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Instant code reloading for Plone using a fork loop.

Project description

sauna.reload: so that you can finish your Plone development today and relax in sauna after calling it a day


sauna.reload partially restarts Plone and reloads your changed source code every time you save a file.

  • Edit your code

  • Save

  • Go to a browser and hit Refresh ➔ your latest changes are active

It greatly simplifies your Plone development workflow and gives back the agility of Python.

It works with any code.

sauna.reload works on OSX and Linux with Plone 4.0 and 4.1. In theory works on Windows, but no one has looked into that yet.

User comments

“I don’t want to use sauna.reload as I can knit a row while I restart …”


Here are brief installation instructions.


In order to take the advantage of sauna.reload

  • You know how to develop your own Plone add-ons and basics of buildout folder structure

  • You know UNIX command line basics

  • You know how to run buildout

No knowledge for warming up sauna is needed in order to use this product.

Using new buildout file for the development

This is the recommended approach how to enable sauna.reload for your development environment.

Use git to fetch sauna.reload source code to your buildout environment:

cd src
git clone git://

Create a new buildout file development.cfg which extends your existing buildout.cfg – this way you can easily keep development stuff separate from your main buildout.cfg which you can also use on the production server.



extends = buildout.cfg

develop +=


# XXX: May conflict with existing zope-conf-additional directives
zope-conf-additional = %import sauna.reload

eggs +=

Then build it out with this special config file:

bin/buildout -c development.cfg

I like to buildout buildout. I like to buildout buildout…

OSX special notes

For OSX you need to install trunk version of WatchDog providing FSEvents based file-system monitoring support.

Use git to fetch watchdog source code to your buildout environment:

cd src
git clone git://

Add watchdog as a developed egg into your buildout configuration just next to sauna.reload.



develop +=

If you are using vim (or macvim) on OSX, you must disable vim’s writebackups to allow WatchDog to see your modifications (otherwise vim will technically create a new file on each save and WatchDog doesn’t really understand what happened).

So, Add the following to the end of your .vimrc:

set noswapfile
set nobackup
set nowritebackup

Updating the existing buildout.cfg

Alternatively you can just hack your existing buildout.cfg to have sauna.reload.

Add this package to your buildout eggs and add following zope-conf-additional line to you instance part of buildout.cfg:

recipe = plone.recipe.zope2instance
zope-conf-additional = %import sauna.reload

Usage: start Plone in reload enabled manner

To start Plone with reload functionality you need to give special environment variable RELOAD_PATH for your instance command:

RELOAD_PATH=src bin/instance fg

Or if you want to optimize load speed you can directly specify only some of your development products:

RELOAD_PATH=src/my.product:src/my.another.product bin/instance fg

When reload is active you should see something like this in your console when Zope starts up:

2011-08-10 13:28:59 INFO sauna.reload Starting file monitor on /Users/moo/code/x/plone4/src
2011-08-10 13:29:02 INFO sauna.reload We saved at least 29.8229699135 seconds from boot up time
2011-08-10 13:29:02 INFO sauna.reload Packages marked for reload are listed in here:
2011-08-10 13:29:02 INFO sauna.reload Fork loop starting on process 14607
2011-08-10 13:29:02 INFO sauna.reload Booted up new new child in 0.104816913605 seconds. Pid 14608

… and when you save some file in src folder:

2011-08-10 13:29:41 INFO SignalHandler Caught signal SIGINT
2011-08-10 13:29:41 INFO Z2 Shutting down
2011-08-10 13:29:42 INFO SignalHandler Caught signal SIGCHLD
2011-08-10 13:29:42 INFO sauna.reload Booted up new new child in 0.123936891556 seconds. Pid 14609

CTRL+C should terminate Zope normally. There might be stil some kinks and error messages with shutdown.

Only eggs loaded through z3c.autoinclude. can be reloaded. Make sure you don’t use buildout.cfg zcml = directive for your eggs or sauna.reload silently ignores changes.

Manual reload

There is also a view on Zope2 root from which it is possible to manually reload code:

Debugging with sauna.reload

Regular import pdb; pdb.set_trace() will work just fine with sauna.reload. When reload happens while in pdb, though, pdb will get killed. To avoid losing your terminal echo, because of reload unexpectedly killing your pdb, you may add the following to your ~/.pdbrc:

import termios, sys
term_fd = sys.stdin.fileno()
term_echo = termios.tcgetattr(term_fd)
term_echo[3] = term_echo[3] | termios.ECHO
term_result = termios.tcsetattr(term_fd, termios.TCSADRAIN, term_echo)

sauna.reload also should work nicely with PdbTextMateSupport and PdbSublimeTextSupport. Unfortunately, we haven’t seen it working with vimpdb yet.


sauna.reload is an attempt to recreate plone.reload without the issues it has. Like being unable to reload new grokked views or portlet code. This project was started on Plone Sauna Sprint 2011. There for the name, sauna.reload.

sauna.reload does reloading by using a fork loop. So actually it does not reload the code, but restarts small part of Zope2. That’s why it can it reload stuff plone.reload cannot.

It does following on Zope2 startup:

  1. Defers loading of your development packages by hooking into PEP 302 loader and changing their z3c.autoinclude target module (and monkeypatching fiveconfigure/metaconfigure for legacy packages).

  2. Starts a watcher thread which monitors changes in your development py-files

  3. Stops loading of Zope2 in zope.processlifetime.IProcessStarting event by stepping into a infinite loop; Just before this, tries to load all non-developed dependencies of your development packages (resolved by z3c.autoinclude)

  4. It forks a new child and lets it pass the loop

  5. Loads all your development packages invoking z3c.autoinclude (and fiveconfigure/metaconfigure for legacy packages). This is fast!

  6. And now every time when the watcher thread detects a change in development files it will signal the child to shutdown and the child will signal the parent to fork a new child when it is just about to close itself

  7. Just before dying, the child saves Data.fs.index to help the new child to see the changes in ZODB (by loading the saved index)

  8. GOTO 4

Internally sauna.reload uses WatchDog Python component for monitoring file-system change events.

See also Ruby guys on fork trick.


sauna.reload emits couple of events during reloading.

Emited immediately after new process is forked. No development packages have been yet installed. Useful if you want to do something before your code gets loaded. Note that you cannot listen this event on a package that is marked for reloading as it is not yet installed when this is fired.

Emitted when all the development packages has been installed to the new forked child. Useful for notifications etc.


sauna.reload has a major pitfall. Because it depends on deferring loading of packages to be watched and reloaded, also every package depending on those packages should be defined to be reloaded (in RELOAD_PATH). And sauna.reload doesn’t resolve those dependencies automatically!

An another potential troublemaker is that sauna.reload performs implicit <includeDependencies package="." /> for every package in RELOAD_PATH (to preload dependencies for those packages to speed up the reload).

We are sorry that sauna.reload may not work for everyone. For example, reloading of core Plone packages could be tricky, if not impossible, because many of them are explicitly included by configure.zcml of CMFPlone and are not using z3c.autoincude at all. You would have to remove the dependency from CMFPlone for development to make it work…

Also because the product installation order is altered (by all the above) you may find some issue if your product does something funky on installation or at import time.

Currently only FileStorage (ZODB) is supported.

Please report any other issues at:


Report all issues on GitHub.

My code does not reload properly

You’ll see reload process going on in the terminal, but your code is still not loaded.

You should see following warnings with zcml-paths from your products:

2011-08-13 09:38:12 ERROR sauna.reload.child Failed to defer
src/sauna.reload/sauna/reload/configure.zcml. IT WILL NOT BE RELOADABLE.

Make sure your code is hooked into Plone through z3c.autoinclude and NOT using explicit zcml = directive in buildout.cfg.

  • Retrofit your eggs with autoinclude support if needed

  • Remove zcml = lines for your eggs in buildout.cfg

  • Rerun buildout (remember bin/buildout -c development.cfg)

  • Restart Plone with sauna.reload enabled

I want to exclude my meta.zcml from reload

It’s possible to manually exclude configuration files from reloading by forcing them to be loaded before forkloop in a custom site.zcml. Be aware, that when site-zcml option is used, zope2instance ignores zcml and zcml-additional options.

Define a custom site.zcml in your buildout.cfg with:

recipe = plone.recipe.zope2instance
site-zcml =
  <configure xmlns=""
    <include package="Products.Five" />
    <meta:redefinePermission from="zope2.Public" to="zope.Public" />
    <five:loadProducts file="meta.zcml"/>

    <!-- Add include for your package's meta.zcml here: -->
    <include package="my.product" file="meta.zcml" />

    <five:loadProducts />
    <five:loadProductsOverrides />
    <securityPolicy component="" />

I want to exclude ALL meta.zcml from reload

Sure. See the tip above and use the snippet below instead:

recipe = plone.recipe.zope2instance
site-zcml =
  <configure xmlns=""
    <include package="Products.Five" />
    <meta:redefinePermission from="zope2.Public" to="zope.Public" />
    <five:loadProducts file="meta.zcml"/>

    <!-- Add autoinclude-directive for deferred meta.zcml here: -->
    <includePlugins package="sauna.reload" file="meta.zcml" />

    <five:loadProducts />
    <five:loadProductsOverrides />
    <securityPolicy component="" />

sauna.reload is not active - nothing printed on console

Check that your buildout.cfg includes zope-conf-additionalzope-conf-additional line.

If using separate development.cfg make sure you run your buildout using it:

bin/buildout -c development.cfg


On GitHub.


  • Esa-Matti Suuronen [esa-matti aet]

  • Asko Soukka [asko.soukka aet]

  • Mikko Ohtamaa (idea, doccing)

  • Vilmos Somogyi (logo). The logo was originally the logo of Sauna Sprint 2011 and it was created by Vilmos Somogyi.

  • Martijn Pieters for teaching us PEP 302 -loader trick at Sauna Sprint 2011.

  • Yesudeep Mangalapilly for creating WatchDog component and providing support for Sauna Sprint team using it

Thanks to all happy hackers on Sauna Sprint 2011!

300 kg of beer was consumed to create this package (at least). Also several kilos of firewood, one axe, one chainsaw and one boat.

We still need testers and contributors. You are very welcome!


0.3.3 – 2011-10-17

  • Fixed an issue in initializing more than one reloaded Archetype products.

0.3.2 – 2011-08-21

  • Fixed to work better with PdbSublimeText/TextMateSupport.

  • README-updates (mainly for exluding zcmls from reload).

0.3.1 – 2011-08-19

  • Support for Five-initialized products (e.g. Archetypes) on Plone 4.1.

  • Licensed under ZPL.

0.3.0 – 2011-08-12

  • Support Plone 4.1

  • Heavily edited readme [miohtama]

  • Show nice error log message if product installation failed to defer ie. is not reloadable.

0.2.1 – 2011-08-03

  • Add INewChildIsReady event and move INewChildForked event

  • Remove overly used prints and use logging

  • Can now reload from package root

0.2.0 – 2011-08-04

  • Support for Five-initialized products (e.g. Archetypes).

  • Browser View for manual reloading

  • Emit INewChildForked events

  • Many bug fixes

0.1.1 – 2011-08-03

  • Added missing egg description.

  • Added forgotten reload for localizations.

  • Prefixed commands in README with $.

0.1.0 – 2011-08-03

  • First experimental release.

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