Semaphore values are not changing in Ubuntu - c

Question

I'm trying to create a solution for the River Crossing Problem from "The Little Book of Semaphores" (Chapter 5, section 7, page 148), I'm using an Ubuntu virtual machine in my PC.
The problem is that the semaphores I created are not changing values, all of them stay at 0, I'm using four files.
What I do is, run buffer and then create two hacker processes and then two serf processes, the thing is that the "Boarding a X" message is printed before the boat is filled (at least four passengers) and when I print the semaphore values all of them are in 0.
header.h, where I declare Semaphore ids and operations:
#ifndef SEMAFOROS_H
#define SEMAFOROS_H
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#define BARRIER 10
#define MUTEX 11
#define SERFQUEUE 12
#define HACKERQUEUE 13
struct buffer {
int hackers;
int serfs;
};
int sem_wait(int semid, int sem_num, int val) {
struct sembuf op;
op.sem_num = sem_num;
op.sem_op = -val;
op.sem_flg = 0;
return semop(semid, &op, 1);
}
int sem_signal(int semid, int sem_num, int val) {
struct sembuf op;
op.sem_num = sem_num;
op.sem_op = val;
op.sem_flg = 0;
return semop(semid, &op, 1);
}
int mutex_wait(int semid, int sem_num) {
return sem_wait(semid, sem_num, 1);
}
int mutex_signal(int semid, int sem_num) {
return sem_signal(semid, sem_num, 1);
}
#endif
buffer.c, where I create the semaphores:
#include "header.h"
int main(int argc, char* argv[])
{
int semid, shmid, i;
key_t key;
if (argc != 1) {
printf("usage: %s\n", argv[0]);
return -1;
}
if ( (key = ftok("/dev/null", 65)) == (key_t) -1 ) {
perror(argv[0]);
return -1;
}
if ( (semid = semget(key, 4, 0666 | IPC_CREAT)) < 0 ) {
perror(argv[0]);
return -1;
}
semctl(semid, BARRIER, SETVAL, 4);
semctl(semid, MUTEX, SETVAL, 1);
semctl(semid, SERFQUEUE, SETVAL, 0);
semctl(semid, HACKERQUEUE, SETVAL, 0);
unsigned short final_values[4];
semctl(semid, 0, GETALL, final_values);
for (i = 0; i < 4; i++) {
printf("%3i", final_values[i]);
}
printf("\n");
if ( (shmid = shmget(key, sizeof(struct buffer), 0666 | IPC_CREAT)) < 0) {
semctl(semid, 0, IPC_RMID, 0);
perror("shmget");
return -1;
}
struct buffer *b = (struct buffer *) shmat(shmid, (void *) 0, 0);
b->hackers = 0;
b->serfs = 0;
shmdt(b);
return 0;
}
hackers.c, code for hackers:
#include "header.h"
#include <time.h>
void a_hacker(char* program) {
int semid, shmid, i, k, isCaptain = 0;
key_t key;
struct buffer *b;
if ( (key = ftok("/dev/null", 65)) == (key_t) -1 ) {
perror(program);
exit(-1);
}
if ( (semid = semget(key, 4, 0666)) < 0 ) {
perror(program);
exit(-1);
}
if ( (shmid = shmget(key, sizeof(struct buffer), 0666)) < 0 ) {
perror("shmid");
exit(-1);
}
b = (struct buffer *) shmat(shmid, (void *) 0, 0);
mutex_wait(semid, MUTEX);
b->hackers += 1;
if (b->hackers == 4) {
sem_signal(semid, HACKERQUEUE, 4);
b->hackers = 0;
isCaptain = 1;
} else if (b->hackers == 2 && b->serfs >= 2) {
sem_signal(semid, HACKERQUEUE, 2);
sem_signal(semid, SERFQUEUE, 2);
b->hackers = 0;
b->serfs -= 2;
isCaptain = 1;
} else {
mutex_signal(semid, MUTEX);
}
unsigned short final_values[4];
semctl(semid, 0, GETALL, final_values);
for (i = 0; i < 4; i++) {
printf("%3i", final_values[i]);
}
printf("\n");
sem_wait(semid, HACKERQUEUE, 1);
printf("Boarding a hacker\n");
semctl(semid, 0, GETALL, final_values);
for (i = 0; i < 4; i++) {
printf("%3i", final_values[i]);
}
printf("\n");
sem_wait(semid, BARRIER, 1);
if (isCaptain) {
printf("Fugaaaa\n");
mutex_signal(semid, MUTEX);
}
sem_signal(semid, BARRIER, 2);
shmdt(b);
exit(0);
}
int main(int argc, char* argv[]) {
int amount_hackers = 0, semid, i, pid;
key_t key;
if (argc != 2) {
printf("usage: %s amount_of_serfs amount_of_hackers\n", argv[0]);
return -1;
}
amount_hackers = atoi(argv[1]);
if (amount_hackers < 1) {
printf("%s: The amount_of_hackers must be a positive number greater than zero.\n", argv[0]);
return -1;
}
for (i = 0; i < amount_hackers; i++) {
if ( (pid = fork()) < 0 ) {
perror("fork");
return -1;
} else if (pid == 0) {
a_hacker(argv[0]);
} else {
}
}
return 0;
}
serfs.c, code for serfs:
#include "header.h"
#include <time.h>
void a_serf(char* program) {
int semid, shmid, i, k, isCaptain = 0;
key_t key;
struct buffer *b;
if ( (key = ftok("/dev/null", 65)) == (key_t) -1 ) {
perror(program);
exit(-1);
}
if ( (semid = semget(key, 4, 0666)) < 0 ) {
perror(program);
exit(-1);
}
if ( (shmid = shmget(key, sizeof(struct buffer), 0666)) < 0 ) {
perror("shmid");
exit(-1);
}
b = (struct buffer *) shmat(shmid, (void *) 0, 0);
mutex_wait(semid, MUTEX);
b->serfs += 1;
if (b->serfs == 4) {
sem_signal(semid, SERFQUEUE, 4);
b->serfs = 0;
isCaptain = 1;
} else if (b->hackers == 2 && b->serfs >= 2) {
sem_signal(semid, HACKERQUEUE, 2);
sem_signal(semid, SERFQUEUE, 2);
b->serfs = 0;
b->hackers -= 2;
isCaptain = 1;
} else {
mutex_signal(semid, MUTEX);
}
unsigned short final_values[4];
semctl(semid, 0, GETALL, final_values);
for (i = 0; i < 4; i++) {
printf("%3i", final_values[i]);
}
printf("\n");
sem_wait(semid, SERFQUEUE, 1);
printf("Boarding a serf\n");
semctl(semid, 0, GETALL, final_values);
for (i = 0; i < 4; i++) {
printf("%3i", final_values[i]);
}
printf("\n");
sem_wait(semid, BARRIER, 1);
if (isCaptain) {
printf("Fugaaaa\n");
mutex_signal(semid, MUTEX);
}
sem_signal(semid, BARRIER, 2);
shmdt(b);
exit(0);
}
int main(int argc, char* argv[]) {
int amount_serfs = 0, semid, i, pid;
key_t key;
if (argc != 2) {
printf("usage: %s amount_of_serfs amount_of_hackers\n", argv[0]);
return -1;
}
amount_serfs = atoi(argv[1]);
if (amount_serfs < 1) {
printf("%s: The amount_of_serfs must be a positive number greater than zero.\n", argv[0]);
return -1;
}
for (i = 0; i < amount_serfs; i++) {
if ( (pid = fork()) < 0 ) {
perror("fork");
return -1;
} else if (pid == 0) {
a_serf(argv[0]);
} else {
}
}
return 0;
}
Can someone please help me?