On Thu, 15 Apr 2021 19:26:48 GMT, Peter Levart <plev...@openjdk.org> wrote:
>> While JDK-8148937 improved StringJoiner class by replacing internal use of >> getChars that copies out characters from String elements into a char[] array >> with StringBuilder which is somehow more optimal, the improvement was >> marginal in speed (0% ... 10%) and mainly for smaller strings, while GC was >> reduced by about 50% in average per operation. >> Initial attempt to tackle that issue was more involved, but was later >> discarded because it was apparently using too much internal String details >> in code that lives outside String and outside java.lang package. >> But there is another way to package such "intimate" code - we can put it >> into String itself and just call it from StringJoiner. >> This PR is an attempt at doing just that. It introduces new package-private >> method in `java.lang.String` which is then used from both pubic static >> `String.join` methods as well as from `java.util.StringJoiner` (via >> SharedSecrets). The improvements can be seen by running the following JMH >> benchmark: >> >> https://gist.github.com/plevart/86ac7fc6d4541dbc08256cde544019ce >> >> The comparative results are here: >> >> https://jmh.morethan.io/?gist=7eb421cf7982456a2962269137f71c15 >> >> The jmh-result.json files are here: >> >> https://gist.github.com/plevart/7eb421cf7982456a2962269137f71c15 >> >> Improvement in speed ranges from 8% (for small strings) to 200% (for long >> strings), while creation of garbage has been further reduced to an almost >> garbage-free operation. >> >> So WDYT? > > Peter Levart has updated the pull request incrementally with one additional > commit since the last revision: > > Add String.join benchmark method to StringJoinerBenchmark and adjust some > parameters to cover bigger range Great work, thanks! I tried to do something similar a couple of years ago but did not submit my patch. One thing that stopped me is that joining many one-character strings was slower with my patch, compared to the baseline. Something like this: // setup String[] strings = new String[100]; Arrays.fill(strings, "a"); // benchmark return String.join(",", strings); Could you add this case to your benchmark, for completeness? ------------- PR: https://git.openjdk.java.net/jdk/pull/3501
