Special care should be given to the way objects are created and destroyed in a multithreaded environment. Not every approach is safe, and it is quite simple to make a mistake that would cause occasional crashes.
The simplest way is to lock all access to an object. If you create it from a critical section, use it from a critical section and destroy it in a critical section, everything will work. This way, however, is very slow and error-prone, as it is quite simple to forget to lock something.
If you create the object before the background tasks are created, and destroy it after the background tasks are destroyed, everything would work, too. If this is a normal object on a non-ARC platform, you are just sharing a pointer ...
