Question

所以我开始用套接字捣乱并异步读取它们。

第一个问题是它之间有什么区别：

socket.BeginReceive(readResult.Buffer, 0, SocketReadResult.BufferSize, 0, new AsyncCallback(ReadCallback), readResult);

和

socket.BeginReceive(readResult.Buffer, 0, SocketReadResult.BufferSize, 0, ReadCallback, readResult);

另外，考虑到这是我的回调函数，为什么我读到的示例在整个事情中有一个try / catch，当然你只需要围绕socket.EndReceive()调用尝试/捕获？

public void ReadCallback(IAsyncResult ar)
{
    try
    {
        var readResult = (SocketReadResult)ar.AsyncState;
        var socket = readResult.Socket;
        int bytesRead = socket.EndReceive(ar);

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

            // Get the rest of the data.
            socket.BeginReceive(readResult.Buffer, 0, SocketReadResult.BufferSize, 0, new AsyncCallback(ReadCallback), readResult);
        }
        else
        {
            var newRead = new SocketReadResult(socket);

            socket.BeginReceive(readResult.Buffer, 0, SocketReadResult.BufferSize, 0, new AsyncCallback(ReadCallback), newRead);

            // All the data has arrived; put it in response.
            if (readResult.Text.Length > 1) ((IMessageSender)this).RouteMessage(this, new MessageString(readResult.Text.ToString()));
        }
    }
    catch (Exception e)
    {
        // TODO: manage this exception.
    }
}

public struct SocketReadResult
{
    StringBuilder Text;
    Socket Socket;
    byte[] Buffer;

    public const int BufferSize = 1024;

    public SocketReadResult(Socket s)
    {
        Socket = s;
        Buffer = new byte[BufferSize];
        Text = new StringBuilder();
    }
}

最后，如果您希望在致电socket.BeginReceive()后优雅地关闭监听器，您会调用哪些功能以及如何管理它？

Answer 1

a）他们是平等的。编译器将为您生成相同的代码

b）如何为异步调用编写一些扩展方法并处理异常，就好像它们是同步调用而不阻塞调用者一样？

try
{
    await socket.ConnectTaskAsync("www.google.com", 80);

    await socket.SendTaskAsync(bytesToSend);

    byte[] buf = new byte[0x8000];
    var bytesRead = await socket.ReceiveTaskAsync(buf, 0, buf.Length);
}
catch (Exception ex)
{
    Console.WriteLine(ex.Message);
}

public static class SocketExtensions
{
    public static Task ConnectTaskAsync(this Socket socket, string host, int port)
    {
        return Task.Factory.FromAsync(
                     socket.BeginConnect(host, port, null, null),
                     socket.EndConnect);
    }

    public static Task<int> ReceiveTaskAsync(this Socket socket, 
                                            byte[] buffer, 
                                            int offset, 
                                            int count)
    {
        return Task.Factory.FromAsync<int>(
           socket.BeginReceive(buffer, offset, count, SocketFlags.None, null, socket),
           socket.EndReceive);
    }


    public static Task SendTaskAsync(this Socket socket, byte[] buffer)
    {
        return Task.Factory.FromAsync<int>(
              socket.BeginSend(buffer,0,buffer.Length,SocketFlags.None, null, socket),
              socket.EndSend);
    }
}

Answer 2

socket.BeginReceive(readResult.Buffer, 0, SocketReadResult.BufferSize, 0, new AsyncCallback(ReadCallback), readResult);

和

socket.BeginReceive(readResult.Buffer, 0, SocketReadResult.BufferSize, 0, ReadCallback, readResult);

两者都是一样的，与

相同

        //both are the same thing
        button1.Click += new EventHandler(button1_Click);
        button1.Click += button1_Click;

Answer 3

两次通话之间的差异可以忽略不计，你可以认为它们是等价的。第二个调用将帮助编译器为您输入类型推理，但在IntelliSense和代码自动完成之外，这将不会非常明显。我个人使用第一种格式，因为它更简洁。

至于为什么try/catch不仅仅是Socket.EndReceive()调用，主要与其他局部变量的范围有关。

考虑一下：

var state = result.AsyncState as SocketStateObject;
var socket = state.Socket;

try
{
  var numberOfBytesRead = socket.EndReceive(result);
}
catch(SocketException ex)
{
  // Handle the exception here.
}

// numberOfBytesRead is not accessible out here!

try
{
  if(socket.Connected)
    socket.BeginReceive(...); // Receive again!
}
catch(SocketException ex)
{
  // Handle the exception here too.
}

正如你在这里看到的，有一些原因可以解释为什么一个较大的try/catch优于两个较小的较小的try。

首先，局部变量仅在try/catch范围内可用。你可以通过在Socket.BeginReceive()块之外定义它来解决这个问题。

其次，可能更重要的是，与减少冗余有关。由于您很可能在回调中再次呼叫try/catch，因此将其置于同一SocketException下是有意义的。否则，您必须在两个地方而不是一个地方处理您的潜在Socket。

至于优雅地关闭Socket.Close()，您可以使用false方法。通常，套接字永远不会被重用，因此您可以为此传递Socket.Dispose()。但是，最好在Socket.Close()电话后拨打IDisposable。如果您将侦听器套接字作为类的成员变量，请确保实现{{1}}接口并正确处理套接字。

异步套接字读取

3 个答案: