[jhdevos]

> Where can i find more information regarding this.

The C++ standard, of course :) But if you prefer some lighter reading, either http://www.cplusplus.com/reference/mutex/mutex/unlock/ or http://en.cppreference.com/w/cpp/thread/mutex/unlock explain what happens, in slightly different ways. I usually prefer the cppreference version, because it uses terminology from the standard more consistently, but there is no harm in reading multiple explanations about difficult concepts like these :)

I'd repeat the explanation here, but I think you'd best be served by reading one of the two links above.