Fix signal handling on Windows

This follows Hypercorn and both switches to signal rather than loop
signal handling if the latter isn't implemented and adds a periodic IO
event as required for Python 3.7.

Author: pgjones

src/quart/app.py

@@ -2,6 +2,7 @@
 
 import asyncio
 import os
+import platform
 import signal
 import sys
 import warnings
@@ -1373,7 +1374,11 @@ def _signal_handler(*_: Any) -> None:
 
         for signal_name in {"SIGINT", "SIGTERM", "SIGBREAK"}:
             if hasattr(signal, signal_name):
-                loop.add_signal_handler(getattr(signal, signal_name), _signal_handler)
+                try:
+                    loop.add_signal_handler(getattr(signal, signal_name), _signal_handler)
+                except NotImplementedError:
+                    # Add signal handler may not be implemented on Windows
+                    signal.signal(getattr(signal, signal_name), _signal_handler)
 
         server_name = self.config.get("SERVER_NAME")
         sn_host = None
@@ -1407,6 +1412,9 @@ def _signal_handler(*_: Any) -> None:
         print(f" * Running on {scheme}://{host}:{port} (CTRL + C to quit)")  # noqa: T201
 
         tasks = [loop.create_task(task)]
+        if platform.system() == "Windows":
+            tasks.append(loop.create_task(_windows_signal_support()))
+
         if use_reloader:
             tasks.append(loop.create_task(observe_changes(asyncio.sleep, shutdown_event)))
 
@@ -1971,3 +1979,11 @@ def _cancel_all_tasks(loop: asyncio.AbstractEventLoop) -> None:
                     "task": task,
                 }
             )
+
+
+async def _windows_signal_support() -> None:
+    # See https://bugs.python.org/issue23057, to catch signals on
+    # Windows it is necessary for an IO event to happen periodically.
+    # Fixed by Python 3.8
+    while True:
+        await asyncio.sleep(1)