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8265237: String.join and StringJoiner can be improved further

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Reviewed-by: rriggs, redestad
This commit is contained in:
Peter Levart 2021-04-21 10:32:03 +00:00
parent ed477da9c6
commit 98cb81b381
6 changed files with 197 additions and 40 deletions
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72
src/java.base/share/classes/java/lang/String.java
View file

@ -43,7 +43,6 @@ import java.util.Locale;
import java.util.Objects;
import java.util.Optional;
import java.util.Spliterator;
import java.util.StringJoiner;
import java.util.function.Function;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;
@ -51,6 +50,8 @@ import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
import jdk.internal.vm.annotation.ForceInline;
import jdk.internal.vm.annotation.IntrinsicCandidate;
import jdk.internal.vm.annotation.Stable;
import sun.nio.cs.ArrayDecoder;
@ -3218,14 +3219,58 @@ public final class String
* @since 1.8
*/
public static String join(CharSequence delimiter, CharSequence... elements) {
Objects.requireNonNull(delimiter);
Objects.requireNonNull(elements);
// Number of elements not likely worth Arrays.stream overhead.
StringJoiner joiner = new StringJoiner(delimiter);
for (CharSequence cs: elements) {
joiner.add(cs);
var delim = delimiter.toString();
var elems = new String[elements.length];
for (int i = 0; i < elements.length; i++) {
elems[i] = String.valueOf(elements[i]);
}
return joiner.toString();
return join("", "", delim, elems, elems.length);
}
/**
* Designated join routine.
*
* @param prefix the non-null prefix
* @param suffix the non-null suffix
* @param delimiter the non-null delimiter
* @param elements the non-null array of non-null elements
* @param size the number of elements in the array (<= elements.length)
* @return the joined string
*/
@ForceInline
static String join(String prefix, String suffix, String delimiter, String[] elements, int size) {
int icoder = prefix.coder() | suffix.coder() | delimiter.coder();
long len = (long) prefix.length() + suffix.length() + (long) Math.max(0, size - 1) * delimiter.length();
// assert len > 0L; // max: (long) Integer.MAX_VALUE << 32
// following loop wil add max: (long) Integer.MAX_VALUE * Integer.MAX_VALUE to len
// so len can overflow at most once
for (int i = 0; i < size; i++) {
var el = elements[i];
len += el.length();
icoder |= el.coder();
}
byte coder = (byte) icoder;
// long len overflow check, char -> byte length, int len overflow check
if (len < 0L || (len <<= coder) != (int) len) {
throw new OutOfMemoryError("Requested string length exceeds VM limit");
}
byte[] value = StringConcatHelper.newArray(len);
int off = 0;
prefix.getBytes(value, off, coder); off += prefix.length();
if (size > 0) {
var el = elements[0];
el.getBytes(value, off, coder); off += el.length();
for (int i = 1; i < size; i++) {
delimiter.getBytes(value, off, coder); off += delimiter.length();
el = elements[i];
el.getBytes(value, off, coder); off += el.length();
}
}
suffix.getBytes(value, off, coder);
// assert off + suffix.length() == value.length >> coder;
return new String(value, coder);
}
/**
@ -3266,11 +3311,16 @@ public final class String
Iterable<? extends CharSequence> elements) {
Objects.requireNonNull(delimiter);
Objects.requireNonNull(elements);
StringJoiner joiner = new StringJoiner(delimiter);
var delim = delimiter.toString();
var elems = new String[8];
int size = 0;
for (CharSequence cs: elements) {
joiner.add(cs);
if (size >= elems.length) {
elems = Arrays.copyOf(elems, elems.length << 1);
}
elems[size++] = String.valueOf(cs);
}
return joiner.toString();
return join("", "", delim, elems, size);
}
/**

4
src/java.base/share/classes/java/lang/System.java
View file

@ -2308,6 +2308,10 @@ public final class System {
return StringConcatHelper.mix(lengthCoder, constant);
}
public String join(String prefix, String suffix, String delimiter, String[] elements, int size) {
return String.join(prefix, suffix, delimiter, elements, size);
}
public Object classData(Class<?> c) {
return c.getClassData();
}

43
src/java.base/share/classes/java/util/StringJoiner.java
View file

@ -24,6 +24,9 @@
*/
package java.util;
import jdk.internal.access.JavaLangAccess;
import jdk.internal.access.SharedSecrets;
/**
* {@code StringJoiner} is used to construct a sequence of characters separated
* by a delimiter and optionally starting with a supplied prefix
@ -63,6 +66,8 @@ package java.util;
* @since 1.8
*/
public final class StringJoiner {
private static final String[] EMPTY_STRING_ARRAY = new String[0];
private final String prefix;
private final String delimiter;
private final String suffix;
@ -158,27 +163,15 @@ public final class StringJoiner {
*/
@Override
public String toString() {
final String[] elts = this.elts;
if (elts == null && emptyValue != null) {
return emptyValue;
}
final int size = this.size;
final int addLen = prefix.length() + suffix.length();
var elts = this.elts;
if (size == 0) {
if (addLen == 0) {
return "";
if (emptyValue != null) {
return emptyValue;
}
return prefix + suffix;
elts = EMPTY_STRING_ARRAY;
}
final String delimiter = this.delimiter;
StringBuilder sb = new StringBuilder(len + addLen).append(prefix);
if (size > 0) {
sb.append(elts[0]);
for (int i = 1; i < size; i++) {
sb.append(delimiter).append(elts[i]);
}
}
return sb.append(suffix).toString();
return JLA.join(prefix, suffix, delimiter, elts, size);
}
/**
@ -233,7 +226,7 @@ public final class StringJoiner {
*/
public StringJoiner merge(StringJoiner other) {
Objects.requireNonNull(other);
if (other.elts == null) {
if (other.size == 0) {
return this;
}
other.compactElts();
@ -241,15 +234,11 @@ public final class StringJoiner {
}
private void compactElts() {
if (size > 1) {
StringBuilder sb = new StringBuilder(len).append(elts[0]);
int i = 1;
do {
sb.append(delimiter).append(elts[i]);
elts[i] = null;
} while (++i < size);
int sz = size;
if (sz > 1) {
elts[0] = JLA.join("", "", delimiter, elts, sz);
Arrays.fill(elts, 1, sz, null);
size = 1;
elts[0] = sb.toString();
}
}
@ -267,4 +256,6 @@ public final class StringJoiner {
return (size == 0 && emptyValue != null) ? emptyValue.length() :
len + prefix.length() + suffix.length();
}
private static final JavaLangAccess JLA = SharedSecrets.getJavaLangAccess();
}