[FELIX-3456] Component ignores required static service addition when in Activating state

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: scr-1.6.0
• Fix Version/s: scr-1.6.2
• Component/s: Declarative Services (SCR)
• Environment: Using org.apache.felix.scr svn rev 1298268 on Mac
• Assignee: David Jencks
• Reporter: Richard Ellis
• Created: 12/Apr/12 17:00
• Updated: 20/Nov/12 10:58
• Resolved: 05/Oct/12 18:42

Description

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