[jira] [Commented] (FELIX-3456) Component ignores required static service addition when in Activating state

["David Jencks (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FELIX-3456?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13252637#comment-13252637 ] 

David Jencks commented on FELIX-3456:
-------------------------------------

After a very brief look I don't understand how this would result in correct behavior.  I think that if the state is "activating" we would need to wait until it gets back to "unsatisfied" and then try activateInternal again.  Otherwise won't we be binding the service but not checking if all the activation conditions are met?  What will check and get the service to activate if all the conditions are now met?  How about if there are 3 required services and we only have 2 of them?

I think we need some thread synchronization and if the state is not unsatisified or active wait until it gets to one of those before proceeding.

As I said this is after a very brief look, please think carefully before agreeing with me :-)
                
> Component ignores required static service addition when in Activating state
> ---------------------------------------------------------------------------
>
>                 Key: FELIX-3456
>                 URL: https://issues.apache.org/jira/browse/FELIX-3456
>             Project: Felix
>          Issue Type: Bug
>          Components: Declarative Services (SCR)
>    Affects Versions:  scr-1.6.0
>         Environment: Using org.apache.felix.scr svn rev 1298268 on Mac
>            Reporter: Richard Ellis
>            Priority: Critical
>
> I have a component with two required static service references (A and B). In my scenario A and B are registered nearly simultaneously on different threads and this causes the DependencyManager to ignore the addition of one of these two services (B). This causes the component to remain unsatisfied and never activate, since the service that was ignored is not re-registered at any time and nothing subsequently causes the component to re-activate.
> This happens as follows:
> 12:30:59:317 Thread 1 - Registers Service B/257
> 12:30:59:320 Thread 2 - Registers Service A/258
> 12:30:59:320 Thread 2 - Dependency Manager: Adding Service A/258
> 12:30:59:321 Thread 2 - Dependency Manager: Service serviceA registered, activate component
> 12:30:59:321 Thread 2 - State transition : Unsatisfied -> Activating
> 12:30:59:321 Thread 2 - Activating component
> 12:30:59:321 Thread 1 - Dependency Manager: Adding Service B/257
> 12:30:59:321 Thread 2 - Dependency not satisfied: serviceB
> 12:30:59:321 Thread 1 - Dependency Manager: Added service serviceB is ignored for static reference <--- I believe we end up here because Thread 2 has moved the component from Unsatisfied to Activating and the reference is a static reference
> 12:30:59:321 Thread 2 - Not all dependencies satisified, cannot activate
> 12:30:59:321 Thread 2 - State transition : Activating -> Unsatisfied
> Because the addition of Service B has been ignored and serviceB is a required dependency my component then never activates even though my reqiured service is present.
> There is a comment in DependencyManager#serviceAdded method:
> // FELIX-1413: if the dependency is static and the component is
> // satisfied (active) added services are not considered until
> // the component is reactivated for other reasons.
> This suggests that the static service should only be ignored if the component is satisfied(active), which would be correct, but in this case the component is only activating (and will fail to activate because one of the two dependencies is not yet satisfied) and there is no check of state at this time.
> A simple fix would be to check the state of the component as well as if the service is static e.g.
> replace if ( m_dependencyMetadata.isStatic() )
> with if ( m_dependencyMetadata.isStatic() && m_componentManager.getState() == AbstractComponentManager.STATE_ACTIVE )
> This is an easy fix, but I guess may leave a small window where a static reference could get replaced while a component was still activating if another instance of the same service was registered on a different thread.
> There are other fixes that could be done by synchronizing more around service additions.
> Is anyone willing to make this fix or does anyone have any thoughts about this issue?
> Thanks

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