RFR: 8316704: Regex-free parsing of Formatter and FormatProcessor specifiers [v3]

[Raffaello Giulietti]

On Thu, 19 Oct 2023 06:38:35 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> @cl4es made performance optimizations for the simple specifiers of String.format in PR https://github.com/openjdk/jdk/pull/2830. Based on the same idea, I continued to make improvements. I made patterns like %2d %02d also be optimized.
>> 
>> The following are the test results based on MacBookPro M1 Pro: 
>> 
>> 
>> -Benchmark                          Mode  Cnt     Score     Error  Units
>> -StringFormat.complexFormat         avgt   15  1862.233 ? 217.479  ns/op
>> -StringFormat.int02Format           avgt   15   312.491 ?  26.021  ns/op
>> -StringFormat.intFormat             avgt   15    84.432 ?   4.145  ns/op
>> -StringFormat.longFormat            avgt   15    87.330 ?   6.111  ns/op
>> -StringFormat.stringFormat          avgt   15    63.985 ?  11.366  ns/op
>> -StringFormat.stringIntFormat       avgt   15    87.422 ?   0.147  ns/op
>> -StringFormat.widthStringFormat     avgt   15   250.740 ?  32.639  ns/op
>> -StringFormat.widthStringIntFormat  avgt   15   312.474 ?  16.309  ns/op
>> 
>> +Benchmark                          Mode  Cnt    Score    Error  Units
>> +StringFormat.complexFormat         avgt   15  740.626 ? 66.671  ns/op (+151.45)
>> +StringFormat.int02Format           avgt   15  131.049 ?  0.432  ns/op (+138.46)
>> +StringFormat.intFormat             avgt   15   67.229 ?  4.155  ns/op (+25.59)
>> +StringFormat.longFormat            avgt   15   66.444 ?  0.614  ns/op (+31.44)
>> +StringFormat.stringFormat          avgt   15   62.619 ?  4.652  ns/op (+2.19)
>> +StringFormat.stringIntFormat       avgt   15   89.606 ? 13.966  ns/op (-2.44)
>> +StringFormat.widthStringFormat     avgt   15   52.462 ? 15.649  ns/op (+377.95)
>> +StringFormat.widthStringIntFormat  avgt   15  101.814 ?  3.147  ns/op (+206.91)
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix FormatterBuilder testcase handle lineSeparator on windows

src/java.base/share/classes/java/util/FormatProcessor.java line 247:

> 245:                 throw new MissingFormatArgumentException(group + " is not immediately followed by an embedded expression");
> 246:             } else {
> 247:                 throw new UnknownFormatConversionException(String.valueOf(c));

I don't think this exception is thrown by the original code.

src/java.base/share/classes/java/util/Formatter.java line 2889:

> 2887:         }
> 2888: 
> 2889:         int parse() {

Since the implementation of this method is far from trivial, it would be very useful to document what it returns.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15776#discussion_r1366679352
PR Review Comment: https://git.openjdk.org/jdk/pull/15776#discussion_r1366703609