''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),
 1. globals assigned to in a function by using the `global` keyword (NOT THREAD-SAFE),
 1. 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 ===

{{{
$ rgrep '^[[:alnum:]_]\+ *= *{' django | grep -v 'svn' | sort | uniq
}}}

yields the following results

{{{
django/conf/global_settings.py:ABSOLUTE_URL_OVERRIDES = {}
django/conf/global_settings.py:DATABASE_OPTIONS = {}          # Set to empty dictionary for default.
django/contrib/admin/utils.py:ROLES = {
django/contrib/admin/views/doc.py:DATA_TYPE_MAPPING = {
django/contrib/formtools/tests.py:test_data = {'field1': u'foo',
django/contrib/localflavor/ca/ca_provinces.py:PROVINCES_NORMALIZED = {
django/contrib/localflavor/in_/in_states.py:STATES_NORMALIZED = {
django/contrib/localflavor/us/us_states.py:STATES_NORMALIZED = {
django/contrib/sites/models.py:SITE_CACHE = {}
django/core/cache/__init__.py:BACKENDS = {
django/core/cache/__init__.py:DEPRECATED_BACKENDS = {
django/core/handlers/wsgi.py:STATUS_CODE_TEXT = {
django/core/serializers/__init__.py:BUILTIN_SERIALIZERS = {
django/core/serializers/__init__.py:_serializers = {}
django/core/servers/basehttp.py:_hop_headers = {
django/core/servers/fastcgi.py:FASTCGI_OPTIONS = {
django/core/urlresolvers.py:_callable_cache = {} # Maps view and url pattern names to their view functions.
django/core/urlresolvers.py:_resolver_cache = {} # Maps urlconf modules to RegexURLResolver instances.
django/db/backends/dummy/creation.py:DATA_TYPES = {}
django/db/backends/dummy/introspection.py:DATA_TYPES_REVERSE = {}
django/db/backends/mysql/creation.py:DATA_TYPES = {
django/db/backends/mysql/introspection.py:DATA_TYPES_REVERSE = {
django/db/backends/mysql_old/creation.py:DATA_TYPES = {
django/db/backends/mysql_old/introspection.py:DATA_TYPES_REVERSE = {
django/db/backends/oracle/creation.py:DATA_TYPES = {
django/db/backends/oracle/creation.py:REMEMBER = {}
django/db/backends/oracle/introspection.py:DATA_TYPES_REVERSE = {
django/db/backends/postgresql/creation.py:DATA_TYPES = {
django/db/backends/postgresql/introspection.py:DATA_TYPES_REVERSE = {
django/db/backends/postgresql_psycopg2/introspection.py:DATA_TYPES_REVERSE = {
django/db/backends/sqlite3/creation.py:DATA_TYPES = {
django/db/backends/sqlite3/introspection.py:BASE_DATA_TYPES_REVERSE = {
django/db/models/fields/related.py:pending_lookups = {}
django/db/models/query.py:LEGACY_ORDERING_MAPPING = {'ASC': '_', 'DESC': '-_', 'RANDOM': '?'}
django/db/transaction.py:dirty = {}
django/db/transaction.py:state = {}
django/dispatch/dispatcher.py:connections = {}
django/dispatch/dispatcher.py:senders = {}
django/dispatch/dispatcher.py:sendersBack = {}
django/template/__init__.py:libraries = {}
django/test/_doctest.py:OPTIONFLAGS_BY_NAME = {}
django/test/_doctest.py:__test__ = {"_TestClass": _TestClass,
django/utils/dates.py:MONTHS = {
django/utils/dates.py:MONTHS_3 = {
django/utils/dates.py:MONTHS_3_REV = {
django/utils/dates.py:MONTHS_AP = { # month names in Associated Press style
django/utils/dates.py:WEEKDAYS = {
django/utils/dates.py:WEEKDAYS_ABBR = {
django/utils/dates.py:WEEKDAYS_REV = {
django/utils/_decimal.py:_condition_map = {ConversionSyntax:InvalidOperation,
django/utils/_decimal.py:_infinity_map = {
django/utils/simplejson/decoder.py:BACKSLASH = {
django/utils/simplejson/decoder.py:_CONSTANTS = {
django/utils/simplejson/encoder.py:ESCAPE_DCT = {
django/utils/termcolors.py:opt_dict = {'bold': '1', 'underscore': '4', 'blink': '5', 'reverse': '7', 'conceal': '8'}
django/utils/translation/trans_null.py:TECHNICAL_ID_MAP = {
django/utils/translation/trans_real.py:_accepted = {}
django/utils/translation/trans_real.py:_active = {}
django/utils/translation/trans_real.py:_translations = {}
}}}

=== Global lists ===