Wondering which language should I study concurrency/multithreading/PC?

https://www.udemy.com/courses/search/?src=ukw&q=concurrent++programming

I'm studying concurrency control in Operating Systems and Database Management Systems. I want to see them implemented. Things like semaphores, mutex, monitors, busy waiting solutions like test and set lock, compare and swap instruction.

Please recommend me a language to use. I unfortunately know only javascript well. I know tidbits of C and Python.