krunner threads kservice

[Harald Sitter]

Hellos

whilest investigating a memleak I noticed that krunner threadweaves
its runners. those runners sometimes use kservice to do queries (e.g.
servicerunner). for servicerunner specifically this seems to run into
fairly unprotected code paths (I know appstreamrunner will run into
the same problem)

runner
-> KServiceTypeTrader::self()->query
-> defaultOffers()
-> KSycoca::self()->ensureCacheValid()
-> potentially starts a qelapsedtimer and closes the database while
another thread might be poking around in it?

if someone has time I think that could use with some looking into :/

HS