8372460: Use EnumMap instead of HashMap for DateTimeFormatter parsing to improve performance

[wenshao]

This PR optimizes the parsing performance of DateTimeFormatter by replacing HashMap with EnumMap in scenarios where the keys are exclusively ChronoField enum values.

When parsing date/time strings, DateTimeFormatter creates HashMaps to store intermediate parsed values. HashMap has more overhead for operations compared to specialized map implementations.

Since ChronoField is an enum and all keys in these maps are ChronoField instances, we can use EnumMap instead, which provides better performance for enum keys due to its optimized internal structure.

Parsing scenarios show improvements from 12% to 95%

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Progress

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Issue

• JDK-8372460: Use EnumMap instead of HashMap for DateTimeFormatter parsing to improve performance (Enhancement - P4)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/28471/head:pull/28471
$ git checkout pull/28471

Update a local copy of the PR:
$ git checkout pull/28471
$ git pull https://git.openjdk.org/jdk.git pull/28471/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 28471

View PR using the GUI difftool:
$ git pr show -t 28471

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Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/28471.diff

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[bridgekeeper]

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[openjdk]

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[openjdk]

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• core-libs
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[wenshao]

1. Shell

We run the following Shell command

# master
git checkout b6495573e9dc5470df268b63f8e7a93f38406cd2
make test TEST="micro:java.time.format.DateTimeFormatterParse"

# this pr
git checkout d8742d7514abfe0e36f105fa7310fdb1755ae546
make test TEST="micro:java.time.format.DateTimeFormatterParse"

2. Raw Benchmark Data

Performance data running on a MacBook M1 Pro:

# b649557 (master)
Benchmark                                           Mode  Cnt     Score     Error   Units
DateTimeFormatterParse.parseInstant                thrpt   15  2066.130 ± 126.134  ops/ms
DateTimeFormatterParse.parseLocalDate              thrpt   15  5014.987 ± 424.759  ops/ms
DateTimeFormatterParse.parseLocalDateTime          thrpt   15  3821.083 ± 390.928  ops/ms
DateTimeFormatterParse.parseLocalDateTimeWithNano  thrpt   15  3529.090 ± 209.195  ops/ms
DateTimeFormatterParse.parseLocalTime              thrpt   15  4275.904 ± 335.752  ops/ms
DateTimeFormatterParse.parseLocalTimeWithNano      thrpt   15  4596.255 ± 195.175  ops/ms
DateTimeFormatterParse.parseOffsetDateTime         thrpt   15  2330.924 ± 152.061  ops/ms
DateTimeFormatterParse.parseZonedDateTime          thrpt   15  1837.753 ± 107.873  ops/ms

# d8742d7 (this pr)
Benchmark                                           Mode  Cnt     Score     Error   Units
DateTimeFormatterParse.parseInstant                thrpt   15  2900.168 ±  56.079  ops/ms
DateTimeFormatterParse.parseLocalDate              thrpt   15  9787.592 ± 384.437  ops/ms
DateTimeFormatterParse.parseLocalDateTime          thrpt   15  5046.838 ± 271.451  ops/ms
DateTimeFormatterParse.parseLocalDateTimeWithNano  thrpt   15  3963.050 ± 434.662  ops/ms
DateTimeFormatterParse.parseLocalTime              thrpt   15  8196.707 ± 329.547  ops/ms
DateTimeFormatterParse.parseLocalTimeWithNano      thrpt   15  8387.213 ± 652.292  ops/ms
DateTimeFormatterParse.parseOffsetDateTime         thrpt   15  3291.076 ± 294.889  ops/ms
DateTimeFormatterParse.parseZonedDateTime          thrpt   15  2069.595 ± 293.385  ops/ms

3. Performance Comparison

Performance Comparison: b649557 vs d8742d7

Benchmark	b649557	d8742d7	Improvement Factor
DateTimeFormatterParse.parseInstant	2066.130 ± 126.134	2900.168 ± 56.079	1.404x
DateTimeFormatterParse.parseLocalDate	5014.987 ± 424.759	9787.592 ± 384.437	1.952x
DateTimeFormatterParse.parseLocalDateTime	3821.083 ± 390.928	5046.838 ± 271.451	1.321x
DateTimeFormatterParse.parseLocalDateTimeWithNano	3529.090 ± 209.195	3963.050 ± 434.662	1.123x
DateTimeFormatterParse.parseLocalTime	4275.904 ± 335.752	8196.707 ± 329.547	1.919x
DateTimeFormatterParse.parseLocalTimeWithNano	4596.255 ± 195.175	8387.213 ± 652.292	1.825x
DateTimeFormatterParse.parseOffsetDateTime	2330.924 ± 152.061	3291.076 ± 294.889	1.412x
DateTimeFormatterParse.parseZonedDateTime	1837.753 ± 107.873	2069.595 ± 293.385	1.126x

[wenshao]

java/time/tck/java/time/temporal/TCKWeekFields.java
java/time/tck/java/time/temporal/TCKIsoFields.java
java/time/tck/java/time/temporal/TCKJulianFields.java
java/time/tck/java/time/format/TCKDateTimeParseResolver.java
java/time/tck/java/time/format/TCKLocalizedFieldParser.java
java/time/tck/java/time/format/TCKDateTimeFormatters.java
java/time/tck/java/time/format/TCKDateTimeFormatterBuilder.java

The existing tests above can cover the cases where there are no non-ChronoFields, so no additional tests are needed.

[mlbridge]

Webrevs

• 01: Full - Incremental (7137d9ec)
• 00: Full (5a050fe9)