Since commit e8662bea3133ba9dbb09b86c3abb1af39425e90d, we're using OSG functionality that contains an unfixed crash bug in version 3.2. The bug is fixed in version 3.4 (OSG commit 6351e5020371b0b72b300088a5c6772f58379b84)
Implement updateCache to delete unreferenced cached objects when they have not been referenced for a while.
Should be thread safe now.