简单地触发因为reorder而产生的问题

mem_order.cpp

#include <semaphore.h>
#include <random>

sem_t begin_sem1;
sem_t begin_sem2;
sem_t end_sem;

int X, Y;
int r1, r2;

void *ThreadFunc1(void *param) {
  for (;;) {
    sem_wait(&begin_sem1);
    X = 1;
    asm volatile("" ::: "memory");
    r1 = Y;
    sem_post(&end_sem);
  }
  return NULL;
}

void *ThreadFunc2(void *param) {
  for (;;) {
    sem_wait(&begin_sem2);
    Y = 1;
    asm volatile("" ::: "memory");
    r2 = X;
    sem_post(&end_sem);
  }
  return NULL;
}

int main(int argc, char *argv[]) {
  sem_init(&begin_sem1, 0, 0);
  sem_init(&begin_sem2, 0, 0);
  sem_init(&end_sem, 0, 0);

  pthread_t thread[2];
  pthread_create(&thread[0], NULL, ThreadFunc1, NULL);
  pthread_create(&thread[1], NULL, ThreadFunc2, NULL);

  int detected = 0;
  for (int i = 1; ; ++i) {
    X = 0;
    Y = 0;
    sem_post(&begin_sem1);
    sem_post(&begin_sem2);
    sem_wait(&end_sem);
    sem_wait(&end_sem);
    if (r1 == 0 && r2 == 0) {
      detected++;
      printf("%d %d\n", detected, i);
    }
  }
  return 0;
}