y</B>
is called when any thread holds <I>rwlock</I>. Attempting to destroy
an uninitialized read-write lock results in undefined behavior. 
</P>
<P>The <B>pthread_rwlock_init</B> function shall allocate any
resources required to use the read-write lock referenced by <I>rwlock</I>
and initializes the lock to an unlocked state with attributes
referenced by <I>attr</I>. If <I>attr</I> is NULL, the default
read-write lock attributes shall be used; the effect is the same as
passing the address of a default read-