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mq_notify(3)
NAME
  mq_notify - Attaches a request for asynchronous signal notification to a
  message queue (P1003.1b)

SYNOPSIS
  #include <mqueue.h>

  int mq_notify (
  mqd_t mqdes,
  const struct sigevent *notification);

LIBRARY
  Realtime Library (librt.so, librt.a)

PARAMETERS
  mqdes
      Specifies a message queue descriptor.

  *notification
      Specifies a signal to be sent when the specified queue accepts a
      message. If the notification argument is NULL, and the process has
      previously attached a notification request to the message queue with
      this mqdes argument, the notification request is detached and the queue
      is available for another process to attach a notification request.

DESCRIPTION
  The mq_notify function attaches a request for asynchronous signal
  notification to a message queue for the calling process. Following a call
  to this function, the specified signal is sent to the calling process when
  the queue transitions from empty to non-empty. Two or more processes cannot
  attach notification requests to the same queue at the same time.

  If a process has attached a notification request and any process is blocked
  in the execution of the mq_receive function waiting to receive a message
  when a message arrives at the queue, then the appropriate mq_receive
  function is completed and the notification remains pending.

  When the notification has been sent, the registration is canceled. In
  effect, it is a one-shot notification and must be re-registered if
  required.

  Note that the POSIX IPC functions are not reentrant with respect to
  signals.  For example, if your application were to use a signal to notify
  it that a queue has become non-empty and then attempt to call mq_receive
  from the signal handler, the signal handler must reside in a thread other
  than the tread that called mq_send. Otherwise, a deadlock on internal locks
  would occur.

RETURN VALUES
  On successful completion, the function returns the value 0 (zero);
  otherwise, the function returns the value -1 and sets errno to indicate the
  error.

ERRORS
  The mq_notify function fails under the following conditions:

  [EBADF]
      The mqdes argument is not a valid message queue descriptor.

  [EBUSY]
      A process has already attached to this message queue for asynchronous
      notification, or the calling process attempted to cancel a request that
      was attached by another process.

  [EINVAL]
      The requested signo is invalid, or the sigev_notify field of the
      notification structure does not equal SIGEV_SIGNAL.

SEE ALSO
  Functions: mq_open(3), mq_send(3)

  Guide to Realtime Programming

Index for Section 3

Alphabetical listing for M

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