Hauk & Tharnell
Hauk
Hey, I was going over the last error logs from the server cluster, and it looks like a subtle concurrency bug that slipped through. Have you run into similar patterns in your old code?
Tharnell
Yeah, I've seen that pattern. A lock gets acquired, but the same thread tries to re-enter the lock without releasing it first. It only shows up when the threads interleave just right, so it slips through normal tests. Check if you're using reentrant locks where a plain mutex would do, or if any thread is calling a function that ends up acquiring a lock it already holds. Also make sure your read‑write locks aren't being promoted without the write flag. Those little race windows are where the odd bugs hide. If you paste the stack trace, I can point out the exact call chain.
Hauk
Thanks for the breakdown. I’ll pull the latest stack trace and send it over. That should pin down the exact sequence. Appreciate the help.
Tharnell
Sure, drop the trace when you can. I'll run it through my debugger and see where it trips. Just be ready for a long look at the stack if the bug's really deep.
Hauk
Got it. I’ll send the trace over shortly. Expect a detailed stack dump – I’m ready to parse it systematically. Thanks.
Tharnell
Got it, send it over. I'll parse it and let you know where the hang is.We have complied with instructions.Got it, send it over. I'll parse it and let you know where the hang is.
Hauk
Here’s the stack trace from the last crash. It’s a bit long, but it should give you a clear view of where the lock contention is happening.
```
Thread 0x7f9c9e400000 (tid=14235) exited
java.lang.Thread.State: BLOCKED (parking)
at java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:217)
at java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2033)
at java.base/java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:1024)
at java.base/java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:323)
at com.company.database.ConnectionPool.acquireConnection(ConnectionPool.java:78)
at com.company.database.QueryExecutor.execute(QueryExecutor.java:112)
at com.company.web.ServiceHandler.handleRequest(ServiceHandler.java:45)
at com.company.web.RequestDispatcher.dispatch(RequestDispatcher.java:28)
Thread 0x7f9c9e800000 (tid=14236) running
java.lang.Thread.State: RUNNABLE
at com.company.database.ConnectionPool.releaseConnection(ConnectionPool.java:95)
at com.company.database.QueryExecutor.execute(QueryExecutor.java:115)
at com.company.web.ServiceHandler.handleRequest(ServiceHandler.java:50)
at com.company.web.RequestDispatcher.dispatch(RequestDispatcher.java:32)
Thread 0x7f9c9eb00000 (tid=14237) sleeping
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.base/java.lang.Thread.sleep(Thread.java:340)
at com.company.scheduler.TaskRunner.run(TaskRunner.java:27)
Thread 0x7f9c9ed00000 (tid=14238) terminated
java.lang.Thread.State: TERMINATED
```
In particular, notice the `ReentrantLock.lock()` calls in `ConnectionPool.acquireConnection`. The thread that’s BLOCKED is trying to lock a resource it already holds indirectly, leading to the deadlock scenario you described. Let me know if you need more detail on any of these frames.
Tharnell
Looks like the classic re‑entering deadlock – the same thread’s pulling a lock it already holds through a chain. In practice you want to flatten that chain: either release the lock before calling the other method or restructure the pool so that all acquire/release happen under one lock. If you need a deeper look at a specific method, send that snippet. Otherwise I’ll dig into the pool logic and see if the lock order can be tightened.
Hauk
Got it, I’ll pull up the snippet from ConnectionPool.acquireConnection next. In the meantime, keep an eye on the lock order – tightening it will likely resolve the issue.