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From Christian Schneider <ch...@die-schneider.net>
Subject Re: Fwd: DOSGi - service not exported consistently
Date Thu, 21 Mar 2013 23:40:02 GMT
Can you open a jira issue to track this and attach the patch there?

Christian

On 20.03.2013 19:25, A. Rothman wrote:
>
> [The message body disappeared for some reason, resending...]
>
>
> Hi,
>
> While trying to use DOSGi (1.4.0, in Karaf 2.3.1) I came across some 
> serious issues, namely when starting up a fresh Karaf instance 
> repeatedly, only about 50% of the time the service actually got 
> exported (as verified with a browser pointing to the appropriate WSDL 
> URL). This is just on a single instance on a local host, before trying 
> to do anything remotely. I started investigating into the matter, 
> which required quite a lot of debugging and code reviewing, and found 
> various issues with the (strangely named?) TopologyManagerExport class 
> which seems to be at the heart of the matter. This took several 
> iterations and includes also non-critical cleanups I did along the way 
> - I'm attaching the final version I arrived at which hopefully 
> addresses the issues, though due to the law of clustering of bugs, I 
> wouldn't be surprised if there are other new or old bugs still lurking 
> there... any feedback and additional code reviews would be greatly 
> appreciated.
>
> Here is a summary of all the changes, big and small:
>
> - fixed typos in docs and logs.
> - fixed formatting to be more consistent and readable.
> - added debug logs to 
> RemoteServiceAdminLifeCycleListener.added/removed callbacks (this 
> proved the serious tracker bug below, but is also useful for general 
> debugging).
> - simplified shouldExportService returned boolean expression.
> - replaced iterations on map keys followed by a get of the 
> corresponding value with an iteration on Map.Entry (prevents 
> unnecessary lookups).
> - replaced map containsKey checks followed by get with a get followed 
> by null check (prevents unnecessary lookups, and theoretically race 
> conditions too).
> - fixed tracker misuse: when tracker callback (added) is called, the 
> tracker itself does not yet reflect the new state, so accessing 
> services (or size) on the tracker from within the callback will fail 
> to include the new service. Although the actual service export 
> triggered by the callback is performed on a separate thread, this 
> still leaves a race condition between the two which sometimes causes 
> the export to fail (with "No RemoteServiceAdmin available!" log). To 
> fix this, the newly added RSA is passed down the method chain to the 
> doExportService method explicitly. doExportService then uses the 
> reference if it is given, or if null (as when called from elsewhere), 
> uses the tracker to get the service list as it did in the past.
> - fixed exportService always overwriting a service's entry in 
> exportedServices with a new empty data structure - now it only does so 
> if it does not already exist.
> - fixed exportedServices inner maps to be created as synchronized maps 
> - previously doExportService wrapped it in a synchronized map on each 
> invocation, which results effectively in no synchronization, since the 
> synchronized wrapper map is local only so each thread accessing the 
> map uses a different lock. Also fixed other accesses of the inner maps 
> to be synchronized (Collections.synchronizedMap requires external 
> synchronization on it when being iterated, as specified in the docs).
> - fixed exports null check in doExportService (in the old code, 
> Collections.synchronizedMap never returns null; In the new code it 
> makes more sense.)
> - removed redundant remoteServiceAdminTracker null check in 
> doExportService (it is already used in the constructor, so can't be 
> null at this point).
> - added cast of null to String when calling getServiceReferences in 
> exportExistingServices, so that it will compile also with the OSGi 
> 4.3.0 and later API (which added an overloaded method accepting a 
> Class). Does not affect previous versions.
> - removed removeExportRegistration, removeExportReference and 
> remoteAdminEvent methods, all of which are both unused and have a 
> no-op implementation.
>
> Feel free to pick out the changes u like...
>
> In addition, I had a few related questions/thoughts, I hope someone 
> here can help with them:
>
> 1. Is DOSGi being updated to work with OSGi 4.3.0/Felix 4.x/Karaf 
> 2.3.x etc.? It seems to be slightly outdated. At a glance, it looks 
> like making it compile against OSGi 4.3.0 requires just a few 
> backward-compatible syntax changes, and hopefully the semantics have 
> not changed too much.
>
> 2. The website says on the Karaf feature page: "CXF DOSGi does not 
> work with Karaf 2.3.0", however it does not mention whether this 
> applies to 2.3.1 as well (is it a DOSGi issue or Karaf issue that 
> prevents it from working?), nor does it say anything about what the 
> problem is, where it might be relevant, or link to any issue in JIRA - 
> could someone in the know please update the text to be a bit more 
> informative? Also, is this indeed just an issue with installation via 
> the feature, or with compatibility between the projects/versions in 
> general regardless of installation method?
>
> 3. After all the fixes above, the export success rate is definitely 
> better than 50%, but still isn't 100% - every once in a while the 
> export still fails. Looking through the logs, I found the message 
> "RemoteServiceAdmin Implementation is shutting down now" - during 
> Karaf startup! I'm still not sure what exactly is going on, but 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. The 
> initial theory is that the dsw Activator might be getting a 
> ConfigurationAdmin updated event with null configuration, which would 
> trigger a shutdown - but I haven't yet confirmed that this is the 
> case, nor why it would happen or what the proper behavior in such a 
> case should be.
>
> I'm totally new to CXF and DOSGi (and pretty new to OSGi too), so 
> please forgive any silly mistakes or assumptions above... but I do 
> hope this will be useful in making it a better product and making it 
> work better out of the box :-)
>
> Thanks to anyone who read this far!
>
> Amichai
>
>
>


-- 
Christian Schneider
http://www.liquid-reality.de

Open Source Architect
http://www.talend.com


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