Christian, I don't think this behaviour can be removed from Blueprint, it's too intrinsic to the design. Anyway, I'm not suggesting making any changes to Blueprint.
Neil On Fri, Sep 13, 2013 at 11:28 AM, Christian Schneider <[email protected]> wrote: > Honestly the proxy creation alone created a lot of issues in the past :-) > > So what would be your preferred solution for blueprint? Stopping the > blueprint context when a required service goes away? > I originally thought it would do that before I learned how it actually > works. > > I am not sure why blueprint works this way but I would be interested to > learn why and what would be better behaviours. Perhaps the blueprint > standard can be enhanced. > > Christian > > > On 13.09.2013 12:19, Neil Bartlett wrote: >> >> Christian, >> >> I consider that to be one of the worst features of Blueprint, so I >> would be very opposed to adding it to DS! >> >> Regards >> Neil >> >> On Fri, Sep 13, 2013 at 11:17 AM, Christian Schneider >> <[email protected]> wrote: >>> >>> I think you can take a look at what aries blueprint does for these cases. >>> They create a proxy for each injected service and switch the service if >>> the >>> original one goes away. If no service is available then I think it >>> waits for some time for a new one to come and throws an exception if a >>> time >>> out happens. >>> >>> Perhaps a similar behaviour can also be added for DS. Not sure if it >>> matches >>> the DS ideas though. >>> >>> Christian >>> >>> >>> On 13.09.2013 12:10, Thomas Diesler wrote: >>> >>> Thank you all for your replies. We ended up with three measures >>> >>> #1 assert that the component is still valid on entry of every public >>> method >>> (AtomicBoolean set by activate/deactivate) >>> #2 Use a ValidatingReference to hold unary references to dependent >>> services >>> (prevents NPE when a dependent service goes away) >>> #3 Throw an InvalidComponentException runtime exception on #1 and #2 >>> >>> The idea is that access to a deactivated reference never throws NPE >>> Access to the public API is prevented from deactivated service instances >>> >>> cheers >>> --thomas >>> >>> On Sep 11, 2013, at 11:11 AM, Richard S. Hall <[email protected]> >>> wrote: >>> >>> Resending my reply from yesterday since my original message didn't seem >>> to >>> go through... >>> >>> ---- >>> >>> Yes, you can do some of these sorts of things with iPOJO. >>> >>> First, iPOJO has the notion of a service-level service dependency as well >>> as >>> an implementation-level service dependency (which is the level of DS >>> dependencies). Second, iPOJO caches services references within a service >>> method invocation so that a thread calling a method on a service will see >>> the same injected services until the thread exits the invoked service >>> method. >>> >>> It doesn't deal with configuration locking (at least not of which I am >>> aware). >>> >>> -> richard >>> >>> On 9/10/13 06:41 , Thomas Diesler wrote: >>> >>> Hi Folks, >>> >>> in Fabric we have a service model whereby services have >>> interdependencies, >>> are configurable and dynamic by nature - all of which is managed in OSGi >>> with the help of Declarative Services. To illustrate I use a simple >>> example >>> >>> ServiceT { >>> >>> @Reference >>> ServiceA serviceA; >>> >>> @Reference >>> ServiceB serviceB; >>> >>> public doStuff() { >>> // that uses serviceA & serviceB >>> } >>> } >>> >>> >>> The injection is handled by the DS framework - there are various >>> callbacks >>> involved. >>> >>> Lets assume the system is fully configured and a client makes a call on >>> ServiceT >>> >>> ServiceT serviceT = getServiceT(); >>> serviceT.doStuff(); >>> >>> >>> Due to the dynamic nature of OSGi services and their respective >>> configuration ServiceT must deal with the following possible/likely >>> situations >>> >>> #1 An instance of a referenced service is not available at the point of >>> access (i.e. serviceA is null) >>> #2 In the context of a single call the service instance may change (i.e. >>> call may span multiple instances of serviceA) >>> #3 In the context of a single call the configuration of a service >>> instance >>> may change (i.e. serviceA is not immutable, sequential operations on A >>> may >>> access different configurations) >>> >>> In OSGi there is no notion of global lock for service/configurations nor >>> a >>> notion of lock of a given set of services/configurations - I cannot do >>> >>> lock(T, A, B); >>> try { >>> ServiceT serviceT = getServiceT(); >>> serviceT.doStuff(); >>> } finally { >>> unlock(T, A, B); >>> } >>> >>> This code is also flawed because it assumes that the caller of doStuff() >>> is >>> aware of the transitive set of services involved in the call and that >>> this >>> set will not change. >>> >>> As a conclusion we can say that the behaviour of doStuff() is only >>> defined >>> when we assume stability in service availability and their respective >>> configuration, which happens to be true most of the time - nevertheless, >>> there are no guarantees for defined behaviour. >>> >>> How about this … >>> >>> The functionality of A and B and its respective configuration is >>> decoupled >>> from OSGi and its dynamicity >>> >>> >>> A { >>> final Map config; >>> public doStuffInA() { >>> } >>> } >>> >>> B { >>> final Map config; >>> public doStuffInB() { >>> } >>> } >>> >>> >>> ServiceA and ServiceB are providers of immutable instances of A and B >>> respectively. There is a notion of CallContext that provides an >>> idempotent >>> set of instances involved in the call. >>> >>> CallContext { >>> public T get(Class<T> type); >>> } >>> >>> This guarantees that throughout the duration of a call we always access >>> the >>> same instance, which itself is immutable. CallContext also takes care of >>> instance availability and may have appropriate timeouts if a given >>> instance >>> type cannot be provided. It would still be the responsibility of A/B to >>> decide wether an operation is permissible on stale configuration. >>> >>> Changes to the system would be non-trival and before I do any prototyping >>> I'd like to hear what you think. >>> >>> cheers >>> --thomas >>> >>> >>> >>> _______________________________________________ >>> OSGi Developer Mail List >>> [email protected] >>> https://mail.osgi.org/mailman/listinfo/osgi-dev >>> >>> >>> _______________________________________________ >>> OSGi Developer Mail List >>> [email protected] >>> https://mail.osgi.org/mailman/listinfo/osgi-dev >>> >>> >>> >>> >>> _______________________________________________ >>> OSGi Developer Mail List >>> [email protected] >>> https://mail.osgi.org/mailman/listinfo/osgi-dev >>> >>> >>> >>> -- >>> Christian Schneider >>> http://www.liquid-reality.de >>> >>> Open Source Architect >>> http://www.talend.com >>> >>> >>> _______________________________________________ >>> OSGi Developer Mail List >>> [email protected] >>> https://mail.osgi.org/mailman/listinfo/osgi-dev >> >> _______________________________________________ >> OSGi Developer Mail List >> [email protected] >> https://mail.osgi.org/mailman/listinfo/osgi-dev > > > > -- > Christian Schneider > http://www.liquid-reality.de > > Open Source Architect > http://www.talend.com > > _______________________________________________ > OSGi Developer Mail List > [email protected] > https://mail.osgi.org/mailman/listinfo/osgi-dev _______________________________________________ OSGi Developer Mail List [email protected] https://mail.osgi.org/mailman/listinfo/osgi-dev
