.\" $OpenBSD: msgsnd.2,v 1.11 2003/06/01 20:25:23 jmc Exp $ .\" $NetBSD: msgsnd.2,v 1.2 1997/03/27 08:20:36 mikel Exp $ .\" .\" Copyright (c) 1995 Frank van der Linden .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed for the NetBSD Project .\" by Frank van der Linden .\" 4. The name of the author may not be used to endorse or promote products .\" derived from this software without specific prior written permission .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\"/ .Dd August 17, 1995 .Dt MSGSND 2 .Os .Sh NAME .Nm msgsnd .Nd send a message to a message queue .Sh SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/ipc.h> .Fd #include <sys/msg.h> .Ft int .Fn msgsnd "int msqid" "const void *msgp" "size_t msgsz" "int msgflg" .Sh DESCRIPTION The .Fn msgsnd function sends a message from the message queue specified in .Fa msqid . .Fa msgp points to a structure containing the message. This structure should consist of the following members: .Bd -literal long mtype; /* message type */ char mtext[1]; /* body of message */ .Ed .Pp .Va mtype is an integer greater than 0 that can be used for selecting messages (see .Xr msgrcv 2 ) , .Va mtext is an array of bytes, with a size up to that of the system limit .Pq Dv MSGMAX . .Pp If the number of bytes already on the message queue plus .Fa msgsz is bigger than the maximum number of bytes on the message queue .Po Va msg_qbytes , see .Xr msgctl 2 .Pc , or the number of messages on all queues system-wide is already equal to the system limit, .Fa msgflg determines the action of .Fn msgsnd . If .Fa msgflg has .Dv IPC_NOWAIT mask set in it, the call will return immediately. If .Fa msgflg does not have .Dv IPC_NOWAIT set in it, the call will block until: .Bl -bullet .It The condition which caused the call to block does no longer exist. The message will be sent. .It The message queue is removed, in which case \-1 will be returned, and .Va errno is set to .Er EINVAL . .It The caller catches a signal. The call returns with .Va errno set to .Er EINTR . .El .Pp After a successful call, the data structure associated with the message queue is updated in the following way: .Bl -bullet .It .Va msg_cbytes is incremented by the size of the message. .It .Va msg_qnum is incremented by 1. .It .Va msg_lspid is set to the pid of the calling process. .It .Va msg_stime is set to the current time. .El .Sh RETURN VALUES Upon successful completion, 0 is returned. Otherwise, \-1 is returned and .Va errno is set to indicate the error. .Sh ERRORS .Fn msgsnd will fail if: .Bl -tag -width Er .It Bq Er EINVAL .Fa msqid is not a valid message queue identifier. .Pp The message queue was removed while .Fn msgsnd was waiting for a resource to become available in order to deliver the message. .Pp .Fa msgsz is less than 0, or greater than .Va msg_qbytes . .It Bq Er EACCES The calling process does not have write access to the message queue. .It Bq Er EAGAIN There was no space for this message either on the queue, or in the whole system, and .Dv IPC_NOWAIT was set in .Fa msgflg . .It Bq Er EFAULT .Fa msgp points to an invalid address. .It Bq Er EINTR The system call was interrupted by the delivery of a signal. .El .Sh SEE ALSO .Xr msgctl 2 , .Xr msgget 2 , .Xr msgrcv 2 .Sh HISTORY Message queues appeared in the first release of AT&T Unix System V. .Sh BUGS .Ox does not define the .Er EIDRM error value, which should be used in the case of a removed message queue.