Introduce WeightedRandomDistributionSelector (xDS-endpoint pt 1)

[jrhee17]

Motivation:

EdfLoadBalancer is a basic load balancer which distributes entries based on weight using Earliest Deadline First Scheduling.

ref: https://github.com/envoyproxy/envoy/blob/b7818b0df716af47ec22982c5a1cbbace5f2ae15/source/common/upstream/load_balancer_impl.h#L508

This is used not only for request load balancing, but also load balancing based on Locality

ref: https://github.com/envoyproxy/envoy/blob/b7818b0df716af47ec22982c5a1cbbace5f2ae15/source/common/upstream/upstream_impl.cc#L625

Within our codebase, it seems like we could use WeightedRandomDistributionEndpointSelector easily for this purpose. I propose that we extract a WeightedRandomDistributionSelector and make it publicly available.

See the following for a sample use-case in #5450
ref:

armeria/xds/src/main/java/com/linecorp/armeria/xds/client/endpoint/HostSet.java

Lines 38 to 39 in bd4968f

	private final WeightedRandomDistributionSelector<LocalityEntry> healthyLocalitySelector;
	private final WeightedRandomDistributionSelector<LocalityEntry> degradedLocalitySelector;

POC: #5450

Modifications:

• Extract WeightedRandomDistributionSelector and move it to the internal package.

Result:

• WeightedRandomDistributionSelector is now ready to be reused.

[codecov]

Codecov Report

Attention: Patch coverage is 92.59259% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 74.04%. Comparing base (4bfa172) to head (05a4594).

❗ Current head 05a4594 differs from pull request most recent head 8892a44. Consider uploading reports for the commit 8892a44 to get more accurate results

Files	Patch %	Lines
...t/endpoint/WeightedRandomDistributionSelector.java	91.83%	1 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5501       +/-   ##
===========================================
+ Coverage        0   74.04%   +74.04%     
- Complexity      0    20801    +20801     
===========================================
  Files           0     1802     +1802     
  Lines           0    76578    +76578     
  Branches        0     9760     +9760     
===========================================
+ Hits            0    56699    +56699     
- Misses          0    15259    +15259     
- Partials        0     4620     +4620     

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[github-actions]

🔍 Build Scan® (commit: 8892a44)

Job name	Status	Build Scan®
build-windows-latest-jdk-19	✅	https://ge.armeria.dev/s/yy74y2q235k5i
build-self-hosted-unsafe-jdk-8	✅	https://ge.armeria.dev/s/q4yu5vd7q47lu
build-self-hosted-unsafe-jdk-19-snapshot-blockhound	✅	https://ge.armeria.dev/s/s6kdtdjlfj24k
build-self-hosted-unsafe-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/3rvyn6p7mz6zw
build-self-hosted-unsafe-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/cjeomepqncgoq
build-self-hosted-unsafe-jdk-17-leak	❌ (failure)	https://ge.armeria.dev/s/xvtxxrb2yd74c
build-self-hosted-unsafe-jdk-11	✅	https://ge.armeria.dev/s/qeccdtesrvjjg
build-macos-12-jdk-19	✅	https://ge.armeria.dev/s/c6ttrcg6k3lmm

[minwoox]

Thanks! I didn't realize that we could use WeightedRandomDistributionSelector instead of the EDF scheduler which uses deadline with the priority queue. 😉