#include <iostream>
#include <sys/types.h>
#include <sys/msg.h>
#include <sys/ipc.h>
#include <errno.h>
#include <unistd.h>
#include "err.h"

using namespace std;

#define	MAX_DATA 64*1024
#define	MAX_NMESG 4096
#define	MAX_NIDS 4096
int max_mesg;

struct mymesg {
  long	type;
  char	data [MAX_DATA];
} mesg;

int main(int argc, char **argv)
{
   int i, j, msqid, qid[MAX_NIDS];

   /* first try and determine maximum amount of data we can send */
   if ((msqid = msgget(IPC_PRIVATE, 0666 | IPC_CREAT)) == -1)
     syserr("msgget1");
   mesg.type = 1;
   for (i = MAX_DATA; i > 0; i -= 4) {
     if (msgsnd(msqid, &mesg, i, 0) == 0) {
       cout << "maximum amount of data per message = " << i << endl;
       max_mesg = i;
       break;
     }
     if (errno != EINVAL) syserr("msgsnd1");
   }
   if (i == 0) syserr("i == 0");
   if (msgctl(msqid, IPC_RMID, NULL) == -1) syserr("msgctl1");
   
   /* see how many messages of varying size can be put onto a queue */
   mesg.type = 1;
   for (i = 8; i <= max_mesg; i *= 2) {
     if ((msqid = msgget(IPC_PRIVATE, 0666 | IPC_CREAT)) == -1)
       syserr("msgget2");
     for (j = 0; j < MAX_NMESG; j++) {
       if (msgsnd(msqid, &mesg, i, IPC_NOWAIT) != 0) {
	 if (errno == EAGAIN) break;
	 syserr("msgsnd2");
	 break;
       }
     }
     cout << j << " " << i << "-byte messages were placed onto queue" << endl;
     cout << i*j << " bytes total" << endl;
     if (msgctl(msqid, IPC_RMID, NULL) == -1) syserr("msgctl2");
   }
   
   /* see how many identifiers we can "open" */
   mesg.type = 1;
   for (i = 0; i <= MAX_NIDS; i++) {
     if ((qid[i] = msgget(IPC_PRIVATE, 0666 | IPC_CREAT)) == -1) {
       cout << i << " identifiers open at once" << endl;
       break;
     }
   }
   for (j = 0; j < i; j++)
     if (msgctl(qid[j], IPC_RMID, NULL) == -1)
       syserr("msgctl3");
   
   exit(0);
}