Re: trying to fork away from Emacs in a sub-process from elisp

[Ehud Karni]

On Tue, 09 Aug 2005 21:57:52 +0100, Nic Ferrier wrote:
>
> I'm writing a tiny image viewer to be used in conjunction with emacs.
>
> I've constructed the viewer so that it need only start once. It sets
> up a named pipe so that all subsequent invocations talk to the initial
> program over the named pipe (imagemagick is supposed to do this with
> the -remote option, but it doesn't work).
>
> I realize that I *could* implement the
> when-is-the-process-the-first-process logic in elisp... but I thought
> it was simpler and neater to have the client program simply daemonize
> itself on the fifo setup invocation.
>
> Trouble is, when the program daemonizes, Emacs doesn't seem to
> recognize it and carries on waiting (waiting for what I'm not sure).
>
> Is there some reason why client programs cannot daemonize when started
> by emacs?
>
>
>
> For reference, my client program is written in python and is following
> this basic procedure:
>
>   fork
>     child:
>       setsid
>       fork
>          child:
>             chdir /
>             close stdout
>             close stdin
>             close stderr
>

I don't know python, but I wrote a small bash script for the same
purpose. I background with nohup. Below are my lisp and bash code.
Also a ps output when displaying 3 files: a doc, a tiff, an html.

Ehud.


(defun ek-view-this-file ()
  "View this file as graphic (on X) in background"
       (interactive)
       (let ((files (dired-get-marked-files t current-prefix-arg)))
           (dired-do-shell-command "ek-view.sh *" t files)))

(define-key dired-mode-map  "s"  'ek-view-this-file)


#! /bin/sh
# View (on X) a graphic file (arg)
# --------------------------------------------------

xmsg ()
{
   BGC=${2:-khaki}
   SPC="                  "
   nohup xmessage \
       -background $BGC -foreground Black -center -file "$1"   \
       -title "$1" -xrm "$1.Scroll:whenNeeded"                 \
       -buttons "$SPC E x i t $SPC"  >  /dev/null &
   sleep 1                                 # allow xmessage to start
}
# ----------------------------------------------------------------------

exec 2>> /dev/null                         # do not show anything !

case `which display` in
    "/usr/bin/"* ) VIEW=display ;;         # use display (from Image Magic)
       *   )   VIEW=xview ;;               # any other case
esac

case `which firefox` in
    "/usr/bin/"* ) HTMV=firefox ;;         # use firefox (when available)
       *   )   HTMV=mozilla ;;             # no firefox, use mozilla
esac

for FLN in "$@"
do
    lFLN=`echo "$FLN" | tr "A-Z" "a-z"`    # name in lower case
    case "$lFLN" in
      *htm | *html)                                # browser
               URL=file://`pwd`/"$FLN"             # file URL
               nohup /usr/bin/$HTMV "$URL" > /dev/null & ;;    # html

      *pdf )   nohup xpdf "$FLN" > /dev/null & ;;  # PDF file

      *mpg | *mpeg )
               nohup xanim "$FLN" > /dev/null & ;; # MPEG - movie

       *.doc )                                     # M$ Word document
           catdoc "$FLN" | fribidi --charset ISO8859-8 --width 90 --rtl > 
"${FLN}_h_txt"
           xmsg "${FLN}_h_txt"                     # show message
           catdoc "$FLN" | fribidi --charset ISO8859-8 --width 90 --ltr > 
"${FLN}_e_txt"
           xmsg "${FLN}_e_txt" cyan
           sleep 2                                 # Allow xmessage to start
           rm -f "${FLN}_h_txt" "${FLN}_e_txt" ;;  # remove input

       *.txt )
           xmsg "$FLN"                             # show message
           cat "$FLN" | fribidi --charset ISO8859-8 --width 90 --ltr > 
"${FLN}_e_txt"
           xmsg "${FLN}_e_txt" cyan
           sleep 2                                 # Allow xmessage to start
           rm -f "${FLN}_e_txt" ;;                 # remove input

       * ) nohup $VIEW "$FLN" > /dev/null & ;;     # any other picture
    esac
done

exec sleep 2                   # Don't kill STARTING background processes

############################## ek-view.sh ##############################


 UID  PID  PPID   SID  START    TIME     COMMAND
ehud  7100     1  6546   Jul 26 07:14:30 emacs-21.3 -geometry 130x62+0+0 
/procom/home/ehud/emacs-21

ehud 26767     1 26745 12:03:04  0:00 xmessage -background khaki -foreground 
Black -center -file Simon.405.doc_h_txt -title
ehud 26771     1 26745 12:03:05  0:00 xmessage -background cyan -foreground 
Black -center -file Simon.405.doc_e_txt -title S
ehud 26778     1 26745 12:03:08  0:01 display Ishur-mas-2006.tiff
ehud 26783     1 26745 12:03:08  0:00 /bin/sh /usr/lib/firefox-1.0.4/firefox 
file:///procom/home/ehud/mail/tmp/zeev-crtf.htm
ehud 26800 26783 26745 12:03:27  0:00 /bin/sh 
/usr/lib/firefox-1.0.4/run-mozilla.sh /usr/lib/firefox-1.0.4/firefox-bin file:
ehud 26805 26800 26745 12:03:27  0:03 /usr/lib/firefox-1.0.4/firefox-bin 
file:///procom/home/ehud/mail/tmp/zeev-crtf.html



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