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From "Amichai Rothman (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DOSGI-160) RemoteServiceAdmin shuts itself down during startup
Date Sun, 24 Mar 2013 09:43:16 GMT

     [ https://issues.apache.org/jira/browse/DOSGI-160?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Amichai Rothman updated DOSGI-160:
----------------------------------

    Attachment: fix_activator_config_and_sync_issues.diff


These are the changes:

- fixed updated callback shutting down service right after it starts (when config is null),
causing service exports to fail sometimes. This is done by simply doing nothing when the configuration
is null, since the service is already started with default parameters when the bundle starts,
so there's no need to change anything when there is no new configuration to use.

- separated stop/start (when bundle is started or stopped) from init/uninit (setting up/tearing
down the services when configuration changes) - solves endless loop caused by start re-registering
the ManagedService, which re-triggers update, which calls start etc. ad infinitum. If there
is anything else in init/uninit that should actually be performed only once at bundle start/stop
(and not when configuration changes), feel free to move it into start/stop respectively.

- synchronized init/uninit/update (since update is called from another thread and so init/uninit
may be called concurrently with undefined results)

- added proper unregistering of managed service, just in case (and for consistency with how
the other two registered services are handled)

- added a few debug logs to be more informative and help follow the sequence of events

                
> RemoteServiceAdmin shuts itself down during startup
> ---------------------------------------------------
>
>                 Key: DOSGI-160
>                 URL: https://issues.apache.org/jira/browse/DOSGI-160
>             Project: CXF Distributed OSGi
>          Issue Type: Bug
>          Components: DSW
>    Affects Versions: 1.4
>         Environment: Oracle JDK 1.7.0_17, Karaf 2.3.1, DOSGi 1.4.0 (installed from Karaf
feature)
>            Reporter: Amichai Rothman
>         Attachments: fix_activator_config_and_sync_issues.diff
>
>
> Every once in a while (quite often) the service export fails. Looking through the logs,
I found the message "RemoteServiceAdmin Implementation is shutting down now" - during Karaf
startup! It appears that the RSA is started, services exported properly etc., but then it
suddenly commits suicide a few moments later with no other error or indication of who/what
initiated the shutdown or why.
> Further investigation shows the DSW Activator is getting a ConfigurationAdmin updated
event with null configuration (according to the OSGi specs, the callback is guaranteed to
be called - either with an existing configuration or with null if none is available). The
current implementation of the callback stops the bundle, shutting down the service and printing
the above log message, but when the configuration is null it does not start it back up, resulting
in the observed behaviour.
> There's also a race condition in the class since from my understanding of the specs the
updated callback is called asynchronously from a separate thread, and since it stops and possibly
starts the bundle, this might cause the start/stop methods to be run concurrently and more
than once (the bundle lifecycle start/stop along with the update-triggered start/stop).
> Finally, while debugging and attempting to fix this I came across a third related issue
- when the bundle is indeed started up again in the updated method (e.g. if removing the null
check or if a configuration is available), the start method then re-registers the ManagedService,
which causes the updated method to be called again, which restarts the bundle again, etc.
- in an infinite loop. In practice I saw the server hang with 100% CPU usage indefinitely,
and in a later session with a debugger the loop was confirmed.
> Attached is a fix for the 3 related issues - when applied together everything seems to
work as expected. I'm new to this project, so please correct anything I've missed.

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