rwlock.h - How to use it *PROPERLY*?

ftp://ftp.qnx.com/usr/free/qnx4/os/libs/sync.tgz

I have a group of file-reading processes and one file-updater process.
How do I use rwlock.h to solve the access conflicts?

The readers open several files, the writer updates the same set of files.
Is rwlock the right tool to use?

Tony.