#include <pthread.h>
#include <assert.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdint.h>
#include <stdatomic.h>

static MODIFIER int  whose_turn_is_it = 0;
_Thread_local int threadid;

static void
enter()
{
    int me = threadid;

    while (whose_turn_is_it != me)
        continue;
}

static void
leave()
{
    int me = threadid;
    int other = 1 - me;

    whose_turn_is_it = other;
}

static long count;

static void *
thread_function (void *_id) 
{
    threadid = (uintptr_t) _id;

    for (int i = 0; i < 100000; i++) {
        enter();
        count++;
        leave();
    }
}

int
main()
{
    pthread_t t[2];
    for (uintptr_t i = 0; i < 2; i++)
        pthread_create(&t[i], NULL, thread_function, (void *) i);

    for (int i = 0; i < 2; i++) {
        pthread_join(t[i], NULL);
    }
    printf("count %ld\n", count);
    return 0;
}