Hi, On 21 nov. 2013, at 14:40, Benjamin Debeerst <[email protected]> wrote:
> Hello all, > > While working with some iPOJO components and mandatory references I stumbled > upon the warning "The dependency is not optional, however no service can be > injected", followed by an NPE. > > The situation is fairly simple: I have a component A with a mandatory > reference to service B. When service B goes away, it is first removed from my > component A, but the @Invalidate callback of A is only called after the fact > - effectively preventing me of doing a proper cleanup and provoking the NPE. > This gets even more complicated when component A has started asynchronous > jobs working with B, because it can't shut down those jobs on time. > > I found a thread from 2009 on this list that treats more or less the same > problem [1], Clement wrote as answer: > > "When a required (not optional) service leaves, it invalidates the instance. > If this instance has an 'invalidate' callback, this callback is called. The > callback is called after its unregistration, that's why the service is no > more available. So, invalidate callbacks must be developed defensively to > check service availability." > > I find this rather counter-intuitive. Why is the invalidate callback called > after the fact? Yet, iPOJO has the information of the leaving mandatory > reference B on time, since it can call the @Unbind callback on time. I am > also comparing to Declarative Services, which guarantees that it will > deactivate your component before it takes away any mandatory references. I > found it a big advantage of iPOJO (compared to DS) to be able to drop the > implementation of the bind/unbind glue and have the references injected in > the fields directly. Now I do not only have write the glue again, moreover I > have to delegate the unbind call to the invalidate() method for each > mandatory reference in my component. > > The thing is that I do not see any advantage of iPOJO's call order compared > to DS's call order. Are there specific reasons for this? I agree this choice is debatable, and is going to change in iPOJO 2.0. The @Invalidate callback should be called while the services are still accessible to ease the cleanup process. So, it’s going to change soon. Regards, Clement > > Regards, > Benjamin > > [1] > http://mail-archives.apache.org/mod_mbox/felix-users/200908.mbox/%[email protected]%3E > Т���������������������������������������������������������������������ХF�V�7V'67&�&R�R���âW6W'2�V�7V'67&�&TfVƗ��6�R��&pФf�"FF�F����6����G2�R���âW6W'2ֆV�fVƗ��6�R��&p� --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
