RFR: 8361076: Add benchmark for ImageReader in preparation for Valhalla changes [v4]

[Chen Liang]

On Tue, 1 Jul 2025 17:02:27 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.
>
> David Beaumont has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Adding comment about maintainability.

Looks reasonable.

As much as this bench is susceptible to JDK changes, many other benchmarks are similarly not robust. We can wait until we run into errors in the benchmarks.

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Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26044#pullrequestreview-3025247133