StreamSocket.InputStreamOptions.ReadAsync 在使用 Wait() 时挂起 [英] StreamSocket.InputStreamOptions.ReadAsync hangs when using Wait()

问题描述

这是最小可能的场景，我能够准备:

This is the smallest possible scenario, I was able to prepare:

• 此代码连接到 imap.gmail.com
• 读取初始服务器问候语(使用 Read 方法)
• 发送 NOOP 命令(无操作)
• 读取 NOOP 命令响应(再次使用 Read 方法)

问题在于第二次读取挂起.如果使用'await ReadAsync'，它可以完美运行.

The problem is that the second Read hangs. It works perfectly if 'await ReadAsync' is used.

当我中断程序时，我可以看到调用堆栈从 task.Wait() 开始并在 System.Threading.Monitor.Wait() 结束.

When I break the program I can see the Call Stack starts at task.Wait() and ends on System.Threading.Monitor.Wait().

如果我一步一步调试它，它不会挂起.我必须承认它看起来像一个 .NET 框架错误，但也许我遗漏了一些明显的东西.

If I debug this step by step, it does not hang. I must admit it looks like a .NET framework bug, but maybe I'm missing something obvious.

private static async Task<byte[]> ReadAsync(StreamSocket socket)
{
    // all responses are smaller that 1024
    IBuffer buffer = new byte[1024].AsBuffer();
    await socket.InputStream.ReadAsync(
            buffer, buffer.Capacity, InputStreamOptions.Partial);
    return buffer.ToArray();
}

private static byte[] Read(StreamSocket socket)
{
    Task<byte[]> task = ReadAsync(socket);
    task.Wait();
    return task.Result;
}

private async void Button_Click(object sender, RoutedEventArgs e)
{
    Encoding encoding = Encoding.GetEncoding("Windows-1250");

    using (StreamSocket socket = new StreamSocket())
    {
        await socket.ConnectAsync(
            new HostName("imap.gmail.com"), "993", SocketProtectionLevel.Ssl);

        // notice we are using Wait() version here without any problems:
        byte[] serverGreetings = Read(socket);              

        await socket.OutputStream.WriteAsync(
            encoding.GetBytes("A0001 NOOP\r\n").AsBuffer());
        await socket.OutputStream.FlushAsync();

        //byte[] noopResponse = await ReadAsync(socket);    // works
        byte[] noopResponse = Read(socket);                 // hangs
    }
}

推荐答案

我解释了这个僵局的原因 在我最近的 MSDN 文章 以及 在我的博客上.

I explain the cause of this deadlock in my recent MSDN article as well as on my blog.

简短的回答是，您不应该在async代码上调用Wait或Result；你应该一直使用 await.

The short answer is that you're not supposed to call Wait or Result on async code; you should use await all the way.

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