/**
 * 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
 *
 * modifications by dheller@cse.psu.edu, 31 Jan. 2014
 */

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

void display(char *prog, char *bytes, int n);

int main(void)
{
  const char *name = "/shm-example";	// file name
  const int SIZE = 4096;		// file size

  const char *message0 = "Studying ";
  const char *message1 = "Operating Systems ";
  const char *message2 = "Is Fun!";
  const char *msg_end  = "\n";

  int shm_fd;		// file descriptor, from shm_open()
  char *shm_base;	// base address, from mmap()
  char *ptr;		// shm_base is fixed, ptr is movable

  /* create the shared memory segment as if it were a file */
  shm_fd = shm_open(name, O_CREAT | O_RDWR, 0666);
  if (shm_fd == -1) {
    printf("prod: Shared memory failed: %s\n", strerror(errno));
    exit(1);
  }

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

  /* map the shared memory segment to the address space of the process */
  shm_base = mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
  if (shm_base == MAP_FAILED) {
    printf("prod: Map failed: %s\n", strerror(errno));
    // close and shm_unlink?
    exit(1);
  }

  /**
   * Write to the mapped shared memory region.
   *
   * We increment the value of ptr after each write, but we
   * are ignoring the possibility that sprintf() fails.
   */
  display("prod", shm_base, 64);
  ptr = shm_base;
  ptr += sprintf(ptr, "%s", message0);
  ptr += sprintf(ptr, "%s", message1);
  ptr += sprintf(ptr, "%s", message2);
  ptr += sprintf(ptr, "%s", msg_end);
  display("prod", shm_base, 64);

  /* remove the mapped memory segment from the address space of the process */
  if (munmap(shm_base, SIZE) == -1) {
    printf("prod: Unmap failed: %s\n", strerror(errno));
    exit(1);
  }

  /* close the shared memory segment as if it was a file */
  if (close(shm_fd) == -1) {
    printf("prod: Close failed: %s\n", strerror(errno));
    exit(1);
  }

  return 0;
}

void display(char *prog, char *bytes, int n)
{
  printf("display: %s\n", prog);
  for (int i = 0; i < n; i++) 
    { printf("%02x%c", bytes[i], ((i+1)%16) ? ' ' : '\n'); }
  printf("\n");
}