bug report for coverage using starlette and async/await sqlalchemy

docker-compose.yml

version: "3.8"
services:
  postgres:
    restart: always
    image: postgres:12-alpine
    environment:
      POSTGRES_USER: "postgres"
      POSTGRES_PASSWORD: "postgres"
    ports:
       - "127.0.0.1:5432:5432"

output.txt

runing with default concurrency
start
{'?column?': 1}
start
{'?column?': 1}
Name                                         Stmts   Miss  Cover
----------------------------------------------------------------
starlette_async_sqlalchemy_coverage_bug.py      29      9    69%
----------------------------------------------------------------
TOTAL                                           29      9    69%

running with greenlet
start
{'?column?': 1}
start
{'?column?': 1}
Name                                         Stmts   Miss  Cover
----------------------------------------------------------------
starlette_async_sqlalchemy_coverage_bug.py      29      6    79%
----------------------------------------------------------------
TOTAL                                           29      6    79%

running with gevent
start
{'?column?': 1}
start
{'?column?': 1}
Name                                         Stmts   Miss  Cover
----------------------------------------------------------------
starlette_async_sqlalchemy_coverage_bug.py      29      6    79%
----------------------------------------------------------------
TOTAL                                           29      6    79%

requirements.txt

sqlalchemy~=1.4
asyncpg
requests
starlette
coverage
gevent

run.sh

docker-compose up -d

echo "runing with default concurrency"
coverage run starlette_async_sqlalchemy_coverage_bug.py
coverage report
coverage html

echo "running with greenlet"
coverage run --concurrency greenlet starlette_async_sqlalchemy_coverage_bug.py
coverage report
coverage html -d htmlcov_greenlet

echo "running with gevent"
coverage run --concurrency greenlet starlette_async_sqlalchemy_coverage_bug.py
coverage report
coverage html -d htmlcov_greenlet

starlette_async_sqlalchemy_coverage_bug.py

import sqlalchemy as sa
from sqlalchemy.ext.asyncio import create_async_engine

from starlette.applications import Starlette
from starlette.testclient import TestClient
from starlette.routing import Route
from starlette.responses import JSONResponse


engine = create_async_engine('postgresql+asyncpg://postgres:postgres@localhost/postgres')
engine2 = sa.create_engine('postgresql+asyncpg://postgres:postgres@localhost/postgres')

async def run(*args, **kwargs):
    print('start')
    async with engine.begin() as conn:
        result = await conn.execute(sa.text("select 1"))
        records = dict(result.mappings().first())

    print(records)
    return JSONResponse(records)

def run2(*args, **kwargs):
    print('start')
    with engine2.begin() as conn:
        result = conn.execute(sa.text("select 1"))
        records = dict(result.mappings().first())

    print(records)
    return JSONResponse(records)


app = Starlette(debug=True, routes=[
    Route('/run', run),
    Route('/run2', run),
])

def test_run():
    client = TestClient(app)
    client.get('/run')
    client.get('/run2')


if __name__ == "__main__":
    test_run()

Updated with greenlet, gevent and thread concurrencies:

Default (threading):

Greenlet and Gevent: