RFR: 8333396: Performance regression of DecimalFormat.format [v16]

[Justin Lu]

On Tue, 2 Jul 2024 02:13:50 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

Thanks @lingjun-cg for your updates.

I went through the newest version and the implementation changes look OK to me. It is a little easier to review without the intermediate StringBuilder method.
It is a large change, so it is good there are multiple sets of eyes here. We will of course still need approval from a **Reviewer**.

Something to note is that there is now some wording in the specification of some java.text.Format.* classes that is technically untrue. For example, in `Format.format(Object obj)`, it states the method is equivalent to calling `Format.format(obj, new StringBuffer(), new FieldPosition(0)).toString())`. It is not the biggest deal since it is just minor supplementary info and can probably simply be removed. However, this should be done as a separate issue, since we would like to backport the changes in this PR.

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

Marked as reviewed by jlu (Committer).

PR Review: https://git.openjdk.org/jdk/pull/19513#pullrequestreview-2158180263