> 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
Сергей Цыпанов has updated the pull request incrementally with one additional
commit since the last revision:
8148937: (str) Update copyright year
-------------
Changes:
- all: https://git.openjdk.java.net/jdk/pull/2627/files
- new: https://git.openjdk.java.net/jdk/pull/2627/files/e0d7d122..b600ea62
Webrevs:
- full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2627&range=02
- incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2627&range=01-02
Stats: 7 lines in 2 files changed: 0 ins; 1 del; 6 mod
Patch: https://git.openjdk.java.net/jdk/pull/2627.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/2627/head:pull/2627
PR: https://git.openjdk.java.net/jdk/pull/2627
