[O] Display org-clock info in header line

[stardiviner]

I found there are configuration like this:

#+begin_src emacs-lisp
;;; display org-clock in head-line.
(setq org-clock-clocked-in-display nil)
(defun my/show-org-clock-in-header-line ()
  (setq-default header-line-format '((" " org-mode-line-string " "))))
(defun my/remove-org-clock-in-header-line ()
  (setq-default header-line-format nil))
(add-hook 'org-clock-in-hook #'my/show-org-clock-in-header-line)
(add-hook 'org-clock-out-hook #'my/remove-org-clock-in-header-line)
(add-hook 'org-clock-cancel-hook #'my/remove-org-clock-in-header-line)
#+end_src

But this header-line is displayed in every window. I wish there is a global 
header-line to display org-clock info.

Why I want this?

Because my notebook screen is small, when I split window, the mode-line is very 
small not enough to display much info for org-clock. I don't want to display 
org-clock info in frame-title. That's not the right place.

I saw some Emacs extensions like tabs package (for example: nerdtab 
https://github.com/casouri/nerdtab) display a global top line instead of 
per-window.

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[ stardiviner ]
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