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Graph/deadlock-from-lock-ordering

AntiPattern

Deadlocks From Lock Misuse

deadlock-from-lock-ordering

Lock contention and lock ordering mistakes (plus exception/locking interactions in callbacks) cause threads to wait on each other circularly, turning parallelism into deadlock and aborting progress or work rather than making forward progress.

Node Details

Public graph metadata

Updated6/26/2026

Connections

30 linked nodes

MATCHESSolution

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.

MATCHESSolution

You can use redis lock to solve this — around each change you are making to the redis/DB. Outcome: put this lock around each change you are making to the redis/DB.

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I suggests you use rapyer, Which takes special care to handle deadlock problems. — Since you are using json models. Tension: deadlock problems.

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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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Changed calling it to `await to_thread(CatalogHandler.catalog_check, user.group_name, req.source, req.csv)` — when this process is running. Tension: It makes function run in a separate thread without blocking main event loop. Outcome: everything seems to work.

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python interpreter just pauses one task and looks at other — In your scenerio where you use asynchronous. Tension: it is not completly usesless. Outcome: Think it like a round-robin.

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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.

MATCHESSolution

bound it with a "progress ceiling" — a process emitting bytes but making NO semantic progress. Tension: a process emitting bytes but making NO semantic progress (livelock) would be shielded forever. Outcome: re-arms recovery after a long no-progress window even while bytes flow.

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Thread a second, lower-level liveness signal into the classifier — the timestamp of the last raw stdout byte from the child. Tension: Dead socket = no bytes = livenessAge grows = still aborts (correct). Alive-but-quiet = bytes flowing = livenessAge fresh = NOT aborted.

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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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you have such an id that is called transaction id. Tension: If none of that is available either. Outcome: you can create a (sort of) mutex variable (let's call it `lock`).

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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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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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Cause of the deadlock.

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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.

MATCHESSolution

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.

MATCHESSolution

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.

MATCHESSolution

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.

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 am seeing an increase in latencies in requests that do succeed — I have a logic of the sort :. Tension: none of them enforce a timeout on the total duration of the request. Outcome: Then properly close the connection in a finally / try-resource block.

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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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adding a pause to your task after connecting — You can also use a 'sleep(delay)' in mysql, to make statements last longer. Tension: to prove your tasks can make parallel statements. Outcome: You'll have time to show processlist by hand now.

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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.

MATCHESSolution

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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There are workarounds, depending on your usecase — calling `.notify_one()` / `.notify_all()` on a destructed `std::atomic`. Tension: There is a C++ Paper - P2616R4 - which would fix this problem. Outcome: using `std::binary_semaphore` delegating `.wait()` and `.notify_xxx()` to a separate atomic variable that has a longer lifetime manually call the futex syscalls and bypass the stdlib.

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Fixed 30s retry on 429 keeps hammering. — when clearly rate-limited. Tension: keeps hammering. Outcome: Exponential backoff + hard rejection during cooldown.

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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

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

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