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Message-ID: <3794EE1F.A98D643B@eng.sun.com>
Date: Tue, 20 Jul 1999 14:46:07 -0700
From: James Todd <james.todd@eng.sun.com>
Organization: Sun Microsystems
MIME-Version: 1.0
To: tomcat-dev@jakarta.apache.org
Subject: Re: request for review: server/config discussion
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 <3794DCB6.D7A9872E@eng.sun.com> <3794E650.D038BB6A@algroup.co.uk>
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Ben Laurie wrote:

> Much as I like the idea of notifying config changes, I think it is
> likely to lead to trouble. Here's the problem in a nutshell: either you
> notify in detail what the changes are, in which case we are looking at
> horrendous complexity and likely lots of interesting failure modes, or
> you just say "it's changed" in which case you only need a single module
> that requires a restart (canonical example: Apache listeners - these
> cannot change without a restart) and every change gives you a restart
> anyway.
> 

this is why i'm presently (informally in this list and a small
bit more formally in the discussion doc) piloting the idea of
"passive" notification from the perspective of the config service.

it could be that an api is provided via the service to "check"
the freshness (born on date) of the data and leave it up to
the client (eg server) to do with what it may with the results.
another passive means might be to throgh some sort of exception
indicating that "data you've obtained from me has since been
modified."

this just feels right at this stage in the game. we could up
the ante a bit and consider an active notification scheme whereby
the config service persists a reference to clients (listeners)
and broadcasts changes accordingly.

i'm a proponent of "passive" notification as 1) it is likely
better then what is available today, 2) the api and subsequent
implementations are rather trivial and 3) it doesn't too tightly
couple subscribers of a service nor mandate too much behaviour.

hope this helps,

- james