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Graph/missing-await-and-coroutine-leak

AntiPattern

Async Await Boundary Misuse

missing-await-and-coroutine-leak

Async/await boundaries break when call sites pass unresolved coroutines or omit required awaits, and when async test scaffolding reuses event-loop/session state, causing context managers and DB session lifecycles to mismatch or leak.

Node Details

Public graph metadata

Updated7/14/2026

Connections

30 linked nodes

MATCHESSolution

Load the async user data with a Suspense-compatible async pattern (e.g., using `leo-query`’s `query`/`subscribe`) so the component waits until `currentUser` is available before rendering.

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handle a scenario when the code is fine but backend went offline — prefetching data with usePrefetchQuery. Tension: prefetch works.

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I'm playing around with NextJS app router, and Suspense — In my App router page. Tension: this suspense boundary won't do anything.

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Mock axios.get and await the assertion with waitFor()

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Manage the refreshing state more robustly — ensuring it only turns off after all async operations are complete. Tension: remove the arbitrary timeout. Outcome: ensure no state updates occur after the component begins to unmount.

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beforeEach(() => { vi.useRealTimers() }) — to the describe of the tests. Tension: I cannot modify and remove the setup scripts. Outcome: afterEach(() => { vi.useFakeTimers() }).

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Wrap you components that rely on React Query data — React Query data. Outcome: with Suspense and HydrationBoundary.

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delete the async from `fake_execute` — your `AsyncContextMock` needs to handle both use cases in your endpoint `await conn.execute()` and `async with conn.execute()`. Outcome: just make it a regular function so it returns your context manager directly, no coroutine wrapper.

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for `cursor.fetchone.return_value`, just use (2,) directly — `cursor.fetchone.return_value`. Tension: AsyncMock already makes it awaitable. Outcome: wrapping it again messes things up.

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single worker running async loop. Outcome: So you have a single worker running async loop and you block that loop.

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Pass `BackgroundTasks` from the route into your dependency. — when declared inside an async dependency. Tension: the background job never runs. Outcome: async def test_route(bg: BackgroundTasks, data=Depends(dependency)):.

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Change the `mocked_app` and database `client` fixtures from `scope='session'` to `scope='function'` so each test gets a fresh app/client setup with a clean lifecycle.

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Using a `session-scoped` pytest fixture, for managing the event loop — which ensures the same event loop will be used. Outcome: loop.close().

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Move the persistence/cleanup logic into code that runs at the end of the background task (or otherwise extend lifecycle explicitly for the background task), rather than relying on the request-scoped `asynccontextmanager` teardown for those updates.

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Use pytest_asyncio.fixture NOT pytest.fixture — @pytest_asyncio.fixture(scope='session', loop_scope='session'). Tension: async def my_fixture():. Outcome: yield 'foo'.

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Change the engine async fixture from session scope to function scope (remove scope="session") so all async fixtures/tests run on the same event loop, preventing the cross-loop Future/Task error.

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using `magicmock` to mock it could lead to unusual or unexpected behavior when checking for call counts — Since `get_item` might be an asynchronous function in your middleware. Tension: using `magicmock` to mock it could lead to unusual or unexpected behavior. Outcome: which is designed to work with async functions.

MATCHESSolution

Using `asyncio.sleep()` in a loop is perfectly fine. Tension: every time you `await` the sleep, you effectively yield control back to the event loop. Outcome: calling `asyncio.sleep(0)` does not sleep at all, but only yields control back to the event loop.

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I'd like to use `AsyncSession.sync_session` — async def get_session() -> AsyncSession: session = SessionLocal(). Tension: the code below fails with error. Outcome: use `AsyncSession.sync_session` but the code below fails with error.

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use `pytest_asyncio` and the async fixture — If you don't want to utilize an `AsyncClient` like the one by `httpx`. Tension: ensuring that the FastAPI app's lifespan context correctly works.

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any time you have an I/O bound process with lots of idle time — waiting for user input, waiting for a TLS handshake. Tension: wrapping it in an async task can let other code run.

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Ensure the S3 download runs in a way that doesn’t block the event loop (i.e., only use asyncio `await` if the underlying operation is truly non-blocking, otherwise move it to a thread/executor). Use `asyncio.sleep()` in the scheduler loop to yield control back to the event loop between updates.

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An async function was passed to useActionState.

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Or you can use `async/await` and `try/catch` — createAsyncThunk. Outcome: return data.

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Avoid running multiple DB operations concurrently on the same session by removing asyncio.gather and iterating sequentially, and/or use an async_scoped_session so each task uses its own session.

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Use React async state management (e.g., `useAsync` or `useEffect` + `useState`) to await `currentSession()`, render a loading UI while pending, and only compute `isGroupOne` from the resolved array (e.g., `groups.some(...)`) after the Promise resolves.

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I think it is better to use a custom context manager — if you need to isolate test methods from each other. Tension: you need to isolate test methods from each other. Outcome: here is what I am using.

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Rewrite the test as an async test and run it with an async test runner (e.g., pytest.mark.asyncio), using await on the async ORM methods (acreate/acount) instead of asyncio.run().

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Use Component.Task (TaskSource) for all async work inside components — inside components. Tension: it auto-cancels when the component is destroyed.

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Kept the protocol mismatch as a classified close cause — Added [REDACTED] and scoped device-auth invalidation for auth-state migrations, but did not clear unrelated browser storage. Tension: The real remediation for the observed loop is closing or hard-refreshing the stale tab so it loads the current SPA bundle. Outcome: Browser harness evidence classified the failure as protocol mismatch with high confidence, while fresh navigation connected normally.

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