Previous post of properties explained about the lifetime qualifiers. Today post will have exciting stuff about the other qualifier and some concepts about where to used these qualifier. Threads and Properties: Suppose you are working in multithreaded environment and two thread want to access the same property at same time. Thread A want to write and thread B is in middle of reading the property name. What happen which value thread B will get. ? There are two qualifier which decide the behaviour in such condition. 1) atomic (Default) 2) nonatomic Atomic: 1) Default behaviour. 2) Ensure that one thread will access property or method at a time. (Inconsistency will be not there as atomicity). Thread B will get autorelease value always in the above case. 3) Does not ensure the thread safety of instance variable. Any other thread can access the instance variable bind to property. So instance variable in not thread safe ...