Ask HN: How do C11 threads compare to POSIX threads?

Some webpages claim that C11's threads.h header provides basically the same things as pthreads, just with slightly different interfaces. However, I've found that several helpful utilities, such as barriers and semaphores, are only in pthreads. Is there any comprehensive list of the differences between C11 threading and POSIX threading, including optional extensions? How do you choose between these libraries?