abhu85 opened a new pull request, #11739:
URL: https://github.com/apache/maven/pull/11739
## Summary
- Make `validIds` field in `DefaultModelValidator` thread-safe using
`ConcurrentHashMap.newKeySet()`
- Add null check before `contains()` since `ConcurrentHashMap` doesn't allow
null keys
## Problem
`DefaultModelValidator.validIds` is a non-thread-safe `HashSet` that can
cause `ClassCastException` when accessed concurrently from multiple threads:
```
java.lang.ClassCastException: class java.util.HashMap$Node cannot be cast to
class java.util.HashMap$TreeNode
at
java.base/java.util.HashMap$TreeNode.moveRootToFront(HashMap.java:1900)
at java.base/java.util.HashMap$TreeNode.putTreeVal(HashMap.java:2079)
at java.base/java.util.HashMap.putVal(HashMap.java:634)
at java.base/java.util.HashMap.put(HashMap.java:608)
at java.base/java.util.HashSet.add(HashSet.java:220)
at
org.apache.maven.model.validation.DefaultModelValidator.validateId(DefaultModelValidator.java:852)
```
This issue manifests when using the BF dependency collector strategy
(`aether.dependencyCollector.impl=bf`) which uses multiple threads for
dependency resolution.
## Solution
Replace `HashSet` with `ConcurrentHashMap.newKeySet()`, which is the same
approach already used in the Maven 4 impl module
(`impl/maven-impl/src/main/java/org/apache/maven/impl/model/DefaultModelValidator.java`).
## Test Plan
- [x] `mvn spotless:apply` - formatting verified
- [x] `mvn test -pl compat/maven-model-builder` - all 161 tests pass
- [x] `git diff --check` - no whitespace issues
## Compatibility
This is a backward-compatible fix. The behavior remains the same, but now
thread-safe.
Fixes #11618
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