Re: [hibernate-dev] Hibernate Search 421 [Exceptions happening in backend are unnoticed]

Hi Sanne Thanks for the advice! I'll take a look at it. Cheers Amin On Sat, Jan 9, 2010 at 1:34 PM, Sanne Grinovero <sanne.grinovero(a)gmail.com&gt; wrote: > > Hi Amin, > I've been looking a bit in this, but didn't take any action as we > didn't discuss any strategy, so glad you join in propose something. > I didn't think of jms, it's ok we provide some way for the end user to > override whatever we provide, but I think we should just provide > the basic stuff: logging the error or propagate it back when possible. > And then add some extensibility like plugin loading the usual way. > > Originally (Hibernate Search 3.0.x) the changes made to different > indexes were serialized, so when using the "sync" backend the same > process would have applied changes to the index and, in case of > exceptions, this would have been propagated up to user's code making > it impossible to go unnoticed, or at least moving responsibility of > handling it to the developer. > When using the "async" mode for backend a different thread would have > handled the indexwriter, so in case of an exception the error would > have killed the separate thread, go unnoticed, and as we use a > ThreadPool a new thread would have been spawned to replace the failed > one. > > Since Search 3.1.x both "sync" and "async" use a separate thread - to > be able to apply changes to different indexes in parallel - so > exceptions are going unnoticed by user code even in "sync" mode. Look > into "run" method of > org.hibernate.search.backend.impl.lucene.LuceneBackendQueueProcessor, > it creates a org.hibernate.search.backend.impl.lucene.QueueProcessors > where most of this logic resides. > This impl will use either runAllAsync() or runAllWaiting() depending > on backend configuration (async/sync). The Async version just > schedules the different tasks, the sync one is going to do the same > but will wait for all of them to have finished before returning > control, making sure to implement the sync behaviour even while using > several threads to perform it. I was inspired by > > java.util.concurrent.AbstractExecutorService.invokeAll(Collection<Callable<T>> > tasks), as mentioned in code comments, which is ignoring > ExecutionException, so this empty catch block should be used now to do > something. > > I'd suggest to provide this defaults: > > * for sync backend: >   by default: rethrow the exception (like old behaviour) >   configurable alternative: log it > > * for async backend: >   log it (it's not useful to rethrow as nobody is listening on it) > > To handle these cases only you would add the log statement, an rethrow > it, fixing the QueueProcessors code. > To give full control to the end user of what to do, I'd suggest to let > him specify an implementationf of > java.lang.Thread.UncaughtExceptionHandler > and so we can set that on the thread. > The backend is using the default JVM "Executors.newFixedThreadPool( 1 > );"  (initialized at > org.hibernate.search.backend.impl.lucene.PerDPResources:51) > but we could change that to use the Search Executor factory > "org.hibernate.search.batchindexing.Executors" I later added for the > batchbackend. > The nice thingy for this Executor is that it customizes the thread > names so you can easily spot Search's threads in monitoring/debugging > tools; > we could have a setUncaughtExceptionHandler( userImplementation ) in > org.hibernate.search.batchindexing.Executors:85. > If you change it there, the same handler would be used to manage > errors in the batch indexer, so you solve both problems at once. > Our "log the error" implementation would be the nice default for an > exception handler, but still I'd like to make sure the user code will > get the error propagated when > using async mode. > > Cheers, > Sanne > > > 2010/1/9 Amin Mohammed-Coleman <aminmc(a)gmail.com&gt;: > > Hi All > > > > Emmanuel asked me to look at this issue (HSearch 421) where exceptions > > happening in backend process which are going unnoticed.  I was wondering > > if > > I could get some advice/thoughts on how to tackle the problem.    The > > issue > > mentioned providing the user the option to decide how to handle > > exceptions > > (for example queues, logs, etc), so I'm guessing there needs to be some > > custom option that the user will need to set up, maybe something like > > this? > > > > exception_handling_strategy=jms > > exception_handling_strategy_jms_queue= > > > > or if they wanted to log the exceptions: > > > > exception_handling_strategy=log > > > > or the user could create a custom class which implements a particular > > interface to handle exceptions > > > > exception_handling_strategy=custom > > exception_handling_custom_class=ExceptionHandling > > > > I could be completely wrong in the above approach and therefore would be > > grateful for any input. > > > > > > Cheers > > Amin > > _______________________________________________ > > hibernate-dev mailing list > > hibernate-dev(a)lists.jboss.org > > https://lists.jboss.org/mailman/listinfo/hibernate-dev > >