Simple monitor implementation

hippos-starter.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>

#define N 50
#define M 1000

int marbles = M;
int scores[N];

// Declare and initialize locks and CVs
pthread_mutex_t mux = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t con_cv = PTHREAD_COND_INITIALIZER;
pthread_cond_t prod_cv = PTHREAD_COND_INITIALIZER;

void print_and_clear_scores() {
        int i; 
        int sum = 0;
        printf("Scores:\n");
        for(i = 0; i < N; i++) {
                printf("%d ", scores[i]);
                sum += scores[i];
                scores[i] = 0;
        }
        printf(" SUM= %d\n", sum);
}

void eat(int id){ 
    
    pthread_mutex_lock(&mux);
    while (marbles == 0) {
        pthread_cond_wait(&con_cv, &mux);
    }
        marbles--;
        scores[id]++;

    pthread_cond_signal(&prod_cv);
    pthread_mutex_unlock(&mux);

}

void restart_game() {

    pthread_mutex_lock(&mux);
    while (marbles > 0) {
        pthread_cond_wait(&prod_cv, &mux);
    }
        print_and_clear_scores();
        marbles = M;
    
    // must broadcast to prevent starvation
    pthread_cond_broadcast(&con_cv);
    pthread_mutex_unlock(&mux);

}

void *hippo(void *id_ptr) {
        long int id = (long int)id_ptr;
        while (1) eat(id);
        pthread_exit(NULL);
}

void *referee(void *ID) {
        while (1) restart_game();
}

int main() {
        pthread_t hippos[N];
        pthread_t ref;

        long i;
        for(i = 0; i < N; i++) {
                scores[i] = 0;
        }

        for(i = 0; i < N; i++) {
                pthread_create(&hippos[i], NULL, hippo, (void *)i);
        }
        pthread_create(&ref, NULL, referee, NULL);

        for(i = 0; i < N; i++) {
                pthread_join(hippos[i], NULL);
        }
        pthread_join(ref, NULL);
        pthread_exit(NULL);
}