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Graph/async-context-misuse

AntiPattern

Async Context Misuse

async-context-misuse

Async code fails when coroutines and context managers are wired incorrectly—objects created outside async flows, async with consuming a coroutine, or blocking sleeps during the event loop—leading to hangs, deadlocks, and missing lifecycle methods.

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Public graph metadata

Updated6/30/2026

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30 linked nodes

MATCHESSolution

const usePermissionsStoreAsync = hook(usePermissionsStore, /*suspense*/false); — const YourComponent = () => {. Tension: if (userPermissions.isLoading) { return Loading... ; } if (userPermissions.error) { return An error occurred ; }. Outcome: Try Leo Query. It handle's async data for Zustand.

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

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If you convert all operations to perform asynchronously (using `aiosqlite`) , the issue will be mitigated. — When a route in FastAPI is listed as asynchronous (`async def`). Tension: that doesn't fully solve the inherent single writer problem of Sqlite. Outcome: Here's a fully operational update of the FastAPI server logic:.

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I also offer an alternative `executor` class which can preserve the contextvar values across threads — when YOUR code is the one making the `loop.run_in_executor` call. Tension: in this example, the code making this is the framework code. Outcome: but that can only be used when YOUR code is the one making the `loop.run_in_executor` call.

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To manage background processes. Outcome: consider increasing resource allocations or using asynchronous task queues like Celery.

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it will be reset as soon as the current HTTP view is done. Tension: unless explicitly saved with something like a `contextvars.copy_context()` call while the task is active. Outcome: the forked context is disposed.

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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'.

MATCHESSolution

You need to install helper packages, such as `anyio` or `pytest-asyncio`. — Async fixtures do not work out of the box. Tension: NB. Use pytest_asyncio.fixture NOT pytest.fixture. Outcome: Example.

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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 `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.

MATCHESSolution

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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the reason for the various threads appearing in the logs — when you pass a synchronous generator to `EventSourceResponse`. Tension: a normal `def` function instead of `async def`. Outcome: please take a look at the implementation of the `EventSourceResponse` class.

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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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Initialize Eureka using the async API (e.g., `eureka_client.init_async(...)`) and/or move initialization into an appropriate async startup hook so it doesn’t start a new event loop at import time.

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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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Update the Context state from within the SignalR handler by invoking context methods (e.g., incorporating/using the patrols and update functions directly in the SignalR call path) so the global state is actually changed when messages arrive.

MATCHESSolution

Use asynchronous sending with callbacks. — If you're using KafkaTemplate.send() without handling the ListenableFuture returned. Tension: you're effectively blocking the calling thread until the message is acknowledged by the Kafka broker. Outcome: The addCallback method allows you to execute code when the send operation succeeds or fails, without blocking the main thread.

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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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the goroutine blocks forever on the channel send because nobody is reading — When the parent context is cancelled, the goroutine blocks forever on the channel send because nobody is reading. Tension: if the result is ready at the exact moment the context cancels, which case fires?

MATCHESSolution

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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