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;
}
}
}
(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
-------------
Commit messages:
- 8261880: Check also delimiter, prefix and suffix
- 8148937: (str) Adapt StringJoiner for Compact Strings
Changes: https://git.openjdk.java.net/jdk/pull/2627/files
Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2627&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8148937
Stats: 77 lines in 3 files changed: 56 ins; 6 del; 15 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
