/* A simple bounded-buffer program using a one-word shared memory. 
 * Created by Henry Walker, 2004
 * Last modified by Janet Davis, 26 September 2006
 */

#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>          
#include <stdio.h>
#include <sys/mman.h>

#define SIZE sizeof(int)   /* size of [int] integer */
#define RUN_LENGTH 10      /* number of iterations in test run */

/* Parent process: writes squares of numbers to shared memory
 * for child to read.
 */
void producer( caddr_t shared_memory ) {
    int i;         /* a counter variable */

    for( i = 0; i < RUN_LENGTH; i++ ) { 
      /* store the square of the counter into shared memory */
      *shared_memory = i * i; 

      printf( "Parent's report: current index = %2d\n", i ); 
      sleep( 1 );  /* wait for child to read value */
    }
}

/* Child process: reads numbers from shared memory and displays them.
 */
void consumer( caddr_t shared_memory ) {
    int i;         /* a counter variable */
    int value;     /* value read by child */

    for( i = 0; i < RUN_LENGTH; i++ ) { 
      sleep( 1 );  /* wait for memory to be updated */
      value = *shared_memory;
      printf( "Child's report:  current value = %2d\n", value );
    }
}

int main (void) {  
  pid_t pid;               /* variable to record process id of child */
  caddr_t shared_memory;   /* shared memory base address */

  /* set up shared memory segment using mmap */
  shared_memory = mmap( 0,               /* start (0 means don't care) */
                        SIZE,                      /* size to allocate */
                        PROT_READ | PROT_WRITE,           /* protection*/
                        MAP_SHARED | MAP_ANONYMOUS, 
			         /* shared memory not backed by a file */
		        -1, 0);  /* ignored; relate to backing by file */

  /* check for errors */
  if( shared_memory == (caddr_t)-1 ) { 
    perror ("error in mmap while allocating shared memory\n");
    exit (1);
  }

  /* apply fork and check for error */
  if (( pid = fork()) < 0 ) {
    perror ("error in fork");  
    exit (1);
  }

  if (0 == pid) { 
    printf( "The child process begins.\n" );
    consumer( shared_memory );
    printf ("The child is done\n");
  } else { 
    printf( "The parent process begins.\n" );
    producer( shared_memory );
    wait( NULL );
    printf( "The parent is done\n" );
  }
  exit( 0 );
}