The pthread_* manpages are really, really sparse in lots of areas; for instance, for all I can tell, the various pthread_attr_set* are completely undocumented — that is, I can’t figure out what each of the various types of attributes actually do!
The only other useful sources of information I’ve found, than the manpages, are the famous pthreads tutorial and pthreads-win32 documentation… neither of which helps in this particular case, and many others.
Where else can I go for information about what pthreads’ various functions actually do, short of digging into an open-source implementation (which is quite likely over my head)?
Perhaps the actual spec for POSIX threads would help?
http://www.opengroup.org/onlinepubs/000095399/functions/xsh_chap02_09.html
I’ve generally found that if I want to know how something works in POSIX-land, it’s easiest to go straight to the spec.