frozenNoob opened a new issue, #15665: URL: https://github.com/apache/dubbo/issues/15665
### Pre-check - [x] I am sure that all the content I provide is in English. ### Search before asking - [x] I had searched in the [issues](https://github.com/apache/dubbo/issues?q=is%3Aissue) and found no similar feature requirement. ### Apache Dubbo Component Java SDK (apache/dubbo) ### Descriptions The issues with the first approach (https://github.com/apache/dubbo/commit/c8a8946f89ef7f1d3bb9725f754465c6bb675834) are as follows: 1. If a large number of read-only operations flood in, it is not appropriate for the first approach to wrap the read-write combination into an atomic operation. This will cause those read-only operations to be executed serially, which is very time-consuming (imagine 10K threads executing the `compute` method’s write operation serially due to the lock imposed by `synchronized`). 2. I believe that in this load balancing algorithm, although the first approach can guarantee consistency, it cannot fundamentally prevent errors. For example: in the time window between the execution of the `compute` method and the `return` of the `doSelect` function, if another thread modifies the service list and rebuilds the corresponding values on the hash ring, then the result returned by the `select` method may be a stale node, which will still trigger subsequent fault-tolerance and retry mechanisms. Of course, since the average time complexity of a `TreeMap` query is O(log n), this time window is short but still exists. 3. The `compute` method itself is not truly atomic—it is closer to being "approximately atomic." From the source code, we can see a situation like this: when adding the first element of a hash bucket, if thread 1 is interrupted (in terms of timing) before executing the `casTabAt` method (which is essentially a CAS, i.e., optimistic lock) by thread 2, the CAS will fail and directly break, returning null. This will result in obtaining a `selector` that is null, and calling `return selector.select(invocation)` will throw a NullPointerException. ### Related issues _No response_ ### Are you willing to submit a pull request to fix on your own? - [x] Yes I am willing to submit a pull request on my own! ### Code of Conduct - [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct) -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
