Terminate function does not work when a stream is cancelled prematurely when in an anyio task group

• asyncpg version: 0.29.0
• PostgreSQL version: 14.10
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: Yes, I can reproduce it locally
• Python version: 3.12
• Platform: linux and Mac OS
• Do you use pgbouncer?: No
• Did you install asyncpg with pip?: Yes
• If you built asyncpg locally, which version of Cython did you use?: n/a
• Can the issue be reproduced under both asyncio and
  uvloop?: No, the issue is not producible with asyncio only with anyio

Hi, I have a Fast API application that uses SQLAlchemy and asyncpg. I opened up a discussion on the SQLAlchemy page here (full discussion) reporting a major problem that affected my application after an update they released.

To summarize the problem and what we concluded in that discussion,

I asynchronously stream data from my API to a client using the starlette StreamingResponse class which takes advantage ofanyio under the hood. For some reason when the anyio task group gets cancelled before the stream is finished the asyncpg terminate function does not terminate the connection when the close function is used first, leaving it stuck in an idle in transaction state. This causes connections to run up eventually stopping other applications from creating new connections.

With some help from the SQLAlchemy folks, after some time working through the problem we were able to reproduce a small example of my problem using only the asyncpg and anyio libraries here (Example of problem)

Any help resolving this issue would be greatly appreciated! If you need any more info from me please do not hesitate to message back

Thanks in advance!

最小复现已链接在 SQLAlchemy 讨论中；首先使用所报告的 asyncpg 和 anyio 设置运行它，并在任务组取消期间跟踪 close-then-terminate 路径。使用 asyncpg 的 terminate 和 close 入口来定位连接生命周期处理逻辑。完成标准是：被取消的流不再让连接处于 idle in transaction 状态。