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

#include <pthread.h>
#include <sys/eventfd.h>

#define SIZE 20

pthread_t threads[SIZE];

int fd; /* event file descriptor */
int counter = 0;

void lock(int fd)
{
    int64_t value;
    int ret = read(fd, &value, sizeof(int64_t));
    if(ret == -1) printf("ERROR: read\n");
}

void unlock(int fd)
{
    int64_t value = 1;
    int ret = write(fd, &value, sizeof(int64_t));
    if(ret == -1) printf("ERROR: write\n");
}

void* execute(void* arg)
{
    for(int i = 0; i < 1000; i++)
    {
        lock(fd);
        counter += 1;
        unlock(fd);
    }
}

void init_threads()
{
    for(int i = 0; i < SIZE; i++)
        pthread_create(&threads[i], NULL, execute, NULL);
}

void destroy_threads()
{
    for(int i = 0; i < SIZE; i++)
        pthread_join(threads[i], NULL);
}

int main(void)
{
    /* create event file descriptor with initval=1 and options=0 */
    fd = eventfd(1, 0);

    init_threads();
    destroy_threads();

    printf("Counter: %d\n", counter);

    return 0;
}