/**
 * Simple program demonstrating shared memory in POSIX systems.
 *
 * This is the producer process that writes to the shared memory region.
 *
 * Figure 3.17
 *
 * @author Silberschatz, Galvin, and Gagne
 * Operating System Concepts  - Ninth Edition
 * Copyright John Wiley & Sons - 2013
 */


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <unistd.h>
#include <sys/types.h>


int main() {

  const int SIZE = 4096;
  const char *name = "OS";
  const char *message0= "Studying ";
  const char *message1= "Operating Systems ";
  const char *message2= "Is Fun!\n";

  int shm_fd;
  void *ptr;

  /* create the shared memory segment */
  shm_fd = shm_open(name, O_CREAT | O_RDWR, 0666);

  /* configure the size of the shared memory segment */
  ftruncate(shm_fd,SIZE);

  /* now map the shared memory segment in the address space of the process */
  ptr = mmap(0,SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
  if (ptr == MAP_FAILED) {
    printf("Map failed\n");
    return -1;
  }

  /**
  * Now write to the shared memory region.
  *
  * Note we must increment the value of ptr after each write.
  */
  sprintf(ptr,"%s",message0);
  ptr += strlen(message0);
  sprintf(ptr,"%s",message1);
  ptr += strlen(message1);
  sprintf(ptr,"%s",message2);
  ptr += strlen(message2);

  return 0;
}