Test for reads from the same address out of order

read-read-reorder.c

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

static volatile unsigned long s;

static void *
write_handler (void *data)
{
    for (;;) {
        unsigned long v;
        v = s;
        v += 1;
        if (!v) {
            exit (0);
            break;
        }
        s = v;
    }

    return NULL;
}

int
main (int argc, char *argv[])
{
    pthread_t th;

    pthread_create (&th, NULL, write_handler, NULL);

    for (;;) {
        unsigned long a, b;

        a = s;
        b = s;

        if (a > b) {
            printf ("a > b %lu %lu !!!!\n", a, b);
            break;
        }
    }

    return 0;
}