RFR: 8361076: Add benchmark for ImageReader in preparation for Valhalla changes

[David Beaumont]

On Mon, 30 Jun 2025 12:27:40 GMT, David Beaumont <duke at openjdk.org> wrote:

> Initial benchmark to capture at least some comparative measures of ImageReader performance.
> 
> Current results on my laptop:
> 
> Benchmark                                         Mode  Cnt   Score    Error  Units
> NewImageBenchmark.warmCache_CountAllNodes         avgt    5   0.785 ±  0.140  ms/op
> NewImageBenchmark.coldStart_CountOnly               ss    5  34.051 ± 17.662  ms/op
> NewImageBenchmark.coldStart_InitAndCount            ss    5  31.006 ±  9.674  ms/op
> NewImageBenchmark.coldStart_LoadJavacInitClasses    ss    5   3.752 ±  6.873  ms/op
> 
> The upcoming changes to ImageReader should show significant improvements to these results.

I removed a JrtFS related benchmark because it tracked the other one closely enough to not be worth it (hence only 1 additional module export needed).

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PR Comment: https://git.openjdk.org/jdk/pull/26044#issuecomment-3018968314