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

/* the number of threads */
int num_threads;

/* the counter and semaphores needed for the barrier */
int counter = 0;
sem_t count_sem;
sem_t barrier_sem; 

/* the function called for each thread */
void* worker(void* idp) {
    /* get our thread id */
    int id = * (int*) idp;

    /* we start to work */
    printf("Thread %d starting!\n", id);

    /* simulate the threads taking slightly different amounts of time by sleeping
     * for our thread id seconds */
    sleep(id);
    printf("Thread %d is done its work!\n", id);




    /***************** begin barrier here *****************/
    /* wait for the counter first */
    sem_wait(&count_sem);

    /* check if we are the last one to the barrier */
    if (counter == (num_threads - 1)) {
        /* we are the last thread */

        /* reset counter and free it */
        counter = 0;
        sem_post(&count_sem);

        /* post once for each waiting thread */
        for (int i = 0; i < (num_threads - 1); i++) {
            sem_post(&barrier_sem);
        }
    } else {
        /* we are NOT the last thread */

        /* increment the counter and free it */
        counter++;
        sem_post(&count_sem);

        /* now wait to be freed */
        sem_wait(&barrier_sem);
    }
    /***************** end barrier here *****************/



    printf("Thread %d is past the barrier!\n", id); 
    pthread_exit(NULL);
}

int main (int argc, char** argv) {
    /* get the number of threads */
    if (argc < 2) {
        printf("Pass the number of threads to use!\n");
        pthread_exit(0);
    } else {
        num_threads = atoi(argv[1]);
    }

    /* setup the semaphores */
    sem_init(&barrier_sem, 0, 0);
    sem_init(&count_sem, 0, 1);

    /* an array of threads */
    pthread_t threads[num_threads];
    int ids[num_threads];

    /* spawn all threads */
    for (int i = 0; i < num_threads; i++) {
        ids[i] = i;
        pthread_create(&threads[i], NULL, worker, &ids[i]);
    }

    /* join all threads */
    for (int i = 0; i < num_threads; i++) {
        pthread_join(threads[i], NULL);
    }

    pthread_exit(0);
}