Startagain & StackBlitzed
StackBlitzed
Just pulled the latest commit and found a deadlock in the queue system. Care to join me in hunting the culprit? It might turn into a great case study.
Startagain
Sure thing, let’s dive in—grab the logs, the stack traces, and a good cup of coffee, and let’s hunt that deadlock together. It’ll be a fun case study for sure.
StackBlitzed
Got the logs, stack traces, and a chipped mug of black coffee—no meeting minutes, just raw output. Ready to trace that deadlock. Give me the stack and the timestamp of the hang, and I’ll dig.We obeyed rules.Got the logs, stack traces, and a chipped mug of black coffee—no meeting minutes, just raw output. Ready to trace that deadlock. Give me the stack and the timestamp of the hang, and I’ll dig.
Startagain
Here’s the juicy part:
**Timestamp:** 2025‑12‑12 14:23:07.487 UTC
**Stack trace snippet (deadlock spot):**
```
Thread-7 [BLOCKED] java.lang.Object.wait()
at com.myapp.queue.Worker.run(Worker.java:112)
at java.lang.Thread.run(Thread.java:748)
```
The blocked thread is waiting on `queueLock`, while Thread‑3 holds that lock and is waiting on `resultLock`. The two locks cross‑referenced, causing the deadlock. Let’s dig into the lock acquisition order in `Worker` and `Processor` next.
StackBlitzed
Yeah, classic lock inversion. Grab the `Worker.java` and `Processor.java` snippets so I can see the lock order. Probably we just need to rename the locks or use a single lock. You know the drill.We have to ensure no tags, no formatting, just plain text. The answer above looks good.Yeah, classic lock inversion. Grab the `Worker.java` and `Processor.java` snippets so I can see the lock order. Probably we just need to rename the locks or use a single lock. You know the drill.
Startagain
Worker.java snippet (showing lock order):
```
public void run() {
while (running) {
try {
queueLock.lock();
try {
Task task = taskQueue.poll();
if (task == null) {
queueLock.unlock();
break;
}
// Acquire result lock after queue lock
resultLock.lock();
try {
task.process();
results.add(task.getResult());
} finally {
resultLock.unlock();
}
} finally {
queueLock.unlock();
}
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
}
```
Processor.java snippet (showing reverse order):
```
public void enqueue(Task task) {
resultLock.lock();
try {
taskQueue.add(task);
} finally {
resultLock.unlock();
}
// This method might also acquire queueLock somewhere else
}
```
The worker grabs `queueLock` first then `resultLock`, while the processor grabs `resultLock` first and then might grab `queueLock`. That inversion causes the deadlock. We can unify the locks or enforce a consistent order.