RFR: 8273140: Replace usages of Enum.class.getEnumConstants() with Enum.values() where possible [v4]

[Thomas Schatzl]

On Tue, 31 Aug 2021 20:04:23 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
>
> Сергей Цыпанов has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8273140: Fix copyright year

Lgtm.

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

Marked as reviewed by tschatzl (Reviewer).

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