Window's PID of the current emacs' process

Question

I use to edit LaTeX documents with okular as pdf viewer in Ubuntu Linux. I have this code:

(defun okular-forward-search ()
  (interactive)
  (start-process
   "okular"
   "okular-output"
   "okular" ;;; src-args
    ;;; args for -sourceposition:
   "--unique"
   (concat
    "file:"
    (concat (file-name-sans-extension (buffer-file-name)) ".pdf")
    "#src:"
    (number-to-string (line-number-at-pos (point)))
    (buffer-file-name))))

that performs forward-search from LaTeX code in emacs to the corresponding page in the generated .pdf file. My problem is that this shift the "focus" from emacs to okular and this is, for me, very annoying.

Is there a hack to keep the focus on emacs?

EDIT I modified the function:

(defun okular-forward-search-mod ()
  (interactive)
  (call-process-shell-command
   (concat "okular --unique file:" (concat (file-name-sans-extension (buffer-file-name)) ".pdf")
       "#src:"
       (number-to-string (line-number-at-pos (point)))
       (buffer-file-name))
   )
  (call-process-shell-command "wmctrl -a emacs"))

But I still have an issue. If more instances of emacs are open the focus is on the first opened. How can I get the window PID of the current emacs' process?

Answer 1

Ok, I solved my problem rewriting my function:

(defun okular-forward-search-mod ()
  (interactive)
  (setq PID (number-to-string (emacs-pid)))
  (call-process-shell-command
   (concat "okular --unique file:" (concat (file-name-sans-extension (buffer-file-name)) ".pdf")
       "#src:"
       (number-to-string (line-number-at-pos (point)))
       (buffer-file-name))
   )
  (call-process-shell-command (concat "wmctrl -ia $(wmctrl -lp | awk -vpid=$PID '$3=="
                      PID
                      " {print $1; exit}')"))
)

It seems to work fine.

I found some hints here https://unix.stackexchange.com/questions/45154/switch-to-an-application-using-its-pid