Re: [Jrdf-general] Concurrent graph access

[Benedikt F. <b.f...@gm...>]

Hi,

I have done some testing and it turns out that neither sparql queries
nor graph changes can be done concurrently at the moment...

I tried using a simple ReadWriteLock (i.e. exclusive write access,
multiple read access), using
java.util.concurrent.locks.ReentrantReadWriteLock, but I still got
bunch of exceptions (not only the ConcurrentModificationException
which I mentioned earlier; for a list including stacktraces see
attachment).

When I switched to using a fully exclusive lock (i.e. only one thread
has access no matter what the thread does), the whole thing started to
behave... Probably at the cost of performance (not verified).

I also started using separate graph instances for all graph access
(even the sparql queries); this did not seem to change anything, so
there might be a bug in there somewhere like you mentioned.

Ben

On 29 March 2010 23:31, Benedikt Forchhammer <b.f...@gm...> wrote:
> Hi,
> Thanks for the quite reply!
>
> On 29 March 2010 22:07, Andrew Newman <and...@gm...> wrote:
>> Yep, it's safest to create a graph for each thread - but I'm not sure
>> that's the error you're getting - if you're just doing queries against
>> the graph you should get a concurrent modification error - it could be
>> a bug in the OptimizingQueryEngine.
>
> I think it was actually a modification and a query at the same time...
>
>> You could implement your own locking or I would do it is use something
>> like Spring's transaction management to add transactions around
>> methods (see the FooService):
>> http://static.springsource.org/spring/docs/3.0.x/reference/html/transaction.html
>
> Thanks for the link. I am a bit hesitant of adding another "big
> library" to my project, but I will have a look...
> For a start I think I am going to try to use separate graphs for
> writes and see if that solves the problem...
>
> Thank you,
> Ben
>