RFR: 8353175: Eliminate double iteration of stream in FieldDescriptor reinitialization [v7]

[Frederic Parain]

On Thu, 10 Apr 2025 14:10:14 GMT, Radim Vansa <rvansa at openjdk.org> wrote:

>> On the reproducer https://bugs.openjdk.org/secure/attachment/113985/CCC.java my local testing shows these numbers:
>> 
>> ### JDK-17
>> 
>> $ hyperfine -w 5 -r 10 '/path/to/jdk-17/bin/java -cp /tmp/ CCC'
>> Benchmark 1: /path/to/jdk-17/bin/java -cp /tmp/ CCC
>>   Time (mean ± σ):      32.5 ms ±   0.9 ms    [User: 27.5 ms, System: 10.6 ms]
>>   Range (min … max):    31.1 ms …  33.7 ms    10 runs
>> 
>> ### JDK-25 before the change applied
>> 
>> $ hyperfine -w 5 -r 10 '/path/to/jdk-25/build/linux-x86_64-server-release/images/jdk/bin/java -cp /tmp/ CCC'
>> Benchmark 1: /path/to/jdk-25/build/linux-x86_64-server-release/images/jdk/bin/java -cp /tmp/ CCC
>>   Time (mean ± σ):     101.6 ms ±   1.5 ms    [User: 96.8 ms, System: 14.6 ms]
>>   Range (min … max):    99.0 ms … 104.5 ms    10 runs
>> 
>> ### JDK-25 with this patch
>> 
>> $ hyperfine -w 5 -r 10 '/path/to/jdk-25/build/linux-x86_64-server-release/images/jdk/bin/java -cp /tmp/ CCC'
>> Benchmark 1: /path/to/jdk-25/build/linux-x86_64-server-release/images/jdk/bin/java -cp /tmp/ CCC
>>   Time (mean ± σ):      75.8 ms ±   1.2 ms    [User: 69.8 ms, System: 16.0 ms]
>>   Range (min … max):    73.8 ms …  78.2 ms    10 runs
>
> Radim Vansa has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revert iterator change

Changes look good to me.
Thank you for finding and fixing this performance issue.

Tests tier1 to tier3 didn't show any issue.

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Marked as reviewed by fparain (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24290#pullrequestreview-2760223621
PR Comment: https://git.openjdk.org/jdk/pull/24290#issuecomment-2796787059