mq_notify man page on SuSE

Man page or keyword search:  
man Server   14857 pages
apropos Keyword Search (all sections)
Output format
SuSE logo
[printable version]

MQ_NOTIFY(3)		   Linux Programmer's Manual		  MQ_NOTIFY(3)

NAME
       mq_notify - register for notification when a message is available

SYNOPSIS
       #include <mqueue.h>

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

       Link with -lrt.

DESCRIPTION
       mq_notify()  allows  the	 calling process to register or unregister for
       delivery of an asynchronous notification when a new message arrives  on
       the empty message queue referred to by the descriptor mqdes.

       The  notification argument is a pointer to a sigevent structure that is
       defined something like the following:

	   union sigval {	   /* Data passed with notification */
	       int     sival_int;	  /* Integer value */
	       void   *sival_ptr;	  /* Pointer value */
	   };

	   struct sigevent {
	       int	    sigev_notify; /* Notification method */
	       int	    sigev_signo;  /* Notification signal */
	       union sigval sigev_value;  /* Data passed with
					     notification */
	       void	  (*sigev_notify_function) (union sigval);
					  /* Function for thread
					     notification */
	       void	   *sigev_notify_attributes;
					  /* Thread function attributes */
	   };

       If notification is a non-NULL pointer, then mq_notify()	registers  the
       calling	process	 to  receive  message  notification.  The sigev_notify
       field of the sigevent to which notification points specifies how	 noti‐
       fication	 is to be performed.  This field has one of the following val‐
       ues:

       SIGEV_NONE
	      A "null" notification: the calling process is registered as  the
	      target  for notification, but when a message arrives, no notifi‐
	      cation is sent.

       SIGEV_SIGNAL
	      Notify  the  process  by	sending	 the   signal	specified   in
	      sigev_signo.  If the signal is caught with a signal handler that
	      was registered using the sigaction(2) SA_SIGINFO flag, then  the
	      following	 fields	 are  set  in  the siginfo_t structure that is
	      passed as the second argument of the handler: si_code is set  to
	      SI_MESGQ;	 si_signo is set to the signal number; si_value is set
	      to the value specified in notification->sigev_value;  si_pid  is
	      set  to the PID of the process that sent the message; and si_uid
	      is set to the real user ID of the	 sending  process.   The  same
	      information  is  available  if the signal is accepted using sig‐
	      waitinfo(2).

       SIGEV_THREAD
	      Deliver	   notification	     by	      invoking	     notifica‐
	      tion->sigev_notify_function  as  the  start  function  of	 a new
	      thread.  The function is invoked with  notification->sigev_value
	      as  its sole argument.  If notification->sigev_notify_attributes
	      is not NULL, then it should point to a pthread_attr_t  structure
	      that defines attributes for the thread.

       Only  one process can be registered to receive notification from a mes‐
       sage queue.

       If notification is NULL, and the calling process	 is  currently	regis‐
       tered  to receive notifications for this message queue, then the regis‐
       tration is removed; another process can then register to receive a mes‐
       sage notification for this queue.

       Message	notification  only  occurs  when a new message arrives and the
       queue was previously empty.  If the queue was not  empty	 at  the  time
       mq_notify()  was	 called, then a notification will only occur after the
       queue is emptied and a new message arrives.

       If another process or thread is waiting to read a message from an empty
       queue  using  mq_receive(3), then any message notification registration
       is ignored: the message is delivered to the process or  thread  calling
       mq_receive(3),  and  the	 message  notification registration remains in
       effect.

       Notification occurs once: after a notification is delivered, the	 noti‐
       fication	 registration is removed, and another process can register for
       message notification.  If the notified process wishes  to  receive  the
       next  notification, it can use mq_notify() to request a further notifi‐
       cation.	This should be done before emptying all unread	messages  from
       the  queue.  (Placing the queue in non-blocking mode is useful for emp‐
       tying the queue of messages without blocking once it is empty.)

RETURN VALUE
       On success mq_notify() returns 0; on error, -1 is returned, with	 errno
       set to indicate the error.

ERRORS
       EBADF  The descriptor specified in mqdes is invalid.

       EBUSY  Another  process	has already registered to receive notification
	      for this message queue.

       EINVAL notification->sigev_notify is not one of the  permitted  values;
	      or  notification->sigev_notify  is  SIGEV_SIGNAL	and  notifica‐
	      tion->sigev_signo is not a valid signal number.

       ENOMEM Insufficient memory.

CONFORMING TO
       POSIX.1-2001.

EXAMPLE
       The following program registers a notification request for the  message
       queue named in its command-line argument.  Notification is performed by
       creating a thread.  The thread executes a function which reads one mes‐
       sage from the queue and then terminates the process.

       #include <pthread.h>
       #include <mqueue.h>
       #include <assert.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       #define handle_error(msg) \
	   do { perror(msg); exit(EXIT_FAILURE); } while (0)

       static void		       /* Thread start function */
       tfunc(union sigval sv)
       {
	   struct mq_attr attr;
	   ssize_t nr;
	   void *buf;
	   mqd_t mqdes = *((mqd_t *) sv.sival_ptr);

	   /* Determine max. msg size; allocate buffer to receive msg */

	   if (mq_getattr(mqdes, &attr) == -1)
	       handle_error("mq_getattr");
	   buf = malloc(attr.mq_msgsize);
	   if (buf == NULL)
	       handle_error("malloc");

	   nr = mq_receive(mqdes, buf, attr.mq_msgsize, NULL);
	   if (nr == -1)
	       handle_error("mq_receive");

	   printf("Read %ld bytes from MQ\n", (long) nr);
	   free(buf);
	   exit(EXIT_SUCCESS);	       /* Terminate the process */
       }

       int
       main(int argc, char *argv[])
       {
	   mqd_t mqdes;
	   struct sigevent not;

	   assert(argc == 2);

	   mqdes = mq_open(argv[1], O_RDONLY);
	   if (mqdes == (mqd_t) -1)
	       handle_error("mq_open");

	   not.sigev_notify = SIGEV_THREAD;
	   not.sigev_notify_function = tfunc;
	   not.sigev_notify_attributes = NULL;
	   not.sigev_value.sival_ptr = &mqdes;	 /* Arg. to thread func. */
	   if (mq_notify(mqdes, ¬) == -1)
	       handle_error("mq_notify");

	   pause();    /* Process will be terminated by thread function */
       }

SEE ALSO
       mq_close(3),   mq_getattr(3),  mq_open(3),  mq_receive(3),  mq_send(3),
       mq_unlink(3), mq_overview(7)

COLOPHON
       This page is part of release 3.15 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2008-08-13			  MQ_NOTIFY(3)
[top]

List of man pages available for SuSE

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net