Manual Pages for UNIX Operating System command usage for man msgsnd

System Calls                                            msgsnd(2)



NAME
     msgsnd - message send operation

SYNOPSIS
     #include 

     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 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:

         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.



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System Calls                                            msgsnd(2)



         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 pro-
               cess. 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.




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System Calls                                            msgsnd(2)



     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  attri-
     butes:



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | Standard                    | See standards(5).           |
    |_____________________________|_____________________________|


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.










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