opt: add comments and optimize logic in RandomLoadBalance

[Linchen-Xu]

What is the purpose of the change

• Add comments in RandomLoadBalance to make it easier for people to understand its logic.
• Rewrite a part of its logic to improve efficiency. Assuming the difference between the expected index to be found and the index returned by Arrays.binarySearch is gap (for example, the returned index is 1 while the expected is 3, then the gap is 2), the previous logic will calculate i 2 * gap times. However, this will be reduced to only gap times after rewriting.

Brief changelog

• Add comments and optimize logic in org.apache.dubbo.rpc.cluster.loadbalance.RandomLoadBalance.

Verifying this change

Checklist

• [x] Make sure there is a GitHub_issue field for the change (usually before you start working on it). Trivial changes like typos do not require a GitHub issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
• [x] Each commit in the pull request should have a meaningful subject line and body.
• [x] Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• [ ] Check if is necessary to patch to Dubbo 3 if you are work on Dubbo 2.7
• [ ] Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• [ ] Add some description to dubbo-website project if you are requesting to add a feature.
• [ ] GitHub Actions works fine on your own branch.
• [ ] If this contribution is large, please follow the Software Donation Guide.

[sonarqubecloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

0.0% Coverage
0.0% Duplication