Using C++ file in Swift Project

I've added a C++ file to my project written in Swift. It only calculates some random numbers and also uses an vector array. It's wrapper is written in Objective-C. When I try to call functions from the cpp file the App crashes after some time. But there's a strange behavior, because it doesn't crash while executing the C++ code (it runs like I expect to), but when I load a navigation controller. This hasn't to do anything with either. The console shows this:

'pthread_mutex_lock(&mutex)' failed with error 'EINVAL'(22)

I googled this bug, but I don't really understand the problem in my case.