最近在写一个CS程序的Demo，其中用到了SocketAsyncEventArgs，据说这个封装了IOCP模型，而且使用方便。
确实，在看了MSDN的例子之后，把微软的列子（在msdn查找SocketAsyncEventArgs就能看到例子程序）稍加修改，完善就写好了服务端。但是在完成用户管理功能时，服务端主动关闭客户端的连接也就是踢掉指定用户遇到了麻烦。
1.例子中包含一个CloseSocket函数，但是此函数并不能主动调用，如果主动调用就会在执行此函数的同时触发SocketAsyncEventArgs的Completed事件，并且标志是Receive，接收字符长度是0，因此再次进入CloseSocket函数重复关闭同一个Socket，于是发生错误，程序退出。
2.客户端主动中断时，是直接接收到0长度数据，然后进入CloseSocket，结果就是正常关闭了。
搜索了半天也没找到一个说的清楚一点的。只依稀记得csdn有个帖子中说道，关闭socket之后立刻处理接收事件，然后再关闭socket就是一个graceful close了。但是明显的，这里不能直接在CloseSocket函数中加入ProcessRecv。于是我又想到设个标志，在userToken中增加一个标志位，进入Closesocket函数之后就置标志，如果发生重入则直接退出。结果异常没有了。但是用户被踢掉之后立刻又重连了。体现在用户的SessionID（我给每一个SocketAsyncEventArgs加了一个ID）换了。吐血。。。
晚上看动画片时还一直在琢磨这事，然后又到msdn把Socket类相关的狂看一遍。看到Socket类有Shutdown和Close，突然想到上面的先关闭，然后处理接收，然后关闭Socket。一下子开窍了。果断地，把Try部分单独移出来。然后踢用户时只是shutdown一下，让它自动触发Completed事件进入ProcessRecv中，然后调用CloseSocket。正常关闭了！
下面是代码的对比
改前：
private void ProcessReceive(SocketAsyncEventArgs e)
{
// check if the remote host closed the connection
AsyncUserToken token = (AsyncUserToken)e.UserToken;
if (e.BytesTransferred > 0 && e.SocketError == SocketError.Success)
{
//increment the count of the total bytes receive by the server
Interlocked.Add(ref m_totalBytesRead, e.BytesTransferred);
Console.WriteLine("The server has read a total of {0} bytes", m_totalBytesRead);
//echo the data received back to the client
e.SetBuffer(e.Offset, e.BytesTransferred);
bool willRaiseEvent = token.Socket.SendAsync(e);
if (!willRaiseEvent)
{
ProcessSend(e);
}
}
else
{
CloseClientSocket(e);
}
}
private void CloseClientSocket(SocketAsyncEventArgs e)
{
AsyncUserToken token = e.UserToken as AsyncUserToken;
// close the socket associated with the client
//就是下面这里了
try
{
token.Socket.Shutdown(SocketShutdown.Send);
}
// throws if client process has already closed
catch (Exception) { }
token.Socket.Close();
// decrement the counter keeping track of the total number of clients connected to the server
Interlocked.Decrement(ref m_numConnectedSockets);
m_maxNumberAcceptedClients.Release();
Console.WriteLine("A client has been disconnected from the server. There are {0} clients connected to the server", m_numConnectedSockets);
// Free the SocketAsyncEventArg so they can be reused by another client
m_readWritePool.Push(e);
}
改后：
private void CloseClientSocket(SocketAsyncEventArgs e)
{
AsyncUserToken token = e.UserToken as AsyncUserToken;
token.Socket.Close();
// decrement the counter keeping track of the total number of clients connected to the server
Interlocked.Decrement(ref m_numConnectedSockets);
m_maxNumberAcceptedClients.Release();
Console.WriteLine("A client has been disconnected from the server. There are {0} clients connected to the server", m_numConnectedSockets);
// Free the SocketAsyncEventArg so they can be reused by another client
m_readWritePool.Push(e);
}
private void tryCloseSocket(SocketAsyncEventArgs e)
{
AsyncUserToken token = e.UserToken as AsyncUserToken;
// close the socket associated with the client
//就是下面这里了
try
{
token.Socket.Shutdown(SocketShutdown.Send);
}
// throws if client process has already closed
catch (Exception) { }
}
原来的执行顺序是
CloseClientSocket => ProcessReceive => CloseClientSocket(重复关闭)
改过之后是
tryCloseSocket => ProcessReceive => CloseClientSocket (graceful Close)
Oh，Yeah！
现在发现一个问题，有个TCP调试助手还是踢不掉，踢掉会自动重连。而换其他的都可以断开。这个软件截图如下：
这样说来，我之前设置标志位的做法可能是能够成功的。懒的再去测试了。