| MQ_NOTIFY(3) | Library Functions Manual | MQ_NOTIFY(3) | 
mq_notify —
#include <mqueue.h>
int
  
  mq_notify(mqd_t
    mqdes, const struct
    sigevent *notification);
NULL, this function will register the calling process
  to be notified of message arrival at an empty message queue associated with
  the specified message queue descriptor, mqdes. The
  notification specified by the notification argument will
  be sent to the process when the message queue transitions from empty to
  non-empty. At any time, only one process may be registered for notification by
  a message queue. If the calling process or any other process has already
  registered for notification of message arrival at the specified message queue,
  subsequent attempts to register for that message queue fails.
If notification is
    NULL and the process is currently registered for
    notification by the specified message queue, the existing registration will
    be removed.
When the notification is sent to the registered process, its registration will be removed. The message queue will then be available for registration.
If a process has registered for notification of message arrival at
    a message queue and some thread is blocked in
    mq_receive() waiting to receive a message when a
    message arrives at the queue, the arriving message will satisfy the
    appropriate mq_receive(). The resulting behavior is
    as if the message queue remains empty, and no notification will be sent.
mq_notify() function returns the value 0 if
  successful; otherwise the value -1 is returned and the global variable
  errno is set to indicate the error.
mq_notify() function fails if:
| June 7, 2010 | NetBSD 10.0 |