I can't find manual pages for any of the functions declared in threads.h added in C11.
There is good documentation for them in https://en.cppreference.com/w/c/11
and in the glibc docs, however I would like to access information through man pages,
like most libc functions are available (e.g man printf).
Where can I find?
References for threads library functions are not well defined. Work seems needed to be done. You are right.