JHM 测试 HashMap 性能优化

1.

2.pom.xml

<dependencies>
    <dependency>
        <groupId>org.openjdk.jmh</groupId>
        <artifactId>jmh-core</artifactId>
        <version>${jmh.version}</version>
    </dependency>
    <dependency>
        <groupId>org.openjdk.jmh</groupId>
        <artifactId>jmh-generator-annprocess</artifactId>
        <version>${jmh.version}</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.junit.jupiter</groupId>
        <artifactId>junit-jupiter-api</artifactId>
        <version>5.5.2</version>
        <scope>test</scope>
    </dependency>
</dependencies>

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

    <!--
        JMH version to use with this project.
      -->
    <jmh.version>1.21</jmh.version>

    <!--
        Java source/target to use for compilation.
      -->
    <javac.target>1.8</javac.target>

    <!--
        Name of the benchmark Uber-JAR to generate.
      -->
    <uberjar.name>benchmarks</uberjar.name>
</properties>

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.1</version>
            <configuration>
                <compilerVersion>${javac.target}</compilerVersion>
                <source>${javac.target}</source>
                <target>${javac.target}</target>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <version>2.2</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                    <configuration>
                        <finalName>${uberjar.name}</finalName>
                        <transformers>
                            <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                <mainClass>org.openjdk.jmh.Main</mainClass>
                            </transformer>
                        </transformers>
                        <filters>
                            <filter>
                                <!--
                                    Shading signed JARs will fail without this.
                                    http://stackoverflow.com/questions/999489/invalid-signature-file-when-attempting-to-run-a-jar
                                -->
                                <artifact>*:*</artifact>
                                <excludes>
                                    <exclude>META-INF/*.SF</exclude>
                                    <exclude>META-INF/*.DSA</exclude>
                                    <exclude>META-INF/*.RSA</exclude>
                                </excludes>
                            </filter>
                        </filters>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
    <pluginManagement>
        <plugins>
            <plugin>
                <artifactId>maven-clean-plugin</artifactId>
                <version>2.5</version>
            </plugin>
            <plugin>
                <artifactId>maven-deploy-plugin</artifactId>
                <version>2.8.1</version>
            </plugin>
            <plugin>
                <artifactId>maven-install-plugin</artifactId>
                <version>2.5.1</version>
            </plugin>
            <plugin>
                <artifactId>maven-jar-plugin</artifactId>
                <version>2.4</version>
            </plugin>
            <plugin>
                <artifactId>maven-javadoc-plugin</artifactId>
                <version>2.9.1</version>
            </plugin>
            <plugin>
                <artifactId>maven-resources-plugin</artifactId>
                <version>2.6</version>
            </plugin>
            <plugin>
                <artifactId>maven-site-plugin</artifactId>
                <version>3.3</version>
            </plugin>
            <plugin>
                <artifactId>maven-source-plugin</artifactId>
                <version>2.2.1</version>
            </plugin>
            <plugin>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.17</version>
            </plugin>
        </plugins>
    </pluginManagement>
</build>

3.

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.infra.Blackhole;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;
@BenchmarkMode(Mode.AverageTime) // 测试完成时间
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Warmup(iterations = 1, time = 1, timeUnit = TimeUnit.SECONDS) // 预热 1 轮，每次 1s
@Measurement(iterations = 5, time = 5, timeUnit = TimeUnit.SECONDS) // 测试 5 轮，每次 3s
@Fork(1) // fork 1 个线程
@State(Scope.Benchmark)
@Threads(100)
public class HashMapTest {

    @Benchmark
    public void noSizeTest(Blackhole blackhole) {
        Map map = new HashMap();
        for (int i = 0; i < 1024; i++) {
            map.put(i, i);
        }
        // 为了避免 JIT 忽略未被使用的结果
        blackhole.consume(map);
    }
    @Benchmark
    public void setSizeTest(Blackhole blackhole) {
        Map map = new HashMap(1367);
        for (int i = 0; i < 1024; i++) {
            map.put(i, i);
        }
        // 为了避免 JIT 忽略未被使用的结果
        blackhole.consume(map);
    }

    public static void main(String[] args) throws RunnerException {
        final Options opt = new OptionsBuilder()
                .include(HashMapTest.class.getSimpleName())
//           .forks(1)
                .build();

        new Runner(opt).run();
    }
}

4.

测试前后结果是对HashMap 集合初始值指定大小 的测试结果比较：差异1.07倍。建议对集合进行初始化大小 。