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Description
I have little expertise in using asyncio. Are any of these problematic?
% ruff check --select=ASYNC,RUF006 --statistics
16 RUF006 asyncio-dangling-task
3 ASYNC110 async-busy-wait
2 ASYNC230 blocking-open-call-in-async-function
1 ASYNC251 blocking-sleep-in-async-function
Found 22 errors.
% ruff rule RUF006 # https://docs.astral.sh/ruff/rules/asyncio-dangling-task
asyncio-dangling-task (RUF006)
Derived from the Ruff-specific rules linter.
What it does
Checks for asyncio.create_task and asyncio.ensure_future calls
that do not store a reference to the returned result.
Why is this bad?
Per the asyncio documentation, the event loop only retains a weak
reference to tasks. If the task returned by asyncio.create_task and
asyncio.ensure_future is not stored in a variable, or a collection,
or otherwise referenced, it may be garbage collected at any time. This
can lead to unexpected and inconsistent behavior, as your tasks may or
may not run to completion.
Example
import asyncio
for i in range(10):
# This creates a weak reference to the task, which may be garbage
# collected at any time.
asyncio.create_task(some_coro(param=i))Use instead:
import asyncio
background_tasks = set()
for i in range(10):
task = asyncio.create_task(some_coro(param=i))
# Add task to the set. This creates a strong reference.
background_tasks.add(task)
# To prevent keeping references to finished tasks forever,
# make each task remove its own reference from the set after
# completion:
task.add_done_callback(background_tasks.discard)References
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