msgsnd(2)							   System Calls 							 msgsnd(2)

NAME

       msgsnd - message send operation

SYNOPSIS

       #include <sys/msg.h>

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

DESCRIPTION

       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 message. The structure below is an example  of  what	this  user-defined
       buffer 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 execution until one of the following occurs:

	       o      The condition responsible for the suspension no longer exists, 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 EIDRM
		      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 respect 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.

RETURN VALUES

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

ERRORS

       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 system.

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

       EINVAL	 The value of msqid is not a valid message queue identifier, 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.

USAGE

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

ATTRIBUTES

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

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+

SEE ALSO

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

NOTES

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

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

SunOS 5.11							    11 Feb 2003 							 msgsnd(2)