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


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 on Plone Sauna Sprint 2011. There for the name, sauna.reload.

It can currently reload following:

  • Portlets
  • Schema Interface changes
  • Adapters
  • Meta programming magic
  • ZCML
  • Translations (changes in PO files)
  • etc.

sauna.reload does reloading by using a fork loop. So actually it does not reload the code, but restarts small part of Zope2.

sauna.reload 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
  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. 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 new a 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


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


Fork loop is not active by default. You can activate it by setting RELOAD_PATH environment variable to your development product path(s). In most setups src is what you want:

$ 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

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


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.


Defering installation of development packages to the end of Plone boot up process means that reloading of Core Plone packages is tricky (or impossible?). For example is depended by CMFPlone and CMFPlone really must be installed before the fork loop or there would be no speed difference between sauna.reload and normal Plone restart. So we cannot defer the installation of to the end of boot up process. You would have to remove the dependency from CMFPlone for development to make it work...

Also because the product installation order is altered you may find some issues if your product does something funky on installation or at import time.

Currently only FileStorage (ZODB) is supported.

Please, report issues at:

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)


Too many files open on OSX

Watchdog, the Python library used by sauna.reload internally, must be compiled with fsevent support to allow file-system monitoring without need to open each individual file. In OSX Snow Leopard the default limit of open file handles is 256 and on OSX raising this limit is made unnecessary difficult.

More info


  • Esa-Matti Suuronen (esa-matti aet
  • Asko Soukka (asko.soukka aet
  • Mikko Ohtamaa (idea)
  • Andreas Jung (approved in IRC)

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

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!

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