8302108: Clean up placeholder supername code

[coleenp]

Please review change to make PlaceholderEntry::_supername a SymbolHandle to correctly refcount the symbol rather than have ad-hoc code. It also moves the private functions to private and asserts invariant that find_and_remove must always find a matching entry. Finally, this also more eagerly removes the supername symbol from the placeholder entry, so I have to fix the test in #12491 before pushing this.
Tested with tier1-4.

---

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Issue

• JDK-8302108: Clean up placeholder supername code

Reviewers

• David Holmes (@dholmes-ora - Reviewer) ⚠️ Review applies to 1d5fd3c0
• Ioi Lam (@iklam - Reviewer)

Reviewing

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[mlbridge]

Webrevs

• 01: Full (378170e6)
• 00: Full (1d5fd3c0)

[dholmes-ora]

Took me a while to get my head around the SymbolHandle mechanics for ref counting, but once I did this looks good. :) Thanks.

[openjdk]

@coleenp 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:

8302108: Clean up placeholder supername code

Reviewed-by: dholmes, iklam

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 28 new commits pushed to the master branch:

• d503c66: 8302155: [AIX] NUM_LCPU is not required variable
• c37e9d1: 8298293: NMT: os::realloc() should verify that flags do not change between reallocations
• 101db26: 8301697: [s390] Optimized-build is broken
• f4d4fa5: 8300255: Introduce interface for GC oop verification in the assembler
• 99b6c0e: 8302289: RISC-V: Use bgez instruction in arraycopy_simple_check when possible
• 57aef85: 8301838: PPC: continuation yield intrinsic: exception check not needed if yield succeeded
• df93880: 8301942: java/net/httpclient/DigestEchoClientSSL.java fail with -Xcomp
• 0025764: 8040793: vmTestbase/nsk/monitoring/stress/lowmem fails on calling isCollectionUsageThresholdExceeded()
• 1f9c110: 8301958: Reduce Arrays.copyOf/-Range overheads
• cb81073: 8300139: [AIX] Use pthreads to avoid JNI_createVM call from primordial thread
• ... and 18 more: https://git.openjdk.org/jdk/compare/db1b48ef3bb4f8f0fbb6879200c0655b7fe006eb...master

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.

[coleenp]

Thanks David. I had printf code to verify what SymbolHandle refcounting did to understand it but it's better that it just works rather than ad-hoc ref counting.
Thanks for reviewing!

[iklam]

LGTM. Just a small nit.

[iklam]

If you just want to change these function to private, instead of moving them, I would suggest adding private: and public: keywords around them. That way we can limit the delta.

[coleenp]

I really wanted them moved to the section of the class where the other private methods are. This class isn't so overgrown that we need to keep switching from private to public, and I want the public methods to be together.
Java is nice in that you can have 'private' and 'public' keywords on each function, but I'd still like to keep the public ones together.

[coleenp]

Thanks for reviewing Ioi!
/integrate

[openjdk]

Going to push as commit abbeb7e.
Since your change was applied there have been 28 commits pushed to the master branch:

• d503c66: 8302155: [AIX] NUM_LCPU is not required variable
• c37e9d1: 8298293: NMT: os::realloc() should verify that flags do not change between reallocations
• 101db26: 8301697: [s390] Optimized-build is broken
• f4d4fa5: 8300255: Introduce interface for GC oop verification in the assembler
• 99b6c0e: 8302289: RISC-V: Use bgez instruction in arraycopy_simple_check when possible
• 57aef85: 8301838: PPC: continuation yield intrinsic: exception check not needed if yield succeeded
• df93880: 8301942: java/net/httpclient/DigestEchoClientSSL.java fail with -Xcomp
• 0025764: 8040793: vmTestbase/nsk/monitoring/stress/lowmem fails on calling isCollectionUsageThresholdExceeded()
• 1f9c110: 8301958: Reduce Arrays.copyOf/-Range overheads
• cb81073: 8300139: [AIX] Use pthreads to avoid JNI_createVM call from primordial thread
• ... and 18 more: https://git.openjdk.org/jdk/compare/db1b48ef3bb4f8f0fbb6879200c0655b7fe006eb...master

Your commit was automatically rebased without conflicts.

[openjdk]

@coleenp Pushed as commit abbeb7e.

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