/* shm_server.cpp  vers. 0.2 Test routine to change from c to c++
 * FAC Sept 2010    Adapted from shm_server.c from:
 * Reference1: http://www.cs.cf.ac.uk/Dave/C/node27.html#SECTION002700000000000000000
 * Reference 2: http://www.go4expert.com/forums/showthread.php?t=8461

 * Compile:  g++ -g -Wall shm_server.cpp -o shm_server
 */
#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 sleep(secs);
     // extern unsigned int sleep (unsigned int __seconds);
#include <stdlib.h>    //Linux req.  exit()

#define SHMSZ 1024


//main()
int main(int argc, char ** argv)
{
    int shmid;
    key_t key;
    long int *shm, *s;   //shared mem address
    long int iln, iln2;  //used for loop index and also data transf.

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

    printf("Creating the shared mem. segment ...\n");
    if ((shmid = shmget(key, SHMSZ, IPC_CREAT | 0666)) < 0) 
    {   perror("shmget");
        exit(1);
    }

   // ? Not clear why NULL is used below)
    printf("Attaching the segment to our data space...\n");
/*  see:  "man shmat" :
    In  SVID  3  (or perhaps earlier) the type of the shmaddr argument was changed
    from char * into const void *, and the returned type of shmat()  from  char  *
    into  void  *.   (Linux libc4 and libc5 have the char * prototypes; glibc2 has
    void *.)
*/
//  http://www.go4expert.com/forums/showthread.php?t=8461 uses:
   //if ((shm = (int *)/*(char *)*/shmat(shmid, 0, 0)) == /*(char *)*/(int *) -1) 
     if ((shm = (long int *)shmat(shmid, 0, 0)) == (long int *) -1) 
     {
   /* None of the below work in c++  : (c++ is such an ass pain!)
   //if ((shm = (char *)shmat(shmid, 0, 0)) == (char *) -1) 
   // if ((shm = shmat(shmid, NULL, 0)) == (char *) -1)
   //shm = shmat(shmid, NULL, 0);
   //shm = shmat(shmid, (void *)0, 0);
   //if(shm == (char *) -1)
   // if(shm == (void *) -1)
   */
        perror("shmat");
        exit(1);
    }
    // shm should now point to the 1st shared mem loc.

  
    printf("Placing numbers into shared mem...\n");
    iln = 0;  // iln & shared mem are all "long int"
    s=shm;   //leave shm same, and use s to index
    while(1)
    {  *s = iln;
       printf("Placed %li in shared mem\n",iln);
       s=s+1;
       iln =iln +1;
       if(iln == 10)break;
    }

    /*
     * Finally, we wait until the other process 
     * changes the first location of our sh memory
     * to '-1', indicating that it has read what we put there.
     */
    printf("Waiting for mstun to write -1 in 1st mem loc....\n");
    while(1)
    {
       //wait(); // do not use wait().  max'es out cpu.
       sleep(3); //sleep() does not max out cpu. See also usleep for microSecs
       iln = *shm;
       if (iln == -1)
       {  // mstun has written a "-1" into first location. 
          printf(" Detected a -1 in 1st mem space\n");
          s = shm;
          s = s+1;
          iln2 = *s;
          printf(" 2nd loc is %li\n",iln2);

          if( iln == 0)
          {  printf("Exiting...\n");
             goto STOP;
          }
          // we are done with reading from client
          *shm = 0; //set to 0 lets client read and write
          printf("Server: Set 1st mem loc to 0\n");
          printf("Waiting for mstun to write -1 in 1st mem loc....\n");
       }
    }
STOP:
    exit(0);
    //could place detach shared mem code here.  If one does
    //not detach it it stays in Linux memory (but can be re-attached
    //when this process, or others are re-activated)
    //use   "ipcs" command to check if active, or observe all sh mem locations.

}  //end of main()