> 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: Fix overflow checking logic, add test for it, avoid branch in loop, add 1-char strings to JHM test ------------- Changes: - all: https://git.openjdk.java.net/jdk/pull/3501/files - new: https://git.openjdk.java.net/jdk/pull/3501/files/6160e5aa..a2d5e819 Webrevs: - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3501&range=02 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3501&range=01-02 Stats: 123 lines in 3 files changed: 110 ins; 4 del; 9 mod Patch: https://git.openjdk.java.net/jdk/pull/3501.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/3501/head:pull/3501 PR: https://git.openjdk.java.net/jdk/pull/3501
