Obviously the canonical use of semaphores is to ration access to a
finite number of resources, say hard disks or memory buffers.  It has
occurred to me that a semaphore could, in theory, also be used to
ration permission to send messages in a TCP-like protocol, where
messages must be acknowledged and sending is permitted only when the
number of unacknowledged messages is less than an arbitrary window
value.  Would such a use be categorized as a legitemate use or an
unjustified abuse of a semaphore?