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.

1 files changed, 32 insertions, 0 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