[Nepomuk] Crash in nepomukqueryservice when running multiple instances of QueryServiceClient

[Dario Freddi]

Hello people,

as I told Sebastian earlier today, I discovered a severe bug in 
nepomukqueryservice. With telepathy-kde, I need to run several 
QueryServiceClient (at least two) at the same time. Note that the application 
has a single thread and every call to each qsc is asynchronous (I'm always 
using sparqlQuery()).

If I instantiate and start more than a QSC, the dbus service crashes all the 
time when calling Soprano::Client::ClientModel::executeQuery() and accessing 
the mutex which is inside it. This situation is always reproducible in a short 
time when instantiating at least 3 QSC.

To test some stuff, I created a workaround that I attached. I created a queue 
that starts a query at a time, waits for its listing to finish, and then 
starts the other queries in queue. This works perfectly for the first round, 
but queryservice always crashes afterwards when trying to pick up changes. 
Probably such a solution needs to be implemented right in queryservice, 
letting one query at a time hit soprano.

If you want to test this yourself, you can apply this merge request: 
http://reviewboard.kde.org/r/3650/ which also includes my "workaround"

-- 
-------------------

Dario Freddi
KDE Developer
GPG Key Signature: 511A9A3B
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