ashb opened a new pull request, #48880:
URL: https://github.com/apache/airflow/pull/48880
The TriggerRunnerSupervisor previoulsy sent messges to the Triggerer directly
when a trigger needed to be created or cancelled, and this initially worked
fine, but when we later added the ability for Triggers to access Connections
and Variables this ended up causing problems.
The issue was that we broke one of the "rules" of comms, which is even
documents as such in `airflow/sdk/exeuction_time/comms.py`:
> * No messages are sent to task process except in response to a request.
> (This is because the task process will be running user's code, so we
can't
> read from stdin until we enter our code, such as when requesting an XCom
) value etc.)
The net result of this was that since the supervisor sent messages
un-solicited, if things were timed badly, then the trigger would send a
request for a Conn, and the supervisor would reply with a trigger to create
etc.
This sort of instability was very likely the cause of our flakeyness in the
`test_trigger_can_access_variables_connections_and_xcoms` test.
This fixes things by making the TriggerRunnerSupervisor collect the triggers
to create/cancel in a deqeue in memory, and respond to the
TriggerStateChanges
messages with TriggerStateSync with the info it would have sent on an
as-needed basis.
In order to make sure that we only send+receive one message at a time I have
swapped from the `threading.lock` to `aiologic.Lock` which allows for better
locking/waiting behaviour between threads (which is what Triggers will use
via
the `sync_to_async`) and the main TriggerRunner.
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