#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/wait.h>
#include <cstdio>
#include <cstdlib>
#include <unistd.h>

union semun {
    int val;
    struct semid_ds *buf;
    unsigned short *array;
    struct seminfo *__buf;
} arg;

int semid;

void philosopher(int i) {
    struct sembuf sbuf[2];
    sbuf[0].sem_num = i;
    sbuf[0].sem_flg = SEM_UNDO;
    sbuf[1].sem_num = (i + 1) % 5;
    sbuf[1].sem_flg = SEM_UNDO;
    while (1) {
        printf("philosopher %d is thinking\n", i);
        sleep(2);
        printf("philosopher %d is hungry\n", i);
        sbuf[0].sem_op = -1;
        sbuf[1].sem_op = -1;
        semop(semid, sbuf, 2);
        printf("philosopher %d is eating\n", i);
        sleep(2);
        sbuf[0].sem_op = 1;
        sbuf[1].sem_op = 1;
        semop(semid, sbuf, 2);
    }
}

int main() {
    key_t key = ftok("fname", 1);
    semid = semget(key, 5, IPC_CREAT | 0666);
    arg.val = 1;
    for (int i = 0; i < 5; i++)
        semctl(semid, i, SETVAL, arg);
    for (int i = 0; i < 5; i++) {
        if (fork() == 0) {
            philosopher(i);
        }
    }
    while (wait(NULL) > 0);
    return 0;
}