SocketModeClient.connect() is a "while True" retry loop that never checks
the client's closed flag, so anything still inside it when the shared
aiohttp session is closed keeps retrying against a session that can never
work again. That is the "Failed to connect (error: Session is closed);
Retrying..." spam in #46990, at a steady ping_interval cadence that only
a process restart clears.
_stop_socket_mode_handler closed the handler first and cancelled
afterwards, which loses the race. close_async() closes that shared
session, and three things can be inside connect() when it does: our own
start_async task, monitor_current_session() (on staleness) and
receive_messages() (on a CLOSE frame), the latter two reaching it
independently through connect_to_new_endpoint(). connect() also rebinds
current_session_monitor and message_receiver to fresh tasks when it
succeeds, so the set of live tasks changes across the awaits inside
close(). Cancelling from a snapshot taken partway through races a moving
target rather than closing the window.
So cancel all four before close_async() instead. With nothing left alive
to enter connect(), no rebinding can happen during teardown and the
window cannot open at all. The client's task attributes are read with
getattr so a rename inside the SDK degrades to a no-op instead of raising
during shutdown, and the wait is asyncio.wait with a timeout rather than
an unbounded await, so a task wedged in a network call cannot hold up
shutdown.
The underlying SDK defect is tracked at slackapi/python-slack-sdk#1913.
This replaces the earlier version of this change, which added a closed
session check when building a handler and another in the watchdog. Both
are unnecessary once teardown stops leaking tasks: each
AsyncSocketModeHandler builds its own SocketModeClient with a fresh
ClientSession, so a new handler cannot inherit a closed session, and the
current handler's session is only closed by the teardown path itself.
Dropping the watchdog check also keeps this off the ping/pong staleness
trigger proposed in #52923, which addresses a wedged live connection
rather than a leaked one.
Fixes#46990
7bbdabbef2