I'd like to report an errata: On page 111 of the February 1998 edition (which I purchased last week at Bookstar), the text states that _POSIX_THREAD_ATTR_PRIORITY_SCHEDULING determines whether a system implements priority scheduling. Page 150 restates this, referring to
the compile-time constant _POSIX_THREAD_PRIORITY_SCHEDULING. An examination of my IRIX 6.4 /usr/include/unistd.h file
indicates that the latter is used. A grep of the entire /usr/include subtree turned up no uses of _POSIX_THREAD_ATTR_PRIORITY_SCHEDULING.