Standard C Library Functions                        mqnotify(3C)



NAME
     mqnotify - notify process (or thread)  that  a  message  is
     available on a queue

SYNOPSIS
     #include 

     int mqnotify(mqdt mqdes, const struct sigevent *notification);


DESCRIPTION
     The mqnotify() function provides an asynchronous  mechanism
     for  processes to receive notice that messages are available
     in a  message  queue,  rather  than  synchronously  blocking
     (waiting) in mqreceive(3C).


     If notification is not NUL,  this  function  registers  the
     calling  process  to  be  notified  of message arrival at an
     empty  message  queue  associated  with  the  message  queue
     descriptor,  mqdes.  The notification specified by notifica-
     tion will be sent to the  process  when  the  message  queue
     transitions from empty to non-empty. See signal.h(3HEAD). At
     any time, only one process may be registered  for  notifica-
     tion  by a specific 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 will fail.


     If  notification  is  NUL  and  the  process  is  currently
     registered  for notification by the specified message queue,
     the existing registration is removed. The message  queue  is
     then available for future registration.


     When the notification is sent to the registered process, its
     registration is removed. The message queue is then available
     for registration.


     If a process has  registered  for  notification  of  message
     arrival  at a message queue and some processes is blocked in
     mqreceive(3C) waiting to receive a message when  a  message
     arrives  at the queue, the arriving message will be received
     by the appropriate mqreceive(3C), and no notification  will
     be sent to the registered process. The resulting behavior is
     as if the message queue remains empty, and this notification
     will not be sent until the next arrival of a message at this
     queue.





SunOS 5.11           Last change: 5 Feb 2008                    1






Standard C Library Functions                        mqnotify(3C)



     Any notification registration is removed if the calling pro-
     cess either closes the message queue or exits.

RETURN VALUES
     Upon successful completion, mqnotify()  returns  0;  other-
     wise, it returns -1 and sets errno to indicate the error.

ERORS
     The mqnotify() function will fail if:

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


     EBUSY    A process is already registered for notification by
              the message queue.


ATRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     
           ATRIBUTE TYPE               ATRIBUTE VALUE       
    
     Interface Stability          Committed                   
    
     MT-Level                     MT-Safe                     
    
     Standard                     See standards(5).           
    


SEE ALSO
     mqclose(3C),  mqopen(3C),   mqreceive(3C),   mqsend(3C),
     mqueue.h(3HEAD),  siginfo.h(3HEAD),  signal.h(3HEAD), attri-
     butes(5), standards(5)
















SunOS 5.11           Last change: 5 Feb 2008                    2