Solved

matrix addition using shared memory

Posted on 2010-11-23
4
1,056 Views
Last Modified: 2012-05-10
I want to add 2 matrices using shared memory and parallel processes, in linux, but my code doesnt run correctly .
Where is the problem?
#include <stdio.h>

#include <sys/shm.h>

#include <sys/stat.h>

#include <stdlib.h>



int main ()

{



int idA,idB,idC, child_id;

int *A,*B, *C;//the 3 arrays

int* child_memory;

int *pA, *pB, *pC;

const int size = 4096;

int i;

//allocate shared memory for an array of 5 integers

idA = shmget(IPC_PRIVATE, 5*sizeof(int), S_IRUSR | S_IWUSR);

idB = shmget(IPC_PRIVATE, 5*sizeof(int), S_IRUSR | S_IWUSR);

idC = shmget(IPC_PRIVATE, 5*sizeof(int), S_IRUSR | S_IWUSR);



//attach shared memory to parent

A = (int *) shmat(idA, NULL, 0);

B = (int *) shmat(idB, NULL, 0);

C = (int *) shmat(idC, NULL, 0);

for(i=0; i<5; i++){

         A[i]=1;

         B[i]=2;

         C[i]=0;

         }

for (i=0; i<5; i++){

    printf("A[%d]=%d B[%d]=%d  C[%d]=%d\n",i,A[i],i,B[i],i,C[i]);

}

printf("\n"); 

for(i=0;i<5; i++){

   child_id=fork();

   if (child_id==0){

       A = (int*) shmat(idA, NULL, 0);

       B = (int*) shmat(idB, NULL, 0);

       C = (int*) shmat(idC, NULL, 0);             

       C[i] = A[i] + B[i];

       

   }

   else if (child_id>0){

    wait(0);

        

   }

   else {perror("fork");exit(1);}

}   

printf("C[%d] = %d ", i,C[i]);       



shmdt(A);shmdt(B);shmdt(C);



shmctl(idA, IPC_RMID, NULL);

shmctl(idB, IPC_RMID, NULL);

shmctl(idC, IPC_RMID, NULL);

return 0;

}

Open in new window

0
Comment
Question by:dimi67
  • 2
  • 2
4 Comments
 
LVL 53

Expert Comment

by:Infinity08
Comment Utility
Could you elaborate a bit on how it doesn't run correctly ? What do you observe ? What did you expect instead ?
0
 

Author Comment

by:dimi67
Comment Utility
.if you run the code you will see that t values of array C don't change at all...
0
 
LVL 53

Accepted Solution

by:
Infinity08 earned 500 total points
Comment Utility
>> printf("C[%d] = %d ", i,C[ i]);  

At this point, i = 5. That'll show an out-of-range value from the array. You probably intended to put this in a loop for i from 0 to 4.

You probably also want to end the children (ie. exit) once they've done their job.

And you probably also want to let the parent wait until the children have done their job.
0
 

Author Closing Comment

by:dimi67
Comment Utility
ok men, I fixed it with exit(0) at the end of the child...
0

Featured Post

How to run any project with ease

Manage projects of all sizes how you want. Great for personal to-do lists, project milestones, team priorities and launch plans.
- Combine task lists, docs, spreadsheets, and chat in one
- View and edit from mobile/offline
- Cut down on emails

Join & Write a Comment

Little introduction about CP: CP is a command on linux that use to copy files and folder from one location to another location. Example usage of CP as follow: cp /myfoder /pathto/destination/folder/ cp abc.tar.gz /pathto/destination/folder/ab…
SSH (Secure Shell) - Tips and Tricks As you all know SSH(Secure Shell) is a network protocol, which we use to access/transfer files securely between two networked devices. SSH was actually designed as a replacement for insecure protocols that sen…
Learn how to navigate the file tree with the shell. Use pwd to print the current working directory: Use ls to list a directory's contents: Use cd to change to a new directory: Use wildcards instead of typing out long directory names: Use ../ to move…
The goal of this video is to provide viewers with basic examples to understand opening and writing to files in the C programming language.

771 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

Need Help in Real-Time?

Connect with top rated Experts

11 Experts available now in Live!

Get 1:1 Help Now