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Graph/event-loop-blocking-semantics

Pattern

Event Loop Blocking Semantics

event-loop-blocking-semantics

Blocking calls and long-lived client/session resources behave differently from naive expectations under an event loop: thread-blocking may still allow progress via periodic GIL release, async streaming can hang, and background tasks can delay shutdown.

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Updated7/5/2026

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30 linked nodes

Deciding where to wire socket event listeners to keep client state in sync: inside React hooks/components (registering callbacks in useEffect) versus inside a middleware/store layer or the socket class itself. The question also asks about the downsides of each approach.

As long as you lock more than a single thing at a time, you risk deadlocks. — lock more than a single thing at a time. Tension: You hold B waiting for A, they hold A waiting for B. Outcome: one of you has to abort or you're stuck.

PointerEvent wasn't properly simulated in the test environment

one failed write aborted the rest of the batch — structured post-turn extraction wrote events and beliefs without per-entry error isolation. Outcome: leaving future event inserts vulnerable once the initial partition window expired.

A component suspended while responding to synchronous input

sometimes the code passes through the await statement, but other times it gets stuck at the await — This code runs without any issues locally, but it hangs when deployed on Vercel. Tension: Sometimes it triggers successfully, while other times it gets stuck at the first call. Outcome: Disable auto pipelining and try running the commands one by one.

if line exists `await startup_consumer()` then there are no logs of `startup_sync_consumer()` and vise a versa — I am running two kafka consummers in fastAPI application. Tension: Looks like each consumer blocks event loop. Outcome: How to fix it?

background task blocks eventloop — reload = True or workers > 1. Tension: I immediately get response in my browser and then background task blocks eventloop.

facing error that `event loop is closed` — I have been working on yet another API using FastAPI and trying to write test cases for the APIs. Tension: using `asyncpg` driver/library to connect to the main db and for testcases using `aiosqlite` driver/library. Outcome: re-run the tests and report back on if it mitigates the issue.

some events are asynchronous and not come from a frontend request.

the two requests are executed "in parallel." — If I make two requests — the first one to the sync endpoint and the second one to the async endpoint — almost at the same time. Tension: I expected the event loop to be blocked. Outcome: the two requests are executed "in parallel.".

Waiting for background tasks to complete. — Whenever I gracefully shut down my FastAPI app by saving a file (with the `--reload` option). Tension: "Shutting down sessions" is never logged because it is waiting for all background tasks to be completed, which will never happen. Outcome: How am I supposed to close my sessions so that FastAPI can properly shut down?

job status stored in one handler is not visible in the waiting code

the reason for the various threads appearing in the logs — when you pass a synchronous generator to `EventSourceResponse`. Tension: you seem to be returning from the `/` endpoint. Outcome: `EventSourceResponse` will execute the `def` function in a separate thread from an external threadpool and then `await` it.

main() resolves, the final JSONL event prints, but the process never exits — Operator-triggered backfill scripts (run_phase3_message_requests_backfill.ts, run_phase3_messages_backfill.ts). Tension: CI/operator scripts kill it with SIGINT or timeout.

Webhook endpoint dispatches registered event jobs in the same process, causing processing delays and even timeouts

Java daemon threads that require access to `ScopedValues` as they were bound at the time the daemon thread is created — for child threads to inherit `ScopedValues` it is required to use the `StructuredTaskScope` fork/join protocol. Tension: that protocol does not work for daemon threads because it is impossible to create a scope for them that never terminates. Outcome: the daemon thread can continue executing after main() ends and any scope created in main() will, by definition, be terminated.

Hard timeout cancels the client future, but successful requests show increased latency

The behavior is that I expected is that each threads enqueues and deques in the sequential order that the threads used in enqueue the values, but this is not the case. — using `built-in java ArrayBlockingQueue` and `custom implementation`. Outcome: q.add(...) and q.poll() may alternate.

the Main thread was blocked till the subscribe method completion — Mono.just(getValue()).subscribe(value -> System.out.println(value));. Outcome: Can someone make this program asynchronous?

But it doesn't work like that. — I wanted to try power of virtual threads in Java in a simple application which consists of many tasks. Tension: My expectation was that the queries are executed almost at the same time because the significant part of task is basically waiting for the response.

events handling is executed in a greedy manner — when every Observer gives all events bef. Tension: it doesn't. Outcome: It is not a bug with the `Scheduler` but the consequence of the `observeOn` which always operates in a greedy manner.

do my fences interrupt other guests on the machine? — running in a VM on a cloud provider. Tension: If not, how's that possible since this is an op implemented in hardware and not software? Outcome: Fences are local, affecting only the current thread.

Go goroutine blocks forever on a channel send after parent context cancellation

After enabling Spring Boot virtual threads, the application deadlocks under load. Thread dumps show virtual threads parked waiting for object monitors inside synchronized methods/blocks.

tasks keep running after the component or GameObject is destroyed — In s&box, async/await in Components. Tension: Using raw Task.Delay means tasks keep running after the component or GameObject is destroyed. Outcome: causing null reference exceptions and ghost behavior.

Checked the production page and direct graph endpoints, then inspected the API stream route and client hook. — The significant-tier route had no explicit warning/error frame contract and could proceed with an empty allocation or empty result. Tension: The client treated a zero-node stream as a normal preview fallback without surfacing why. Outcome: Existing tests covered normal compact frames but did not assert empty significant-tier recovery or diagnostic frames.

SESSION_HANDOFF.md only gets written at clean session end — crash/OOM/gateway restart. Tension: not during unexpected termination.

the custom requestAnimationFrame loop never went idle — after live graph traversal events. Tension: those unresolved pulses stayed in the pulse map. Outcome: The renderer also performed full instanced-node matrix updates during pulse-only frames and kept expensive force-graph link rendering active longer than necessary.

the implementation still enqueued a sweep unconditionally for message and message-request writes — A TypeScript service documented that asynchronous privacy sweeps should only be queued when synchronous findings exist or a deferred-scan predicate matches. Tension: the implementation still enqueued a sweep unconditionally. Outcome: for message and message-request writes.

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