[Python] RuntimeError: unable to perform operation on TCPTransport the handler is closed

I'm trying to make an HTTP benchmark test on my local machine with autocannon tool to my fresh, brand-new project setup that I've built on FastAPI + uvicorn.

But at some point or randomly (I don't know what's happening) I'm having an ASGI exception.

[2019-11-14 14:16:40 +0100] [98098] [ERROR] Exception in ASGI application
Traceback (most recent call last):
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/uvicorn/protocols/http/httptools_impl.py", line 385, in run_asgi
result = await app(self.scope, self.receive, self.send)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/uvicorn/middleware/proxy_headers.py", line 45, in __call__
return await self.app(scope, receive, send)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/fastapi/applications.py", line 139, in __call__
await super().__call__(scope, receive, send)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/applications.py", line 134, in __call__
await self.error_middleware(scope, receive, send)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/middleware/errors.py", line 178, in __call__
raise exc from None
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/middleware/errors.py", line 156, in __call__
await self.app(scope, receive, _send)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/exceptions.py", line 73, in __call__
raise exc from None
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/exceptions.py", line 62, in __call__
await self.app(scope, receive, sender)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/routing.py", line 590, in __call__
await route(scope, receive, send)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/routing.py", line 208, in __call__
await self.app(scope, receive, send)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/routing.py", line 44, in app
await response(scope, receive, send)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/responses.py", line 125, in __call__
"headers": self.raw_headers,
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/exceptions.py", line 59, in sender
await send(message)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/starlette/middleware/errors.py", line 153, in _send
await send(message)
File "/Users/yigidix/Projects/url_shortener/lib/python3.7/site-packages/uvicorn/protocols/http/httptools_impl.py", line 482, in send
self.transport.write(b"".join(content))
File "uvloop/handles/stream.pyx", line 673, in uvloop.loop.UVStream.write
File "uvloop/handles/handle.pyx", line 159, in uvloop.loop.UVHandle._ensure_alive
RuntimeError: unable to perform operation on <TCPTransport closed=True reading=False 0x7fb255569780>; the handler is closed


To start my application, I do:

gunicorn url_shortener:app -w 1 -k uvicorn.workers.UvicornWorker

I tried to raise the number of the workers. I still get these exceptions.
​

To benchmark test, I do:

autocannon -c 100 -d 40 -p 10 localhost:8000/shorten -H "Content-Type: application/json" -m POST -b '{"url": "http://yigitgenc.com"}'


P.S: My database (PostgreSQL) works on Docker container. And also I do async database interactions (for sure). Maybe adding this info would be helpful.

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