[BUG] Error with the reloader

Describe the bug

Whenever I do

uvicorn api.index:app --reload

Then change the file index, I get an error like this

Accept failed on a socket
socket: <asyncio.TransportSocket fd=592, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('127.0.0.1', 8000)>
(See the full log below)

To Reproduce

1. Create a file with:

# api/index.py
from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def index():
    print("boo")
    return {"Hello": "World"}

1. run the app using uvicorn api.index:app --reload.
2. Open the browser and call the endpoint /.
3. Change the content of the file api/index.py so that the reloader gets triggered.
4. I expected it to reload the server, instead the error specified below happened.

Expected behavior

Reload the application, and continue to work as normal.

Environment

• OS: Windows
• FastAPI Version [e.g. 0.3.0]:

python -c "import fastapi; print(fastapi.__version__)"
email-validator not installed, email fields will be treated as str.
To install, run: pip install email-validator
0.44.0

• Python version:

python --version
Python 3.8.0

Logs

uvicorn index:app --reload ?[32mINFO?[0m: Uvicorn running on ?[1mhttp://127.0.0.1:8000?[0m (Press CTRL+C to quit) ?[32mINFO?[0m: Started reloader process [?[36m?[1m1232?[0m] ?[33mWARNING?[0m: email-validator not installed, email fields will be treated as str. To install, run: pip install email-validator ?[32mINFO?[0m: Started server process [?[36m13256?[0m] ?[32mINFO?[0m: Waiting for application startup. ?[32mINFO?[0m: Application startup complete. ?[33mWARNING?[0m: Detected file change in ‘index.py’. Reloading… ?[33mWARNING?[0m: email-validator not installed, email fields will be treated as str. To install, run: pip install email-validator ?[32mINFO?[0m: Started server process [?[36m1064?[0m] ?[31mERROR?[0m: Accept failed on a socket socket: <asyncio.TransportSocket fd=592, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=(‘127.0.0.1’, 8000)> Traceback (most recent call last): File “C:\Users\wass1\AppData\Local\Programs\Python\Python38\Lib\asyncio\proactor_events.py”, line 817, in loop f = self._proactor.accept(sock) File “C:\Users\wass1\AppData\Local\Programs\Python\Python38\Lib\asyncio\windows_events.py”, line 545, in accept self._register_with_iocp(listener) File “C:\Users\wass1\AppData\Local\Programs\Python\Python38\Lib\asyncio\windows_events.py”, line 714, in _register_with_iocp _overlapped.CreateIoCompletionPort(obj.fileno(), self._iocp, 0, 0) OSError: [WinError 87] The parameter is incorrect ?[32mINFO?[0m: Waiting for application startup. ?[32mINFO?[0m: Application startup complete.

[yuuuxt]

I encountered this issue too. I turned to use docker and it won’t bother. Here’s what I found, hope it helps:

use tiangolo/uvicorn-gunicorn and use CMD /start-reload.sh in Dockerfile;

set volume in the docker-compose.yml

volumes:
 - .:/app

[dmontagu]

I believe this is an issue with uvicorn on Windows. I think if you use the asyncio event loop the issue goes away. I can’t easily look for them now but I recall one or two recent issues where this was raised and solved. @euri10 might know more?