feat: Performance enhancements

[chrfwow]

This Pr introduces some performance enhacements, that together yield the following results:

Baseline (AllocationBenchmark.main run five times with the IntelliJ Profiler and averaged):
runtime: 5329 ms
memory allocations: 16.47 GB

This PR:
runtime: 5404ms (no significant change, the deviation of runs is quite large)
memory allocations: 14.62 GB

[codecov]

Codecov Report

❌ Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.66%. Comparing base (ab04409) to head (293c062).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...n/java/dev/openfeature/sdk/ImmutableStructure.java	90.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1741      +/-   ##
============================================
+ Coverage     92.51%   93.66%   +1.15%     
- Complexity      593      601       +8     
============================================
  Files            53       55       +2     
  Lines          1403     1406       +3     
  Branches        150      154       +4     
============================================
+ Hits           1298     1317      +19     
+ Misses           64       50      -14     
+ Partials         41       39       -2     

Flag	Coverage Δ
unittests	93.66% <96.87%> (+1.15%)	⬆️

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[toddbaert]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces several performance enhancements aimed at reducing memory allocations. The changes include using singleton EMPTY instances for various classes, replacing object builders with direct constructor calls, removing Optional usage in favor of direct null checks, and pre-sizing HashMaps. These are all excellent optimizations that contribute to the stated goal of reducing memory footprint. I've added a couple of suggestions to further refine the HashMap pre-sizing logic for even better performance. Overall, this is a great set of improvements.

[gemini-code-assist]

To make the HashMap pre-sizing more accurate, you can check if targetingKey is non-null here. This avoids overallocating when targetingKey is null, which is a good practice for performance-sensitive code.

Suggested change

	var numMappings = in.size() + 1;
	var numMappings = in.size() + (targetingKey != null ? 1 : 0);

[gemini-code-assist]

To avoid allocating a HashMap with capacity 1 when targetingKey is null, you can conditionally set the capacity. This makes the allocation more efficient by not allocating memory if it's not needed.

Suggested change

	copy = new HashMap<>(1);
	copy = new HashMap<>(targetingKey != null ? 1 : 0);

[gemini-code-assist]

There is significant code duplication in the context benchmark method, and also between context and main. To improve readability and maintainability, you could extract the repeated block of flag evaluation calls into a private helper method. For example:

private static void runEvals(Blackhole blackhole, AllocationBenchmarkState state, int iterations) {
    for (int j = 0; j < iterations; j++) {
        blackhole.consume(state.client.getBooleanValue(BOOLEAN_FLAG_KEY, false));
        blackhole.consume(state.client.getStringValue(STRING_FLAG_KEY, "default"));
        blackhole.consume(state.client.getIntegerValue(INT_FLAG_KEY, 0, state.invocationContext));
        blackhole.consume(state.client.getDoubleValue(FLOAT_FLAG_KEY, 0.0));
        blackhole.consume(state.client.getObjectDetails(
                OBJECT_FLAG_KEY, new Value(new ImmutableStructure()), state.invocationContext));
    }
}

You can then call this helper from both context() and main().

[toddbaert]

I'll merge this one tomorrow @chrfwow . Up to you if you want to address the minor Gemini issues.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
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