extern void abort(void);
void assume_abort_if_not(int cond) {
  if(!cond) {abort();}
}
extern void abort(void);
#include <assert.h>
void reach_error() { assert(0); }
extern void __VERIFIER_atomic_begin(void);
extern void __VERIFIER_atomic_end(void);

#include <pthread.h>

#define assume(e) assume_abort_if_not(e)
#undef assert
#define assert(e) { if(!(e)) { ERROR: {reach_error();abort();}(void)0; } }

int w=0, r=0, x, y;

void __VERIFIER_atomic_w()
{
    assume(w==0);
    assume(r==0);
    w = 1;
}

void* thr1(void* arg) { //writer
  __VERIFIER_atomic_w();
  x = 3;
  __VERIFIER_atomic_begin();
  w = 0;
  __VERIFIER_atomic_end();

  return 0;
}

void __VERIFIER_atomic_r()
{
    assume(w==0);
    r = r+1;
}

void* thr2(void* arg) { //reader
  __VERIFIER_atomic_r();
  __VERIFIER_atomic_begin();
  int l = x;
  __VERIFIER_atomic_end();
  __VERIFIER_atomic_begin();
  y = l;
  __VERIFIER_atomic_end();
  __VERIFIER_atomic_begin();
  int ly = y;
  __VERIFIER_atomic_end();
  __VERIFIER_atomic_begin();
  int lx = x;
  __VERIFIER_atomic_end();
  assert(ly == lx);
  __VERIFIER_atomic_begin();
  int lr = r;
  __VERIFIER_atomic_end();
  __VERIFIER_atomic_begin();
  r = lr-1;
  __VERIFIER_atomic_end();

  return 0;
}

int main()
{
  pthread_t t;

  pthread_create(&t, 0, thr1, 0);
  thr2(0);

  return 0;
}