8270333: -XX:+VerifyStringTableAtExit should not do linear search #4772

iklam · 2021-07-14T02:34:19Z

The implementation of -XX:+VerifyStringTableAtExit used a linear search to check for duplicated strings in the interned string table. This would be excessively slow if there were more than a few thousand strings.

This PR uses a hashtable so we can avoid doing a linear search. The table is sized such that each bucket has 8 items on average.

Since this code is executed only for verification, I added a new java_lang_String::hash_code_noupdate(oop) function, so we can avoid causing side effects.

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JDK-8270333: -XX:+VerifyStringTableAtExit should not do linear search

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David Holmes (@dholmes-ora - Reviewer) ⚠️ Review applies to 66c4d4e
Yumin Qi (@yminqi - Reviewer)

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bridgekeeper · 2021-07-14T02:35:32Z

👋 Welcome back iklam! 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 · 2021-07-14T02:37:54Z

@iklam The following label will be automatically applied to this pull request:

hotspot-runtime

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mlbridge · 2021-07-14T02:45:24Z

Webrevs

dholmes-ora

Changes seem fine, but I don't like your use of templates here.

Thanks,
David

dholmes-ora · 2021-07-14T05:13:48Z

src/hotspot/share/classfile/javaClasses.cpp

+template<bool update>
+unsigned int java_lang_String::hash_code_impl(oop java_string) {


This looks like a really weird way to pass a parameter! Why do we want a template here?

Hi David, thanks for the review. I replaced the template function with an inline function.

openjdk · 2021-07-14T05:14:51Z

@iklam 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:

8270333: -XX:+VerifyStringTableAtExit should not do linear search

Reviewed-by: dholmes, minqi

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 14 new commits pushed to the master branch:

c0d4eff: 6506405: Math.abs(float) is slow
357fe09: 8247351: [aarch64] NullPointerException during stack walking (clhsdb "where -a")
589a1d5: 8270155: ARM32: Improve register dump in hs_err
b6d7653: 8264419: Remove has_max_index argument from G1BlockOffsetTablePart::block_at_or_preceding
4a7ccf3: Merge
8583aab: 8270025: DynamicCallSiteDesc::withArgs doesn't throw NPE
d32e42c: 8270184: [TESTBUG] Add coverage for jvmci ResolvedJavaType.toJavaName() for lambdas
b2416b6: 8269281: java/foreign/Test{Down,Up}call.java time out
bd95c0c: 8269635: Stress test SEGV while emitting OldObjectSample
00ef65f: 8269525: Deadlock during Volano with JFR
... and 4 more: https://git.openjdk.java.net/jdk/compare/9cac94d581f240c10fe8fff2f803109a1ae30637...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.

dholmes-ora

Okay ... I'm not sure why you want the code to be duplicated though?

iklam · 2021-07-14T06:43:05Z

Okay ... I'm not sure why you want the code to be duplicated though?

I could add a new bool update parameter to java_lang_String::hash_code(oop java_string), but I worry about performance impacts.

It probably doesn't matter, but I just don't want to deal with any potential performance issues when changing code used only for debugging.

yminqi

Looks good, but one question.

yminqi · 2021-07-14T15:05:58Z

src/hotspot/share/classfile/stringTable.cpp

 public:
  size_t _errors;
-  VerifyCompStrings(GrowableArray<oop>* oops) : _oops(oops), _errors(0) {}
+  VerifyCompStrings() : _table(unsigned(_items_count + 8 / 8)), _errors(0) {}


I guess you mean unsigned((_items_count + 8) / 8)?

Thanks for the review. I changed it to _table(unsigned(_items_count / 8) + 1)

yminqi

LGTM.

iklam · 2021-07-15T05:14:28Z

Thanks @dholmes-ora and @yminqi for the review.
/integrate

openjdk · 2021-07-15T05:15:32Z

Going to push as commit 1ebd946.
Since your change was applied there have been 29 commits pushed to the master branch:

04b73bc: 8269656: The test test/langtools/tools/javac/versions/Versions.java has duplicate test cycles
7c23491: 8269598: Regressions up to 5% on aarch64 seems due to JDK-8268858
7d0edb5: Merge
7b4d84c: 8270422: Test build/AbsPathsInImage.java fails after JDK-8259848
72db09b: 8266313: (JEP-356) - RandomGenerator spec implementation requirements tightly coupled to JDK internal classes
3bbd233: 8270075: SplittableRandom extends AbstractSplittableGenerator
381bd62: 8266889: [macosx-aarch64] Crash with SIGBUS in MarkActivationClosure::do_code_blob during vmTestbase/nsk/jvmti/.../bi04t002 test run
82c256e: 8259499: Handling type arguments from outer classes for inner class in javadoc
e5db9a9: 8268620: InfiniteLoopException test may fail on x86 platforms
67273ae: 8269865: Async UL needs to handle ERANGE on exceeding SEM_VALUE_MAX
... and 19 more: https://git.openjdk.java.net/jdk/compare/9cac94d581f240c10fe8fff2f803109a1ae30637...master

Your commit was automatically rebased without conflicts.

openjdk · 2021-07-15T05:15:49Z

@iklam Pushed as commit 1ebd946.

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

8270333: -XX:+VerifyStringTableAtExit should not do linear search

2285cf9

openjdk bot added the hotspot-runtime label Jul 14, 2021

iklam marked this pull request as ready for review Jul 14, 2021

openjdk bot added the rfr label Jul 14, 2021

ioilam added 2 commits Jul 14, 2021

replace template with inline function

cf913b1

fixed build and make sure table size is not zero

66c4d4e

dholmes-ora approved these changes Jul 14, 2021

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72d0f8e

yminqi approved these changes Jul 14, 2021

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openjdk bot closed this Jul 15, 2021

openjdk bot added integrated and removed ready rfr labels Jul 15, 2021

8270333: -XX:+VerifyStringTableAtExit should not do linear search #4772

8270333: -XX:+VerifyStringTableAtExit should not do linear search #4772

iklam commented Jul 14, 2021 •

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		template<bool update>
		unsigned int java_lang_String::hash_code_impl(oop java_string) {

8270333: -XX:+VerifyStringTableAtExit should not do linear search #4772

8270333: -XX:+VerifyStringTableAtExit should not do linear search #4772

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iklam commented Jul 14, 2021 • edited by openjdk[bot] bot

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