test

test.c

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

int x;
int y;
int a;
int b;

void* f1(void* arg)
{
    y = 1;
    a = x;
    return NULL;
}

void* f2(void* arg)
{
    x = 1;
    b = y;
    return NULL;
}

int main()
{
    while (1) {
        x = y = 0;
        a = b = -1;
        pthread_t t1, t2;
        pthread_create(&t1, NULL, f1, NULL);
        pthread_create(&t2, NULL, f2, NULL);
        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
        if (a == 0 && b == 0) {
            puts("Hello world!");
        }
    }
    return 0;
}