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

static int shared_counter = 0;
static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;

static void *worker(void *arg) { (void)arg;
    (void)arg;
    for (int i = 0; i < 5000; ++i) {
        pthread_mutex_lock(&mtx);
        ++shared_counter;
        pthread_mutex_unlock(&mtx);
    }
    return NULL;
}

int main(void) {
    pthread_t t1, t2;
    pthread_create(&t1, NULL, worker, NULL);
    pthread_create(&t2, NULL, worker, NULL);
    pthread_join(t1, NULL);
    pthread_join(t2, NULL);
    printf("Shared counter is %d\n", shared_counter);
    return 0;
}