Concurrent access exception (sqlalchemy asyncio)

Describe the bug

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/baloneo/PycharmProjects/sanic-learn/venv/lib/python3.8/site-packages/sanic/request.py", line 187, in respond
    response = await self.app._run_response_middleware(
  File "_run_response_middleware", line 22, in _run_response_middleware
    from ssl import Purpose, SSLContext, create_default_context
  File "/home/baloneo/PycharmProjects/sanic-learn/app/__init__.py", line 26, in close_session
    _base_model_session_ctx.reset(request.ctx.session_ctx_token)
RuntimeError: <Token used var=<ContextVar name='session' at 0x7fcebbce4b80> at 0x7fceb99a45c0> has already been used once
[2021-11-03 13:32:36 +0800] [1826175] [ERROR] Exception occurred in one of response middleware handlers
Traceback (most recent call last):
  File "/home/baloneo/PycharmProjects/sanic-learn/venv/lib/python3.8/site-packages/sanic/http.py", line 141, in http1
    await self.protocol.request_handler(self.request)
  File "handle_request", line 100, in handle_request
    "_future_routes",
  File "/home/baloneo/PycharmProjects/sanic-learn/venv/lib/python3.8/site-packages/sanic/response.py", line 122, in send
    await self.stream.send(data, end_stream=end_stream)
  File "http1_response_header", line 70, in http1_response_header
  File "send", line 7, in send
asyncio.exceptions.CancelledError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/baloneo/PycharmProjects/sanic-learn/venv/lib/python3.8/site-packages/sanic/request.py", line 187, in respond
    response = await self.app._run_response_middleware(
  File "_run_response_middleware", line 22, in _run_response_middleware
    from ssl import Purpose, SSLContext, create_default_context
  File "/home/baloneo/PycharmProjects/sanic-learn/app/__init__.py", line 26, in close_session
    _base_model_session_ctx.reset(request.ctx.session_ctx_token)
RuntimeError: <Token used var=<ContextVar name='session' at 0x7fcebbce4b80> at 0x7fceb990d240> has already been used once

To Reproduce

Follow the tutorial: https://sanicframework.org/en/guide/how-to/orm.html#sqlalchemy

same code

from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import sessionmaker

_base_model_session_ctx = ContextVar("session")


@app.middleware("request")
async def inject_session(request):
    request.ctx.session = sessionmaker(engine, AsyncSession, expire_on_commit=False)()
    request.ctx.session_ctx_token = _base_model_session_ctx.set(request.ctx.session)


@app.middleware("response")
async def close_session(request, response):
    if hasattr(request.ctx, "session_ctx_token"):
        _base_model_session_ctx.reset(request.ctx.session_ctx_token)
        await request.ctx.session.close()

@bp.route('/data', methods=['GET'])
async def get_data(request: Request):
    session: AsyncSession = request.ctx.session
    async with session.begin():
        stmt = select(Data)
        row = await session.execute(stmt)
        for i in row:
            print(i)

    return json({})

using wrk, https://github.com/wg/wrk

➜  /tmp wrk -t5 -d10s -c100 http://127.0.0.1:8000/api/v1/data
Running 10s test @ http://127.0.0.1:8000/api/v1/data
  5 threads and 100 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     1.05s   187.32ms   1.99s    90.38%
    Req/Sec    23.39     15.98    80.00     61.19%
  715 requests in 10.03s, 67.03KB read
  Socket errors: connect 0, read 0, write 0, timeout 102
Requests/sec:     71.25
Transfer/sec:      6.68KB

Versions

• OS:Linuxmint 20.2 uma
• Python:3.8
• SQLAlchemy:1.4.26
• Database:MySQL8.0
• DBAPI (eg: psycopg, cx_oracle, mysqlclient):aiomysql

Additional context

No response

[ahopkins]

cancel() also accepts a “msg” argument, might it be a good idea for this “message” to be added to places like

I like this idea.

[ahopkins]

OK this would in theory be a response timeout but per the above doc that defaults to 60 seconds, so unless they are changing that, it’s not possible this particular cancel() is it because their whole test case runs in 10 seconds.

Yes. Brain fart. I meant response, which as you mentioned defaults to 60s.