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

[Joe Darcy]

On Mon, 30 Aug 2021 14:26:56 GMT, Сергей Цыпанов <github.com+10835776+stsypanov at openjdk.org> wrote:

> 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

src/java.desktop/share/classes/sun/font/AttributeValues.java line 2:

> 1: /*
> 2:  * Copyright (c) 2004, 2014, Oracle and/or its affiliates. All rights reserved.

Per OpenJDK conventions, the original copyright year must be preserved when a file is updated so

"Copyright (c) 2004, 2021,"

in this case.

-------------

PR: https://git.openjdk.java.net/jdk/pull/5303