scope newPing_addToStack

asclass #StackEntry implements Runnable {
  Runnable previous;
  
  *(Runnable *previous) {}
  
  abstract void impl {}
  
  run {
    callF(previous);
  }
}

static AutoCloseable newPing_addToStack(Thread thread default currentThread(), Runnable r) {
  if (r == null) null;
  ThreadLocal<Runnable> tl = newPing_actionTL();
  var old = tl.get();
  tl.set(new StackEntry(old) {
    void impl { r.run(); }
  });
  ret () -> { tl.set(old); }
}

end scope