8273140: Replace usages of Enum.class.getEnumConstants() with Enum.values() where possible

[stsypanov]

Just a very tiny clean-up.

There are some places in JDK code base where we call Enum.class.getEnumConstants() to get all the values of the referenced enum. This is excessive, less-readable and slower than just calling Enum.values() as in getEnumConstants() we have volatile access:

public T[] getEnumConstants() {
    T[] values = getEnumConstantsShared();
    return (values != null) ? values.clone() : null;
}

private transient volatile T[] enumConstants;

T[] getEnumConstantsShared() {
    T[] constants = enumConstants;
    if (constants == null) { /* ... */ }
    return constants;
}

Calling values() method is slightly faster:

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"})
public class EnumBenchmark {

  @Benchmark
  public Enum[] values() {
    return Enum.values();
  }

  @Benchmark
  public Enum[] getEnumConstants() {
    return Enum.class.getEnumConstants();
  }

  private enum Enum {
    A,
    B
  }
}

Benchmark                                                        Mode  Cnt     Score     Error   Units
EnumBenchmark.getEnumConstants                                   avgt   15     6,265 ±   0,051   ns/op
EnumBenchmark.getEnumConstants:·gc.alloc.rate                    avgt   15  2434,075 ±  19,568  MB/sec
EnumBenchmark.getEnumConstants:·gc.alloc.rate.norm               avgt   15    24,002 ±   0,001    B/op
EnumBenchmark.getEnumConstants:·gc.churn.G1_Eden_Space           avgt   15  2433,709 ±  70,216  MB/sec
EnumBenchmark.getEnumConstants:·gc.churn.G1_Eden_Space.norm      avgt   15    23,998 ±   0,659    B/op
EnumBenchmark.getEnumConstants:·gc.churn.G1_Survivor_Space       avgt   15     0,009 ±   0,003  MB/sec
EnumBenchmark.getEnumConstants:·gc.churn.G1_Survivor_Space.norm  avgt   15    ≈ 10⁻⁴              B/op
EnumBenchmark.getEnumConstants:·gc.count                         avgt   15   210,000            counts
EnumBenchmark.getEnumConstants:·gc.time                          avgt   15   119,000                ms

EnumBenchmark.values                                             avgt   15     4,164 ±   0,134   ns/op
EnumBenchmark.values:·gc.alloc.rate                              avgt   15  3665,341 ± 120,721  MB/sec
EnumBenchmark.values:·gc.alloc.rate.norm                         avgt   15    24,002 ±   0,001    B/op
EnumBenchmark.values:·gc.churn.G1_Eden_Space                     avgt   15  3660,512 ± 137,250  MB/sec
EnumBenchmark.values:·gc.churn.G1_Eden_Space.norm                avgt   15    23,972 ±   0,529    B/op
EnumBenchmark.values:·gc.churn.G1_Survivor_Space                 avgt   15     0,017 ±   0,003  MB/sec
EnumBenchmark.values:·gc.churn.G1_Survivor_Space.norm            avgt   15    ≈ 10⁻⁴              B/op
EnumBenchmark.values:·gc.count                                   avgt   15   262,000            counts
EnumBenchmark.values:·gc.time                                    avgt   15   155,000                ms

---

Progress

• Change must not contain extraneous whitespace
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• Change must be properly reviewed

Issue

• JDK-8273140: Replace usages of Enum.class.getEnumConstants() with Enum.values() where possible

Reviewers

• Thomas Schatzl (@tschatzl - Reviewer) ⚠️ Review applies to 90319b2

Reviewing

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[openjdk]

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[mlbridge]

Webrevs

• 03: Full - Incremental (a5f58fe2)
• 02: Full - Incremental (171ecd4e)
• 01: Full - Incremental (1cfb0af3)
• 00: Full (90319b2f)

[kevinrushforth]

You missed two of the copyright year problems.

[tschatzl]

Lgtm.

[openjdk]

⚠️ @stsypanov the full name on your profile does not match the author name in this pull requests' HEAD commit. If this pull request gets integrated then the author name from this pull requests' HEAD commit will be used for the resulting commit. If you wish to push a new commit with a different author name, then please run the following commands in a local repository of your personal fork:

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[openjdk]

@stsypanov 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:

8273140: Replace usages of Enum.class.getEnumConstants() with Enum.values() where possible

Reviewed-by: tschatzl

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 27 new commits pushed to the master branch:

• 0e14bf7: 8273176: handle latest VS2019 in abstract_vm_version
• f1c5e26: 8273206: jdk/jfr/event/gc/collection/TestG1ParallelPhases.java fails after JDK-8159979
• e600fe1: 8272618: Unnecessary Attr.visitIdent.noOuterThisPath
• 2fce7cb: 8272963: Update the java manpage markdown source
• 18a731a: 8269770: nsk tests should start IOPipe channel before launch debuggee - Debugee.prepareDebugee
• 9c392d0: 8273197: ProblemList 2 jtools tests due to JDK-8273187
• 3d657eb: 8262186: Call X509KeyManager.chooseClientAlias once for all key types
• c1e0aac: 8273186: Remove leftover comment about sparse remembered set in G1 HeapRegionRemSet
• 683e30d: 8273169: java/util/regex/NegativeArraySize.java failed after JDK-8271302
• 1996f64: 8273092: Sort classlist in JDK image
• ... and 17 more: https://git.openjdk.java.net/jdk/compare/fbffa54efe447a4c911af2be1d7774a8c60d6ede...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.

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➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

[stsypanov]

/integrate

[openjdk]

@stsypanov
Your change (at version a5f58fe) is now ready to be sponsored by a Committer.

[tschatzl]

/sponsor

[openjdk]

Going to push as commit 152e669.
Since your change was applied there have been 38 commits pushed to the master branch:

• 857a930: 8263375: Support stack watermarks in Zero VM
• 6cfe314: 8272970: Parallelize runtime/InvocationTests/
• a9a83b2: 8273256: runtime/cds/appcds/TestEpsilonGCWithCDS.java fails due to Unrecognized VM option 'ObjectAlignmentInBytes=64' on x86_32
• 1a5a2b6: 8271745: Correct block size for KW,KWP mode and use fixed IV for KWP mode for SunJCE
• 2f01a6f: 8273157: Add convenience methods to Messager
• 9689f61: 8272788: Nonleaf ranked locks should not be safepoint_check_never
• 4ee0dac: 8273248: ProblemList java/lang/instrument/BootClassPath/BootClassPathTest.sh on all configs
• 655ea6d: 8270489: Support archived heap objects in EpsilonGC
• dacd197: 8273217: Make ParHeapInspectTask _safepoint_check_never
• 02822e1: 8272377: assert preconditions that are ensured when created in add_final_edges
• ... and 28 more: https://git.openjdk.java.net/jdk/compare/fbffa54efe447a4c911af2be1d7774a8c60d6ede...master

Your commit was automatically rebased without conflicts.

[openjdk]

@tschatzl @stsypanov Pushed as commit 152e669.

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