Fixed #30451 -- Added ASGI handler and coroutine-safety.

This adds an ASGI handler, asgi.py file for the default project layout,
a few async utilities and adds async-safety to many parts of Django.

4 files changed, 40 insertions, 6 deletions

diff --git a/django/utils/asyncio.py b/django/utils/asyncio.py
new file mode 100644
index 0000000000..c4de04ba12
--- /dev/null
+++ b/django/utils/asyncio.py
@@ -0,0 +1,32 @@
+import asyncio
+import functools
+
+from django.core.exceptions import SynchronousOnlyOperation
+
+
+def async_unsafe(message):
+    """
+    Decorator to mark functions as async-unsafe. Someone trying to access
+    the function while in an async context will get an error message.
+    """
+    def decorator(func):
+        @functools.wraps(func)
+        def inner(*args, **kwargs):
+            # Detect a running event loop in this thread.
+            try:
+                event_loop = asyncio.get_event_loop()
+            except RuntimeError:
+                pass
+            else:
+                if event_loop.is_running():
+                    raise SynchronousOnlyOperation(message)
+            # Pass onwards.
+            return func(*args, **kwargs)
+        return inner
+    # If the message is actually a function, then be a no-arguments decorator.
+    if callable(message):
+        func = message
+        message = 'You cannot call this from an async context - use a thread or sync_to_async.'
+        return decorator(func)
+    else:
+        return decorator
diff --git a/django/utils/timezone.py b/django/utils/timezone.py
index 58e92c1fa8..4c43377447 100644
--- a/django/utils/timezone.py
+++ b/django/utils/timezone.py
@@ -6,9 +6,9 @@ import functools
 import warnings
 from contextlib import ContextDecorator
 from datetime import datetime, timedelta, timezone, tzinfo
-from threading import local
 
 import pytz
+from asgiref.local import Local
 
 from django.conf import settings
 from django.utils.deprecation import RemovedInDjango31Warning
@@ -89,7 +89,7 @@ def get_default_timezone_name():
     return _get_timezone_name(get_default_timezone())
 
 
-_active = local()
+_active = Local()
 
 
 def get_current_timezone():
diff --git a/django/utils/translation/reloader.py b/django/utils/translation/reloader.py
index 8e2d320208..2d69ad44e0 100644
--- a/django/utils/translation/reloader.py
+++ b/django/utils/translation/reloader.py
@@ -1,6 +1,7 @@
-import threading
 from pathlib import Path
 
+from asgiref.local import Local
+
 from django.apps import apps
 
 
@@ -25,5 +26,5 @@ def translation_file_changed(sender, file_path, **kwargs):
         gettext._translations = {}
         trans_real._translations = {}
         trans_real._default = None
-        trans_real._active = threading.local()
+        trans_real._active = Local()
         return True
diff --git a/django/utils/translation/trans_real.py b/django/utils/translation/trans_real.py
index f4985fb3c1..e089597ccb 100644
--- a/django/utils/translation/trans_real.py
+++ b/django/utils/translation/trans_real.py
@@ -5,7 +5,8 @@ import os
 import re
 import sys
 import warnings
-from threading import local
+
+from asgiref.local import Local
 
 from django.apps import apps
 from django.conf import settings
@@ -20,7 +21,7 @@ from . import to_language, to_locale
 # Translations are cached in a dictionary for every language.
 # The active translations are stored by threadid to make them thread local.
 _translations = {}
-_active = local()
+_active = Local()
 
 # The default translation is based on the settings file.
 _default = None