static S renderUserThreadsWithStackTraces() {
  ret renderUserThreadsWithStackTraces(mapWithout(Thread.getAllStackTraces(), currentThread()));
}

static S renderUserThreadsWithStackTraces(Map<Thread, StackTraceElement[]> threadMap) {
  ret renderUserThreadsWithStackTraces(threadMap, "thread");
}

static S renderUserThreadsWithStackTraces(Map<Thread, StackTraceElement[]> threadMap, S threadDescription) {
  new StringBuilder bufRunnable;
  new StringBuilder bufWaiting;
  
  int nRunnable = 0, nWaiting = 0, nSystem = 0;
  for (t, stackTrace : threadMap) {
    bool runnable = isThreadRunnable_x(t, stackTrace);
    var buf = runnable ? bufRunnable : bufWaiting;
    
    ThreadGroup g = t.getThreadGroup();
    if (g != null && g.getName().equals("system"))
      continue with ++nSystem;
    if (runnable) ++nRunnable; else ++nWaiting;
    printTo(buf, t);
    for (StackTraceElement e : threadMap.get(t))
      printTo(buf, "  " + e);
    printTo(buf);
  }
  
  ret asciiHeading2(n2(nRunnable, "runnable " + threadDescription))
      + "\n" + bufRunnable
    + asciiHeading2(n2(nWaiting, "sleeping " + threadDescription)
      + " (+" + n2(nSystem, "system thread") + ")")
      + "\n" + bufWaiting;
}