here is a bit of background on what I am trying to do for this class assignment. I am going to have 10 total programs that are going using semaphores to be synchronized to accessing a shared memory construct that is going to hold an Integer. This integer will hold the amount of text that has currently been read. How exactly am I am going to take this setup from my textbook for strings and convert it for use with Integers?
The 9 of the programs will only increment the value of the shared memory and then one of the programs will just read the shared memory value for later use. "Producer" is going to be the 9 programs that will increment the value of the shared memory. "Consumer" is going to be the single program that will read the value later on to do separate operations.
The "Consumer" program will be initializing the shared memory and setting the int value to 0.
Below is the "Producer" program that will build and write to the shared memory construct.
#include <stdio.h>
#include <stlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/shm.h>
#include <sys/stat.h>
int main()
{
/* the size (in bytes) of shared memory object */
const int SIZE 4096;
/* name of the shared memory object */
const char *name = "OS";
/* strings written to shared memory */
const char *message 0 = "Hello";
const char *message 1 = "World!";
/* shared memory file descriptor */
int shm fd;
/* pointer to shared memory obect */
void *ptr;
/* create the shared memory object */
shm fd = shm open(name, O CREAT | O RDRW, 0666);
/* configure the size of the shared memory object */
ftruncate(shm fd, SIZE);
/* memory map the shared memory object */
ptr = mmap(0, SIZE, PROT WRITE, MAP SHARED, shm fd, 0);
/* write to the shared memory object */
sprintf(ptr,"%s",message 0);
ptr += strlen(message 0);
sprintf(ptr,"%s",message 1);
ptr += strlen(message 1);
return 0;
}
Now below is the "Consumer" program that will read from the shared memory
#include <stdio.h>
#include <stlib.h>
#include <fcntl.h>
#include <sys/shm.h>
#include <sys/stat.h>
int main()
{
/* the size (in bytes) of shared memory object */
const int SIZE 4096;
/* name of the shared memory object */
const char *name = "OS";
/* shared memory file descriptor */
int shm fd;
/* pointer to shared memory obect */
void *ptr;
/* open the shared memory object */
shm fd = shm open(name, O RDONLY, 0666);
/* memory map the shared memory object */
ptr = mmap(0, SIZE, PROT READ, MAP SHARED, shm fd, 0);
/* read from the shared memory object */
printf("%s",(char *)ptr);
/* remove the shared memory object */
shm unlink(name);
return 0;
}
My idea of how to change this is to end up having the following changes for the Producer
- change SIZE to 4 bytes for the size of Int
- read the value of the int from shared memory assign that value to shmValue
- shmValue then gets incremented
- shmValue then gets written back to shared memory
My idea of how to change the Consumer program
- change SIZE to 4 bytes for the size of Int
- initialize the shared memory to int with a value of 0
- reads shared memory to shmValue
- then uses shmValue for later operations.
Again, guys, I would very much appreciate the help in dealing with this issue that I am having in understanding how to use this technology. Thank you for the help in advance!!
