/*  shm_client.c   Test program for sh mem.   FAC Sept 2010
 * Reference: http://www.cs.cf.ac.uk/Dave/C/node27.html#SECTION002700000000000000000
 * 2ndary reference: http://www.go4expert.com/forums/showthread.php?t=8461
 */

/*
 * shm_client : client program to test shared mem.
 */
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>
#include <time.h>      //used for sleep() in Linux. ?
#include <unistd.h>    //Linux  for sleep()
#include <stdlib.h>    //Linux req.  exit()

#define SHMSZ 1024

int main(int argc, char ** argv )  //argc and argv are not used here.
{
    int shmid;
    key_t key;
    long int *shm, *s;  //shared mem address
    int i;     //loop index
    long int iln;

    key = 91810; //number just refers to creation date, is a
                 //name for the shared mem segment.

    printf("shm_client: Finding shared mem...\n");
    //  Create (find) the segment based on key
    if ((shmid = shmget(key, SHMSZ, 0666)) < 0) 
    {   perror("shmget");
        exit(1);
    }

    //  Attach the segment to our data space.
    printf("shm_client: Attaching shared mem...\n");
    // C++ doesnt like the c line:
    // if ((shm = shmat(shmid, NULL, 0)) == (char *) -1) {
    if ((shm = (long int *)shmat(shmid, 0, 0)) == (long int *) -1)
    {   perror("shmat");
        exit(1);
    }

    // Check to see if server has witten something
    // Server will set 1st loc of sh mem to 0
    while(1)
    {   //wait();  //hopefully pause for a while. wait() uses full cpu
      sleep(3);    //sleep for 3 secs (Linux).
      iln = *shm;
      printf("shm_client: Detected %li in loc 0...\n",iln);
      if (iln == 0)
      {  // yes, first location is zero, Server has witten data
         // Fetch the first 10 locations only. All integers.
         i=0;
         s=shm;   //use "s" to increment memory index. Leave "shm" alone.
         while(1)
         {   printf("shm_client: read loc. %i , ptr= %p, contains= %li\n",i,s,*s);
             i=i+1;
             s=s+1;
             if(i ==10) break;
         }

         printf("Enter an integer for 2nd sh mem loc.(0=quit): ");
         //Note: there is no check for bad input. Causes crash or endless loop.
         // See mstun.cpp for fix.
         scanf("%li", &iln);
         s=shm+1;
         *s = iln; //sets 2nd loc. to user input
         *shm = -1; //tells server we are done with shared mem.
         if(iln == 0)
         {  printf("shm_client: exiting...\n");
            exit(0);
         }
      }

    }  //end of overall while loop.

}  //end of main()