Org-mode with Parallel Babel

Update 2017: a block with sem -j ... seems to block in recent versions of Emacs until all subtasks are done. It would be great if someone could figure out why (though it likely is the right thing to do). To circumvent that, you can daemonize the job in sem, but that might have unwanted side-effects: sem "[job] &"

Babel in Org

Emacs Org-mode provides the wonderful babel-capability: Including code-blocks in any language directly in org-mode documents in plain text.

In default usage, running such code freezes my emacs until the code is finished, though.

Up to a few weeks ago, I solved this with a custom function, which spawns a new emacs as script runner for the specific code:

; Execute babel source blocks asynchronously by just opening a new emacs.
(defun bab/org-babel-execute-src-block-new-emacs ()
  "Execute the current source block in a separate emacs,
so we do not block the current emacs."
  (let ((line (line-number-at-pos))
        (file (buffer-file-name)))
    (async-shell-command (concat 
                          "TERM=vt200 emacs -nw --find-file " 
                          " --eval '(goto-line "
                          (number-to-string line) 
                          ")' --eval "
     "'(let ((org-confirm-babel-evaluate nil))(org-babel-execute-src-block t))' "
                          "--eval '(kill-emacs 0)'"))))

and its companion for exporting to beamer-latex presentation pdf:

; Export as pdf asynchronously by just opening a new emacs.
(defun bab/org-beamer-export-new-emacs ()
  "Export the current file in a separate emacs,
so we do not block the current emacs."
  (let ((line (line-number-at-pos))
        (file (buffer-file-name)))
    (async-shell-command (concat 
                          "TERM=vt200 emacs -nw --find-file " 
                          " --eval '(goto-line " 
                          (number-to-string line) 
                          ")' --eval "
     "'(let ((org-confirm-babel-evaluate nil))(org-beamer-export-to-pdf))' "
                          "--eval '(kill-emacs 0)'"))))

But for shell-scripts there’s a much simpler alternative:

GNU Parallel to the rescue! Process-pool made easy.

Instead of spawning an external process, I can just use GNU Parallel for the long-running program-calls in the shell-code. For example like this (real code-block):

#+BEGIN_SRC sh :exports none
  cd ~/tm5tools/plotting
  filename="./obsheat-increasing.png" >/dev/null 2>/dev/null
  sem -j -1 ./ -c ~/sun-work/ct-production-out-5x7e300m1.0 -C "aircraft" -c ~/sun-work/ct-production-out-5x7e300m1.0no-aircraft -C "continuous"  --obsheat --station allnoaa --title "\"Reducing observation coverage\"" -o ${oldPWD}/${filename}
  cd -

Let me explain this.

sem is a part of GNU parallel which makes parallel execution easy. Essentially it gives us a simple version of the convenience we know from make.

for i in {1..100}; do 
    sem -j -1 [code] # run N-1 processes with N as the number of
                     # pocessors in my computer

This means that the above org-mode block will finish instantly, but there will be a second process managed by GNU parallel which executes the plotting script.

The big advantage here is that I can also set this to execute on exporting a document which might run hundreds of code-blocks. If I did this with naive multiprocessing, that would spawn 100 processes which overwhelm the memory of my system (yes, I did that…).

sem -j -1 ensures, that this does not happen. Essentially it provides a process-pool with which it executes the code.

If you use this on export, take care to add a final code-block which waits until all other blocks finished:

sem --wait

A word of caution: Shell escapes

If you use GNU parallel to run programs, the arguments are interpreted two times: once when you pass them to sem and a second time when sem passes them on. Due to this, you have to add escaped quote-marks for every string which contains whitespace. This can look like the following code (the example above reduced to its essential parts):

sem -j -1 ./ --title "\"Reducing observation coverage\""

I stumbled over this a few times, but the convenience of GNU parallel is worth the small extra-caution.

Besides: For easier editing of inline-source-code, set org-src-fontify-natively to true (t), either via M-x customize-variable or by adding the following to your .emacs:

(setq org-src-fontify-natively t)


With the tool sem from GNU parallel you get parallel execution of shell code-blocks in emacs org-mode using the familiar syntax from make:

sem -j -1 [escaped code]

Use Node:

⚙ Babcom is trying to load the comments ⚙

This textbox will disappear when the comments have been loaded.

If the box below shows an error-page, you need to install Freenet with the Sone-Plugin or set the node-path to your freenet node and click the Reload Comments button (or return).

If you see something like Invalid key: There is no @ in that URI! (Sone/search.html), you need to setup Sone and the Web of Trust

If you had Javascript enabled, you would see comments for this page instead of the Sone page of the sites author.

Note: To make a comment which isn’t a reply visible to others here, include a link to this site somewhere in the text of your comment. It will then show up here. To ensure that I get notified of your comment, also include my Sone-ID.

Link to this site and my Sone ID: sone://6~ZDYdvAgMoUfG6M5Kwi7SQqyS-gTcyFeaNN1Pf3FvY

This spam-resistant comment-field is made with babcom.

Inhalt abgleichen
Willkommen im Weltenwald!

Beliebte Inhalte

Draketo neu: Beiträge

Ein Würfel System news