8353175: Eliminate double iteration of stream in FieldDescriptor reinitialization

[rvansa]

This backport is a partial fix for a performance regression and prerequisite for backport of openjdk/jdk#24847 (will be done through https://github.com/rvansa/jdk21u-dev/tree/refs/heads/rvansa/backport-8352075)

The backport was not clean; a notable new change is in reflectionUtils.hpp (later JDK versions remove the affected class) - I am adding friend class FieldStream to InstanceKlass to accomodate for this.

Backport-of: f169fc5a99ee2b485e156c043134ab76b7e5ebd9

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8353175 needs maintainer approval

Issue

• JDK-8353175: Eliminate double iteration of stream in FieldDescriptor reinitialization (Bug - P3 - Requested)

Reviewers

• Aleksey Shipilev (@shipilev - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk21u-dev.git pull/2010/head:pull/2010
$ git checkout pull/2010

Update a local copy of the PR:
$ git checkout pull/2010
$ git pull https://git.openjdk.org/jdk21u-dev.git pull/2010/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 2010

View PR using the GUI difftool:
$ git pr show -t 2010

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk21u-dev/pull/2010.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back rvansa! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@rvansa Please do not rebase or force-push to an active PR as it invalidates existing review comments. Note for future reference, the bots always squash all changes into a single commit automatically as part of the integration. See OpenJDK Developers’ Guide for more information.

[mlbridge]

Webrevs

• 00: Full (620d6aa2)

[rvansa]

/approval request Fixes performance regression introduced in 21

[openjdk]

@rvansa
8353175: The approval request has been created successfully.

[GoeLin]

Hi @rvansa , please first get a review before labeling fix-request.

[shipilev]

The change looks fine. But you need to name the PR Backport f169fc5a99ee2b485e156c043134ab76b7e5ebd9, not just the changeset, to get it properly hooked up.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

⚠️ @rvansa This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[rvansa]

/approval request Partially fixes performance regression introduced in 21

[openjdk]

@rvansa
8353175: The approval request has been updated successfully.

[jerboaa]

https://bugs.openjdk.org/browse/JDK-8352075 is a fairly recent change (June 2025) in JDK 25 and touches core parts of the VM. We should stage this backport. Deferring to January as we'd have at least some real-world usage in JDK 25 at this point.