RFR: 8254082: AbstractStringBuilder.insert(int dstOffset, CharSequence s, int start, int end) is missing fast-path for String
Сергей Цыпанов
github.com+10835776+stsypanov at openjdk.java.net
Tue Nov 24 22:13:03 UTC 2020
Original mail: https://mail.openjdk.java.net/pipermail/core-libs-dev/2020-September/069197.html
Hello,
while working with `StringBuilder.insert()` I've spotted that its delegate `AbstractStringBuilder.insert()` is missing
a fast-path for the most frequent case when its argument is `String`.
Previously they did similart optimization for `StirngBuilder.append(CharSequence, int, int)`,
see https://bugs.openjdk.java.net/browse/JDK-8224986
I'd like to contribute a trivial patch that brings improvement for the case when SB's content is Latin1
and inserted String is Latin1 as well.
To measure improvement I've used simple benchmark:
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"})
public class StringBuilderInsertBenchmark {
@Benchmark
public StringBuilder insert(Data data) {
String string = data.string;
return new StringBuilder().append("ABC").insert(1, string, 1, data.length + 1);
}
@State(Scope.Thread)
public static class Data {
String string;
@Param({"true", "false"})
private boolean latin;
@Param({"8", "64", "128", "1024"})
private int length;
@Setup
public void setup() {
String alphabet = latin
? "abcdefghijklmnopqrstuvwxyz" // English
: "абвгдеёжзиклмнопрстуфхцчшщьыъэюя"; // Russian
string = new RandomStringGenerator().randomString(alphabet, length + 2);
}
}
}
public final class RandomStringGenerator {
public String randomString(String alphabet, int length) {
char[] chars = alphabet.toCharArray();
ThreadLocalRandom random = ThreadLocalRandom.current();
char[] array = new char[length];
for (int i = 0; i < length; i++) {
array[i] = chars[random.nextInt(chars.length)];
}
return new String(array);
}
}
Which gives
(latin) (length) original patched Units
insert true 8 24.2 ± 0.1 22.2 ± 0.0 ns/op
insert true 64 53.8 ± 0.2 36.1 ± 0.1 ns/op
insert true 128 80.9 ± 0.2 44.6 ± 0.0 ns/op
insert true 1024 365.4 ± 0.5 109.8 ± 3.9 ns/op
insert false 8 33.5 ± 0.5 32.3 ± 0.2 ns/op
insert false 64 73.2 ± 0.3 73.2 ± 0.2 ns/op
insert false 128 103.9 ± 0.6 103.3 ± 0.1 ns/op
insert false 1024 576.5 ± 4.8 569.5 ± 2.0 ns/op
Patch is attached. As of tests tier1 and tier2 are ok.
With best regards,
Sergey Tsypanov
-------------
Commit messages:
- 8254082: Add fast-path for String into AbstractStringBuilder.insert(int, CharSequence, int, int)
Changes: https://git.openjdk.java.net/jdk/pull/402/files
Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=402&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8254082
Stats: 23 lines in 1 file changed: 13 ins; 4 del; 6 mod
Patch: https://git.openjdk.java.net/jdk/pull/402.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/402/head:pull/402
PR: https://git.openjdk.java.net/jdk/pull/402
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