Sun Microsystems, Inc. gratefully acknowledges The Open Group for
permission to reproduce portions of its copyrighted documentation.
Original documentation from The Open Group can be obtained online at
http://www.opengroup.org/bookstore/.
The Institute of Electrical and Electronics Engineers and The Open
Group, have given us permission to reprint portions of their
documentation.
In the following statement, the phrase ``this text'' refers to portions
of the system documentation.
Portions of this text are reprinted and reproduced in electronic form
in the SunOS Reference Manual, from IEEE Std 1003.1, 2004 Edition,
Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6,
Copyright (C) 2001-2004 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy
between these versions and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html.
This notice shall appear on any product containing this material.
The contents of this file are subject to the terms of the
Common Development and Distribution License (the "License").
You may not use this file except in compliance with the License.
You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
or http://www.opensolaris.org/os/licensing.
See the License for the specific language governing permissions
and limitations under the License.
When distributing Covered Code, include this CDDL HEADER in each
file and include the License file at usr/src/OPENSOLARIS.LICENSE.
If applicable, add the following below this CDDL HEADER, with the
fields enclosed by brackets "[]" replaced with your own identifying
information: Portions Copyright [yyyy] [name of copyright owner]
Portions Copyright (c) 1992, X/Open Company Limited. All Rights Reserved.
Copyright (c) 2003, Sun Microsystems, Inc. All Rights Reserved.
#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 message, 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:
The number of bytes already on the queue is equal to msg_qbytes. See Intro(2).
The total number of messages on the queue would exceed the maximum allowed by the system. See NOTES.
These actions are as follows:
If (msgflg&IPC_NOWAIT) is non-zero, the message will not be sent and the calling process will return immediately.
If (msgflg&IPC_NOWAIT) is 0, the calling process will suspend execution until one of the following occurs:
The condition responsible for the suspension no longer exists, in which case the message is sent.
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.
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)):
msg_qnum is incremented by 1.
msg_lspid is set equal to the process ID of the calling process.
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).
The message cannot be sent for one of the reasons cited above and (msgflg&IPC_NOWAIT) is non-zero.
The message queue identifier msgid is removed from the system.
The msgsnd() function was interrupted by a signal.
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.
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 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.