如何在不阻塞主线程的情况下实现UDP

Question

我使用的数据通过 UDP 到达。我想在不阻塞主线程的情况下创建几个 UDP 连接。我已经同步和异步地实现了 UDP 连接，但是它们都保持主线程锁定。我的代码永远不会到达 'Console.WriteLine("Past the Async")'

目标是让 UDP 连接在后台运行。

谁能提供一些关于下一步要尝试什么，或者如何正确实现允许主线程仍然接收命令的异步版本的 UDP 的指导？

我将异步版本的 ReceiveUdpData() 注释掉。

class Program
{
    // The whole point of this is to not block the main thread.  
    static async Task Main(string[] args)
    {
        ReceiveUdpData();
        Console.WriteLine("Past Receive UDP Data");

        await foreach (var item in MessagesAsync())
        {
            Console.WriteLine(item);
        }
        Console.WriteLine("Past The Async");

    }
    // Synchronous connection to UDP.
    public static void ReceiveUdpData()
    {
        IPEndPoint remoteEndPoint = new IPEndPoint(IPAddress.Any, 0);
        var count = 0;
        using (UdpClient client = new UdpClient(12345))
        {
            while (true)
            {
                Byte[] receiveBytes = client.Receive(ref remoteEndPoint);
                count++;
                Console.WriteLine(count);
            }
        }
    }
    // Async UDP connection
    private static async IAsyncEnumerable<object> MessagesAsync()
    {
        IPEndPoint remoteEndPoint = new IPEndPoint(IPAddress.Any, 0);
        var count = 0;
        using (UdpClient client = new UdpClient(12345))
        {
            while (true)
            {
                UdpReceiveResult test = await client.ReceiveAsync();
                count++;
                yield return test.ToString();
            }
        }
    }
}

Answer 1

await 将通过调度方法的其余部分在给定任务继续后运行来“阻止”当前方法。它有点相似（在语义上与Task.ContinueWith 不同）所以csharp Console.WriteLine("Past The Async") 将仅在收到所有消息后执行。

您不能通过以“即发即弃”的方式枚举单独任务上的 IAsyncEnumerable 来等待消息：

static async Task Main(string[] args)
{
   PrintMessages();

   Console.WriteLine("Past The Async");
}

public static async Task PrintMessages()
{
   await foreach (var item in MessagesAsync())
   {
       Console.WriteLine(item);
   }
}

但如果你这样做，你的程序将在Main 退出时立即终止，所以你可能真的想等待，或者你可能还有其他工作可以执行。

Answer 2

这是我用来使用异步 udp 的程序的基础：

样本：

using System;
using System.Net.Sockets;
using System.Net;

class Program {
    static void OnUpdateData(IAsyncResult result) {
        UdpClient socket = result.AsyncState as UdpClient;
        IPEndPoint source = new IPEndPoint(0, 0);
        byte[] message = socket.EndReceive(result, ref source);

        Console.WriteLine($"Received {message.Length} bytes from {source}");
        // schedule the next receive operation once reading is done:
        socket.BeginReceive(new AsyncCallback(OnUpdateData), socket);
    }
    static void Main(string[] args) {
        UdpClient socket = new UdpClient(12345); 
        socket.BeginReceive(new AsyncCallback(OnUpdateData), socket);

        //send message with same program or use another program
        IPEndPoint target = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 12345);
        // send a couple of sample messages:
        for (int num = 1; num <= 3; num++) {
            byte[] message = new byte[num];
            socket.Send(message, message.Length, target);
        }
        Console.ReadKey();
    }
}