asclass AbstractProfiler is AutoCloseable {
  // config
  settable int interval = 40; // 25 Hz
  settable bool skipSleeping;
  
  // results
  new MultiSet<S> stackTraceMultiSet;
  gettable volatile int samples;
  
  // temporary
  java.util.Timer timer;
  Lock lock = lock();

  void start {
    lock lock;
    assertCanStart();
    printWithMS("Starting " + this);
    stop();
    clear();
    timer = doEvery_daemon("Profiler", interval, r stepImpl);
  }
  
  void assertCanStart {}
  abstract void stepImpl();

  public void stop aka close() {
    lock lock;
    if (timer != null) {
      stopTimer(timer);
      timer = null;
      printWithMS("Stopped " + this);
    }
  }

  void clear() {
    lock lock;
    stackTraceMultiSet.clear();
    samples = 0;
  }

  MultiSet<S> results() {
    lock lock;
    ret cloneMultiSet(stackTraceMultiSet);
  }

  MultiSet<S> stopAndGetResults() {
    lock lock;
    stop();
    ret results();
  }
  
  S renderFullResults(bool mostImportantLast) {
    var traces = results();
    int n = traces.size();
    int percent = ratioToIntPercent(l(traces), samples);
    ret (samples == 0 ? "Nothing sampled"
      : percent + "% core activity [" + n2(samples, "sample") + " taken]") + "\n\n"
      + joinMap(mostImportantLast ? traces.lowestFirst() : traces.highestFirst(), trace ->
      traces.get(trace) + "/" + n + "\n" + trace + "\n\n"
    );
  }
  
  // must be locked first
  protected void addSample(StackTraceElement[] stackTrace) {
    stackTraceMultiSet.add(stackTraceToString(stackTrace));
  }
}