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From Clement Escoffier <clement.escoff...@gmail.com>
Subject Re: A couple of questions regarding iPojo interceptors
Date Mon, 03 Mar 2014 14:46:27 GMT

On 3 mars 2014, at 15:18, Bengt Rodehav <bengt@rodehav.com> wrote:

> Hi Clement,
> 
> Yes, I use the filter to make sure that the instance does not become valid
> until it has been intercepted - that part seems to work. However, in my
> case, the instance become valid AFTER my accept() method has been called
> but BEFORE my getServiceReferences() method has been called. This is
> causing my problems.
> 
> I'm a little curious regarding your wording:
> 
> "A (mandatory) dependency becomes valid only if the selected service set is
> not empty. In other words, all your interceptors should have been called
> before deciding to set the dependency state to valid."
> 
> I don't see how the first sentence has anything to do with the second
> sentence.

This is how iPOJO resolves services. It first considers the services from the service registry
(called base service set). This set is processed by tracking interceptor (such as LDAP filter…)
to get a matching service set. Then, a ranking interceptor is called to sort the set, and
to get the selected service set. A mandatory service dependency cannot be valid if this last
set is empty (in theory). That means that both accept and getServiceReferences should have
been called to determine whether or not the dependency is valid. The accept method is called
to build the matching service set, while getServiceReferences is called to retrieve the selected
service set.

> 
> I have a dependency declared as follows:
> 
>  @Requires(optional = false, id = "extenders", filter =
> "(intercepted=true)")
>  private IRouteExtender[] mExtenders;
> 
> Thus it is mandatory. Also, there are services of type IRouteExtender
> registered so that part is resolved. But until the accept() method has been
> called the "(intercepted=true)" part is not satisfied. When my accept()
> method has been called the "(intercepted=true)" part becomes satisfied and
> my instance becomes valid right away instead of waiting for the result of
> the getServiceReferences() method. This is the problem because in my
> getServiceReferences() method I evalutate the matching dependencies (by
> looking at a property) and determine that they are not valid. I therefore
> return an empty set of matching service references and the instance now
> becomes invalid.
> 
> I do not think it should be possible to validate an instance "in the midst
> of intercepting" as is the case for me. I must be completely done
> intercepting first.

That should not be the case. Definitely a bug…. The dependency state should not be re-evaluated
before having notified the ranking interceptor.

So far, you are implementing only getServiceReferences, can you implement and add traces in
onServiceArrival ?

Clement



> 
> /Bengt
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 2014-03-03 13:51 GMT+01:00 Clement Escoffier <clement.escoffier@gmail.com>:
> 
>> Hi,
>> 
>> On 3 mars 2014, at 13:14, Bengt Rodehav <bengt@rodehav.com> wrote:
>> 
>>> Hello again Clement!
>>> 
>>> Skiing trip is now over - time to get back to the interceptors...
>>> 
>>> Regarding your questions in the last post: Yes, I only add a property on
>>> the chosen service reference (intercepted is set to true), I do not
>> change
>>> the filter.
>>> 
>>> I have tested the theory regarding config admin / file install and it is
>>> not the problem.
>>> 
>>> It seems to me that there is no guarantee that both accept() and the
>>> getServiceReferences() are both called before an instance becomes valid.
>> I
>>> haven't looked at the source code in detail yet but is the design such
>> that
>>> this is not supposed to be possible or am I requesting a new feature? In
>>> other words, have I found a bug or not?
>>> 
>>> Ideally I think it should work as follows:
>>> 
>>> - When in "interceptor mode" the state of the instance should not change
>>> until all the interceptors (and all callbacks of the interceptors) have
>>> taken effect.
>>> 
>>> - Initially then instance should not become valid until all the
>>> interceptors (and all callbacks of the interceptors) have taken effect.
>>> 
>>> With "interceptor mode" I mean that something has triggered iPojo to
>> begin
>>> calling the registered interceptors.
>>> 
>>> Not sure if this is in accordance with your design. How is it supposed to
>>> work?
>> 
>> 
>> It might be a bug and a new feature.
>> 
>> I designed interceptors to be highly dynamic, so can come and leave at
>> anytime, and without having the components aware of them. That's why
>> service dependencies do not know which interceptors handle them.
>> Unfortunately, this design has some trade-off / drawbacks. If your instance
>> starts before the interceptors, it might be valid for a little amount of
>> time, until the interceptors handle the dependency. However in your case
>> you have a filter on the dependency that should avoid this case.
>> 
>> If you still have this filter, it is definitely a bug.  A (mandatory)
>> dependency becomes valid only if the selected service set is not empty. In
>> other words, all your interceptors should have been called before deciding
>> to set the dependency state to valid.
>> 
>> About the feature, I start thinking that the independence between the
>> interceptor and the dependencies may be problematic. For instance, I've
>> another use case where they implement a new handler (an extension of the
>> dependency handler) to ensure the availability of one specific interceptor.
>> The dependency is invalid until the interceptor arrives.
>> 
>> Clement
>> 
>>> 
>>> /Bengt
>>> 
>>> 
>>> 
>>> 
>>> 2014-02-24 8:17 GMT+01:00 Clement Escoffier <clement.escoffier@gmail.com
>>> :
>>> 
>>>> 
>>>> On 21 févr. 2014, at 14:15, Bengt Rodehav <bengt@rodehav.com> wrote:
>>>> 
>>>>> Hello Clement,
>>>>> 
>>>>> Some comments inline below.
>>>>> 
>>>>> /Bengt
>>>>> 
>>>>> 
>>>>> 
>>>>> 2014-02-21 12:53 GMT+01:00 Clement Escoffier <
>>>> clement.escoffier@gmail.com>:
>>>>> 
>>>>>> Hi,
>>>>>> 
>>>>>> On 20 févr. 2014, at 13:22, Bengt Rodehav <bengt@rodehav.com>
wrote:
>>>>>> 
>>>>>>> This is a follow up on another discussion I had with Clement
on this
>>>>>>> mailing list:
>>>>>>> 
>>>>>>> 
>>>>>> 
>>>> 
>> http://apache-felix.18485.x6.nabble.com/Using-iPojo-interceptors-tt5006168.html#a5006276
>>>>>>> 
>>>>>>> I'm now trying to get the interceptor solution into production.
>>>>>>> 
>>>>>>> Remember that I have to invalidate my instances when their
>>>> configuration
>>>>>> is
>>>>>>> changed. This is because I need to re-evalutate the dependencies
for
>>>> the
>>>>>>> instance.
>>>>>>> 
>>>>>>> Originally, I only called the invalidateSelectedServices() method
on
>>>> the
>>>>>>> DependencyModel. This worked mostly but not when starting a fresh
>>>>>> container
>>>>>>> (I use Karaf and start it with "bin\karaf.bat clean"). My instance
>> then
>>>>>>> first becomes valid but then becomes invalid. I think this is
because
>>>> of
>>>>>>> the ordering. The accept() method had not been called prior to
>>>>>>> the getServiceReferences() method. The dependency is therefore
not
>> set
>>>> to
>>>>>>> "intercepted=true" which makes it invalid.
>>>>>> 
>>>>>> the filter is updated by the interceptor. (just want to be sure I
>>>>>> understand). In that case, if the interceptor arrives after the
>> instance
>>>>>> creation, the filter will be set when the interceptor arrives.
>>>>>> 
>>>>> 
>>>>> Yes, my interceptor sets intercepted to true on the dependency which
>>>> makes
>>>>> sure that the filter match.
>>>> 
>>>> So the filter is not modified by the interceptor, it just add a new
>>>> property on the chosen service reference to match the filter.
>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>>> 
>>>>>>> 
>>>>>>> Replacing the call to  invalidateSelectedServices() with a call
to
>>>>>>> invalidateMatchingServices() seems to do the trick. However,
there is
>>>> one
>>>>>>> small glitch that I would like to fix.
>>>>>>> 
>>>>>>> If I have a configuration that should not be valid (e g I specified
>> an
>>>>>>> extender id that is not present) the instance should never be
valid.
>>>> But,
>>>>>>> when starting Karaf (both with "bin\karaf.bat" and "bin\karaf.bat
>>>>>> clean"),
>>>>>>> the instance becomes valid before it becomes invalid. It does
end up
>> in
>>>>>> the
>>>>>>> right state (invalid in this case) but for a short period of
time it
>> is
>>>>>>> valid which will cause a lot of things to happen in my code that
then
>>>>>> must
>>>>>>> be reversed when it becomes invalid.
>>>>>>> 
>>>>>>> I logged the sequence of events and it seems that the accept()
method
>>>> is
>>>>>>> called first. I will then set "intercepted=true". This immediately
>>>> makes
>>>>>>> the instance valid. Shortly thereafter getServiceReferences()
is
>>>> called.
>>>>>> I
>>>>>>> will then re-calculate the dependency requirements and when I
later
>>>>>>> invalidate the dependencies the instance will become valid.
>>>>>>> 
>>>>>>> So, there is a short time frame where the instance is valid although
>> it
>>>>>>> shouldn't be. How can I fix that?
>>>>>> 
>>>>>> This looks like a bug, as the dependency can be valid only if the
set
>> of
>>>>>> selected services is not empty. From what you say, it looks like
the
>>>>>> dependency is valid because the set of matching services is not empty.
>>>>>> 
>>>>> 
>>>>> Is there anything I can do to investigate this? Is it possible for you
>> to
>>>>> take a look if there is indeed a "gap" where this can happen?
>>>> 
>>>> My first guess would be in the ServiceReferenceManager coordinating the
>>>> interceptors.
>>>> 
>>>>> 
>>>>> I think that things are a little complicated since I also listen on
>>>>> configuration changes. I need to recalculate the matching services when
>>>> the
>>>>> configuration of the intercepted instance changes. When starting the
>>>>> container (Karaf), I get more than one configuration change and thus
>> the
>>>>> dependencies are invalidated more than once. What if the sequence were:
>>>>> 
>>>>> 1. Configuration change causing the dependencies to become invalidated
>>>>> 2. Accept. Will set intercepted to true
>>>>> 3. getServiceReferences which will calculate the required dependencies
>>>>> 4. Configuration change again causing the dependencies to become
>>>> invalidated
>>>>> 5. Accept. Will set intercepted to true
>>>>> 6. getServiceReferences which will calculate the required dependencies
>>>>> 
>>>>> Not sure if there is any point in which an instance could become valid
>>>> when
>>>>> it shouldn't.
>>>>> 
>>>>> I will also try to see if the problem could be the configuration
>> admin. I
>>>>> use file install for my configuration. I have a feeling that the first
>>>>> configuration being pushed is a default configuration and not the one
>>>> from
>>>>> the configuration file. Then that might explain it.
>>>>> 
>>>> 
>>>> Oh, that's an interesting hint. That's definitely possible.
>>>> 
>>>> Enjoy your vacations, mine are over....
>>>> 
>>>> 
>>>> Regards,
>>>> 
>>>> Clement
>>>> 
>>>>> 
>>>>>>> 
>>>>>>> From my point of view this is similar to a transaction. I do
not want
>>>> the
>>>>>>> instance to become valid before I have done all my "intercepting"
>> which
>>>>>> is
>>>>>>> after BOTH the accept() method AND the getServiceReferences()
method
>>>> have
>>>>>>> been called.
>>>>>> 
>>>>>> In theory, it is how it should work...
>>>>>> 
>>>>>>> 
>>>>>>> BTW I also noted that the "dependencies" member in
>>>>>>> the DefaultDependencyInterceptor class (I extend the
>>>>>>> DefaultServiceRankingInterceptor class) seems to contain duplicates
>> of
>>>> my
>>>>>>> dependency. The same DependencyModel instance occurs twice in
the
>> List.
>>>>>>> Seems like a bug to me. Perhaps the List should be a Set?
>>>>>> 
>>>>>> Definitely, could you open an issue ?
>>>>>> 
>>>>>> Clement
>>>>>> 
>>>>>>> 
>>>>>>> /Bengt
>>>>>> 
>>>>>> 
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>> 
>> 
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