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Merge pull request #10276 from amitiw4u/BAEL-4686-ConcurrentVsSynchronizedMap

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Bael 4686 concurrent vs synchronized map
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Greg 2020-12-22 13:07:54 -05:00 committed by GitHub
commit 96ca95aee1
4 changed files with 244 additions and 1 deletions
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6
core-java-modules/core-java-collections-maps-3/pom.xml
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@ -15,7 +15,11 @@
</parent>
<dependencies>
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-core</artifactId>
<version>${jmh-core.version}</version>
</dependency>
</dependencies>
<properties>

96
core-java-modules/core-java-collections-maps-3/src/main/java/com/baeldung/map/concurrenthashmap/MapPerformanceComparison.java Normal file
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package com.baeldung.map.concurrenthashmap;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
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.Mode;
import org.openjdk.jmh.annotations.OutputTimeUnit;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Threads;
import org.openjdk.jmh.annotations.Warmup;
@Fork(5)
@Threads(10)
@Warmup(iterations = 5)
@State(Scope.Benchmark)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
public class MapPerformanceComparison {
private int TEST_NO_ITEMS;
public static void main(String[] args) throws Exception {
org.openjdk.jmh.Main.main(args);
}
@Setup
public void setup() {
TEST_NO_ITEMS = 1000;
}
@Benchmark
public void randomReadAndWriteSynchronizedMap() {
Map<String, Integer> map = Collections.synchronizedMap(new HashMap<String, Integer>());
performReadAndWriteTest(map);
}
@Benchmark
public void randomReadAndWriteConcurrentHashMap() {
Map<String, Integer> map = new ConcurrentHashMap<>();
performReadAndWriteTest(map);
}
private void performReadAndWriteTest(final Map<String, Integer> map) {
for (int i = 0; i < TEST_NO_ITEMS; i++) {
Integer randNumber = (int) Math.ceil(Math.random() * TEST_NO_ITEMS);
map.get(String.valueOf(randNumber));
map.put(String.valueOf(randNumber), randNumber);
}
}
@Benchmark
public void randomWriteSynchronizedMap() {
Map<String, Integer> map = Collections.synchronizedMap(new HashMap<String, Integer>());
performWriteTest(map);
}
@Benchmark
public void randomWriteConcurrentHashMap() {
Map<String, Integer> map = new ConcurrentHashMap<>();
performWriteTest(map);
}
private void performWriteTest(final Map<String, Integer> map) {
for (int i = 0; i < TEST_NO_ITEMS; i++) {
Integer randNumber = (int) Math.ceil(Math.random() * TEST_NO_ITEMS);
map.put(String.valueOf(randNumber), randNumber);
}
}
@Benchmark
public void randomReadSynchronizedMap() {
Map<String, Integer> map = Collections.synchronizedMap(new HashMap<String, Integer>());
performReadTest(map);
}
@Benchmark
public void randomReadConcurrentHashMap() {
Map<String, Integer> map = new ConcurrentHashMap<>();
performReadTest(map);
}
private void performReadTest(final Map<String, Integer> map) {
for (int i = 0; i < TEST_NO_ITEMS; i++) {
Integer randNumber = (int) Math.ceil(Math.random() * TEST_NO_ITEMS);
map.get(String.valueOf(randNumber));
}
}
}

70
core-java-modules/core-java-collections-maps-3/src/test/java/com/baeldung/map/concurrenthashmap/ConcurrentModificationErrorUnitTest.java Normal file
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package com.baeldung.map.concurrenthashmap;
import java.util.Collections;
import java.util.ConcurrentModificationException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;
import java.util.concurrent.ConcurrentHashMap;
import org.junit.Assert;
import org.junit.Test;
public class ConcurrentModificationErrorUnitTest {
@Test(expected = ConcurrentModificationException.class)
public void whenRemoveAndAddOnHashMap_thenConcurrentModificationError() {
Map<Integer, String> map = new HashMap<>();
map.put(1, "baeldung");
map.put(2, "HashMap");
Map<Integer, String> synchronizedMap = Collections.synchronizedMap(map);
Iterator<Entry<Integer, String>> iterator = synchronizedMap.entrySet().iterator();
while (iterator.hasNext()) {
synchronizedMap.put(3, "Modification");
iterator.next();
}
}
@Test(expected = ConcurrentModificationException.class)
public void whenRemoveAndAddOnTreeMap_thenConcurrentModificationError() {
Map<Integer, String> map = new TreeMap<>();
map.put(1, "baeldung");
map.put(2, "HashMap");
Map<Integer, String> synchronizedMap = Collections.synchronizedMap(map);
Iterator<Entry<Integer, String>> iterator = synchronizedMap.entrySet().iterator();
while (iterator.hasNext()) {
synchronizedMap.put(3, "Modification");
iterator.next();
}
}
@Test(expected = ConcurrentModificationException.class)
public void whenRemoveAndAddOnLinkedHashMap_thenConcurrentModificationError() {
Map<Integer, String> map = new LinkedHashMap<>();
map.put(1, "baeldung");
map.put(2, "HashMap");
Map<Integer, String> synchronizedMap = Collections.synchronizedMap(map);
Iterator<Entry<Integer, String>> iterator = synchronizedMap.entrySet().iterator();
while (iterator.hasNext()) {
synchronizedMap.put(3, "Modification");
iterator.next();
}
}
@Test
public void whenRemoveAndAddOnConcurrentHashMap_thenNoError() {
Map<Integer, String> map = new ConcurrentHashMap<>();
map.put(1, "baeldung");
map.put(2, "HashMap");
Iterator<Entry<Integer, String>> iterator = map.entrySet().iterator();
while (iterator.hasNext()) {
map.put(3, "Modification");
iterator.next();
}
Assert.assertEquals(3, map.size());
}
}

73
core-java-modules/core-java-collections-maps-3/src/test/java/com/baeldung/map/concurrenthashmap/NullAllowInMapUnitTest.java Normal file
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package com.baeldung.map.concurrenthashmap;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.ConcurrentHashMap;
import org.junit.Assert;
import org.junit.Test;
public class NullAllowInMapUnitTest {
@Test
public void givenHashMapBackedSynchronizedMap_whenNullAsKey_thenNoError() {
Map<String, Integer> map = Collections
.synchronizedMap(new HashMap<String, Integer>());
map.put(null, 1);
Assert.assertTrue(map.get(null).equals(1));
}
@Test(expected = NullPointerException.class)
public void givenTreeMapBackedSynchronizedMap_whenNullAsKey_thenException() {
Map<String, Integer> map = Collections.synchronizedMap(new TreeMap<String, Integer>());
map.put(null, 1);
Assert.assertTrue(map.get(null).equals(1));
}
@Test
public void givenLinkedHashMapBackedSynchronizedMap_whenNullAsKey_thenNoError() {
Map<String, Integer> map = Collections
.synchronizedMap(new LinkedHashMap<String, Integer>());
map.put(null, 1);
Assert.assertTrue(map.get(null).equals(1));
}
@Test(expected = NullPointerException.class)
public void givenConcurrentHasMap_whenNullAsKey_thenException() {
Map<String, Integer> map = new ConcurrentHashMap<>();
map.put(null, 1);
}
@Test
public void givenHashMapBackedSynchronizedMap_whenNullAsValue_thenNoError() {
Map<String, Integer> map = Collections.synchronizedMap(new HashMap<String, Integer>());
map.put("1", null);
Assert.assertNull(map.get("1"));
}
@Test
public void givenTreeMapBackedSynchronizedMap_whenNullAsValue_thenNoError() {
Map<String, Integer> map = Collections.synchronizedMap(new TreeMap<String, Integer>());
map.put("1", null);
Assert.assertNull(map.get("1"));
}
@Test
public void givenLinkedHashMapBackedSynchronizedMap_whenNullAsValue_thenNoError() {
Map<String, Integer> map = Collections
.synchronizedMap(new LinkedHashMap<String, Integer>());
map.put("1", null);
Assert.assertNull(map.get("1"));
}
@Test(expected = NullPointerException.class)
public void givenConcurrentHasMap_whenNullAsValue_thenException() {
Map<String, Integer> map = new ConcurrentHashMap<>();
map.put("1", null);
}
}