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https://issues.apache.org/jira/browse/FELIX-3456?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael Fraenkel updated FELIX-3456:
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Attachment: FELIX-3456-1.1.diff
The first patch needs to synchronize access when retrieving the actual Service.
There is a race when a component is activated and then registers its service.
If you have multiple dependents, one of them can request the service before it
completes all binds. Logically, the transition to REGISTERED is not complete
until the service has completed registration.
> 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
> Attachments: FELIX-3456-1.1.diff, FELIX-3456-1.diff,
> FELIX-3456-3.diff, FELIX-3456-4.diff
>
>
> 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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