Johan,
Thank you, that really helps. In my particular case I am finalizing my Neo4j
package for RingoJS. It is not a ServletContextListener so I can make
graphDb "final" in the JavaScript sense ({writable: false, value:
seal(graphDb)}).
graphDb is assigned at the moment of first import (require("...")) in
RingoJS which makes it something like an executable static import. graphDb
is never null until the shut down hook.
I'll post the link to the RingoJS package soon and I hope I can get more
advice if anyone sees any multi threading problems.
Thanks,
McKinley
On Tue, Jun 7, 2011 at 2:28 AM, Johan Svensson <jo...@neotechnology.com>wrote:
> Since it is volatile you could remove the synchronized on
> getGraphDatabase() but if your app depends on getting null graphdb
> when context has been destroyed you would have to rewrite the
> contextDestroyed to something like:
>
> public void contextDestroyed( ServletContextEvent event )
> {
> synchronized ( GraphDatabaseContext.class )
> {
> GraphDatabaseService neo = graphDb;
> graphDb = null;
> if ( neo != null ) neo.shutdown();
> }
> }
>
> What we really want is final but not possible to do here.
>
> -Johan
>
> On Tue, Jun 7, 2011 at 10:12 AM, McKinley <mckinley1...@gmail.com> wrote:
> > Johan,
> >
> > In that Servlet example is the synchronized get on the graphDb reference
> > still necessary on the ServletContextListener?
> >
> > Thanks,
> >
> > McKinley
> >
> > On Tue, Jun 7, 2011 at 1:03 AM, Johan Svensson <jo...@neotechnology.com
> >wrote:
> >
> >> Hi,
> >>
> >> You can assume all Neo4j APIs are thread safe. If something is not
> >> thread safe it will be explicitly stated in the javadocs.
> >>
> >> If you keep all state that has to be shared between threads in the
> >> graph and all other state thread local you don't have to perform any
> >> external (or extra) synchronization at all. If you have state that is
> >> not graph data and needs to be shared between threads keep that in
> >> separate synchronization blocks without invoking any mutating
> >> operations on the graph.
> >>
> >> Regards,
> >> Johan
> >>
> >> On Sat, Jun 4, 2011 at 7:22 PM, McKinley <mckinley1...@gmail.com>
> wrote:
> >> > I'm working with Neo4j as an EmbeddedGraphDatabase on a web server. It
> is
> >> > not Servlets, but the same multi threaded concerns apply. Is this
> >> > http://wiki.neo4j.org/content/Servlets_with_Neo4j still the most
> current
> >> > example of dealing with multi threaded concerns?
> >> >
> >> > I see many mentions on avoiding unnecessary uses of synchronized in
> the
> >> > current documentation at http://docs.neo4j.org/. Can those warnings
> in
> >> the
> >> > documentation have a simple multi threaded example included too?
> >> >
> >> > Thanks,
> >> >
> >> > McKinley
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