<i18n dev> RFR: 8333396: Performance regression of DecimalFormat.format [v5]

[Justin Lu]

On Wed, 5 Jun 2024 03:59:24 GMT, lingjun-cg <duke at openjdk.org> wrote:

>> ### Performance regression of DecimalFormat.format
>> From the output of perf, we can see the hottest regions contain atomic instructions.  But when run with JDK 11, there is no such problem. The reason is the removed biased locking.  
>> The DecimalFormat uses StringBuffer everywhere, and StringBuffer itself contains many synchronized methods.
>> So I added support for some new methods that accept StringBuilder which is lock-free.
>> 
>> ### Benchmark testcase
>> 
>> @BenchmarkMode(Mode.AverageTime)
>> @Warmup(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
>> @Measurement(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
>> @State(Scope.Thread)
>> @OutputTimeUnit(TimeUnit.NANOSECONDS)
>> public class JmhDecimalFormat {
>> 
>>     private DecimalFormat format;
>> 
>>     @Setup(Level.Trial)
>>     public void setup() {
>>         format = new DecimalFormat("#0.00000");
>>     }
>> 
>>     @Benchmark
>>     public void testNewAndFormat() throws InterruptedException {
>>         new DecimalFormat("#0.00000").format(9524234.1236457);
>>     }
>> 
>>     @Benchmark
>>     public void testNewOnly() throws InterruptedException {
>>         new DecimalFormat("#0.00000");
>>     }
>> 
>>     @Benchmark
>>     public void testFormatOnly() throws InterruptedException {
>>         format.format(9524234.1236457);
>>     }
>> }
>> 
>> 
>> ### Test result
>> #### Current JDK before optimize
>> 
>>  Benchmark                             Mode  Cnt    Score   Error  Units
>> JmhDecimalFormat.testFormatOnly       avgt   50  642.099 ? 1.253  ns/op
>> JmhDecimalFormat.testNewAndFormat     avgt   50  989.307 ? 3.676  ns/op
>> JmhDecimalFormat.testNewOnly          avgt   50  303.381 ? 5.252  ns/op
>> 
>> 
>> 
>> #### Current JDK after optimize
>> 
>> Benchmark                          Mode  Cnt    Score   Error  Units
>> JmhDecimalFormat.testFormatOnly    avgt   50  351.499 ? 0.761  ns/op
>> JmhDecimalFormat.testNewAndFormat  avgt   50  615.145 ? 2.478  ns/op
>> JmhDecimalFormat.testNewOnly       avgt   50  209.874 ? 9.951  ns/op
>> 
>> 
>> ### JDK 11 
>> 
>> Benchmark                          Mode  Cnt    Score   Error  Units
>> JmhDecimalFormat.testFormatOnly    avgt   50  364.214 ? 1.191  ns/op
>> JmhDecimalFormat.testNewAndFormat  avgt   50  658.699 ? 2.311  ns/op
>> JmhDecimalFormat.testNewOnly       avgt   50  248.300 ? 5.158  ns/op
>
> lingjun-cg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8333396: Performance regression of DecimalFormat.format

After an initial pass, at first glance I don't see compatibility concerns since there no behavioral changes to the public/protected members of the Format/Format.FieldDelegate classes/subclasses and we have left the abstract methods untouched. This change allows internally for StringBuilder to be utilized via the proxy and the newly added package-private methods added to NumberFormat.

Since we are already in the scope of Format, I think something to consider is whether we might want to include the other possible classes, such as DateFormat.format(Date) in this change as well. Although it might get quite messy if corresponding changes are made to all Format subclasses where possible; just like this change, I'm sure it would kick off a chain of buffer to proxy changes everywhere.

I'm sure there is more discussion to be had in general.

src/java.base/share/classes/java/text/CompactNumberFormat.java line 885:

> 883:     }
> 884: 
> 885:     private StringBuilderBufferProxy format(BigInteger number, StringBuilderBufferProxy result,

While the DecimalFormat and CompactNumberFormat BigInteger and BigDecimal `format` methods will always return a StringBuffer, we must change the method signatures to use the proxy, otherwise we would need to define alternate methods all the way at the `Format.FieldDelegate` level. So I think this is a lesser of two evils.

src/java.base/share/classes/java/text/StringBuilderBufferProxy.java line 30:

> 28:  * Provide the least interfaces that support both:
> 29:  * NumberFormat#format((double|long), StringBuilder, FieldPosition)
> 30:  * and NumberFormat#format(double, StringBuffer, FieldPosition)

Shouldn't this be `NumberFormat#format((double|long), StringBuffer, FieldPosition)`?

src/java.base/share/classes/java/text/StringBuilderBufferProxy.java line 150:

> 148:     class StringBufferImpl implements StringBuilderBufferProxy {
> 149: 
> 150:         private StringBuffer sb;

Should this be `final`?

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

PR Review: https://git.openjdk.org/jdk/pull/19513#pullrequestreview-2116341710
PR Review Comment: https://git.openjdk.org/jdk/pull/19513#discussion_r1638667165
PR Review Comment: https://git.openjdk.org/jdk/pull/19513#discussion_r1638686606
PR Review Comment: https://git.openjdk.org/jdk/pull/19513#discussion_r1638540586