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From "Felix Meschberger (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FELIX-3577) Refactor helpers and service trackers
Date Thu, 05 Jul 2012 12:27:34 GMT

    [ https://issues.apache.org/jira/browse/FELIX-3577?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13407042#comment-13407042
] 

Felix Meschberger commented on FELIX-3577:
------------------------------------------

The last change introduced a race condition between service registration (particularly ManagedServiceFactory)
and concurrent configuration update (example uses ManagedServiceFactory):

T2: creates/updates configuration
 - create factory config
 - update factory config
     - store config
     - update internal factory map
 - T2 preempted

T1: register service
 - ServiceTracker calls addingService
 - gets the service PIDs
 - for each PID:
   - find config
   - check config (ignoring new configs)
   - schedule update
 - T1 preempted

T2: picks up again to continue persisting the configuration
     - internally set config non-new
     - schedule update

The configuration update (on the ConfigurationUpdateThread) in T2 may not find a registered
service because addingService in T1 has not completed yet and thus the service is not yet
officially known by the ServiceTracker, which in turn is used by the ConfigurationUpdate to
look for targets to configure.

The configuration update due to T1 fails because the ManagedServiceFactoryUpdate constructor
may find a configuration but ignores it because it is still new (Configuration.update(Dictionary)
in T2 has not yet completed its work). On the ConfigurationUpdateThread the ManagedServiceFactoryUpdate
does nothing because there is no valid configuration to provide.
                
> Refactor helpers and service trackers
> -------------------------------------
>
>                 Key: FELIX-3577
>                 URL: https://issues.apache.org/jira/browse/FELIX-3577
>             Project: Felix
>          Issue Type: Improvement
>          Components: Configuration Admin
>    Affects Versions: configadmin-1.4.0
>            Reporter: Felix Meschberger
>            Assignee: Felix Meschberger
>             Fix For: configadmin-1.6.0
>
>
> The ConfigurationManager class currently hosts quite a number of inner classes to help
with its tasks. A few of these classes have overlapping functionality which makes it hard
to easily implement targeted PIDs these functionalities should be better aligned:
>  * ManagedService[Factory]Tracker don't really get the services but maintain a map of
PIDs and assigned
>       configurations (most importantly the targeted PID and configuration modification
counter)
>  * ManagedService[Factory] callbacks are also executed by the tracker classes
>  * The ManagedService[Factory]Helper classes are renamed to [Factory]ConfigurationHelper
since
>        they are helpers to convey configuration to ManagedService[Factory] services through
the respective
>        trackers.
>  * The ServiceHolder class is replaced by the ConfigurationMap class managed by the trackers.

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