https://sungwookkang.com/1478 https://hwanseok-dev.github.io/python/python3-GIL/#gil%EC%9D%98-%EC%98%81%ED%96%A5%EC%9D%84-%EB%B0%9B%EC%A7%80-%EC%95%8A%EB%8A%94-%EA%B2%BD%EC%9A%B0
