JMH Java准测试工具套件
什么是JMH
官网
http://openjdk.java.net/projects/code-tools/jmh/
创建JMH测试
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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>
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idea安装JMH插件 JMH plugin v1.0.3
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由于用到了注解,打开运行程序注解配置
compiler -> Annotation Processors -> Enable Annotation Processing
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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; } }
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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(); } }
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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)
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
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阅读测试报告
JMH中的基本概念
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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 -
Mesurement
总共执行多少次测试 -
Timeout
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Threads
线程数,由fork指定 -
Benchmark mode
基准测试的模式 -
Benchmark
测试哪一段代码