c# - 为什么我的表单在调用 BeginConnect 时卡住？

Question

我正在使用来自 Asynchronous Client Socket Example 的示例

using System;  
using System.Net;  
using System.Net.Sockets;  
using System.Threading;  
using System.Text;  

// State object for receiving data from remote device.  
public class StateObject {  
    // Client socket.  
    public Socket workSocket = null;  
    // Size of receive buffer.  
    public const int BufferSize = 256;  
    // Receive buffer.  
    public byte[] buffer = new byte[BufferSize];  
    // Received data string.  
    public StringBuilder sb = new StringBuilder();  
}  

public class AsynchronousClient {  
    // The port number for the remote device.  
    private const int port = 11000;  

    // ManualResetEvent instances signal completion.  
    private static ManualResetEvent connectDone =   
        new ManualResetEvent(false);  
    private static ManualResetEvent sendDone =   
        new ManualResetEvent(false);  
    private static ManualResetEvent receiveDone =   
        new ManualResetEvent(false);  

    // The response from the remote device.  
    private static String response = String.Empty;  

    private static void StartClient() {  
        // Connect to a remote device.  
        try {  
            // Establish the remote endpoint for the socket.  
            // The name of the   
            // remote device is "host.contoso.com".  
            IPHostEntry ipHostInfo = Dns.GetHostEntry("host.contoso.com");  
            IPAddress ipAddress = ipHostInfo.AddressList[0];  
            IPEndPoint remoteEP = new IPEndPoint(ipAddress, port);  

            // Create a TCP/IP socket.  
            Socket client = new Socket(ipAddress.AddressFamily,  
                SocketType.Stream, ProtocolType.Tcp);  

            // Connect to the remote endpoint.  
            client.BeginConnect( remoteEP,   
                new AsyncCallback(ConnectCallback), client);  
            connectDone.WaitOne();  

            // Send test data to the remote device.  
            Send(client,"This is a test<EOF>");  
            sendDone.WaitOne();  

            // Receive the response from the remote device.  
            Receive(client);  
            receiveDone.WaitOne();  

            // Write the response to the console.  
            Console.WriteLine("Response received : {0}", response);  

            // Release the socket.  
            client.Shutdown(SocketShutdown.Both);  
            client.Close();  

        } catch (Exception e) {  
            Console.WriteLine(e.ToString());  
        }  
    }  

    private static void ConnectCallback(IAsyncResult ar) {  
        try {  
            // Retrieve the socket from the state object.  
            Socket client = (Socket) ar.AsyncState;  

            // Complete the connection.  
            client.EndConnect(ar);  

            Console.WriteLine("Socket connected to {0}",  
                client.RemoteEndPoint.ToString());  

            // Signal that the connection has been made.  
            connectDone.Set();  
        } catch (Exception e) {  
            Console.WriteLine(e.ToString());  
        }  
    }  

    private static void Receive(Socket client) {  
        try {  
            // Create the state object.  
            StateObject state = new StateObject();  
            state.workSocket = client;  

            // Begin receiving the data from the remote device.  
            client.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0,  
                new AsyncCallback(ReceiveCallback), state);  
        } catch (Exception e) {  
            Console.WriteLine(e.ToString());  
        }  
    }  

    private static void ReceiveCallback( IAsyncResult ar ) {  
        try {  
            // Retrieve the state object and the client socket   
            // from the asynchronous state object.  
            StateObject state = (StateObject) ar.AsyncState;  
            Socket client = state.workSocket;  

            // Read data from the remote device.  
            int bytesRead = client.EndReceive(ar);  

            if (bytesRead > 0) {  
                // There might be more data, so store the data received so far.  
            state.sb.Append(Encoding.ASCII.GetString(state.buffer,0,bytesRead));  

                // Get the rest of the data.  
                client.BeginReceive(state.buffer,0,StateObject.BufferSize,0,  
                    new AsyncCallback(ReceiveCallback), state);  
            } else {  
                // All the data has arrived; put it in response.  
                if (state.sb.Length > 1) {  
                    response = state.sb.ToString();  
                }  
                // Signal that all bytes have been received.  
                receiveDone.Set();  
            }  
        } catch (Exception e) {  
            Console.WriteLine(e.ToString());  
        }  
    }  

    private static void Send(Socket client, String data) {  
        // Convert the string data to byte data using ASCII encoding.  
        byte[] byteData = Encoding.ASCII.GetBytes(data);  

        // Begin sending the data to the remote device.  
        client.BeginSend(byteData, 0, byteData.Length, 0,  
            new AsyncCallback(SendCallback), client);  
    }  

    private static void SendCallback(IAsyncResult ar) {  
        try {  
            // Retrieve the socket from the state object.  
            Socket client = (Socket) ar.AsyncState;  

            // Complete sending the data to the remote device.  
            int bytesSent = client.EndSend(ar);  
            Console.WriteLine("Sent {0} bytes to server.", bytesSent);  

            // Signal that all bytes have been sent.  
            sendDone.Set();  
        } catch (Exception e) {  
            Console.WriteLine(e.ToString());  
        }  
    }  

    public static int Main(String[] args) {  
        StartClient();  
        return 0;  
    }  
}  

我正在对我的应用程序的网络端进行编程，现在只是一些测试，但我遇到了一个奇怪的问题。当我调用 StartClient 方法时，我的 UI 卡住了。这个例子在一个单独的类中，只需在我的主窗体中调用它:AsynchronousClient.Startclient();

我需要提一下，现在没有服务器在监听，但为什么表单会卡住，毕竟我没有使用同步示例。我在互联网上读到这可能是因为表单线程必须从主线程运行，但我没有对此进行任何更改。在我看来，即使无法连接，表单也应该继续运行。

我如何实现这一目标？我可以给你我的代码，但我认为它不是很相关。就像我说的，我从 AsynchronousClient 类中调用 StartClient 方法，它是静态的，然后在我的主类中的某个地方调用它。 (现在在一个按钮中)。

我认为不相关，但我知道数据包已发送，我已经用 wireshark 检查过。

Answer 1

根据我的评论，AsynchronousClient.Startclient() 不是异步的，因为它使用 ManualResetEvent 来阻止。

我个人建议不要直接使用Socket。这实际上取决于您在做什么，但是有更好的 API 可用于远程通信。

HTTP、Json-RPC、gRPC、ZeroMQ 等...取决于您的用例。使用原始 TCP 套接字几乎总是矫枉过正。

无论如何，要使该方法真正异步，您必须摆脱 WaitOne 调用。
WaitOne 调用首先存在的原因，我相信，是为了使代码更具可读性，但理论上您可以在“连接”回调中执行“发送”逻辑并执行““发送”回调中的“接收”逻辑。

像这样

using System;  
using System.Net;  
using System.Net.Sockets;  
using System.Threading;  
using System.Text;  

// State object for receiving data from remote device.  
public class StateObject {  
    // Client socket.  
    public Socket workSocket = null;  
    // Size of receive buffer.  
    public const int BufferSize = 256;  
    // Receive buffer.  
    public byte[] buffer = new byte[BufferSize];  
    // Received data string.  
    public StringBuilder sb = new StringBuilder();  
}  

public class AsynchronousClient {  
    // The port number for the remote device.  
    private const int port = 11000;  

    // ManualResetEvent instances signal completion.  
    private static ManualResetEvent connectDone =   
        new ManualResetEvent(false);  
    private static ManualResetEvent sendDone =   
        new ManualResetEvent(false);  
    private static ManualResetEvent receiveDone =   
        new ManualResetEvent(false);  

    // The response from the remote device.  
    private static String response = String.Empty;  

    private static void StartClient() {  
        // Connect to a remote device.  
        try {  
            // Establish the remote endpoint for the socket.  
            // The name of the   
            // remote device is "host.contoso.com".  
            IPHostEntry ipHostInfo = Dns.GetHostEntry("host.contoso.com");  
            IPAddress ipAddress = ipHostInfo.AddressList[0];  
            IPEndPoint remoteEP = new IPEndPoint(ipAddress, port);  

            // Create a TCP/IP socket.  
            Socket client = new Socket(ipAddress.AddressFamily,  
                SocketType.Stream, ProtocolType.Tcp);  

            // Connect to the remote endpoint.  
            client.BeginConnect( remoteEP,   
                new AsyncCallback(ConnectCallback), client);  


        } catch (Exception e) {  
            Console.WriteLine(e.ToString());  
        }  
    }  

    private static void ConnectCallback(IAsyncResult ar) {  
        try {  
            // Retrieve the socket from the state object.  
            Socket client = (Socket) ar.AsyncState;  

            // Complete the connection.  
            client.EndConnect(ar);  

            Console.WriteLine("Socket connected to {0}",  
                client.RemoteEndPoint.ToString());  

            // we do it here now...
            Send(client,"This is a test<EOF>");  
        } catch (Exception e) {  
            Console.WriteLine(e.ToString());  
        }  
    }  

    private static void Receive(Socket client) {  
        try {  
            // Create the state object.  
            StateObject state = new StateObject();  
            state.workSocket = client;  

            // Begin receiving the data from the remote device.  
            client.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0,  
                new AsyncCallback(ReceiveCallback), state);  
        } catch (Exception e) {  
            Console.WriteLine(e.ToString());  
        }  
    }  

    private static void ReceiveCallback( IAsyncResult ar ) {  
        try {  
            // Retrieve the state object and the client socket   
            // from the asynchronous state object.  
            StateObject state = (StateObject) ar.AsyncState;  
            Socket client = state.workSocket;  

            // Read data from the remote device.  
            int bytesRead = client.EndReceive(ar);  

            if (bytesRead > 0) {  
                // There might be more data, so store the data received so far.  
            state.sb.Append(Encoding.ASCII.GetString(state.buffer,0,bytesRead));  

                // Get the rest of the data.  
                client.BeginReceive(state.buffer,0,StateObject.BufferSize,0,  
                    new AsyncCallback(ReceiveCallback), state);  
            } else {  
                // All the data has arrived; put it in response.  
                if (state.sb.Length > 1) {  
                    response = state.sb.ToString();  
                }  

                // after all is done, we shut down the socket
                client.Shutdown(SocketShutdown.Both);  
                client.Close();  
            }  
        } catch (Exception e) {  
            Console.WriteLine(e.ToString());  
        }  
    }  

    private static void Send(Socket client, String data) {  
        // Convert the string data to byte data using ASCII encoding.  
        byte[] byteData = Encoding.ASCII.GetBytes(data);  

        // Begin sending the data to the remote device.  
        client.BeginSend(byteData, 0, byteData.Length, 0,  
            new AsyncCallback(SendCallback), client);  
    }  

    private static void SendCallback(IAsyncResult ar) {  
        try {  
            // Retrieve the socket from the state object.  
            Socket client = (Socket) ar.AsyncState;  

            // Complete sending the data to the remote device.  
            int bytesSent = client.EndSend(ar);  
            Console.WriteLine("Sent {0} bytes to server.", bytesSent);  

            // We do it here now...
            Receive(client); 
        } catch (Exception e) {  
            Console.WriteLine(e.ToString());  
        }  
    }  

    public static int Main(String[] args) {  
        StartClient();  
        return 0;  
    }  
} 

这应该有效。这样，StartClient 就不会阻塞。它在调用 BeginConnect 后立即返回。

但是，这是一个非常古老和肮脏的 API，这就是为什么我在使用 native Socket 之前会三思而后行。

你可以更好地解释你的目标，我会尝试提供更好的东西。