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

#define NTHREADS 4
#define NINCS 1000

typedef struct {
    int val;
    pthread_mutex_t mtx;
} ctr_t;

void ctr_init(ctr_t *c) {
    c->val = 0;
    pthread_mutex_init(&c->mtx, NULL);
}

void ctr_inc(ctr_t *c) {
    pthread_mutex_lock(&c->mtx);
    c->val++;
    pthread_mutex_unlock(&c->mtx);
}

int ctr_get(ctr_t *c) {
    pthread_mutex_lock(&c->mtx);
    int v = c->val;
    pthread_mutex_unlock(&c->mtx);
    return v;
}

void *worker(void *arg) { (void)arg;
    ctr_t *c = arg;
    for (int i = 0; i < NINCS; i++)
        ctr_inc(c);
    return NULL;
}

int main(void) {
    ctr_t c;
    ctr_init(&c);
    pthread_t th[NTHREADS];
    for (int i = 0; i < NTHREADS; i++)
        pthread_create(&th[i], NULL, worker, &c);
    for (int i = 0; i < NTHREADS; i++)
        pthread_join(th[i], NULL);
    printf("Final counter: %d\n", ctr_get(&c));
    pthread_mutex_destroy(&c.mtx);
    return 0;
}