From: Brian Candler <b.candler@...>
Date: 2009-05-19T22:46:07+09:00
Subject: Re: Detect TCPSocket interruptions/disappearance

Andrew Edwards wrote:
> I have put together a skeleton process to monitor this, shown below.
> However I am not sure how to reliably detect when the phone system
> goes away, say it is rebooted or similar.

Try setting SO_KEEPALIVE on your socket.

It's easier if you can send a periodic message to the far side and check 
you get a response within a second or two. However if you can't do that 
- i.e. you have to be an entirely passive listener - then SO_KEEPALIVE 
sends periodic probes at the TCP layer. It may take a few minutes to 
detect that the connection has gone though.
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