8292818: replace 96-bit representation for field metadata with variable-sized streams

[fparain]

Please review this change re-implementing the FieldInfo data structure.

The FieldInfo array is an old data structure storing fields metadata. It has poor extension capabilities, a complex management code because of lack of strong typing and semantic overloading, and a poor memory efficiency.

The new implementation uses a compressed stream to store those metadata, achieving better memory density and providing flexible extensibility, while exposing a strongly typed set of data when uncompressed. The stream is compressed using the unsigned5 encoding, which alreay present in the JDK (because of pack200) and the JVM (because JIT compulers use it to comrpess debugging information).

More technical details are available in the CR: https://bugs.openjdk.org/browse/JDK-8292818

Those changes include a re-organisation of fields' flags, splitting the previous heterogeneous AccessFlags field into three distincts flag categories: immutable flags from the class file, immutable fields defined by the JVM, and finally mutable flags defined by the JVM.

The SA, CI, and JVMCI, which all used to access the old FieldInfo array, have been updated too to deal with the new FieldInfo format.

Tested with mach5, tier 1 to 7.

Thank you.

---

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

Issue

• JDK-8292818: replace 96-bit representation for field metadata with variable-sized streams

Reviewers

• David Holmes (@dholmes-ora - Reviewer) ⚠️ Review applies to f81337f7
• Coleen Phillimore (@coleenp - Reviewer) ⚠️ Review applies to 12b4f1b4
• Chris Plummer (@plummercj - Reviewer) ⚠️ Review applies to f81337f7
• Doug Simon (@dougxc - Committer) ⚠️ Review applies to f81337f7

Contributors

• John R Rose <jrose@openjdk.org>
• Chris Plummer <cjplummer@openjdk.org>

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk pull/12855/head:pull/12855
$ git checkout pull/12855

Update a local copy of the PR:
$ git checkout pull/12855
$ git pull https://git.openjdk.org/jdk pull/12855/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 12855

View PR using the GUI difftool:
$ git pr show -t 12855

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/12855.diff

[bridgekeeper]

👋 Welcome back fparain! 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]

@fparain The following labels will be automatically applied to this pull request:

• hotspot
• serviceability

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing lists. If you would like to change these labels, use the /label pull request command.

[fparain]

/contributor add jrose

[openjdk]

@fparain
Contributor John R Rose <jrose@openjdk.org> successfully added.

[mlbridge]

Webrevs

• 06: Full (626bac20)
• 05: Full - Incremental (ab57b03a)
• 04: Full - Incremental (f81337f7)
• 03: Full - Incremental (12b4f1b4)
• 02: Full - Incremental (322b626d)
• 01: Full - Incremental (ce1180ef)
• 00: Full (42a4d6a0)

[dholmes-ora]

HI Fred,

I've taken one pass through this but it is a huge set of changes to try and digest. At this stage just a bunch of style nits.

Thanks.

[fparain]

/label hotspot-runtime

[openjdk]

@fparain
The hotspot-runtime label was successfully added.

[coleenp]

I was able to do a first pass through the vm code except for jvmci. I didn't look at tests or SA in this pass.

[fparain]

/contributor add cjplummer

[openjdk]

@fparain
Contributor Chris Plummer <cjplummer@openjdk.org> successfully added.

[coleenp]

Most minor comments but one .inline.hpp still in an hpp file.

[coleenp]

I should point out that I only skimmed the SA and JVMCI changes.

[coleenp]

All my comments are addressed. Thank you! This is significant work.

[openjdk]

@fparain This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8292818: replace 96-bit representation for field metadata with variable-sized streams

Co-authored-by: John R Rose <jrose@openjdk.org>
Co-authored-by: Chris Plummer <cjplummer@openjdk.org>
Reviewed-by: dholmes, coleenp, cjplummer, dnsimon

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 2 new commits pushed to the master branch:

• 4486f1b: 8304367: jlink --include-locales=* attempts to parse non .class resource files with classfile reader
• 8d2ebf2: 8303697: ProcessTools doesn't print last line of process output

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[plummercj]

SA changes looks good. Thanks for taking care of this!

[dholmes-ora]

Nice piece of work Fred - I won't pretend to follow every detail.

A few nits on unnecessary alignment (which may match pre-existing style not evident in the diff).

Thanks.

[openjdk]

@fparain this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout fieldinfo_unsigned5
git fetch https://git.openjdk.org/jdk master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

[fparain]

Chris, Doug, thank you for your reviews and your help.
Coleen, David, Andrey, thank you for your reviews.

[fparain]

/integrate

[openjdk]

Going to push as commit bfb812a.
Since your change was applied there have been 4 commits pushed to the master branch:

• 932be35: 8298469: Obsolete legacy parallel class loading workaround for non-parallel-capable class loaders
• 02a4ee2: 8303921: serviceability/sa/UniqueVtableTest.java timed out
• 4486f1b: 8304367: jlink --include-locales=* attempts to parse non .class resource files with classfile reader
• 8d2ebf2: 8303697: ProcessTools doesn't print last line of process output

Your commit was automatically rebased without conflicts.

[openjdk]

@fparain Pushed as commit bfb812a.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

[dougxc]

One side-effect of this change is that verifying certain old classes (think JCK) can take a long time. For example:

Test.java:

import java.lang.classfile.ClassFile;
import java.lang.constant.ClassDesc;
import static java.lang.constant.ConstantDescs.CD_int;

public class Test {
    public static void main(String[] args) throws Exception {
        int numberOfFields = 65_000;
        ClassDesc classDesc = ClassDesc.of("ManyFieldsClass");

        byte[] classfile = ClassFile.of().build(classDesc, classBuilder -> {
            int flags = ClassFile.ACC_STATIC | ClassFile.ACC_PUBLIC;
            classBuilder.withVersion(ClassFile.JAVA_5_VERSION, 0);
            classBuilder.withField("myField0", CD_int, flags);
            for (int i = 1; i < numberOfFields; i++) {
                classBuilder.withField("myField" + i, CD_int, flags);
            }
        });

        ClassLoader cl = new ClassLoader() {
            @Override
            protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
                if (name.equals("ManyFieldsClass")) {
                    return defineClass(name, classfile, 0, classfile.length);
                }
                return super.loadClass(name, resolve);
            }
        };

        long start = System.currentTimeMillis();
        var c = Class.forName("ManyFieldsClass", true, cl);
        System.out.printf("took %,d ms to load %s%n", (System.currentTimeMillis() - start), c);
    }
}

> java Test.java
took 19,854 ms to load class ManyFieldsClass

Probably not worth worrying about - just wanted to point out something I hit while processing the JCK with Native Image.