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8358533: Improve performance of java.io.Reader.readAllLines

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Reviewed-by: rriggs, sherman
This commit is contained in:
Brian Burkhalter 2025-07-09 16:15:36 +00:00
parent 6249259c80
commit 6e203384f8
3 changed files with 198 additions and 16 deletions
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73
src/java.base/share/classes/java/io/Reader.java
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@ -27,8 +27,11 @@ package java.io;
import java.nio.CharBuffer;
import java.nio.ReadOnlyBufferException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Objects;
import jdk.internal.util.ArraysSupport;
/**
* Abstract class for reading character streams. The only methods that a
@ -397,16 +400,6 @@ public abstract class Reader implements Readable, Closeable {
*/
public abstract int read(char[] cbuf, int off, int len) throws IOException;
private String readAllCharsAsString() throws IOException {
StringBuilder result = new StringBuilder();
char[] cbuf = new char[TRANSFER_BUFFER_SIZE];
int nread;
while ((nread = read(cbuf, 0, cbuf.length)) != -1) {
result.append(cbuf, 0, nread);
}
return result.toString();
}
/**
* Reads all remaining characters as lines of text. This method blocks until
* all remaining characters have been read and end of stream is detected,
@ -457,7 +450,57 @@ public abstract class Reader implements Readable, Closeable {
* @since 25
*/
public List<String> readAllLines() throws IOException {
return readAllCharsAsString().lines().toList();
List<String> lines = new ArrayList<>();
char[] cb = new char[1024];
int start = 0;
int pos = 0;
int limit = 0;
boolean skipLF = false;
int n;
while ((n = read(cb, pos, cb.length - pos)) != -1) {
limit = pos + n;
while (pos < limit) {
if (skipLF) {
if (cb[pos] == '\n') {
pos++;
start++;
}
skipLF = false;
}
while (pos < limit) {
char c = cb[pos++];
if (c == '\n' || c == '\r') {
lines.add(new String(cb, start, pos - 1 - start));
skipLF = (c == '\r');
start = pos;
break;
}
}
if (pos == limit) {
int len = limit - start;
if (len >= cb.length/2) {
// allocate larger buffer and copy chars to beginning
int newLength = ArraysSupport.newLength(cb.length,
TRANSFER_BUFFER_SIZE, cb.length);
char[] tmp = new char[newLength];
System.arraycopy(cb, start, tmp, 0, len);
cb = tmp;
} else if (start != 0 && len != 0) {
// move fragment to beginning of buffer
System.arraycopy(cb, start, cb, 0, len);
}
pos = limit = len;
start = 0;
break;
}
}
}
// add a string if EOS terminates the last line
if (limit > start)
lines.add(new String(cb, start, limit - start));
return Collections.unmodifiableList(lines);
}
/**
@ -499,7 +542,13 @@ public abstract class Reader implements Readable, Closeable {
* @since 25
*/
public String readAllAsString() throws IOException {
return readAllCharsAsString();
StringBuilder result = new StringBuilder();
char[] cbuf = new char[TRANSFER_BUFFER_SIZE];
int nread;
while ((nread = read(cbuf, 0, cbuf.length)) != -1) {
result.append(cbuf, 0, nread);
}
return result.toString();
}
/** Maximum skip-buffer size */

75
test/jdk/java/io/Reader/ReadAll.java
View File

@ -66,12 +66,55 @@ public class ReadAll {
int size = rnd.nextInt(2, 16386);
int plen = PHRASE.length();
List<String> strings = new ArrayList<String>(size);
StringBuilder sb = new StringBuilder(plen);
List<String> strings = new ArrayList<>(size);
while (strings.size() < size) {
int fromIndex = rnd.nextInt(0, plen / 2);
int toIndex = rnd.nextInt(fromIndex, plen);
strings.add(PHRASE.substring(fromIndex, toIndex));
String s = PHRASE.substring(fromIndex, toIndex);
sb.append(s);
int bound = toIndex - fromIndex;
if (bound > 0) {
int offset = bound/2;
int n = rnd.nextInt(0, bound);
for (int i = 0; i < n; i++) {
String f = null;
switch (rnd.nextInt(7)) {
case 0 -> f = "";
case 1 -> f = "\r";
case 2 -> f = "\n";
case 3 -> f = "\r\n";
case 4 -> f = "\r\r";
case 5 -> f = "\n\n";
case 6 -> f = " ";
}
sb.insert(offset, f);
}
}
strings.add(sb.toString());
sb.setLength(0);
}
String p4096 = PHRASE.repeat((4096 + plen - 1)/plen);
String p8192 = PHRASE.repeat((8192 + plen - 1)/plen);
String p16384 = PHRASE.repeat((16384 + plen - 1)/plen);
for (int i = 0; i < 64; i++) {
for (int j = 0; j < 32; j++) {
switch (rnd.nextInt(8)) {
case 0 -> sb.append("");
case 1 -> sb.append(" ");
case 2 -> sb.append("\n");
case 3 -> sb.append(PHRASE);
case 5 -> sb.append(p4096);
case 6 -> sb.append(p8192);
case 7 -> sb.append(p16384);
}
}
strings.add(sb.toString());
sb.setLength(0);
}
Files.write(path, strings);
System.out.println(strings.size() + " lines written");
}
@ -85,6 +128,7 @@ public class ReadAll {
@Test
public void readAllLines() throws IOException {
// Reader implementation
System.out.println("Reader implementation");
List<String> lines;
try (FileReader fr = new FileReader(file)) {
lines = fr.readAllLines();
@ -92,9 +136,21 @@ public class ReadAll {
System.out.println(lines.size() + " lines read");
List<String> linesExpected = Files.readAllLines(path);
assertEquals(linesExpected, lines);
int count = linesExpected.size();
if (lines.size() != count)
throw new RuntimeException("Size mismatch: " + lines.size() + " != " + count);
for (int i = 0; i < count; i++) {
String expected = linesExpected.get(i);
String actual = lines.get(i);
if (!actual.equals(expected)) {
String msg = String.format("%d: \"%s\" != \"%s\"",
i, actual, expected);
throw new RuntimeException(msg);
}
}
// Reader.of implementation
System.out.println("Reader.of implementation");
String stringExpected = Files.readString(path);
int n = rnd.nextInt(stringExpected.length()/2);
String substringExpected = stringExpected.substring(n);
@ -103,7 +159,18 @@ public class ReadAll {
r.skip(n);
lines = r.readAllLines();
}
assertEquals(linesExpected, lines);
count = linesExpected.size();
if (lines.size() != count)
throw new RuntimeException("Size mismatch: " + lines.size() + " != " + count);
for (int i = 0; i < count; i++) {
String expected = linesExpected.get(i);
String actual = lines.get(i);
if (!actual.equals(expected)) {
String msg = String.format("%d: \"%s\" != \"%s\"",
i, actual, expected);
throw new RuntimeException(msg);
}
}
}
@Test

66
test/micro/org/openjdk/bench/java/io/ReaderReadAllLines.java Normal file
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@ -0,0 +1,66 @@
/*
* Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package org.openjdk.bench.java.io;
import java.io.CharArrayReader;
import java.io.IOException;
import java.io.Reader;
import java.util.List;
import java.util.Random;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
@State(Scope.Benchmark)
public class ReaderReadAllLines {
private char[] chars = null;
@Setup
public void setup() throws IOException {
final int len = 128_000;
chars = new char[len];
Random rnd = new Random(System.nanoTime());
int off = 0;
while (off < len) {
int lineLen = 40 + rnd.nextInt(8192);
if (lineLen > len - off) {
off = len;
} else {
chars[off + lineLen] = '\n';
off += lineLen;
}
}
}
@Benchmark
public List<String> readAllLines() throws IOException {
List<String> lines;
try (Reader reader = new CharArrayReader(chars)) {
lines = reader.readAllLines();
}
return lines;
}
}