chennaji9 opened a new issue, #11281:
URL: https://github.com/apache/rocketmq/issues/11281
### Description
`example/src/main/java/org/apache/rocketmq/example/simple/RandomAsyncCommit.java`
(the lite-pull random-commit example) has two defects.
**1. `commitableOffset` throws `NoSuchElementException` once every cached
message has been consumed**
```java
public long commitableOffset(final MessageQueue mq) {
CachedQueue cachedQueue = this.mqCachedTable.get(mq);
if (null != cachedQueue) {
return cachedQueue.getMsgCachedTable().firstKey();
}
return -1;
}
```
`getMsgCachedTable()` is a `TreeMap<Long, MessageExt>`. After `putMessages`
adds a batch and `removeMessage` removes the last entry (all messages
consumed), the `CachedQueue` object still exists but its TreeMap is empty, and
`firstKey()` throws `NoSuchElementException`. The same state is reached by
`putMessages(mq, emptyList)`. The `-1` sentinel is only returned for an unknown
queue, not for an empty cache.
**2. Concurrent first access can silently lose a cached batch**
```java
public void putMessages(final MessageQueue mq, final List<MessageExt> msgs) {
CachedQueue cachedQueue = this.mqCachedTable.get(mq);
if (null == cachedQueue) {
cachedQueue = new CachedQueue();
this.mqCachedTable.put(mq, cachedQueue);
}
...
}
```
The map is a `ConcurrentHashMap` but initialization is get-then-put. Two
threads consuming/committing the same queue for the first time can each
construct a `CachedQueue`; the second `put` overwrites the first, so the batch
cached by the first thread disappears from `commitableOffset`'s view.
Additionally the inner `TreeMap` is read and written from `putMessages`,
`removeMessage` and `commitableOffset` without any synchronization.
### Expected behavior
- `commitableOffset` returns the `-1` sentinel when there is nothing
committable (empty cache), instead of throwing.
- Concurrent use of the example class must not lose cached messages:
initialization should be atomic (e.g. `computeIfAbsent`) and the three public
methods should be safe against concurrent TreeMap mutation.
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