C source code

#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <stdlib.h>
#include <mqueue.h>

#define PROCESS_COUNT 10

struct my_msgbuf {
   long mtype;
   int marker;
};

struct sembuf sops[2];
struct my_msgbuf mqbuf;

int semid,msqid;

void child(int procnum);

int main(){
 int pid,i;
 int flg = 0600 | IPC_CREAT;
 key_t skey = 999, mkey=888;
 mqbuf.mtype = 1;
 mqbuf.marker = 0;

 /* create a semaphore set with 10 semaphore: */
 if ((semid = semget(skey, PROCESS_COUNT, flg)) == -1) {
  perror("semget");
  exit(1);
 }

 if ((msqid = msgget(mkey, flg)) == -1) {
  perror("msgget");
  exit(1);
 }

 printf("Go...\n");

 for(i = 0; i < PROCESS_COUNT; i++){

  /*locks the semaphore*/
  sops[0].sem_num = i;
  sops[0].sem_op = 1;

  if (semop(semid, sops, 1) == -1) {
   perror("semop");
   exit(1);
  }
  printf("Parent sem %d locked\n",i);

  pid = fork();
  if(pid == 0){
   child(i);
   exit(1);
  }
 }

  printf("Parent sent message\n");
  if (msgsnd(msqid, &mqbuf, sizeof(mqbuf), 0) == -1)
   perror("msgsnd");

 for(i = 0; i < PROCESS_COUNT; i++){

  printf("Parent sem %d unlocked\n",i);
  /*unlcok*/
  sops[0].sem_num = i;
  sops[0].sem_op = -1;
  /*wait for child to finish*/
  sops[1].sem_num = i;
  sops[1].sem_op = 0;
  if (semop(semid, sops, 2) == -1) {
   perror("semop");
   exit(1);
  }

  /*lock*/
  printf("Parent sem %d wait\n",i);
 }

 wait();

 if (msgrcv(msqid, &mqbuf, sizeof(mqbuf), 0, 0) == -1) {
  perror("msgrcv");
  exit(1);
 }

 printf("Result %d\n",mqbuf.marker);

 /* remove sem and mq*/
 if (semctl(semid, 0, IPC_RMID) == -1) {
  perror("semctl");
  exit(1);
 }
 if (msgctl(msqid, IPC_RMID, NULL) == -1) {
  perror("msgctl");
  exit(1);
 }

 return 0;
}

void child(int procnum){

        /*waits for unlocking*/
        sops[0].sem_num = procnum;
        sops[0].sem_op = 0;
        /*lock*/
        sops[1].sem_num = procnum;
        sops[1].sem_op = 1;
        printf("Child sem %d wait\n",procnum);

        if (semop(semid, sops, 2) == -1) {
          perror("semop");
          exit(1);
        }

        printf("Child sem locked %d\n",procnum);

        printf("Child %d receive message\n",procnum);
        if (msgrcv(msqid, &mqbuf, sizeof(mqbuf), 0, 0) == -1) {
         perror("msgrcv");
         exit(1);
        }
        mqbuf.marker +=2;
        printf("Child %d sent message\n",procnum);
        if (msgsnd(msqid, &mqbuf, sizeof(mqbuf), 0) == -1)
         perror("msgsnd");

        /*unlock*/
        sops[0].sem_op = -1;

        if (semop(semid, sops, 1) == -1) {
          perror("semop");
          exit(1);
        }

        printf("Child sem unlocked %d\n",procnum);
}