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Graph/shared-state-concurrency-misuse

AntiPattern

Shared-State Concurrency Misuse

shared-state-concurrency-misuse

Shared-state concurrency misuse causes thread contention and lost parallelism when tasks race on global locks, shared RNG/driver synchronization, or pre-release thread-pool slots, while resources like containers/observations get reused across runs, leading to inconsistent throughput and flaky isolation.

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Public graph metadata

Updated7/3/2026

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30 linked nodes

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Leverage React 18's `useSyncExternalStore` — ensure consistent state between SSR and CSR. Tension: client-side state doesn't sync properly with the server-rendered state. Outcome: to ensure consistent state between SSR and CSR.

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Treat the selected value as a shared reference (avoid unnecessary cloning/deriving new arrays/objects in selectors). If memory pressure occurs, ensure large datasets are not being copied or accidentally retained (e.g., avoid creating new Float32Array/object instances per render; consider weak caching patterns such as WeakMap only for derived mappings).

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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.

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provided it's called within the same process — workers might be pre-forked. Tension: the cache doesn't work across processes. Outcome: each process got its own cache.

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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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Create a lifespan-managed shared state (e.g., instantiate a state manager/model in FastAPI lifespan) and store the loaded model in that state so request handlers can access it via Request/app state or a dependency that reads from lifespan.

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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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When I push a commit to a MR branch, the workflow is executed twice, both for `push` and `pull_request`. Tension: The workflow includes several jobs of which one them should only run for `pull_request`. Outcome: Maybe a bit late, but you could use Concurrency:.

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Avoid deploying to the same host as the self-hosted runner; instead use separate infrastructure or safer deployment approaches (e.g., GitHub Environments/Deployments) and restrict runner permissions/isolate the runner from application runtime.

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Do not use `Thread.stop()`. Tension: you need to really validate your assumptions of what is possible in your complicated code base.

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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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In general this calls for a mutex. — If the language does not provide mutexes out of the box. Outcome: you can create a mutex.

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Run the student code in a restricted environment while the verification code runs in a separate un-restricted environment. Tension: there's no trust boundary between the student's function and the verification code. Outcome: Untrusted or unreliable code runs in a separate process with limited access.

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if all you're trying to do is share something between multiple threads — consider using `Arc` instead. Outcome: this implements a thread-safe reference counted smart pointer.

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depending on your latency budget. Outcome: Same idea, but the state lives outside the process boundary.

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Use virtual threads for blocking DB/IO work to improve scalability under the same small pool, or switch to a reactive database driver/event-loop model to avoid blocking carrier threads; adjust concurrency/throttling accordingly (semaphore/backpressure) rather than assuming the current JDBC + thread pool design remains optimal.

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Your code doesn't use any shared state (or even objects) between the different threads — running this code in a multithreaded environment. Tension: The only thing that may looks marignally relevant is calling the static `OPCPackage.open` method. Outcome: there shouldn't be any problem running this code in a multithreaded environment.

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use a set to define which are currently running, and remove from set at end rather than before calling `process(client)` — You could use a counter (AtomicInteger) instead of `HashSet`, or `Semaphore`. Tension: your locks don't prevent more than MAX_THREAD_POOL running threads at once. Outcome: which is intended for this type of use.

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Try to to decouple thread creation from task execution. — The CPU maintains a queue and a pool of worker threads (only 3). Tension: Clients submit tasks (like your cpu.execute()). Outcome: Each worker takes a task from the queue, processes it, and picks the next.

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Use synchronization primitives, locks, or other publication mechanisms that establish a happens-before between the write and subsequent read

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Ensure each actor uses its own independent result/recording variables (do not share the same result instance between actors), e.g., allocate separate result storage per actor or otherwise remove shared mutable state.

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Mysql driver 9.0.0+ (currently 9.1.0) has ReentrantLock(s) now — IF they were not hooked on mysql internal synchronized blocks. Tension: it should have helped. Outcome: and it should work as this enabled the virtual thread to go do something else.

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So I change to `ThreadLocalRandom`. — I realize that I use `java.util.Random` shared between threads. Outcome: there's ThreadLocal, which does have a seed value but each thread has its own completely independent rng and seed.

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java.lang.Thread.State: is the thread status from the application's perspective — In below thread dump. Tension: two different “perspectives” the JVM has over a thread state. Outcome: thread_state: the low-level thread state used internally by the JVM.

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Only if all threads of your program use `seq_cst` memory order for operations and fences. — The C++ guarantee of sequential consistency for data-race free programs only applies if all atomic operations are `seq_cst`, or if you use equivalent fences. Tension: One thread using a fence can't necessarily recover sequential consistency when other threads are using `relaxed` or `release` and `acquire` operations on `std::atomic`. Outcome: use `seq_cst` memory order for operations and fences.

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for Discord. Tension: Multiple users sharing DM session. Outcome: The intended value for DM isolation on channel-peer-keyed plugins.

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after each allocation that may trigger GC. Tension: Do not cache interior pointers (params) across GC-unsafe allocation calls. Outcome: Apply same fix pattern to sampled_data_continue.

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Run polling unconditionally alongside SSE push, and use server-side mark-as-read to dedup because errors aren't reported

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Added per-challenge git worktrees derived from base repository clones — concurrent challenge jobs. Tension: do not race on checkout state. Outcome: so concurrent challenge jobs do not race on checkout state.

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Use for persistent state that all clients need. — [Sync] Attribute - State Replication. Outcome: Use for actions, events, and host-authoritative operations.

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