Oh, I was unaware of it! Thanks!
13.02.2020, 21:49, "Brent Christian" <brent.christ...@oracle.com>: > As a point of interest, some investigation of updating StringJoiner for > CompactStrings was done a while back. > > See https://bugs.openjdk.java.net/browse/JDK-8148937 > > -Brent > > On 2/3/20 2:38 PM, Сергей Цыпанов wrote: >> Hello, >> >> as of JDK14 java.util.StringJoiner still uses char[] as a storage of glued >> 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 invoked, byte[] stored in >> String is inflated in order to fill in char[] and >> finally 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[] -> char[] >> >> 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 detecting cases when String.isLatin1() returns true >> for all involved Strings. >> >> I've prepared a patch along with benchmark proving that this change is >> correct and brings improvement. >> The only concern I have is about String.isLatin1(): as far as String >> belongs to java.lang and StringJoiner to java.util >> package-private String.isLatin1() cannot be directly accessed, we need to >> make it public for successful compilation. >> >> Another solution is to create an intermediate utility class located in >> java.lang which delegates the call to String.isLatin1(): >> >> package java.lang; >> >> public class StringHelper { >> public static boolean isLatin1(String str) { >> return str.isLatin1(); >> } >> } >> >> This allows to keep java.lang.String intact and have access to it's >> package-private method outside of java.lang package. >> >> Below I've added results of benchmarking for specified case (all Strings >> are Latin1). The other case (at least one String is UTF-8) uses existing >> code so there will be only a tiny regression due to several if-checks. >> >> With best regards, >> Sergey Tsypanov >> >> (count) (length) Original >> Patched Units >> stringJoiner 1 1 26.7 ± 1.3 38.2 ± 1.1 ns/op >> stringJoiner 1 5 27.4 ± 0.0 40.5 ± 2.2 ns/op >> stringJoiner 1 10 29.6 ± 1.9 38.4 ± 1.9 ns/op >> stringJoiner 1 100 61.1 ± 6.9 47.6 ± 0.6 ns/op >> stringJoiner 5 1 91.1 ± 6.7 83.6 ± 2.0 ns/op >> stringJoiner 5 5 96.1 ± 10.7 85.6 ± 1.1 ns/op >> stringJoiner 5 10 105.5 ± 14.3 84.7 ± 1.1 ns/op >> stringJoiner 5 100 266.6 ± 30.1 139.6 ± 14.0 ns/op >> stringJoiner 10 1 190.7 ± 23.0 162.0 ± 2.9 ns/op >> stringJoiner 10 5 200.0 ± 16.9 167.5 ± 11.0 ns/op >> stringJoiner 10 10 216.4 ± 12.4 164.8 ± 1.7 ns/op >> stringJoiner 10 100 545.3 ± 49.7 282.2 ± 12.0 ns/op >> stringJoiner 100 1 1467.0 ± 90.3 1302.0 ± 18.5 ns/op >> stringJoiner 100 5 1491.8 ± 166.2 1493.0 ± 135.4 ns/op >> stringJoiner 100 10 1768.8 ± 160.6 1760.8 ± 111.4 ns/op >> stringJoiner 100 100 3654.3 ± 113.1 3120.9 ± 175.9 ns/op >> >> stringJoiner:·gc.alloc.rate.norm 1 1 120.0 ± 0.0 120.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 1 5 128.0 ± 0.0 120.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 1 10 144.0 ± 0.0 136.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 1 100 416.0 ± 0.0 312.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 5 1 144.0 ± 0.0 136.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 5 5 200.0 ± 0.0 168.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 5 10 272.0 ± 0.0 216.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 5 100 1632.0 ± 0.0 1128.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 10 1 256.0 ± 0.0 232.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 10 5 376.0 ± 0.0 312.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 10 10 520.0 ± 0.0 408.0 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 10 100 3224.1 ± 0.0 2216.1 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 100 1 1760.2 ± 14.9 1544.2 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 100 5 2960.3 ± 14.9 2344.2 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 100 10 4440.4 ± 0.0 3336.3 ± 0.0 B/op >> stringJoiner:·gc.alloc.rate.norm 100 100 31449.3 ± 12.2 21346.7 ± 14.7 B/op
