allow async signal receivers

CHANGES.rst

@@ -30,6 +30,7 @@ Unreleased
     decorated function if locking is needed. :issue:`4993`
 -   Signals are always available. ``blinker>=1.6.2`` is a required dependency. The
     ``signals_available`` attribute is deprecated. :issue:`5056`
+-   Signals support ``async`` subscriber functions. :pr:`5049`
 -   Remove uses of locks that could cause requests to block each other very briefly.
     :issue:`4993`
 -   Use modern packaging metadata with ``pyproject.toml`` instead of ``setup.cfg``.

src/flask/app.py

@@ -1389,7 +1389,7 @@ class Flask(Scaffold):
         .. versionadded:: 0.3
         """
         exc_info = sys.exc_info()
-        got_request_exception.send(self, exception=e)
+        got_request_exception.send(self, _async_wrapper=self.ensure_sync, exception=e)
         propagate = self.config["PROPAGATE_EXCEPTIONS"]
 
         if propagate is None:
@@ -1493,7 +1493,7 @@ class Flask(Scaffold):
         self._got_first_request = True
 
         try:
-            request_started.send(self)
+            request_started.send(self, _async_wrapper=self.ensure_sync)
             rv = self.preprocess_request()
             if rv is None:
                 rv = self.dispatch_request()
@@ -1521,7 +1521,9 @@ class Flask(Scaffold):
         response = self.make_response(rv)
         try:
             response = self.process_response(response)
-            request_finished.send(self, response=response)
+            request_finished.send(
+                self, _async_wrapper=self.ensure_sync, response=response
+            )
         except Exception:
             if not from_error_handler:
                 raise
@@ -2052,7 +2054,7 @@ class Flask(Scaffold):
                 for func in reversed(self.teardown_request_funcs[name]):
                     self.ensure_sync(func)(exc)
 
-        request_tearing_down.send(self, exc=exc)
+        request_tearing_down.send(self, _async_wrapper=self.ensure_sync, exc=exc)
 
     def do_teardown_appcontext(
         self, exc: t.Optional[BaseException] = _sentinel  # type: ignore
@@ -2077,7 +2079,7 @@ class Flask(Scaffold):
         for func in reversed(self.teardown_appcontext_funcs):
             self.ensure_sync(func)(exc)
 
-        appcontext_tearing_down.send(self, exc=exc)
+        appcontext_tearing_down.send(self, _async_wrapper=self.ensure_sync, exc=exc)
 
     def app_context(self) -> AppContext:
         """Create an :class:`~flask.ctx.AppContext`. Use as a ``with``

src/flask/ctx.py

@@ -242,7 +242,7 @@ class AppContext:
     def push(self) -> None:
         """Binds the app context to the current context."""
         self._cv_tokens.append(_cv_app.set(self))
-        appcontext_pushed.send(self.app)
+        appcontext_pushed.send(self.app, _async_wrapper=self.app.ensure_sync)
 
     def pop(self, exc: t.Optional[BaseException] = _sentinel) -> None:  # type: ignore
         """Pops the app context."""
@@ -260,7 +260,7 @@ class AppContext:
                 f"Popped wrong app context. ({ctx!r} instead of {self!r})"
             )
 
-        appcontext_popped.send(self.app)
+        appcontext_popped.send(self.app, _async_wrapper=self.app.ensure_sync)
 
     def __enter__(self) -> "AppContext":
         self.push()

src/flask/helpers.py

@@ -327,8 +327,10 @@ def flash(message: str, category: str = "message") -> None:
     flashes = session.get("_flashes", [])
     flashes.append((category, message))
     session["_flashes"] = flashes
+    app = current_app._get_current_object()  # type: ignore
     message_flashed.send(
-        current_app._get_current_object(),  # type: ignore
+        app,
+        _async_wrapper=app.ensure_sync,
         message=message,
         category=category,
     )

src/flask/templating.py

@@ -126,9 +126,13 @@ class DispatchingJinjaLoader(BaseLoader):
 
 def _render(app: "Flask", template: Template, context: t.Dict[str, t.Any]) -> str:
     app.update_template_context(context)
-    before_render_template.send(app, template=template, context=context)
+    before_render_template.send(
+        app, _async_wrapper=app.ensure_sync, template=template, context=context
+    )
     rv = template.render(context)
-    template_rendered.send(app, template=template, context=context)
+    template_rendered.send(
+        app, _async_wrapper=app.ensure_sync, template=template, context=context
+    )
     return rv
 
 
@@ -163,11 +167,15 @@ def _stream(
     app: "Flask", template: Template, context: t.Dict[str, t.Any]
 ) -> t.Iterator[str]:
     app.update_template_context(context)
-    before_render_template.send(app, template=template, context=context)
+    before_render_template.send(
+        app, _async_wrapper=app.ensure_sync, template=template, context=context
+    )
 
     def generate() -> t.Iterator[str]:
         yield from template.generate(context)
-        template_rendered.send(app, template=template, context=context)
+        template_rendered.send(
+            app, _async_wrapper=app.ensure_sync, template=template, context=context
+        )
 
     rv = generate()