Potential concurrency issue during Component Service registration
-----------------------------------------------------------------
Key: FELIX-3317
URL: https://issues.apache.org/jira/browse/FELIX-3317
Project: Felix
Issue Type: Bug
Components: Declarative Services (SCR)
Affects Versions: scr-1.6.0
Reporter: Felix Meschberger
Assignee: Felix Meschberger
Fix For: scr-1.6.2
In our Sling-based application we saw the following behavior: The Sling
ResourceResolverFactory is a component being activated. Yet every now and then
a field of that component seems to become null which is not expected for an
activated ResourceResolverFactory component and thus causes a
NullPointerException.
Upon inspection I saw, that for the same Declarative Services component two
Services have been registered where only one was actually expected.
Turns out that consumers of the ResoureResovlerFactory where all bound to the
same service. The component on the other hand has been cycled due to a
configuration update. So one service is backed by a deactivated component
(whose field has been reset to null already) and the other service is live.
The problem is that the service backed by the deactivated method has not been
unregistered and thus all consumers are hooked up to the deactivated instance
causing all sorts of problems ...
This is what most probably happens in the AbstractComponentManager:
* T1 Unsatisfied.activate has set the state to Active already before
calling registerService
* T1 registerService is called but the service registration field
field is not assigned yet
during registerService ServiceListeners are called
* T2 A Configuration update comes in and Satisfied(Active).deactivate
is called
* T2 calls unregisterComponentService; does nothing because the
service registration field is not assigned
* T2 destroys component
* T1 assigns field from service registration
As a result the deactivated object's service registration may be unregistered
later when the component is cycled again and the second service registration
will only be unregistered when the providing bundle is restarted.
--
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
