_run_compaction_for_sliding_window task can be garbage collected mid-execution

[cdombroski-google]

asyncio.create_task must have a strong reference otherwise they can get garbage collected.

https://docs.python.org/3/library/asyncio-task.html#asyncio.create_task:

Important Save a reference to the result of this function, to avoid a task disappearing mid-execution. The event loop only keeps weak references to tasks. A task that isn’t referenced elsewhere may get garbage collected at any time, even before it’s done. For reliable “fire-and-forget” background tasks, gather them in a collection:

adk-python/src/google/adk/runners.py

Lines 413 to 424 in 05aa3fa

	# Run compaction after all events are yielded from the agent.
	# (We don't compact in the middle of an invocation, we only compact at the end of an invocation.)
	if self.app and self.app.events_compaction_config:
	logger.info('Running event compactor.')
	# Run compaction in a separate task to avoid blocking the main thread.
	# So the users can still finish the event loop from the agent while the
	# compaction is running.
	asyncio.create_task(
	_run_compaction_for_sliding_window(
	self.app, session, self.session_service
	)
	)

Note that the create_task result is not stored.

[hangfei]

Good point. Do you happen to have any code to test the failure scenario that can be triggered by garbage collection ?

[cdombroski-google]

No. I found it while reading code trying to figure out internal b/446735634

[samiriff]

I run into this issue consistently in my CL - cl/824515017. Since my LLM call for summarizing events is a bit time-consuming, the _run_compaction_for_sliding_window_task seems to be killed before I can obtain a summary from the LLM and return compacted events.
However, if I await the _run_compaction_for_sliding_window_task task, then I see compacted events in my flow.