On Thu, 18 Feb 2021 14:30:15 GMT, Сергей Цыпанов <github.com+10835776+stsypa...@openjdk.org> wrote:
> Hello, > > as of now `java.util.StringJoiner` still uses `char[]` as a storage for > joined Strings. > > This applies for the cases when all joined Strings as well as delimiter, > prefix and suffix contain only ASCII symbols. > > As a result when `StringJoiner.toString()` is called `byte[]` stored in > Strings is inflated in order to fill in `char[]` and after that `char[]` is > compressed when constructor of String is called: > String delimiter = this.delimiter; > char[] chars = new char[this.len + addLen]; > int k = getChars(this.prefix, chars, 0); > if (size > 0) { > k += getChars(elts[0], chars, k); // inflate byte[] > > for(int i = 1; i < size; ++i) { > k += getChars(delimiter, chars, k); > k += getChars(elts[i], chars, k); > } > } > > k += getChars(this.suffix, chars, k); > return new String(chars); // compress char[] -> byte[] > This can be improved by utilizing new method `String.getBytes(byte[], int, > int, byte, int)` [introduced](https://github.com/openjdk/jdk/pull/402) in > [JDK-8224986](https://bugs.openjdk.java.net/browse/JDK-8254082) > covering both cases when resulting String is Latin1 or UTF-16 > > I've prepared a patch along with benchmark proving that this change is > correct and brings improvement. > > @BenchmarkMode(Mode.AverageTime) > @OutputTimeUnit(TimeUnit.NANOSECONDS) > @Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"}) > public class StringJoinerBenchmark { > > @Benchmark > public String stringJoiner(Data data) { > String[] stringArray = data.stringArray; > return Joiner.joinWithStringJoiner(stringArray); > } > > @State(Scope.Thread) > public static class Data { > > @Param({"latin", "cyrillic", "mixed"}) > private String mode; > > @Param({"8", "32", "64"}) > private int length; > > @Param({"5", "10", "100"}) > private int count; > > private String[] stringArray; > > @Setup > public void setup() { > RandomStringGenerator generator = new RandomStringGenerator(); > > stringArray = new String[count]; > > for (int i = 0; i < count; i++) { > String alphabet = getAlphabet(i, mode); > stringArray[i] = generator.randomString(alphabet, length); > } > } > > private static String getAlphabet(int index, String mode) { > var latin = "abcdefghijklmnopqrstuvwxyz"; //English > var cyrillic = "абвгдеёжзиклмнопрстуфхцчшщьыъэюя"; // Russian > > String alphabet; > switch (mode) { > case "mixed" -> alphabet = index % 2 == 0 ? cyrillic : latin; > case "latin" -> alphabet = latin; > case "cyrillic" -> alphabet = cyrillic; > default -> throw new RuntimeException("Illegal mode " + mode); > } > return alphabet; > } > } > } > > public class Joiner { > > public static String joinWithStringJoiner(String[] stringArray) { > StringJoiner joiner = new StringJoiner(",", "[", "]"); > for (String str : stringArray) { > joiner.add(str); > } > return joiner.toString(); > } > } > > > (count) (length) (mode) > Java 14 patched Units > stringJoiner 5 8 latin 78.836 > ± 0.208 67.546 ± 0.500 ns/op > stringJoiner 5 32 latin 92.877 > ± 0.422 66.760 ± 0.498 ns/op > stringJoiner 5 64 latin 115.423 > ± 0.883 73.224 ± 0.289 ns/op > stringJoiner 10 8 latin 152.587 > ± 0.429 161.427 ± 0.635 ns/op > stringJoiner 10 32 latin 189.998 > ± 0.478 164.099 ± 0.963 ns/op > stringJoiner 10 64 latin 238.679 > ± 1.419 176.825 ± 0.533 ns/op > stringJoiner 100 8 latin 1215.612 > ± 17.413 1541.802 ± 126.166 ns/op > stringJoiner 100 32 latin 1699.998 > ± 28.407 1563.341 ± 4.439 ns/op > stringJoiner 100 64 latin 2289.388 > ± 45.319 2215.931 ± 137.583 ns/op > stringJoiner 5 8 cyrillic 96.692 > ± 0.947 80.946 ± 0.371 ns/op > stringJoiner 5 32 cyrillic 107.806 > ± 0.429 84.717 ± 0.541 ns/op > stringJoiner 5 64 cyrillic 150.762 > ± 2.267 96.214 ± 1.251 ns/op > stringJoiner 10 8 cyrillic 190.570 > ± 0.381 182.754 ± 0.678 ns/op > stringJoiner 10 32 cyrillic 240.239 > ± 1.110 187.991 ± 1.575 ns/op > stringJoiner 10 64 cyrillic 382.493 > ± 2.692 219.358 ± 0.967 ns/op > stringJoiner 100 8 cyrillic 1737.435 > ± 16.171 1658.379 ± 56.225 ns/op > stringJoiner 100 32 cyrillic 2321.106 > ± 13.583 1942.028 ± 3.418 ns/op > stringJoiner 100 64 cyrillic 3189.563 > ± 10.135 2484.796 ± 7.572 ns/op > stringJoiner 5 8 mixed 88.743 > ± 0.709 76.049 ± 0.685 ns/op > stringJoiner 5 32 mixed 103.425 > ± 0.745 81.006 ± 0.184 ns/op > stringJoiner 5 64 mixed 146.441 > ± 0.763 93.071 ± 0.858 ns/op > stringJoiner 10 8 mixed 169.262 > ± 0.482 158.890 ± 0.598 ns/op > stringJoiner 10 32 mixed 218.566 > ± 0.945 170.415 ± 1.172 ns/op > stringJoiner 10 64 mixed 361.412 > ± 1.546 200.374 ± 0.683 ns/op > stringJoiner 100 8 mixed 1594.544 > ± 5.761 1476.689 ± 2.004 ns/op > stringJoiner 100 32 mixed 2221.333 > ± 28.320 1879.071 ± 52.729 ns/op > stringJoiner 100 64 mixed 3115.786 > ± 22.485 2400.644 ± 4.401 ns/op > > stringJoiner:·gc.alloc.rate.norm 5 8 latin 248.023 > ± 0.001 136.015 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 5 32 latin 608.045 > ± 0.001 256.022 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 5 64 latin 1088.067 > ± 0.002 416.030 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 10 8 latin 464.044 > ± 0.001 264.029 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 10 32 latin 1184.085 > ± 0.003 504.044 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 10 64 latin 2144.123 > ± 0.005 824.065 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 100 8 latin 3872.367 > ± 8.002 2024.269 ± 8.016 B/op > stringJoiner:·gc.alloc.rate.norm 100 32 latin 11048.803 > ± 7.988 4416.393 ± 0.004 B/op > stringJoiner:·gc.alloc.rate.norm 100 64 latin 20657.194 > ± 9.775 7640.642 ± 9.819 B/op > stringJoiner:·gc.alloc.rate.norm 5 8 cyrillic 360.029 > ± 0.001 184.020 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 5 32 cyrillic 960.060 > ± 0.002 424.032 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 5 64 cyrillic 1760.088 > ± 0.003 744.043 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 10 8 cyrillic 664.063 > ± 0.001 352.038 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 10 32 cyrillic 1864.128 > ± 0.003 832.067 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 10 64 cyrillic 3464.206 > ± 0.007 1472.094 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 100 8 cyrillic 5704.541 > ± 0.006 2928.317 ± 8.002 B/op > stringJoiner:·gc.alloc.rate.norm 100 32 cyrillic 17705.090 > ± 0.045 7720.658 ± 0.007 B/op > stringJoiner:·gc.alloc.rate.norm 100 64 cyrillic 33689.855 > ± 9.786 14121.042 ± 0.015 B/op > stringJoiner:·gc.alloc.rate.norm 5 8 mixed 360.028 > ± 0.001 184.016 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 5 32 mixed 960.059 > ± 0.002 424.031 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 5 64 mixed 1760.088 > ± 0.003 744.041 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 10 8 mixed 664.052 > ± 0.001 352.035 ± 0.002 B/op > stringJoiner:·gc.alloc.rate.norm 10 32 mixed 1864.116 > ± 0.005 832.064 ± 0.001 B/op > stringJoiner:·gc.alloc.rate.norm 10 64 mixed 3464.196 > ± 0.006 1472.088 ± 0.002 B/op > stringJoiner:·gc.alloc.rate.norm 100 8 mixed 5672.448 > ± 8.002 2920.314 ± 0.006 B/op > stringJoiner:·gc.alloc.rate.norm 100 32 mixed 17681.092 > ± 9.824 7728.653 ± 8.008 B/op > stringJoiner:·gc.alloc.rate.norm 100 64 mixed 33697.818 > ± 8.011 14120.977 ± 0.034 B/op This pull request has now been integrated. Changeset: 000012a3 Author: Sergey Tsypanov <sergei.tsypa...@yandex.ru> Committer: Claes Redestad <redes...@openjdk.org> URL: https://git.openjdk.java.net/jdk/commit/000012a3 Stats: 135 lines in 2 files changed: 113 ins; 10 del; 12 mod 8148937: (str) Adapt StringJoiner for Compact Strings Reviewed-by: redestad, chegar ------------- PR: https://git.openjdk.java.net/jdk/pull/2627