Will calling a sessionmaker or closing a session block?

[Chris Withers]

Hi All,

Given this async function (asgi middleware, as it happens):

@app.middleware('http')
async def make_db_session(request: Request, call_next):
    request.state.db = Session()
    response = await call_next(request)
    request.state.db.close()
    return response

Would either the call to Session, which is a sessionmaker, or
db.close(), be expected to block?
I can't remember whether instantiating a session will open a network
connection, or whether close will similarly do network io, so thought
I'd ask...

Chris

[Mike Bayer]

So that's an empty Session, which won't do anything immediately, however if anything is done on it that uses a database, then that all blocks, and if so, db.close() can also block because it has to cleanup the database connection which is definitely blocking IO stuff.   If you didn't do anything with engines or connections, then db.close() won't block.

If you aren't doing anything with the database then I can't imagine why you'd want to use a Session inside of an async though.  

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