以编程方式减少TIME_WAIT或CLOSE_WAIT

Question

In an .aspx page, I need to bind a socket to a port, use it, and then dispose of it. It works the first time, but the second time I access the page I get the following exception:

[Exception in bind: System.Net.Sockets.SocketException (0x80004005): Only one usage of each socket 
 address (protocol/network address/port) is normally permitted
at System.Net.Sockets.Socket.DoBind(EndPoint endPointSnapshot, 
 SocketAddress socketAddress)
at System.Net.Sockets.Socket.Bind(EndPoint localEP)
[...]

This is the code, with the Exception triggering the error. Please note the fact that Accept() blocks is perfectly acceptable in my scenario.

IPAddress ipAddress = IPAddress.Parse(ip);
Socket s1 = new Socket(ipAddress.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
IPEndPoint ep = new IPEndPoint(ipAddress, port);
try {
    s1.Bind(ep);
} catch(Exception ex) {
    HttpContext.Current.Response.Write("[Exception in bind: "+ ex + "\n");
    return;
}
s1.Listen(32);
// block until there's a connection
Socket s2 = s1.Accept();
// save for later
Session["s1"] = s1;
Session["s2"] = s2;

The socket is retrieved through the Session and used later, and destroyed:

Socket s1 = Session["s1"] as Socket;
Socket s2 = Session["s2"] as Socket;

// ... use the socket ...

// cleanup
s2.Shutdown(SocketShutdown.Both);
s2.Disconnect(true);
s2.Close();
s2.Dispose();
s1.Shutdown(SocketShutdown.Both);
s1.Disconnect(true);
s1.Close();
s1.Dispose();

I've tried various combinations of flags such as Linger , ReuseAddress , ExclusiveAddressUse and values for the Listen backlog but nothing changes.

An important note: without the ReuseAddress option the socket is in TIME_WAIT as shown by netstat -ano . When I use ReuseAddress , the socket is stuck in CLOSE_WAIT .

I am fully aware of the implications : is there a way to programmatically reduce the CLOSE_WAIT or TIME_WAIT intervals for a specific socket without having to touch the registry?

I'm wondering if I'm forgetting something when trying to dispose of the socket...

Answer 1

It turns out that leveraging the Session object is not ideal. The port would be left open after the first use, and according to the PID shown with netstat , an IIS Worker would own it. Therefore it appears like it's impossible to call Close() on it.

The solution was to close the server socket ( s1 in my example) after Accept :

[...]
s1.Listen(32);
// block until there's a connection
Socket s2 = s1.Accept();
// *close the server socket*
s1.Close();
// only save s2 for later
Session["s2"] = s2;

Then use only s2 , for example:

// ...later on
Socket s1 = Session["s1"] as Socket;
try {
    while ((bytesRead = s1.Receive(receiveBuffer)) > 0 ) {
        byte[] received = new byte[bytesRead];
        Array.Copy(receiveBuffer, received , bytesRead);
        Response.BinaryWrite(received);
    }
} catch(Exception ex){
[...]

The previous solution makes the "cleanup" unnecessary.