BewareMyPower commented on PR #23217:
URL: https://github.com/apache/pulsar/pull/23217#issuecomment-2309627169
BTW, the API document in `ConcurrentSkipListMap#computeIfAbsent` is clear
for this behavior:
```java
* The function
* is <em>NOT</em> guaranteed to be applied once atomically only
* if the value is not present.
```
It's required by the `Map#computeIfAbsent` API documentation:
```
* In particular, all implementations of
* subinterface {@link java.util.concurrent.ConcurrentMap} must document
* whether the mapping function is applied once atomically only if the
value
* is not present.
```
Here is the document for `ConcurrentHashMap`:
```java
* The supplied
* function is invoked exactly once per invocation of this method
* if the key is absent, else not at all. Some attempted update
* operations on this map by other threads may be blocked while
* computation is in progress, so the computation should be short
* and simple.
*
* <p>The mapping function must not modify this map during computation.
```
I believe many calls of `ConcurrentHashMap#computeIfAbsent` are not proper
(not short and simple) or even wrong (trying to modify the map) in Pulsar, but
it's another topic.
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