#include <pthread.h> 
int turn; // integer variable to hold the ID of the thread whose turn is it
int x; // variable to test mutual exclusion
int flag1 = 0, flag2 = 0; // boolean flags

void thr1() { // frontend produces 12 transitions from this thread. It would be better if it would produce only 8!
  flag1 = 1;
  turn = 1;
  do {} while (flag2==1 && turn==1);
  // begin: critical section
  x = 0;
  assert(x<=0);
  // end: critical section
  flag1 = 0;
}

void thr2() {
  flag2 = 1;
  turn = 0;
  do {} while (flag1==1 && turn==0);
  // begin: critical section
  x = 1;
  assert (x>=1);
  // end: critical section
  flag2 = 0;
}

int main() {
  pthread_t t1, t2;
  pthread_create(&t1, NULL, thr1, NULL);
  pthread_create(&t2, NULL, thr2, NULL);
  return 0;
}
