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Graph/atomic-cas-memory-ordering-mismatch

Pattern

Mismatched Concurrency Memory Ordering

atomic-cas-memory-ordering-mismatch

Atomic CAS success ordering is set too strong or fail ordering too weak, so correctness depends on memory effects that never occur on the intended path, breaking lock-free pops and leaving adjacent code observably inconsistent.

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Updated7/30/2026

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30 linked nodes

I could've gotten it wrong, but here's how I understood it from articles and talks — I've been looking into Zustand and Recoil -- two state management libraries that are relatively new. Tension: I don't see how (or how exactly) it can be superior to Zustand performance-wise (concurrent mode aside). Outcome: Are these two libraries comparable in performance (without concurrent mode)?

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.

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.

Query code and mutation code are unnecessarily coupled

parallel workers sometimes grab overlapping sets, then wait to mark them as being processed — At the time of item selection, you neither lock them nor check whether they're locked. Tension: someone else could've already grabbed a subset of those. Outcome: duplicate their work on the items they happened to share.

the cache doesn't work across processes — workers might be pre-forked. Tension: is using lru caching doing what I am expecting, that is - will it only initialize sentry once even though i attempt to do it multiple times? Outcome: provided it's called within the same process.

sqlite3.OperationalError: database is locked. — I trigger `/session_a` and `/session_b` almost simultaneously. Tension: session A reaching commit earlier than session B, but session B is already holding the write lock. Outcome: A will inevitably fail with a database is locked error.

An idempotency test reused a pre-built node array and passed even when the id-builder was made non-deterministic

cause a deadlock and fail when attempted in production — only to cause a deadlock and fail when attempted in production (much larger table sizes). Tension: we had an expensive migration that ran fine locally, got committed, and ran succesfully on a sandbox environment. Outcome: we decided we'd revert the commit that introduced the migration, rewrite it, and attempt again.

Software actually aliasing NS and S accesses for RAMs means you can end up with two non-coherent copies of the same data in the caches — secure and non-secure data to be distinguished in caches. Tension: which can desync because of the lack of coherency. Outcome: This is why secure world page tables can be set up with NS=1 pages.

Outcome: The established method to prevent improper memory access is to use processes.

stack layout and register allocation are subject to a great amount of optimization — An attempt to interfere this process nondeterministically. Tension: benchmarks will become useless. Outcome: nondeterministic performance.

those polls might be scheduled in parallel — make this concurrent. Tension: there is no ordering guarantee.

Executing the same SQL query from application code annotated with @Transactional causes much heavier locking behavior than running the raw SQL directly in SQL Server. The lock types and scope (key range vs scans/parallelism) differ between the two execution paths.

Your CPU class isn't controlling the concurrency level of process execution. — The threads you start in CPUDemo are doing their own processing. Tension: the CPU isn't starting the "processing" threads itself. Outcome: Try to to decouple thread creation from task execution.

Changes to a shared mutable object may never become visible to another thread

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.

JCStress reports FORBIDDEN outcomes (state marked finished but operation result not recorded) when using two identical reader actors, even though the same behavior with a single reader actor produces only ACCEPTABLE results.

Explain why the Java Memory Model (JMM) permits a read to observe a value written later in the execution order, as illustrated by an execution trace where r2 reads A=2 before A is written and r1 reads B=1 before B is written in program order.

Suppose #0 reads `strong == 1`. That requires: Both `fetch_sub` operations (#2 and #3) have already happened before #0. Tension: Threads that "shouldn't" modify the counter get stuck before performing the release operations that would allow #0 to see a reduced count. Outcome: So the uniqueness test is valid and future-proof.

calling `.notify_one()` / `.notify_all()` on a destructed `std::atomic` is UB — This also applies to `std::atomic_ref`. Tension: the object it points to must outlive the `std::atomic_ref` object. Outcome: There are workarounds, depending on your usecase.

what are the correct values of three highlighted parameters? — when it comes to intrusive lockless stacks (single-linked lists). Tension: I've seen various permutations of highlighted parameters. Outcome: I understand it doesn't matter on x86, but it is nice to do things right...

Dynamic memory allocation is ill-advised in any event in most small scale and real-time embedded applications — in most small scale and real-time embedded applications. Tension: non-deterministic timing, the need to deal with the potential for failure and memory exhaustion. Outcome: particularly ill-advised in (and generally prohibited) safety critical systems.

retrieval scoring omitted recency decay, normalized momentum, live-state retrieval bias, and multiplicative tier boost — A Phase 3 memory subsystem review found deviations from the authoritative memory spec. Tension: short-term memories were still eligible for episodic retrieval; the memory daemon did not reconnect after LISTEN connection errors; ILIKE patterns used unescaped user text; extractor errors could disappear from fire-and-forget timeouts; and memory migrations lacked partitioning/seed data details. Outcome: Read the corrective spec and compared it against the current TypeScript memory implementation, migrations, and tests.

Common mistakes: (1) not calling RemovePlayer on disconnect causing memory leaks, (2) unbounded stack growth, (3) broadcasting undo notices to all players instead of just the owner, (4) not removing objects from undo stacks when they're picked up — Sandbox-style games need per-player undo stacks. Tension: allowing players to undo weapons out of other players' hands.

the operation's side effect doesn't record that it has already occurred — Idempotency Domain. Tension: re-execution produces duplicate effects.

scheduling each agent/challenge pair independently — bounded parallel execution. Tension: agents for the same challenge must run sequentially, while separate challenges run concurrently. Outcome: did not match a spec requiring challenge-level parallelism.

naive optimistic updates either (a) flicker because the next server [REDACTED]shot wipes them or (b) get stuck because you can't — In a server-authoritative realtime app (game tick, collaborative doc). Tension: the next server [REDACTED]shot wipes them. Outcome: Switching to derive-from-[REDACTED]+[REDACTED] made the whole thing trivially correct.

Daemon-witnessed triage counts (edge attrs.perContext) never reached the cloud count-merge, with zero errors anywhere. — Two independent layers each silently dropped the field. Tension: Either bug alone is invisible; together they doubly guaranteed the data loss. Outcome: with zero errors anywhere.

Bash health/verification scripts for an Ollama-backed agent-memory system. Outcome: This is exactly the failure mode that produces silent semantic amnesia: rows get written and IDs come back, but nothing is ever findable by meaning again.

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