Hi,
I'd like to discuss the proposed change of "active service" to
"available service". The basic reason is that as a client I don't really
care if the service is active or not at a particular time. I do care
whether it's available or not though, and so it would be good to be able
to ask the API about whether a particular service is available.
In the API, isActive() in ServiceReference would be changed to
isAvailable() so that this could be queried for.
The default would be that all native Qi4j services are available. For
imported services the current isActive method would be renamed to
isAvailable, and it can implement it any way it wants to.
For services that want to support it, what I usually do is to have a
property "enabled" in the ConfigurationComposite of the service that I
want to enable/disable. Usually these services communicate with an
external service, and so if I know that it's not available (e.g. a mail
server, web service, or database), I will set it to "disabled" in the
configuration. The configuration of the connection might be there (e.g.
database URL, username/password, etc.), it's just that at the moment I
don't want the application to even try making a connection.
With the introduction of a circuit breaker, that might be an additional
way to mark the service as unavailable. I.e. the service itself is
available, but it detected that the external service is currently not
available, and so want to make this clear to the rest of the application.
This is the basic need that I have. The easiest way to support this
would be to have an additional Available interface (with an isAvailable
method) that a service can implement, and which would typically either
delegate to the "enabled" configuration or the circuit breaker (or both,
in that order). Then it would be very easily for my application to
degrade gracefully, and would also make it easy to make JMX tools to
expose this using MBeans.
WDYT? Does that sound like an ok way to do it?
/Rickard
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