perf: avoid calling Object.hashCode()#2382
Merged
Merged
Conversation
Contributor
There was a problem hiding this comment.
Pull request overview
This PR aims to prevent performance regressions caused by converting identity-based maps to Map.of(...)/Map.ofEntries(...), which can trigger megamorphic Object.hashCode() calls when keys are heterogeneous (e.g., multiple entity classes).
Changes:
- Replace deep-copy helpers that used
Map.ofEntries(...)withMap.copyOf(...)to avoid building immutable maps that depend onObject.hashCode(). - Preserve
IdentityHashMapusage for hot-path entity lookups by avoiding conversions that lose identity semantics. - Minor loop micro-optimizations (
int i→var i) in a couple of hot-path loops.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| core/src/main/java/ai/timefold/solver/core/impl/domain/variable/declarative/DefaultVariableReferenceGraph.java | Changes map finalization strategy for entity→nodes lookup used to initialize the updater. |
| core/src/main/java/ai/timefold/solver/core/impl/domain/variable/declarative/AbstractVariableReferenceGraph.java | Replaces Map.ofEntries(...) deep-copy helpers with Map.copyOf(...) to avoid Object.hashCode() megamorphism and removes helper methods accordingly. |
Christopher-Chianelli
approved these changes
Jun 17, 2026
Replacing IdentityHashMap with a Map.of(...) when the keys in that map are of several different classes (such as multiple entity classes) will result in System.identityHashCode(...) being replaced by Object.hashCode() - a megamorphic call that the JVM can't optimize.
|
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Replacing IdentityHashMap with a Map.of(...) when the keys in that map are of several different classes (such as multiple entity classes) will result in System.identityHashCode(...) being replaced by Object.hashCode() - a megamorphic call that the JVM can't optimize.