[
https://issues.apache.org/jira/browse/FELIX-3456?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13278389#comment-13278389
]
Felix Meschberger commented on FELIX-3456:
------------------------------------------
ComponentContext.enable and .disable must set the enabled and disabled state
immediately but any action resulting from this must be asynchronous. The
current implementation violates the spec in that the status is not immediately
set. But the actual action occurrs asynchronously as mandated in section
112.5.1.
This is to my knowledge the only explicit notion of timing. Particularly there
is no requirement to either activate or deactivate components synchronously or
asynchronously on SCR or bundle startup or stop. Experience showed me that any
attempt to make these asynchronous (remember we had them both asynchronous at
one point in time) had issues.
Stopping components asynchronously on bundle or SCR shutdown or service
unregistration causes problems (been there done that).
Starting components asynchronously causes non-deterministic startup behaviour
while not being much more stable with respect to deadlocks.
So, I really don't want to change that.
If we need to fix something to make ComponentContext.enable and .disable more
spec compliant (setting the state immediately while doing the action
asynchronously), we can do so....
> 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, FELIX-3456-5.diff, FELIX-3456-5a.diff,
> FELIX-3456-5b.diff, FELIX-3456-fmeschbe.patch
>
>
> 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
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators:
https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
