Part of DjangoSpecifications

Threading improvements in Django

According to tickets #5632, #6950 and discussions ​http://groups.google.com/group/django-users/browse_frm/thread/a7d42475b66530bd, ​http://groups.google.com/group/django-developers/browse_thread/thread/fbcfa88c997d1bb3, at least the following components of Django are not entirely thread-safe:

• django.template.loader
• django.db.models
• django.contrib.sessions

This specification outlines the changes that need to be implemented to solve these issues.

A related task is to identify other components not mentioned here that have threading issues.

See #1442 and ​http://groups.google.com/group/django-developers/browse_thread/thread/905f79e350525c95 for threading discussions.

Globals

There are three types of globals:

1. read-only globals that are never assigned to (THREAD-SAFE),
2. globals assigned to in a function by using the global keyword (NOT THREAD-SAFE),
3. global mutable data structures (lists and dictionaries, also instances) that are assigned to at module level but whose elements are modified in functions and that are accessed without using the global keyword (NOT THREAD-SAFE unless never modified).

We won't deal with read-only globals. grep in Django source finds the following other globals.

Globals accessed with the global keyword

$ grep -r '^[[:space:]]*global ' django/ | egrep -v '(\.svn|\.html|\.css|\.pyc|doctest)' | sort | uniq

yields the following results

django/contrib/sites/models.py:        global SITE_CACHE
django/core/management/__init__.py:    global _commands
django/template/context.py:    global _standard_context_processors
django/template/__init__.py:                    global invalid_var_format_string
django/template/loader.py:    global template_source_loaders
django/utils/translation/trans_real.py:    global _accepted
django/utils/translation/trans_real.py:    global _active
django/utils/translation/trans_real.py:    global _default, _active
django/utils/translation/trans_real.py:        global _translations
django/utils/translation/trans_real.py:    global _translations

Global dictionaries

Global lists