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[BUG] WinError 10022 when run on Windows with workers > 1

See original GitHub issue

The error observed on Windows 10 with Python-3.6-amd64, Python-3.7-amd64, Python-3.8-amd64. Sample app:

async def app(scope, receive, send):
    assert scope['type'] == 'http'
    await send({
        'type': 'http.response.start',
        'status': 200,
        'headers': [
            [b'content-type', b'text/plain'],
        ]
    })
    await send({
        'type': 'http.response.body',
        'body': b'Uvicorn is the best!',
    })

OK when workers=1:

(venv) C:\Users\vasiliy.pankov\Projects\uvicorn-lab>uvicorn server:app
[32mINFO[0m:     Started server process [[36m17728[0m]
[32mINFO[0m:     Uvicorn running on [1mhttp://127.0.0.1:8000[0m (Press CTRL+C to quit)
[32mINFO[0m:     Waiting for application startup.
[32mINFO[0m:     ASGI 'lifespan' protocol appears unsupported.
[32mINFO[0m:     Application startup complete.
[32mINFO[0m:     Shutting down
[32mINFO[0m:     Finished server process [[36m17728[0m]

WinError 10022 When workers > 1

(venv) C:\Users\vasiliy.pankov\Projects\uvicorn-lab>uvicorn --workers 2 server:app
[32mINFO[0m:     Uvicorn running on [1mhttp://127.0.0.1:8000[0m (Press CTRL+C to quit)
[32mINFO[0m:     Started parent process [[36m[1m13020[0m]
[32mINFO[0m:     Started server process [[36m6888[0m]
[32mINFO[0m:     Waiting for application startup.
[32mINFO[0m:     ASGI 'lifespan' protocol appears unsupported.
[32mINFO[0m:     Application startup complete.
[32mINFO[0m:     Started server process [[36m19460[0m]
Process SpawnProcess-1:
Traceback (most recent call last):
  File "C:\Python\Python38\lib\multiprocessing\process.py", line 313, in _bootstrap
    self.run()
  File "C:\Python\Python38\lib\multiprocessing\process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "c:\users\vasiliy.pankov\projects\uvicorn-lab\venv\lib\site-packages\uvicorn\subprocess.py", line 73, in subprocess_started
    target(sockets=sockets)
  File "c:\users\vasiliy.pankov\projects\uvicorn-lab\venv\lib\site-packages\uvicorn\main.py", line 341, in run
    loop.run_until_complete(self.serve(sockets=sockets))
  File "C:\Python\Python38\lib\asyncio\base_events.py", line 608, in run_until_complete
    return future.result()
  File "c:\users\vasiliy.pankov\projects\uvicorn-lab\venv\lib\site-packages\uvicorn\main.py", line 358, in serve
    await self.startup(sockets=sockets)
  File "c:\users\vasiliy.pankov\projects\uvicorn-lab\venv\lib\site-packages\uvicorn\main.py", line 386, in startup
    server = await loop.create_server(
  File "C:\Python\Python38\lib\asyncio\base_events.py", line 1469, in create_server
    server._start_serving()
  File "C:\Python\Python38\lib\asyncio\base_events.py", line 309, in _start_serving
    sock.listen(self._backlog)
OSError: [WinError 10022] An invalid argument was supplied