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8332842: Optimize empty CopyOnWriteArrayList allocations

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Reviewed-by: shade, alanb
This commit is contained in:
John Engebretson 2024-08-14 14:11:53 +00:00 committed by Aleksey Shipilev
parent fbe4f05636
commit a5d948fb98
2 changed files with 184 additions and 4 deletions
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22
src/java.base/share/classes/java/util/concurrent/CopyOnWriteArrayList.java
View File

@ -100,6 +100,8 @@ public class CopyOnWriteArrayList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable {
private static final long serialVersionUID = 8673264195747942595L;
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* The lock protecting all mutators. (We have a mild preference
* for builtin monitors over ReentrantLock when either will do.)
@ -128,7 +130,7 @@ public class CopyOnWriteArrayList<E>
* Creates an empty list.
*/
public CopyOnWriteArrayList() {
setArray(new Object[0]);
setArray(EMPTY_ELEMENTDATA);
}
/**
@ -143,6 +145,8 @@ public class CopyOnWriteArrayList<E>
Object[] es;
if (c.getClass() == CopyOnWriteArrayList.class)
es = ((CopyOnWriteArrayList<?>)c).getArray();
else if (c.isEmpty())
es = EMPTY_ELEMENTDATA;
else {
es = c.toArray();
if (c.getClass() != java.util.ArrayList.class)
@ -159,7 +163,10 @@ public class CopyOnWriteArrayList<E>
* @throws NullPointerException if the specified array is null
*/
public CopyOnWriteArrayList(E[] toCopyIn) {
setArray(Arrays.copyOf(toCopyIn, toCopyIn.length, Object[].class));
if (toCopyIn.length == 0)
setArray(EMPTY_ELEMENTDATA);
else
setArray(Arrays.copyOf(toCopyIn, toCopyIn.length, Object[].class));
}
/**
@ -533,6 +540,8 @@ public class CopyOnWriteArrayList<E>
Object[] newElements;
if (numMoved == 0)
newElements = Arrays.copyOf(es, len - 1);
else if (len == 1)
newElements = EMPTY_ELEMENTDATA;
else {
newElements = new Object[len - 1];
System.arraycopy(es, 0, newElements, 0, index);
@ -618,6 +627,11 @@ public class CopyOnWriteArrayList<E>
if (index < 0)
return false;
}
if (len == 1) {
// one element exists and that element should be removed
setArray(EMPTY_ELEMENTDATA);
return true;
}
Object[] newElements = new Object[len - 1];
System.arraycopy(current, 0, newElements, 0, index);
System.arraycopy(current, index + 1,
@ -804,7 +818,7 @@ public class CopyOnWriteArrayList<E>
*/
public void clear() {
synchronized (lock) {
setArray(new Object[0]);
setArray(EMPTY_ELEMENTDATA);
}
}
@ -1022,7 +1036,7 @@ public class CopyOnWriteArrayList<E>
// Read in array length and allocate array
int len = s.readInt();
SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, len);
Object[] es = new Object[len];
Object[] es = (len == 0 ? EMPTY_ELEMENTDATA : new Object[len]);
// Read in all elements in the proper order.
for (int i = 0; i < len; i++)

166
test/micro/org/openjdk/bench/java/util/concurrent/CopyOnWriteArrayListBenchmark.java Normal file
View File

@ -0,0 +1,166 @@
/*
* Copyright Amazon.com Inc. 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.util.concurrent;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.TimeUnit;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Fork;
import org.openjdk.jmh.annotations.Measurement;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Warmup;
@BenchmarkMode(Mode.AverageTime)
@State(Scope.Benchmark)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Fork(1)
@Warmup(iterations = 3, time = 1, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
public class CopyOnWriteArrayListBenchmark {
private static byte[] getSerializedBytes(CopyOnWriteArrayList<?> list) throws IOException {
ByteArrayOutputStream bytesOut = new ByteArrayOutputStream();
ObjectOutputStream objectOut = new ObjectOutputStream(bytesOut);
objectOut.writeObject(list);
objectOut.close();
return bytesOut.toByteArray();
}
private Collection<Object> emptyCollection = new ArrayList<>();
private Object[] emptyArray = new Object[0];
private Collection<Object> oneItemCollection = Arrays.asList("");
private Object[] oneItemArray = new Object[] { "" };
private CopyOnWriteArrayList<?> emptyInstance = new CopyOnWriteArrayList<>();
private CopyOnWriteArrayList<?> oneItemInstance = new CopyOnWriteArrayList<>(oneItemArray);
private byte[] emptyInstanceBytes;
private byte[] oneInstanceBytes;
public CopyOnWriteArrayListBenchmark() {
try {
emptyInstanceBytes = getSerializedBytes(emptyInstance);
oneInstanceBytes = getSerializedBytes(oneItemInstance);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
@Benchmark
public void clear() {
// have to create a new instance on each execution
((CopyOnWriteArrayList<?>) oneItemInstance.clone()).clear();
}
@Benchmark
public void clearEmpty() {
emptyInstance.clear();
}
@Benchmark
public CopyOnWriteArrayList<?> createInstanceArray() {
return new CopyOnWriteArrayList<>(oneItemArray);
}
@Benchmark
public CopyOnWriteArrayList<?> createInstanceArrayEmpty() {
return new CopyOnWriteArrayList<>(emptyArray);
}
@Benchmark
public CopyOnWriteArrayList<?> createInstanceCollection() {
return new CopyOnWriteArrayList<>(oneItemCollection);
}
@Benchmark
public CopyOnWriteArrayList<?> createInstanceCollectionEmpty() {
return new CopyOnWriteArrayList<>(emptyCollection);
}
@Benchmark
public CopyOnWriteArrayList<?> createInstanceDefault() {
return new CopyOnWriteArrayList<Object>();
}
@Benchmark
public CopyOnWriteArrayList<?> readInstance() throws IOException, ClassNotFoundException {
try (ObjectInputStream objIn = new ObjectInputStream(new ByteArrayInputStream(oneInstanceBytes))) {
return (CopyOnWriteArrayList<?>) objIn.readObject();
}
}
@Benchmark
public CopyOnWriteArrayList<?> readInstanceEmpty() throws IOException, ClassNotFoundException {
try (ObjectInputStream objIn = new ObjectInputStream(new ByteArrayInputStream(emptyInstanceBytes))) {
return (CopyOnWriteArrayList<?>) objIn.readObject();
}
}
@Benchmark
public CopyOnWriteArrayList<?> removeObjectLastRemaining() {
CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
list.add("");
list.remove("");
return list;
}
@Benchmark
public CopyOnWriteArrayList<?> removeIndexLastRemaining() {
CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
list.add("");
list.remove(0);
return list;
}
@Benchmark
public CopyOnWriteArrayList<?> removeObject() {
CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
list.add("");
list.add("a");
list.remove("");
return list;
}
@Benchmark
public CopyOnWriteArrayList<?> remove() {
CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
list.add("");
list.add("a");
list.remove(0);
return list;
}
}