeedData>> ReadAsync(string[] feedUrlStrings) {
    List<FeedData> result = new List<FeedData>(feedUrlStrings.Length);
    foreach (string url in feedUrlStrings) {
        result.Add(await this.ReadAsync(url));
    }
    return result;
}