Sockets will not close problem

Question

Hi all,
We have a cient/server system that handles many connections using a dynamic pool of sockets (grows to a maximum and shrinks when not in use) spawned from a ServerSocket. The clients come and go with great frequency. They connect, pass some info, and disconnect again. The protocol implemented is that when the client wants to disconnect, it tells the server that it is finished using one of the fields in the message, and the server does the disconnect. The server side code that reacts to such a request to disconnect is as follows (btw, this is nicely indented for real, but can't get it to look right here):
try
logger.log(3, "CLOSE CLIENT INPUT STREAM");
if(client_input != null)
client_input.close();
client_input = null;
} catch(Exception se)
logger.log(0, "Input Stream Close Error: "+ se);
try
logger.log(3, "CLOSE CLIENT OUTPUT STREAM");
if(client_output != null)
client_output.close();
client_output = null;
} catch(Exception se)
logger.log(0, "Output Stream Close Error: "+ se);
try
logger.log(3, "CLOSE CLIENT SOCKET");
if(clientSocket != null)
clientSocket.close();
clientSocket = null;
} catch(Exception se)
logger.log(0, "Client Socket Close Error: "+ se);
finally
if(clientSocket != null)
try
clientSocket.close();
clientSocket = null;
} catch(Exception ex)
{} // nothing can be done
By far most of the times this works perfectly. The problem is this. With some clients only (it's a public internet app and we get all kinds of clients, and it's not always the same client type where this happens - i.e. sometimes Win2000 using JDK 1.3.1, sometimes another) the server reports through the logger that the socket is closed and everthing appears OK, but it didn't really close the socket! Running netstat shows those connections as still ESTABLISHED. With the amount of re-connecting these clients do, it only takes 2 or 3 such "ill behaved clients" and we soon run up to our stated "maximum" number of sockets for the pool, and everything comes to a grinding halt!
Searched the forums and only found one (very old) topic similar to this, with no answer.
So the question is: IS THERE ANY WAY TO REALLY FORCE THE CLOSING OF A SOCKET AT THE SERVER END?
Any thoughts appreciated.
thanks,
glitch

Answer 1

Reposted all, with code tags
Hi all,
We have a cient/server system that handles many
connections using a dynamic pool of sockets (grows to
a maximum and shrinks when not in use) spawned from a
ServerSocket. The clients come and go with great
frequency. They connect, pass some info, and
disconnect again. The protocol implemented is that
when the client wants to disconnect, it tells the
server that it is finished using one of the fields in
the message, and the server does the disconnect. The
server side code that reacts to such a request to
disconnect is as follows (btw, this is nicely indented
for real, but can't get it to look right here):
try
logger.log(3, "CLOSE CLIENT INPUT STREAM");
if(client_input != null)
client_input.close();
client_input = null;
} catch(Exception se)
logger.log(0, "Input Stream Close Error: "+ se);
try
logger.log(3, "CLOSE CLIENT OUTPUT STREAM");
if(client_output != null)
client_output.close();
client_output = null;
} catch(Exception se)
logger.log(0, "Output Stream Close Error: "+ se);
try
logger.log(3, "CLOSE CLIENT SOCKET");
if(clientSocket != null)
clientSocket.close();
clientSocket = null;
} catch(Exception se)
logger.log(0, "Client Socket Close Error: "+
r: "+ se);
finally
if(clientSocket != null)
try
clientSocket.close();
clientSocket = null;
} catch(Exception ex)
{} // nothing can be done
>
By far most of the times this works perfectly. The
problem is this. With some clients only (it's a
public internet app and we get all kinds of clients,
and it's not always the same client type where this
happens - i.e. sometimes Win2000 using JDK 1.3.1,
sometimes another) the server reports through the
logger that the socket is closed and everthing appears
OK, but it didn't really close the socket! Running
netstat shows those connections as still ESTABLISHED.
With the amount of re-connecting these clients do, it
only takes 2 or 3 such "ill behaved clients" and we
soon run up to our stated "maximum" number of sockets
for the pool, and everything comes to a grinding
halt!
Searched the forums and only found one (very old)
topic similar to this, with no answer.
So the question is: IS THERE ANY WAY TO REALLY FORCE
THE CLOSING OF A SOCKET AT THE SERVER END?
Any thoughts appreciated.
thanks,
glitch