C# Socket连接请求超时机制

最新推荐文章于 2024-10-09 15:11:16 发布

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最新推荐文章于 2024-10-09 15:11:16 发布

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分类专栏： c# 网络编程文章标签： socket c# exception null .net string

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本文介绍了一种实现方法，通过使用ManualResetEvent和超时控制机制，解决了.NET Socket连接请求在服务器未监听或网络故障时长时间等待的问题。实现的关键在于设置超时时间并在连接成功或失败时正确响应。

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介绍
您可能注意到了，.Net的System.Net.Sockets.TcpClient和System.Net.Sockets.Socket都没有直接为Connect/BeginConnect提供超时控制机制。因此，当服务器未处于监听状态，或者发生网络故障时，客户端连接请求会被迫等待很长一段时间，直到抛出异常。默认的等待时间长达20~30s。.Net Socket库的SocketOptionName.SendTimeout提供了控制发送数据的超时时间，但并非本文讨论的连接请求的超时时间。

实现
下面是实现的关键代码：

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class TimeOutSocket
{
private static bool IsConnectionSuccessful = false;
private static Exception socketexception;
private static ManualResetEvent TimeoutObject = new ManualResetEvent(false);
public static TcpClient TryConnect(IPEndPoint remoteEndPoint, int timeoutMiliSecond)
{
TimeoutObject.Reset();
socketexception = null;
string serverip = Convert.ToString(remoteEndPoint.Address);
int serverport = remoteEndPoint.Port;
TcpClient tcpclient = new TcpClient();
tcpclient.BeginConnect(serverip, serverport,
new AsyncCallback(CallBackMethod), tcpclient);
if (TimeoutObject.WaitOne(timeoutMiliSecond, false))
{
if (IsConnectionSuccessful)
{
return tcpclient;
}
else
{
throw socketexception;
}
}
else
{
tcpclient.Close();
throw new TimeoutException("TimeOut Exception");
}
}
private static void CallBackMethod(IAsyncResult asyncresult)
{
try
{
IsConnectionSuccessful = false;
TcpClient tcpclient = asyncresult.AsyncState as TcpClient;
if (tcpclient.Client != null)
{
tcpclient.EndConnect(asyncresult);
IsConnectionSuccessful = true;
}
}
catch (Exception ex)
{
IsConnectionSuccessful = false;
socketexception = ex;
}
finally
{
TimeoutObject.Set();
}
}
}

class TimeOutSocket
{
    private static bool IsConnectionSuccessful = false;
    private static Exception socketexception;
    private static ManualResetEvent TimeoutObject = new ManualResetEvent(false);

public static TcpClient TryConnect(IPEndPoint remoteEndPoint, int timeoutMiliSecond)
    {
        TimeoutObject.Reset();
        socketexception = null;

string serverip = Convert.ToString(remoteEndPoint.Address);
        int serverport = remoteEndPoint.Port;           
        TcpClient tcpclient = new TcpClient();
        
        tcpclient.BeginConnect(serverip, serverport, 
            new AsyncCallback(CallBackMethod), tcpclient);

if (TimeoutObject.WaitOne(timeoutMiliSecond, false))
        {
            if (IsConnectionSuccessful)
            {
                return tcpclient;
            }
            else
            {
                throw socketexception;
            }
        }
        else
        {
            tcpclient.Close();
            throw new TimeoutException("TimeOut Exception");
        }
    }
    private static void CallBackMethod(IAsyncResult asyncresult)
    {
        try
        {
            IsConnectionSuccessful = false;
            TcpClient tcpclient = asyncresult.AsyncState as TcpClient;
             
            if (tcpclient.Client != null)
            {
                tcpclient.EndConnect(asyncresult);
                IsConnectionSuccessful = true;
            }
        }
        catch (Exception ex)
        {
            IsConnectionSuccessful = false;
            socketexception = ex;
        }
        finally
        {
            TimeoutObject.Set();
        }
    }
}

这里，ManualResetEvent的WaitOne(TimeSpan, Boolean)起到了主要的作用。它将阻止当前线程，直到ManualResetEvent对象被Set或者超过timeout时间。上面的代码中，调用BeginConnect后通过WaitOne方法阻止当前线程，如果在timeoutMiliSecond时间内连接成功，将在CallBackMethod回调中调用TimeoutObject.Set，解除被阻塞的连接线程并返回；否则，连接线程会在等待超时后，主动关闭连接并抛出TimeoutException。