sclass FlexibleRateTimer implements AutoCloseable {
  double hertz;
  transient Runnable action;
  transient double timestamp;
  transient DoLater doLater;
  transient new Flag started;
  transient volatile bool disposed;
  
  *() {}
  *(double *hertz) {}
  *(double *hertz, Runnable *action) {}
  
  void start {
    if (!started.raise()) ret;
    _kaboom();
  }
  
  void _kaboom {
    if (disposed) ret;
    dispose doLater;
    if (timestamp == 0) timestamp = sysNow();
    timestamp += 1000/getFrequency();
    doLater = new DoLater(iround(timestamp), r {
      pcallF(action);
      _kaboom();
    });
    doLater.enable();
  }
  
  void cancel { close(); }
  
  public void close {
    set disposed;
    dispose doLater;
  }
  
  void setRunnableAndStart(Runnable action) {
    this.action = action;
    start();
  }
  
  // takes affect _after_ next trigger
  synchronized void setFrequency(double hertz) {
    this.hertz = hertz;
  }
  
  synchronized double getFrequency() { ret hertz; }
}