Re: Determining whether a TCP connection is up

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> Another option is to kill connections after some time of inactivity,
>> rather than leave them open and suffer a timeout next time we need to
>> use it.
> Yes.  But it's not very nice for the servers.  NNTP and IMAP servers do
> the access control stuff upon connection, which can be
> resource-intensive.

Those servers don't like to have thousands of idle connections tying up
resources either.
If you kill your connections after a reasonable amount of inactivity,
the cost of connection is not that bad.

> The earliest version of the ... Mozilla? or whatever they were called at
> the time? (I think) ... news reader famously was written in a
> connection-less method which made a news connection for every action it
> made.  It DDoS-ed several NNTP servers.

I think that "after some time of inactivity" is not quite the same as "a
news connection for every action".
E.g.: Use (process-put <proc> 'last-time (float-time)) in the process
filter, then use an idle timer to kill connections older than some
limit.  And when sending a command, check that last-time stamp, and
consider the process dead if it's older than the limit (in case the
idle-timer didn't do its job (yet) for some reason).


        Stefan