Make Context Managers (fallbacks and auto_populate) Thread Safe (#657)

modeltranslation/fields.py

@@ -4,6 +4,7 @@ from django.core.exceptions import ImproperlyConfigured
 from django.db.models import fields
 
 from modeltranslation import settings as mt_settings
+from modeltranslation.thread_context import fallbacks_enabled
 from modeltranslation.utils import (
     get_language,
     build_localized_fieldname,
@@ -350,7 +351,7 @@ class TranslationFieldDescriptor(object):
             val = getattr(instance, loc_field_name, None)
             if self.meaningful_value(val, undefined):
                 return val
-        if mt_settings.ENABLE_FALLBACKS and self.fallback_value is not NONE:
+        if fallbacks_enabled() and self.fallback_value is not NONE:
             return self.fallback_value
         else:
             if default is NONE:

modeltranslation/manager.py

@@ -17,8 +17,8 @@ from django.db.models.query import QuerySet, ValuesIterable
 from django.db.models.utils import create_namedtuple_class
 from django.utils.tree import Node
 
-from modeltranslation import settings
 from modeltranslation.fields import TranslationField
+from modeltranslation.thread_context import auto_populate_mode
 from modeltranslation.utils import (
     auto_populate,
     build_localized_fieldname,
@@ -376,7 +376,7 @@ class MultilingualQuerySet(QuerySet):
     def _populate_mode(self):
         # Populate can be set using a global setting or a manager method.
         if self._populate is None:
-            return settings.AUTO_POPULATE
+            return auto_populate_mode()
         return self._populate
 
     # This method was not present in django-linguo

modeltranslation/thread_context.py

@@ -0,0 +1,48 @@
+import threading
+from typing import Union
+from typing_extensions import Literal
+
+from modeltranslation import settings
+
+
+AutoPopulate = Union[bool, Literal["all", "default", "required"]]
+
+
+class ModelTranslationThreadLocal(threading.local):
+    """Holds thread-local data for modeltranslation."""
+
+    auto_populate: Union[AutoPopulate, None] = None
+    enable_fallbacks: Union[bool, None] = None
+
+
+_mt_thread_context = ModelTranslationThreadLocal()
+
+
+def set_auto_populate(value: Union[AutoPopulate, None]) -> None:
+    """Set the auto_populate for the current thread."""
+    _mt_thread_context.auto_populate = value
+
+
+def set_enable_fallbacks(value: Union[bool, None]) -> None:
+    """Set the enable_fallbacks for the current thread."""
+    _mt_thread_context.enable_fallbacks = value
+
+
+def auto_populate_mode() -> AutoPopulate:
+    """Return the auto_populate mode for the current thread."""
+    auto_populate = _mt_thread_context.auto_populate
+
+    if auto_populate is not None:
+        return auto_populate
+
+    return settings.AUTO_POPULATE
+
+
+def fallbacks_enabled() -> bool:
+    """Return whether fallbacks are enabled for the current thread."""
+    enable_fallbacks = _mt_thread_context.enable_fallbacks
+
+    if enable_fallbacks is not None:
+        return enable_fallbacks
+
+    return settings.ENABLE_FALLBACKS

modeltranslation/translator.py

@@ -22,6 +22,7 @@ from modeltranslation.manager import (
     rewrite_lookup_key,
     append_translated,
 )
+from modeltranslation.thread_context import auto_populate_mode
 from modeltranslation.utils import build_localized_fieldname, parse_field
 
 
@@ -389,7 +390,7 @@ def populate_translation_fields(sender, kwargs):
     defined (for example to make lookups / filtering without resorting to
     query fallbacks).
     """
-    populate = mt_settings.AUTO_POPULATE
+    populate = auto_populate_mode()
     if not populate:
         return
     if populate is True:

modeltranslation/utils.py

@@ -6,6 +6,11 @@ from django.utils.translation import get_language_info
 from django.utils.functional import lazy
 
 from modeltranslation import settings
+from modeltranslation.thread_context import (
+    set_auto_populate,
+    set_enable_fallbacks,
+    fallbacks_enabled,
+)
 
 
 def get_language():
@@ -112,8 +117,9 @@ def resolution_order(lang, override=None):
     First is always the parameter language, later are fallback languages.
     Override parameter has priority over FALLBACK_LANGUAGES.
     """
-    if not settings.ENABLE_FALLBACKS:
+    if not fallbacks_enabled():
         return (lang,)
+
     if override is None:
         override = {}
     fallback_for_lang = override.get(lang, settings.FALLBACK_LANGUAGES.get(lang, ()))
@@ -141,12 +147,11 @@ def auto_populate(mode='all'):
         with auto_populate('required'):
             call_command('loaddata', 'fixture.json')
     """
-    current_population_mode = settings.AUTO_POPULATE
-    settings.AUTO_POPULATE = mode
+    set_auto_populate(mode)
     try:
         yield
     finally:
-        settings.AUTO_POPULATE = current_population_mode
+        set_auto_populate(None)
 
 
 @contextmanager
@@ -163,12 +168,11 @@ def fallbacks(enable=True):
     processing or check if there is a value for the current language (not
     knowing the language)
     """
-    current_enable_fallbacks = settings.ENABLE_FALLBACKS
-    settings.ENABLE_FALLBACKS = enable
+    set_enable_fallbacks(enable)
     try:
         yield
     finally:
-        settings.ENABLE_FALLBACKS = current_enable_fallbacks
+        set_enable_fallbacks(None)
 
 
 def parse_field(setting, field_name, default):