Re: Strange Socket problem

Knute Johnson <>
Thu, 01 Mar 2012 16:43:25 -0800
On 3/1/2012 2:15 PM, Martin Gregorie wrote:

On Thu, 01 Mar 2012 11:49:30 -0800, Knute Johnson wrote:

I'm having a problem in some production code that I can't figure out.
I'll post the complete actual code below. This code is running in three
places and has the same problem in two of them at the same time. The
other I'm not sure, it may be that the personnel operating it are
restarting the program and so don't complain. This piece of code is a
simple client that connects via a Socket to a server. The server
supplies some data and the client reads that data and files it away. It
is supposed to restart itself if there is a connection failure or fault
for whatever reason. The problem is that at some random point in time
the Socket disconnects, the code logs the disconnect but never restarts.
   It does print the "SportsWinClient Disconnected" message but never
executes the "fireconnectionEvent()" method after creating a new Socket.
   It doesn't print any Exception message. I'm not sure how it gets out
of the try block without printing the "End of Stream" message or an
exception message.

The crazy part is that all night long when there is no activity from the
server it times out and restarts with no problems.

I notice that InetAddress.getByName() can throw UnknownHostException (and
this exception isn't explicitly handled. Is it possible that this call
can time out when the network is busy?

That's possible I guess but I would think it would still throw an
UnknownHostException. Also, since I pass it a string with the IP
address specified with digits, it doesn't have to do any DNS lookup.

However, as UnknownHostException is a subclass of IOException I don't see
how it avoids being caught, unless a timeout causes a null to be
returned: the description of getByName() isn't at all clear about when a
null is returned instead of throwing an exception. Pulling this out of
the new Socket() statement so it can be tested for a null return would at
least show whether this is happening.

Also, I don't see why you're using InetAddress to pass what is apparently
a remote address to the Socket constructor as localAddress, or why you're
using port zero as the local port.

The computer has two NICs. The LOCAL_IP is the address of the NIC that
I want to use to connect to the server. Having to use InetAddress is a
limitation of the Socket constructor. Port 0 is the ephemeral port. It
allows the socket implementation to select any available port for the
client end. I'm not sure how InetAddress.getByName() can return a null.


Knute Johnson

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