RFR: JDK-8282625 Formatter caches Locale/DecimalFormatSymbols poorly

[Naoto Sato]

On Fri, 4 Mar 2022 17:54:20 GMT, Jim Laskey <jlaskey at openjdk.org> wrote:

> Several attempts have been made to improve Formatter's numeric performance by caching the current Locale zero. Such fixes, however, ignore the real issue, which is the slowness of fetching DecimalFormatSymbols. By directly caching DecimalFormatSymbols in the Formatter, this enhancement streamlines the process of accessing Locale DecimalFormatSymbols and specifically getZeroDigit(). The result is a general improvement in the performance of numeric formatting. 
> 
> 
> @Benchmark 
> public void bigDecimalDefaultLocale() { 
>     result = String.format("%1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f", X); 
> } 
> 
> @Benchmark 
> public void bigDecimalLocaleAlternate() { 
>     result = String.format(THAI, "%1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f", X); 
>     other = String.format(DEFAULT, "%1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f", X); 
> } 
> 
> @Benchmark 
> public void bigDecimalThaiLocale() { 
>     result = String.format(THAI, "%1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f %1$f", X); 
> } 
> 
> @Benchmark 
> public void integerDefaultLocale() { 
>     result = String.format("%1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d", x); 
> } 
> 
> @Benchmark 
> public void integerLocaleAlternate() { 
>     result = String.format(THAI, "%1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d", x); 
>     other = String.format(DEFAULT, "%1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d", x); 
> } 
> 
> @Benchmark 
> public void integerThaiLocale() { 
>     result = String.format(THAI, "%1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d %1$d", x); 
> } 
> 
> 
> Before: 
> Benchmark Mode Cnt Score Error Units 
> MyBenchmark.bigDecimalDefaultLocale thrpt 25 75498.923 ± 3686.966 ops/s 
> MyBenchmark.bigDecimalLocaleAlternate thrpt 25 39068.721 ± 162.983 ops/s 
> MyBenchmark.bigDecimalThaiLocale thrpt 25 77256.530 ± 294.743 ops/s 
> MyBenchmark.integerDefaultLocale thrpt 25 344093.071 ± 6189.002 ops/s 
> MyBenchmark.integerLocaleAlternate thrpt 25 165685.488 ± 440.857 ops/s 
> MyBenchmark.integerThaiLocale thrpt 25 327461.302 ± 1168.243 ops/s 
> 
> After: 
> Benchmark Mode Cnt Score Error Units 
> MyBenchmark.bigDecimalDefaultLocale thrpt 25 94735.293 ± 674.587 ops/s 
> MyBenchmark.bigDecimalLocaleAlternate thrpt 25 44215.547 ± 291.664 ops/s 
> MyBenchmark.bigDecimalThaiLocale thrpt 25 91390.997 ± 658.677 ops/s 
> MyBenchmark.integerDefaultLocale thrpt 25 363722.977 ± 2864.554 ops/s 
> MyBenchmark.integerLocaleAlternate thrpt 25 165789.514 ± 779.656 ops/s 
> MyBenchmark.integerThaiLocale thrpt 25 351400.818 ± 1030.246 ops/s

Good to see the performance improvement. Since you are adding a new public method, a CSR is needed for this change.

src/java.base/share/classes/java/text/DecimalFormatSymbols.java line 194:

> 192:      * Gets the locale used to create this table.
> 193:      *
> 194:      * @return the the locale used to create this table

`table` does not read right here, also `@since 19` is needed.

src/java.base/share/classes/java/util/Formatter.java line 2016:

> 2014:     static DecimalFormatSymbols getDecimalFormatSymbols(Locale locale) {
> 2015:         DecimalFormatSymbols dfs = DFS;
> 2016:         if (dfs != null && dfs.getLocale() == locale) {

`Locale` should be compared using `equals()`.

src/java.base/share/classes/java/util/Formatter.java line 2026:

> 2024:     // Caching zero.
> 2025:     static char getZero(Locale locale) {
> 2026:         return locale == null ? '0' : getDecimalFormatSymbols(locale).getZeroDigit();

While we are at it, it would be beneficial to cache locale-dependent grouping and decimal separators too.

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

PR: https://git.openjdk.java.net/jdk/pull/7703