Revert "Enable async JupyterApp" (#385)

This reverts commit e33fb74.

jupyter_core/application.py

@@ -29,7 +29,7 @@
     jupyter_path,
     jupyter_runtime_dir,
 )
-from .utils import ensure_dir_exists, get_event_loop
+from .utils import ensure_dir_exists
 
 # mypy: disable-error-code="no-untyped-call"
 
@@ -259,11 +259,6 @@ def initialize(self, argv: t.Any = None) -> None:
         self.update_config(cl_config)
         if allow_insecure_writes:
             issue_insecure_write_warning()
-        return
-
-    async def initialize_async(self) -> None:
-        """Perform async initialization of the application, will be called
-        after synchronous initialize."""
 
     def start(self) -> None:
         """Start the whole thing"""
@@ -279,33 +274,14 @@ def start(self) -> None:
             self.write_default_config()
             raise NoStart()
 
-        return
-
-    async def start_async(self) -> None:
-        """Perform async start of the app, will be called after sync start."""
-
     @classmethod
-    async def _async_launch_instance(cls, argv: t.Any = None, **kwargs: t.Any) -> None:
-        """Launch the instance from inside an event loop."""
+    def launch_instance(cls, argv: t.Any = None, **kwargs: t.Any) -> None:
+        """Launch an instance of a Jupyter Application"""
         try:
-            app = cls.instance(**kwargs)
-            app.initialize(argv)
-            await app.initialize_async()
-            app.start()
-            await app.start_async()
+            super().launch_instance(argv=argv, **kwargs)
         except NoStart:
             return
 
-    @classmethod
-    def launch_instance(cls, argv: t.Any = None, **kwargs: t.Any) -> None:
-        """Launch a global instance of this Application
-
-        If a global instance already exists, this reinitializes and starts it
-        """
-        loop = get_event_loop()
-        coro = cls._async_launch_instance(argv, **kwargs)
-        loop.run_until_complete(coro)
-
 
 if __name__ == "__main__":
     JupyterApp.launch_instance()

jupyter_core/utils/__init__.py

@@ -158,8 +158,18 @@ def wrapped(*args: Any, **kwargs: Any) -> Any:
         except RuntimeError:
             pass
 
-        loop = get_event_loop()
-        return loop.run_until_complete(inner)
+        # Run the loop for this thread.
+        # In Python 3.12, a deprecation warning is raised, which
+        # may later turn into a RuntimeError.  We handle both
+        # cases.
+        with warnings.catch_warnings():
+            warnings.simplefilter("ignore", DeprecationWarning)
+            try:
+                loop = asyncio.get_event_loop()
+            except RuntimeError:
+                loop = asyncio.new_event_loop()
+                asyncio.set_event_loop(loop)
+            return loop.run_until_complete(inner)
 
     wrapped.__doc__ = coro.__doc__
     return wrapped
@@ -184,21 +194,3 @@ async def ensure_async(obj: Awaitable[T] | T) -> T:
         return result
     # obj doesn't need to be awaited
     return cast(T, obj)
-
-
-def get_event_loop() -> asyncio.AbstractEventLoop:
-    # Get the loop for this thread.
-    # In Python 3.12, a deprecation warning is raised, which
-    # may later turn into a RuntimeError.  We handle both
-    # cases.
-    with warnings.catch_warnings():
-        warnings.simplefilter("ignore", DeprecationWarning)
-        try:
-            loop = asyncio.get_event_loop()
-        except RuntimeError:
-            if sys.platform == "win32":
-                loop = asyncio.WindowsSelectorEventLoopPolicy().new_event_loop()
-            else:
-                loop = asyncio.new_event_loop()
-            asyncio.set_event_loop(loop)
-    return loop

tests/test_application.py

@@ -125,17 +125,3 @@ def test_runtime_dir_changed():
     app.runtime_dir = td
     assert os.path.isdir(td)
     shutil.rmtree(td)
-
-
-class AsyncApp(JupyterApp):
-    async def initialize_async(self):
-        self.value = 10
-
-    async def start_async(self):
-        assert self.value == 10
-
-
-def test_async_app():
-    AsyncApp.launch_instance([])
-    app = AsyncApp.instance()
-    assert app.value == 10