sclass DoubleVar {
  double a; // you can access this directly if you use one thread
  
  *() {}
  *(double *a) {}
  
  public synchronized void set(double v) {
    if (v != a) {
      a = v;
      notifyAll();
    }
  }
  
  public synchronized double get() { ret a; }

  synchronized double waitForValue(double x) ctex {
    while (a != x) wait();
    ret a;
  }
  
  toString { ret str(this!); }
}

Began life as a copy of #1033409