52.6. Message Notification

A feature that distinguishes POSIX message queues from their System V counterparts is the ability to receive asynchronous notification of the availability of a message on a previously empty queue (i.e., when the queue transitions from being empty to nonempty). This feature means that instead of making a blocking mq_receive() call or marking the message queue descriptor nonblocking and performing periodic mq_receive() calls (“polls”) on the queue, a process can request a notification of message arrival and then perform other tasks until it is notified. A process can choose to be notified either via a signal or via invocation of a function in a separate thread.

Note:

The notification feature of POSIX message queues is similar to the notification facility that we described for POSIX timers in Section 23.6. (Both of these APIs originated in POSIX.1b.)