perf: avoid ImmutableStructure allocation for empty ImmutableContext

[tobias-ibounig-dt]

This PR

• Add ImmutableStructure.EMPTY singleton (package-private)
• ImmutableContext() and ImmutableContext(String) pass Collections.emptyMap() instead of new HashMap<>()
• ImmutableContext(String targetingKey, Map attributes) reuses ImmutableStructure.EMPTY when targetingKey is null and attributes are empty
• Tests to guard the constructor branch logic

Related Issues

None

Notes

Before-hook implementations commonly return new ImmutableContext() to signal no context change. Each call previously allocated a throwaway HashMap as the constructor argument, then a second HashMap inside ImmutableStructure. Passing Collections.emptyMap() eliminates the first allocation; reusing ImmutableStructure.EMPTY eliminates both the ImmutableStructure and its backing map entirely.

The sharing should be fine: ImmutableStructure never mutates attributes — getValue clones values, asMap/keySet return copies.

The ConstructorBranches tests guard the targetingKey != null branch so that a future refactor cannot accidentally return EMPTY for a context that carries a targeting key.

Metric	main	This PR	Delta
run:+totalAllocatedInstances	2,145,282	1,825,005	−320,277 (−14.9%)
run:+totalAllocatedBytes	102,105,728	93,695,320	−8,410,408 (−8.2%)

⚠️ seems I might have used another branch as baseline instead of main. Result proportions should be right, but not the exact values.

Follow-up Tasks

• More PRs with memory improvements
• Update benchmark.txt after all are applied

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: d9dbeb10-cc4f-4351-8e62-cdc5aa0e68ef

📥 Commits

Reviewing files that changed from the base of the PR and between db2a77a and af146d6.

📒 Files selected for processing (3)

• src/main/java/dev/openfeature/sdk/ImmutableContext.java
• src/main/java/dev/openfeature/sdk/ImmutableStructure.java
• src/test/java/dev/openfeature/sdk/ImmutableContextTest.java

🚧 Files skipped from review as they are similar to previous changes (3)

• src/main/java/dev/openfeature/sdk/ImmutableStructure.java
• src/test/java/dev/openfeature/sdk/ImmutableContextTest.java
• src/main/java/dev/openfeature/sdk/ImmutableContext.java

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📝 Walkthrough

Walkthrough

ImmutableStructure gains a package-visible EMPTY static constant backed by Collections.emptyMap(). ImmutableContext constructors are updated to pass Collections.emptyMap() instead of allocating new HashMap<>(), and the two-arg constructor assigns ImmutableStructure.EMPTY when the targeting key is null and attributes are null or empty. Tests covering all four targeting-key/attributes constructor branches are added.

Changes

ImmutableContext/ImmutableStructure allocation optimization

Layer / File(s)	Summary
ImmutableStructure.EMPTY constant src/main/java/dev/openfeature/sdk/ImmutableStructure.java	Adds java.util.Collections import and a package-visible static final EMPTY field initialized via ImmutableStructure(Collections.emptyMap()).
ImmutableContext constructor optimization and tests src/main/java/dev/openfeature/sdk/ImmutableContext.java, src/test/java/dev/openfeature/sdk/ImmutableContextTest.java	Removes HashMap import; no-arg and single-arg constructors delegate with Collections.emptyMap(); the two-arg constructor assigns ImmutableStructure.EMPTY when targetingKey is null and attributes are null or empty. A new @Nested test class (ConstructorBranches) validates all four combinations of null/non-null targeting key and empty/null attributes.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• open-feature/java-sdk#1975: Updates NoOpTransactionContextPropagator.getTransactionContext() to return ImmutableContext.EMPTY singleton, complementing this PR's introduction of the EMPTY constant.

Suggested reviewers

• toddbaert

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 37.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely summarizes the main optimization: avoiding unnecessary ImmutableStructure allocation for empty ImmutableContext instances.
Description check	✅ Passed	The description provides comprehensive context for the changes, including the rationale, implementation details, performance metrics, and test coverage strategy.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.19%. Comparing base (e014572) to head (af146d6).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1972      +/-   ##
============================================
+ Coverage     92.13%   93.19%   +1.05%     
- Complexity      662      669       +7     
============================================
  Files            59       59              
  Lines          1628     1631       +3     
  Branches        184      185       +1     
============================================
+ Hits           1500     1520      +20     
+ Misses           80       66      -14     
+ Partials         48       45       -3     

Flag	Coverage Δ
unittests	93.19% <100.00%> (+1.05%)	⬆️

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[toddbaert]

⚠️ seems I might have used another branch as baseline instead of main. Result proportions should be right, but not the exact values.

haha ya, I first looked at the raw numbers and I was shocked - but still, these improvements are valid! Thanks as always.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud