dining_philosopher

//
// Created by aqib on 8/9/20.
//

#include <bits/stdc++.h>

#include <pthread.h>
#include <semaphore.h>
#include <cstdio>
#include <unistd.h>
#include <ctime>

#define N 5
#define THINKING 2
#define HUNGRY 1
#define EATING 0
#define LEFT (philosopher_number + 4) % N
#define RIGHT (philosopher_number + 1) % N

//int j=0;
int flag[N] = {0};
char status[][10] = {"EATING", "HUNGRY", "THINKING"};

int state[N];
int phil[N] = {0, 1, 2, 3, 4};

sem_t mutex;
sem_t S[N];

void showStatus() {
    printf("\n");
    for (int k = 0; k < 5; k++) {
        if (flag[k] != 0)
            printf("Philosopher %d is %s \t", k + 1, status[state[k]]);
    }
    printf("\n");
    sleep(3);
}


void test(int philosopher_number) {
    if (state[philosopher_number] == HUNGRY
        && state[LEFT] != EATING
        && state[RIGHT] != EATING) {
        // state that eating
        state[philosopher_number] = EATING;
        sleep(2);
        printf("\nPhilosopher %d takes fork %d and %d\n", philosopher_number + 1, LEFT + 1, philosopher_number + 1);
        showStatus();
        // sem_post(&S[philosopher_number]) has no effect
        // during take_fork
        // used to wake up hungry philosophers
        // during put_fork
        sem_post(&S[philosopher_number]);
    }
}

// take up chopsticks
void take_fork(int philosopher_number) {
    sem_wait(&mutex);
    // state that hungry
    state[philosopher_number] = HUNGRY;
    showStatus();
    // eat if neighbours are not eating
    test(philosopher_number);
    sem_post(&mutex);
    // if unable to eat wait to be signalled
    sem_wait(&S[philosopher_number]);
    sleep(1);
}

// put down chopsticks
void put_fork(int philosopher_number) {
    sem_wait(&mutex);
    // state that thinking
    state[philosopher_number] = THINKING;
    printf("\nPhilosopher %d putting fork %d and %d down\n",
           philosopher_number + 1, LEFT + 1, philosopher_number + 1);
    showStatus();
    test(LEFT);
    test(RIGHT);
    sem_post(&mutex);
}

void *philosopher(void *num) {
    for (int j = 0; j < 3; j++) {
        int *i = (int *) num;
        sleep(1);
        take_fork(*i);
        sleep(0);
        put_fork(*i);
        printf("\n\n");
    }
    return num;
}


int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    pthread_t thread_id[N];
    struct timespec stop{}, start{};
    clock_gettime(CLOCK_REALTIME, &start);
    std::cout << start.tv_sec << " " << start.tv_nsec << '\n';
    // initialize the semaphores
    sem_init(&mutex, 0, 1);
    for (auto & i : S)
        sem_init(&i, 0, 0);
    for (int i = 0; i < N; i++) {
        // create philosopher processes
        pthread_create(&thread_id[i], nullptr,
                       philosopher, &phil[i]);
        clock_gettime(CLOCK_REALTIME, &stop);
        printf("\nAt %lu micro-seconds Philosopher %d is created and he starts thinking\n", ((stop.tv_nsec - start.tv_nsec) / 1000), i + 1);
        flag[i] = 1;
    }
    for (unsigned long i : thread_id) pthread_join(i, nullptr);
}