Just to add a bit of detail… If you wait for 5 service instances before performing your initialisation, that’s great. But bear in mind that you might get a 6th and a 7th very soon afterwards, and depending on your implementation you may have to re-initialise each time that happens.
If your (re)initialisation is expensive, you might want to avoid doing it too many times, especially if there is a rapid sequence of changes. This is typically the case during application startup for example. There are two general solutions to this: 1) You could start a timer each time the service set changes. If there are no further changes before the timer expires, then you do your reinitialisation. If there *are* changes then you cancel the existing timer and start a new one. 2) Use the Coordinator Service (OSGi Compendium Specification, chapter 130). Whoever is making changes to the set of installed bundles — e.g. the launcher, or some kind of management agent like FileInstall — should start a Coordination before it does anything, and end the coordination after that series of changes. Your component should be a Participant which detects whether there is a current coordination. If there is NO current coordination then it should immediately action any changes in the service set. However if there is a current coordination, then those changes should only be actioned when the coordination ends. This has the advantage that you don’t waste time waiting for an arbitrary-length timer to expire. Hope that helps. Regards, Neil > On 7 Sep 2015, at 16:16, Benson Margulies <[email protected]> wrote: > > That is precisely what I needed. Thanks. > On Sep 7, 2015 11:06 AM, "David Jencks" <[email protected]> > wrote: > >> Hi Benson, >> >> I don’t really understand what you are asking, but I’m going to guess. >> >> I think you have say 5 B2 services and you want B3 to wait to activate >> until all 5 B2’s are available? >> >> There is a way to do this with DS 1.3, but you have to make B3 >> configuration-policy=REQUIRE. >> >> So you have in B3: >> @Component(configuration-policy=REQUIRE) >> public class B3 { >> >> @Reference(cardinality=MULTIPLE) >> void setB2(B2 b2) {} >> } >> In your (required) configuration for B3 you put a property >> >> B2.cardinality.minimum: 5 >> >> that is, <reference-name>.cardinality.minimum = <number of required B2’s> >> >> Don’t mess with start levels, they will be unreliable for this purpose. >> There’s no guarantee that a bundle starting will start all the DS services >> it provides. They might have all sorts of unsatisfied dependencies….. such >> as missing configurations. >> >> Let me know if this guess is a total miss :-) >> >> thanks >> david jencks >> >> >> >>> On Sep 7, 2015, at 10:52 AM, Benson Margulies <[email protected]> >> wrote: >>> >>> I am hoping that David Jencks will continue his charity to strangers >> here. >>> >>> David, if you have any gogo jiras you'd like help with in return, just >> ask. >>> >>> Three bundles: >>> >>> B1 registers service S1. >>> >>> B2 consumes S1 and uses it in the implementation of S2. That is to >>> say, it picks up a reference to S1 with a DS @Reference with >>> cardinality MANDATORY. >>> >>> B3 consumes B2, but it anticipates that B2 will have siblings. So it >>> consumes a reference to a List<S2> with cardinality AT_LEAST_ONE. >>> >>> It can take B2 and buddies a bit of time to activate. >>> >>> I appreciate that the most general case is intended to be that >>> services come and go, and B3 should dynamically reconfigure itself. >>> I'd rather not do that yet; I'd like to arrange things so that B3 >>> waits to finish starting itself until all the B2-ish guys are fully >>> set up. >>> >>> Assuming that B2 and friends are all started at an earlier start >>> level, is there an 'esthetic' way to arrange this? Or should I really >>> suck it up and do the late-binding so that B3 says, 'OK, _now_ I need >>> B2 service x=y, block until it's available?' >>> >>> --------------------------------------------------------------------- >>> To unsubscribe, e-mail: [email protected] >>> For additional commands, e-mail: [email protected] >>> >> >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: [email protected] >> For additional commands, e-mail: [email protected] >> >> --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
