assert rwlock covers

Informs LockLint of the existence of a hierarchical locking relationship. A readers-writer lock may be used in conjunction with other locks (mutex or readers-writer) in the following way to increase performance in certain situations:

• A certain readers-writer lock, called the cover, must be held while any of a set of other covered locks is held. That is, it is illegal (under these conventions) to hold a covered lock while not also holding the cover, with at least read access.

• While holding the cover for write access, you can access any variable protected by one of the covered locks without holding the covered lock. This works because it is impossible for another thread to hold the covered lock (since it would also have to be holding the cover). The time saved by not locking the covered locks can increase performance if there is not excessive contention over the cover.

  Using assert rwlock covers prevents LockLint from issuing error messages when a thread accesses variables while holding the cover for write access but not the covered lock. It also enables checks to ensure that a covered lock is never held when its cover is not.