<i18n dev> RFR: 8335252: Reduce size of j.u.Formatter.Conversion#isValid [v4]

[Shaojin Wen]

On Fri, 28 Jun 2024 16:29:02 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

>> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   fix comment
>
> That's a clever change and more preferable (but still potentially fragile in the source to bytecode translation process). However I still don't understand the overall motivation, why does it matter?

@PaulSandoz 
String.format is widely used. In some performance-critical scenarios, when doing performance profiling, it is often found that String.format calls consume a lot of time. My suggestion is to replace `String.format` with `String concat` or StringBuilder.


String info = String.format("xxxx %s", str);


replace to

String info = "xxxx %s" + str;


or

String info = new StringBuilder("xxxx ").append(str).toString();


Let's do a Benchmark comparison:

class StringFormat{
    @Benchmark
    public String stringIntFormat() {
        return "%s %d".formatted(s, i);
    }

    @Benchmark
    public String stringIntIndy() {
        return s + " " + i;
    }

    @Benchmark
    public String stringIntStringBuilder() {
        return new StringBuilder(s).append(" ").append(i).toString();
    }    
}




Benchmark                            Mode  Cnt   Score   Error  Units
StringFormat.stringIntFormat         avgt   15  87.451 ? 2.890  ns/op
StringFormat.stringIntIndy           avgt   15   6.471 ? 0.089  ns/op
StringFormat.stringIntStringBuilder  avgt   15   7.949 ? 0.067  ns/op


It can be seen that the performance of using StringConcat and StringBuilder is 10 times that of using String.format.

StringTemplate (JEP 430/459/465) was an attempt to improve performance, but the API was not friendly.

I was going to contribute to StringTemplate, (PR #16044 / PR #16021/PR #16017,) but StringTemplate has been removed.

I'm working on improving the performance of String.format.

The PR I submitted before: [8316704: Regex-free parsing of Formatter and FormatProcessor specifiers](https://github.com/openjdk/jdk/pull/15776)

This PR is a very minor improvement, We may also need to do further work to provide a fastpath for common scenarios to improve performance. I also plan to do such work.

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

PR Comment: https://git.openjdk.org/jdk/pull/19926#issuecomment-2197391335