Fix OSError: [WinError 87] The parameter is incorrect

tests/test_config.py

@@ -544,3 +544,22 @@ def test_bind_fd_works_with_reload_or_workers(reload, workers):  # pragma: py-wi
     assert sock.getsockname() == ""
     sock.close()
     fdsock.close()
+
+
+@pytest.mark.parametrize(
+    "reload, workers, expected",
+    [
+        (True, 1, True),
+        (False, 2, True),
+        (False, 1, False),
+    ],
+    ids=[
+        "--reload=True --workers=1",
+        "--reload=False --workers=2",
+        "--reload=False --workers=1",
+    ],
+)
+def test_config_use_subprocess(reload, workers, expected):
+    config = Config(app=asgi_app, reload=reload, workers=workers)
+    config.load()
+    assert config.use_subprocess == expected

uvicorn/config.py

@@ -503,7 +503,7 @@ 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(reload=self.reload)
+            loop_setup(reload=self.reload, workers=self.workers)
 
     def bind_socket(self) -> socket.socket:
         logger_args: List[Union[str, int]]

uvicorn/loops/asyncio.py

@@ -1,11 +1,17 @@
 import asyncio
 import logging
 import sys
+from typing import Optional
 
 logger = logging.getLogger("uvicorn.error")
 
 
-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.")
+def asyncio_setup(
+    reload: bool = False, workers: Optional[int] = None
+) -> None:  # pragma: no cover
+    if (
+        sys.version_info >= (3, 8)
+        and sys.platform == "win32"
+        and any([reload, workers])
+    ):
         asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())

uvicorn/loops/auto.py

@@ -1,11 +1,14 @@
-def auto_loop_setup(reload: bool = False) -> None:
+from typing import Optional
+
+
+def auto_loop_setup(reload: bool = False, workers: Optional[int] = None) -> None:
     try:
         import uvloop  # noqa
     except ImportError:  # pragma: no cover
         from uvicorn.loops.asyncio import asyncio_setup as loop_setup
 
-        loop_setup(reload=reload)
+        loop_setup(reload=reload, workers=workers)
     else:  # pragma: no cover
         from uvicorn.loops.uvloop import uvloop_setup
 
-        uvloop_setup(reload=reload)
+        uvloop_setup(reload=reload, workers=workers)

uvicorn/loops/uvloop.py

@@ -1,7 +1,8 @@
 import asyncio
+from typing import Optional
 
 import uvloop
 
 
-def uvloop_setup(reload: bool = False) -> None:
+def uvloop_setup(reload: bool = False, workers: Optional[int] = None) -> None:
     asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())