Solved

Message Q error

Posted on 2004-09-28
7
187 Views
Last Modified: 2010-04-21
working on message Q with a parent and child process and the Q is not being created, getting an Error # 38 on it.  This is the program:

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/msg.h>
#include <sys/ipc.h>
#include <errno.h>


struct myMessage
      {
            long int message_type;
            char some_text[3];
      };
      
int main()
{
      int messageQ;
      pid_t processNum= fork();            
      
      // create messageQ
      
      if(processNum==0)
      {   printf("child: create and send messQ, process=0 ");
            messageQ=getmsg((key_t)1234, 0666|IPC_CREAT);
            fprintf(stderr,"messageerror: %d\n",errno);
            printf("creatQ = %d ",messageQ);
            //create message
      
            struct myMessage message;
            message.message_type=0;
            message.some_text[0]='1';
            message.some_text[1]='2';
            message.some_text[2]='3';
      
            //send message
            msgsnd(messageQ,(void *)&message,3,0);
            printf("MSG sent ");
            printf("sentQ = %d ",messageQ);
      
      }
      
      if(processNum!=0)
      {      printf("Waiting ");
            printf("%d ",processNum);
            wait(10);
      }

      
      
      // create struct pointer to return results into
      int success = 0;
      if(processNum!=0)
      {      struct myMessage recievedMsg;
            success=msgrcv(messageQ, (void *)&recievedMsg,3, 0 ,0);
            printf("recQ = %d ",messageQ);
              printf("success: %d",success);

      }
      

      
      return 0;
      
}


0
Comment
Question by:johnduff
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
7 Comments
 
LVL 11

Accepted Solution

by:
cjjclifford earned 200 total points
ID: 12171297
I would guess that the messageQ would have to be created before the fork(), or at least the line:

messageQ=getmsg((key_t)1234, 0666|IPC_CREAT);

should be also in the parent block, before the msgrcv() call...

Also, the child and parent code blocks shouldn't flow into each other... currently, the child code runs straight into the parent logic - put in an else { } for the parent logic, rather than continually checking if this is the parent, just do it once...

what's happening now is the variable messageQ is only getting assigned to in the child, so the parent doesn't have a Q to connect to...
0
 
LVL 2

Author Comment

by:johnduff
ID: 12172245
when the getmsg() is called for the first time the messeageQ that is returned is -1, which I'm taking it to mean that the messageQ is not being created at all.  Tried moving that line before the fork and the only thing it fixes is that when the parent calls msgrcv() it's getting -1 returned as well, before it was getting a random int value.
0
 
LVL 2

Author Comment

by:johnduff
ID: 12172647
Tried to do just the msgget to create the message Q and it dosn't do anyhting, returns -1, please help if you can
0
 
LVL 2

Author Comment

by:johnduff
ID: 12173831
okay, i created a new file and just did the msgget() and for some reason now when i create a messageQ it returns 0 instead of -1, which means it was created.  so this is solved for now, i will post to this again if i come across a real problem and not just the computer being stupid.

John
0
 
LVL 11

Expert Comment

by:cjjclifford
ID: 12419170
From the author's first comment it looks like my answer did help a bit....
0

Featured Post

Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

The purpose of this article is to fix the unknown display problem in Linux Mint operating system. After installing the OS if you see Display monitor is not recognized then we can install "MESA" utilities to fix this problem or we can install additio…
The purpose of this article is to demonstrate how we can upgrade Python from version 2.7.6 to Python 2.7.10 on the Linux Mint operating system. I am using an Oracle Virtual Box where I have installed Linux Mint operating system version 17.2. Once yo…
In a recent question (https://www.experts-exchange.com/questions/29004105/Run-AutoHotkey-script-directly-from-Notepad.html) here at Experts Exchange, a member asked how to run an AutoHotkey script (.AHK) directly from Notepad++ (aka NPP). This video…
Are you ready to implement Active Directory best practices without reading 300+ pages? You're in luck. In this webinar hosted by Skyport Systems, you gain insight into Microsoft's latest comprehensive guide, with tips on the best and easiest way…

735 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question