Read/write locks are recursive

The i5/OS implementation of read/write locks provides a recursive behavior not only for shared read locks (as the thread standard specifies), but for exclusive write locks as well. The following statements apply to read/write locks on i5/OS:

• A thread can acquire any number of shared read locks on a read/write lock. Each successful shared read lock that is acquired must be released by a call to pthread_rwlock_unlock().
• A thread can acquire any number of exclusive write locks on a read/write lock. Each successful exclusive write lock that is acquired must be released by a call to pthread_rwlock_unlock().