Hi, On Thu, Sep 29, 2011 at 2:09 PM, Markus Joschko <[email protected]> wrote: > I want to get some assumptions of mine clarified regarding the usage > of classes like Session and ResourceResolver in event handlers. > > 1. The jackrabbit session is not threadsafe > 2. ResourceResolvers are not threadsafe > 3. Event services (EventHandler, JobProcessor, > javax.jcr.observation.Eventlistener) can be called concurrently
All true AFAIK, ResourceResolvers are probably threadsafe by themselves but use JCR sessions which are not. Actually, reading from sessions from multiple threads is safe, it's writing concurrently that's not ok. > > -> Sessions and Resolvers should not be stored as instance members but > opened and closed in the in the process/handleEvent methods. If you're reading only you can use a session concurrently. If you're writing rarely you can synchronize on the session object when writing for example. > > If this is true, how expensive is the creation of a session? I read in > a blog, that the creation is considered expensive and wonder if it > makes more sense > to create the session new every time (and we have quite a lot of > events processed by the handlers), or to synchronize access to an > instance session? Jackrabbit session creation is cheap, the idea is that you can create a session on every HTTP request for example. IMO synchronizing might cause more performance and latency issues as creating new sessions as needed, but it depends on your usage patterns I guess. I'd start with whatever feels right and measure response times as needed. -Bertrand
