This chapter describes POSIX message queues, which allow processes to exchange data in the form of messages. POSIX message queues are similar to their System V counterparts, in that data is exchanged in units of whole messages. However, there are also some notable differences:
POSIX message queues are reference counted. A queue that is marked for deletion is removed only after it is closed by all processes that are currently using it.
Each System V message has an integer type, and messages can be selected in a variety of ways using msgrcv(). By contrast, POSIX messages have an associated priority, and messages are always strictly queued (and thus received) in priority order.
POSIX message queues provide a feature ...