Hi > http://issues.apache.org/jira/browse/JCR-2443.
Unfortunately this bug doesn't have a test case. Also I didn't find a thread dump that shows what the problem was exactly. I can't say what was the problem there. Observation is definitely an area where synchronization can potentially lead to deadlocks. Maybe observation needs to use its own session(s) so that it can't block. This is not a new issue however: most writes are already synchronized (not all writes however). I'm hesitant to change synchronization with the current implementation: doing that would very likely lead to Java level deadlocks. We need to make sure synchronization is always done on the same level, and in the same order. With the current implementation, that's challenging. Of course performance and concurrency is very important. But the current approach (mutable data structures, some writes are synchronized) is quite dangerous. Instead, immutable data structures should be used, at least for values and objects in the shared cache. Everything else should be properly synchronized if mutable, or - if that's too slow - the proper data structures should be used, for example ConcurrentHashMap, CopyOnWriteArrayList, CopyOnWriteArraySet. Regards, Thomas
