How to safely write to multiprocessing.Manager().dict()?

Question

Python

I want to use a dictionary like multiprocessing.Manager().dict() to write data in each running process. Each process must check if there is a value with the given key, if not, then create an entry. Do I need to use multiprocessing.Lock() before reading/writing or is this dictionary type thread safe? If the dictionary is thread-safe, is it best to create values ​​in one call via setdefault? Thank you.
UPDATE: I checked how setdefault works without lock(), it turned out that it is twice as slow as normal writing with lock(), what is the reason for such slow work?