RockteMQ-AI commented on issue #10630:
URL: https://github.com/apache/rocketmq/issues/10630#issuecomment-5020496611
**Issue Evaluation**
Category: `type/bug` | Status: **Confirmed**
The reported data race and TOCTOU inconsistency in
`DefaultLitePullConsumerImpl.taskTable` has been verified against the current
`develop` branch codebase.
**Root Cause:**
The `startPullTask()` method (line 455-462) uses a non-atomic `containsKey →
put` pattern on `ConcurrentHashMap`:
```java
if (!this.taskTable.containsKey(messageQueue)) {
PullTaskImpl pullTask = new PullTaskImpl(messageQueue);
this.taskTable.put(messageQueue, pullTask);
this.scheduledThreadPoolExecutor.schedule(pullTask, 0,
TimeUnit.MILLISECONDS);
}
```
This is a classic check-then-act race. Multiple callers
(`updateAssignPullTask`, `updatePullTask`, rebalance callbacks) can invoke
`startPullTask` concurrently, leading to:
1. **Duplicate pull tasks** — Two threads both observe `containsKey ==
false` and each schedules a `PullTaskImpl`. The second `put` overwrites the
first in the map, but the first task keeps running untracked.
2. **Orphaned queues** — Concurrent iteration+removal in
`updateAssignPullTask`/`updatePullTask` can remove an entry another thread just
added, silently stopping polling for that queue.
**Impact:** Silent message consumption stalls or duplicate processing in
`LitePullConsumer` under concurrent rebalance/assignment scenarios.
**Severity:** Medium-High — silent data path corruption, no exception or log
to indicate the cause.
**Suggested Fix:**
- Replace `containsKey + put` with `putIfAbsent` to make the
check-and-insert atomic.
- Consider synchronizing the iterate-then-mutate sequences in
`updateAssignPullTask` / `updatePullTask` / `removePullTask`, or use a
consistent locking strategy.
An automated fix proposal can be generated. Reply `/approve` to proceed with
PR generation.
---
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