Override default asyncio event loop with reload only on Windows (#1257)

* Override default asyncio loop with reload only

* shortened warning

* Added type hints for keyword arguments

* Changed to explicit reload keyword argument for loop setups

uvicorn/config.py

@@ -493,7 +493,7 @@ def load(self) -> None:
     def setup_event_loop(self) -> None:
         loop_setup: Optional[Callable] = import_from_string(LOOP_SETUPS[self.loop])
         if loop_setup is not None:
-            loop_setup()
+            loop_setup(reload=self.reload)
 
     def bind_socket(self) -> socket.socket:
         logger_args: List[Union[str, int]]

uvicorn/loops/asyncio.py

@@ -1,7 +1,11 @@
 import asyncio
+import logging
 import sys
 
+logger = logging.getLogger("uvicorn.error")
 
-def asyncio_setup() -> None:  # pragma: no cover
-    if sys.version_info >= (3, 8) and sys.platform == "win32":
+
+def asyncio_setup(reload: bool = False) -> None:  # pragma: no cover
+    if sys.version_info >= (3, 8) and sys.platform == "win32" and reload:
+        logger.warning("The --reload flag should not be used in production on Windows.")
         asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())

uvicorn/loops/auto.py

@@ -1,11 +1,11 @@
-def auto_loop_setup() -> None:
+def auto_loop_setup(reload: bool = False) -> None:
     try:
         import uvloop  # noqa
     except ImportError:  # pragma: no cover
         from uvicorn.loops.asyncio import asyncio_setup as loop_setup
 
-        loop_setup()
+        loop_setup(reload=reload)
     else:  # pragma: no cover
         from uvicorn.loops.uvloop import uvloop_setup
 
-        uvloop_setup()
+        uvloop_setup(reload=reload)

uvicorn/loops/uvloop.py

@@ -3,5 +3,5 @@
 import uvloop
 
 
-def uvloop_setup() -> None:
+def uvloop_setup(reload: bool = False) -> None:
     asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())