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msgsnd(2)			 System	Calls			     msgsnd(2)

       msgsnd -	message	send operation

       #include	<sys/msg.h>

       int msgsnd(int msqid, const void	*msgp, size_t msgsz, int msgflg);

       The msgsnd() function is	used to	send a message to the queue associated
       with the	message	queue identifier specified by msqid.

       The msgp	argument points	to a user-defined  buffer  that	 must  contain
       first  a	 field of type long int	that will specify the type of the mes-
       sage, and then a	data portion that will hold the	data bytes of the mes-
       sage.  The structure below is an	example	of what	this user-defined buf-
       fer might look like:

       struct  mymsg {
	       long  mtype;	/* message type	*/
	       char  mtext[1];	/* message text	*/

       The mtype member	is a non-zero positive type long int that can be  used
       by the receiving	process	for message selection.

       The  mtext member is any	text of	length msgsz bytes. The	msgsz argument
       can range from 0	to a system-imposed maximum.

       The msgflg argument specifies the action	to be taken if one or more  of
       the following are true:

	 o  The	 number	 of bytes already on the queue is equal	to msg_qbytes.
	    See	intro(2).

	 o  The	total number of	messages on the	queue would exceed the maximum
	    allowed by the system. See NOTES.

       These actions are as follows:

	 o  If	(msgflg&IPC_NOWAIT)  is	non-zero, the message will not be sent
	    and	the calling process will return	immediately.

	 o  If (msgflg&IPC_NOWAIT) is 0, the calling process will suspend exe-
	    cution until one of	the following occurs:

	      o	 The  condition	 responsible  for the suspension no longer ex-
		 ists, in which	case the message is sent.

	      o	 The message queue identifier msqid is removed from the	system
		 (see  msgctl(2)); when	this occurs, errno is set equal	to EI-
		 DRM and -1 is returned.

	      o	 The calling process receives a	signal that is to  be  caught;
		 in  this case the message is not sent and the calling process
		 resumes execution in the manner prescribed in sigaction(2).

       Upon successful completion, the following actions are  taken  with  re-
       spect to	the data structure associated with msqid (see intro(2)):

	 o  msg_qnum is	incremented by 1.

	 o  msg_lspid is set equal to the process ID of	the calling process.

	 o  msg_stime is set equal to the current time.

       Upon  successful	 completion, 0 is returned. Otherwise, -1 is returned,
       no message is sent, and errno is	set to indicate	the error.

       The msgsnd() function will fail if:

       EACCES	       Operation permission is denied to the calling  process.
		       See intro(2).

       EAGAIN	       The message cannot be sent for one of the reasons cited
		       above and (msgflg&IPC_NOWAIT) is	non-zero.

       EIDRM	       The message queue identifier msgid is removed from  the

       EINTR	       The msgsnd() function was interrupted by	a signal.

       EINVAL	       The value of msqid is not a valid message queue identi-
		       fier, or	the value of mtype is less than	1.

		       The value of msgsz is less than 0 or greater  than  the
		       system-imposed limit.

       The msgsnd() function may fail if:

	EFAULT	       The msgp	argument points	to an illegal address.

       The  value passed as the	msgp argument should be	converted to type void

       See attributes(5) for descriptions of the following attributes:

       |      ATTRIBUTE	TYPE	     |	    ATTRIBUTE VALUE	   |
       |Interface Stability	     |Standard			   |

       rctladm(1M), intro(2),  msgctl(2),  msgget(2),  msgrcv(2),  setrctl(2),
       sigaction(2), attributes(5), standards(5)

       The  maximum number of messages allowed on a message queue is the mini-
       mum enforced value of the process.max-msg-messages resource control  of
       the  creating  process  at  the time msgget(2) was used to allocate the

	See rctladm(1M)	and setrctl(2) for information	about  using  resource

SunOS 5.10			  11 Feb 2003			     msgsnd(2)


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