If you need really good synchronization primitives while Glibc is fixing things then I've had a lot of success with *NSYNC https://github.com/google/nsync which is what Cosmopolitan Libc uses to implement pthread_cond_t.
Yes. *NSYNC was built by Mike Burrows. The guy famous for building Chubby and Altavista. You wouldn't think it though, considering the project only has 188 stars.