JMH-压测工具

官网

http://openjdk.java.net/projects/code-tools/jmh/

创建JMH测试

1. 创建Maven项目，添加依赖

   <?xml version="1.0" encoding="UTF-8"?>
   <project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <encoding>UTF-8</encoding>
        <java.version>1.8</java.version>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>
    <groupId>mashibing.com</groupId>
    <artifactId>HelloJMH2</artifactId>
    <version>1.0-SNAPSHOT</version>
    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.openjdk.jmh/jmh-core -->
        <dependency>
            <groupId>org.openjdk.jmh</groupId>
            <artifactId>jmh-core</artifactId>
            <version>1.21</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.openjdk.jmh/jmh-generator-annprocess -->
        <dependency>
            <groupId>org.openjdk.jmh</groupId>
            <artifactId>jmh-generator-annprocess</artifactId>
            <version>1.21</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
   </project>

2. idea安装JMH插件 JMH plugin v1.0.3
   

3. 由于用到了注解，打开运行程序注解配置

   compiler -> Annotation Processors -> Enable Annotation Processing

4. 定义需要测试类PS (ParallelStream)

   package com.mashibing.jmh;
   import java.util.ArrayList;
   import java.util.List;
   import java.util.Random;
   public class PS {
    static List<Integer> nums = new ArrayList<>();
    static {
        Random r = new Random();
        for (int i = 0; i < 10000; i++) nums.add(1000000 + r.nextInt(1000000));
    }
    static void foreach() {
        nums.forEach(v->isPrime(v));
    }
    static void parallel() {
        nums.parallelStream().forEach(PS::isPrime);
    }
   
    static boolean isPrime(int num) {
        for(int i=2; i<=num/2; i++) {
            if(num % i == 0) return false;
        }
        return true;
    }
   }
   

5. 写单元测试

   这个测试类一定要在test package下面

package com.mashibing.jmh;
import org.openjdk.jmh.annotations.Benchmark;
import static org.junit.jupiter.api.Assertions.*;
public class PSTest {
    @Benchmark
    public void testForEach() {
        PS.foreach();
    }
}

1. 运行测试类，如果遇到下面的错误：

   ERROR: org.openjdk.jmh.runner.RunnerException: ERROR: Exception while trying to acquire the JMH lock (C:\WINDOWS\/jmh.lock): C:\WINDOWS\jmh.lock (拒绝访问。), exiting. Use -Djmh.ignoreLock=true to forcefully continue.
    at org.openjdk.jmh.runner.Runner.run(Runner.java:216)
    at org.openjdk.jmh.Main.main(Main.java:71)
   

2. 这个错误是因为JMH运行需要访问系统的TMP目录，解决办法是：
   打开RunConfiguration -> Environment Variables -> include system environment viables

3. 阅读测试报告
   

   JMH中的基本概念

4. Warmup 预热，由于JVM中对于特定代码会存在优化（本地化），预热对于测试结果很重要
   

5. Mesurement 总共执行多少次测试
   
6. Timeout
   
7. Threads 线程数，由fork指定
   
8. Benchmark mode 基准测试的模式
   
9. Benchmark 测试哪一段代码
   

   Next

   官方样例： http://hg.openjdk.java.net/code-tools/jmh/file/tip/jmh-samples/src/main/java/org/openjdk/jmh/samples/