c# – 为什么异步CTP性能不佳?
发布时间:2020-12-15 08:45:33 所属栏目:百科 来源:网络整理
导读:我真的不明白为什么await和async不会在这里提高我的代码性能 like they’re supposed to. 虽然持怀疑态度,但我认为编译器应该重写我的方法,以便下载并行完成…但似乎并没有真正发生. (我确实认识到await和async不会创建单独的线程;但是,操作系统应该在parall
我真的不明白为什么await和async不会在这里提高我的代码性能
like they’re supposed to.
虽然持怀疑态度,但我认为编译器应该重写我的方法,以便下载并行完成…但似乎并没有真正发生. 我是否使用异步并等待不正确?使用它们的正确方法是什么? 码: 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",}; { 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); } } } 输出: 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?? 解决方法
克里斯的答案几乎是正确的,但引入了竞争条件并同步阻止所有任务.
作为一般规则,如果您有await / async可用,最好不要使用任务延续.另外,不要使用WaitAny / WaitAll – 异步等价物是WhenAny和WhenAll. 我会这样写: static async Task<int> SumPageSizesAsync(IEnumerable<string> uris) { // Start one Task<byte[]> for each download. var tasks = uris.Select(uri => new WebClient().DownloadDataTaskAsync(uri)); // Asynchronously wait for them all to complete. var results = await TaskEx.WhenAll(tasks); // Calculate the sum. return results.Sum(result => result.Length); } (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |