如何优雅地终止 BLOCKED 线程？

Question

有很多地方可以优雅地终止 C# 线程。但是，它们依赖于循环或在循环内执行的 if 条件，假设该语句将被频繁执行；因此，当设置stop bool 标志时，线程会快速退出。

如果我有一个不正确的线程怎么办？在我的例子中，这是一个设置为从服务器接收的线程，它经常阻塞从输入流中读取数据的调用，其中尚未提供任何数据，因此它会等待。

这是有问题的循环：

    while (true)
        {
            if (EndThread || Commands.EndRcvThread)
            {
                Console.WriteLine("Ending thread.");
                return;
            }

            data = "";
            received = new byte[4096];

            int bytesRead = 0;
            try
            {
                bytesRead = stream.Read(received, 0, 4096);
            }
            catch (Exception e)
            {
                Output.Message(ConsoleColor.DarkRed, "Could not get a response from the server.");
                if (e.GetType() == Type.GetType("System.IO.IOException"))
                {
                    Output.Message(ConsoleColor.DarkRed, "It is likely that the server has shut down.");
                }
            }

            if (bytesRead == 0)
            {
                break;
            }

            int endIndex = received.Length - 1;
            while (endIndex >= 0 && received[endIndex] == 0)
            {
                endIndex--;
            }

            byte[] finalMessage = new byte[endIndex + 1];
            Array.Copy(received, 0, finalMessage, 0, endIndex + 1);

            data = Encoding.ASCII.GetString(finalMessage);

            try
            {
                ProcessMessage(data);
            }
            catch (Exception e)
            {
                Output.Message(ConsoleColor.DarkRed, "Could not process the server's response (" + data + "): " + e.Message);
            }
        }

块顶部的if 语句执行通常的停止线程优雅设置所做的工作：检查标志，如果设置了则终止线程。然而，这个线程通常会在下面几行之后找到，位于stream.Read。

鉴于此，有什么方法可以优雅地终止这个线程（即没有Aborting），并清理它的资源（有一个需要关闭的客户端）？

Answer 1

假设您可以使用 async / Tasks，完全停止异步和 IO 操作的方法是使用连接到 CancelationTokenSource 的 CancelationToken。下面的代码 sn-p 说明了将其应用于您的代码的简化版本时的简化示例。

class MyNetworkThingy 
{
    public async Task ReceiveAndProcessStuffUntilCancelled(Stream stream, CancellationToken token)
    {
        var received = new byte[4096];
        while (!token.IsCancellationRequested)
        {
            try
            {
                var bytesRead = await stream.ReadAsync(received, 0, 4096, token);
                if (bytesRead == 0 || !DoMessageProcessing(received, bytesRead))
                    break; // done.
            }
            catch (OperationCanceledException)
            {
                break; // operation was canceled.
            }
            catch (Exception e)
            {
                // report error & decide if you want to give up or retry.
            }
        }
    }

    private bool DoMessageProcessing(byte[] buffer, int nBytes)
    {
        try
        {
            // Your processing code.
            // You could also make this async in case it does any I/O.
            return true;
        }
        catch (Exception e)
        {
            // report error, and decide what to do.
            // return false if the task should not
            // continue.
            return false;
        }
    }
}

class Program
{
    public static void Main(params string[] args)
    {
        using (var cancelSource = new CancellationTokenSource())
        using (var myStream = /* create the stream */)
        {
            var receive = new MyNetworkThingy().ReceiveAndProcessStuffUntilCancelled(myStream, cancelSource.Token);
            Console.WriteLine("Press <ENTER> to stop");
            Console.ReadLine();
            cancelSource.Cancel();
            receive.Wait();
        }
    }
}

.