PRRWLock is not documented in MDC

Hi,

I found that there is inbuilt support for reader-writer lock in libnspr 
using PRRWLock.
I am confused about using it, because it is not documented in Mozilla 
Development Center.
Is there any problem in using it?
I found the documentation in 'prrwlock.h' in the include directory of nspr. 
But not in MDC.

One more question: How is this implemented? Using 1) Locks and conditional 
variables or, 2) Semaphores?
I want to avoid semaphores as much as possible.

The documentation of  PR_NewRWLock says: "If the lock cannot be created 
because of resource constraints, NULL is returned."
That is my second consideration. If it is implemented using semaphore, I can 
not create a lot of locks. I need at about 500 locks.

-- 
Regards,
Sabyasachi.