Objective-C : Invalid mutex value

In programming, mutexes (mutual exclusions) are used to synchronize simultaneously running threads, and only the thread that owns the mutex can release it, i.e. transfer to the marked state.

The purpose of the mutex is to protect the object from access to other threads, other than the one that owns the mutex. In this case, only one thread can own an object protected by a mutex at any particular time.

Uninitialized or nil value used as mutex. No thread safety is guaranteed.