jvanneman opened a new pull request, #3992:
URL: https://github.com/apache/solr/pull/3992

   
   https://issues.apache.org/jira/browse/SOLR-18051
   
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   # Description
   
   [PR 2402](https://github.com/apache/solr/pull/2402) added support for 
CompletableFuture which accidentally introduced a double registration bug in 
HttpJettySolrClient by calling onRequestQueued/onComplete twice with 
asyncListener.queuedListener/completeListener. The registration is added once 
in the `makeRequest` helper and a second time below that during the following 
sequence:
   
   ```java
       mrrv.request
           .onRequestQueued(asyncTracker.queuedListener)
           .onComplete(asyncTracker.completeListener)
   ```
   
   This introduces three undesirable scenarios: 
   
   1. Potential deadlock due to a surge in requests that all acquire 1 permit 
and cannot acquire a second
   2. Unnecessary system throttling when a request acquires a single permit but 
can't acquire a second due to in flight requests and new requests that arrived 
after the first token acquisition but before the second.
   3. Half the number of permits available
   
   # Solution
   
   Remove the duplicate registration.
   
   
   # Tests
   
   This is a difficult bug to reproduce in a test, open to ideas if there's a 
clean way to verify a single registration
   
   # Checklist
   
   Please review the following and check all that apply:
   
   - [ ] I have reviewed the guidelines for [How to 
Contribute](https://github.com/apache/solr/blob/main/CONTRIBUTING.md) and my 
code conforms to the standards described there to the best of my ability.
   - [ ] I have created a Jira issue and added the issue ID to my pull request 
title.
   - [ ] I have given Solr maintainers 
[access](https://help.github.com/en/articles/allowing-changes-to-a-pull-request-branch-created-from-a-fork)
 to contribute to my PR branch. (optional but recommended, not available for 
branches on forks living under an organisation)
   - [ ] I have developed this patch against the `main` branch.
   - [ ] I have run `./gradlew check`.
   - [ ] I have added tests for my changes.
   - [ ] I have added documentation for the [Reference 
Guide](https://github.com/apache/solr/tree/main/solr/solr-ref-guide)
   - [ ] I have added a [changelog 
entry](https://github.com/apache/solr/blob/main/dev-docs/changelog.adoc) for my 
change
   


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