JMH的使用和代码

概述

JMH 是一个由 OpenJDK/Oracle 里面那群开发了 Java 编译器的大牛们所开发的 Micro Benchmark Framework 。何谓 Micro Benchmark 呢？简单地说就是在 method 层面上的 benchmark，精度可以精确到微秒级。可以看出 JMH 主要使用在当你已经找出了热点函数，而需要对热点函数进行进一步的优化时，就可以使用 JMH 对优化的效果进行定量的分析。

使用场景

(1)想定量地知道某个函数需要执行多长时间，以及执行时间和输入 n 的相关性
(2)一个函数有两种不同实现(例如实现 A 使用了 FixedThreadPool，实现 B 使用了 ForkJoinPool)，不知道哪种实现性能更好

配置

<dependency>
    <groupId>org.openjdk.jmh</groupId>
    <artifactId>jmh-core</artifactId>
    <version>1.19</version>
</dependency>
<dependency>
    <groupId>org.openjdk.jmh</groupId>
    <artifactId>jmh-generator-annprocess</artifactId>
    <version>1.19</version>
    <scope>provided</scope>
</dependency>

代码

package com.songguo.jmhtest.JMH;

import org.openjdk.jmh.annotations.*;
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;

import java.util.concurrent.TimeUnit;

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@State(Scope.Thread)
public class JMHFirstBenchmark {


    @Benchmark//对要被测试性能的代码添加注解，说明该方法是要被测试性能的
    public int sleepAWhile() {
        try {
            Thread.sleep(50);
        } catch (InterruptedException e) {
            // ignore
        }
        return 0;
    }


    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(JMHFirstBenchmark.class.getSimpleName())
                .forks(1)
                .warmupIterations(3)
                .measurementIterations(3)
                .build();

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

我再把代码贴出来

/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/bin/java "-javaagent:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=53834:/Applications/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/lib/tools.jar:/Users/sgcx251/rqk/jmhtest/target/classes:/Users/sgcx251/.m2/repository/org/springframework/boot/spring-boot-starter-web/2.1.7.RELEASE/spring-boot-starter-web-2.1.7.RELEASE.jar:/Users/sgcx251/.m2/repository/org/springframework/boot/spring-boot-starter/2.1.7.RELEASE/spring-boot-starter-2.1.7.RELEASE.jar:/Users/sgcx251/.m2/repository/org/springframework/boot/spring-boot/2.1.7.RELEASE/spring-boot-2.1.7.RELEASE.jar:/Users/sgcx251/.m2/repository/org/springframework/boot/spring-boot-autoconfigure/2.1.7.RELEASE/spring-boot-autoconfigure-2.1.7.RELEASE.jar:/Users/sgcx251/.m2/repository/org/springframework/boot/spring-boot-starter-logging/2.1.7.RELEASE/spring-boot-starter-logging-2.1.7.RELEASE.jar:/Users/sgcx251/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar:/Users/sgcx251/.m2/repository/ch/qos/logback/logback-core/1.2.3/logback-core-1.2.3.jar:/Users/sgcx251/.m2/repository/org/apache/logging/log4j/log4j-to-slf4j/2.11.2/log4j-to-slf4j-2.11.2.jar:/Users/sgcx251/.m2/repository/org/apache/logging/log4j/log4j-api/2.11.2/log4j-api-2.11.2.jar:/Users/sgcx251/.m2/repository/org/slf4j/jul-to-slf4j/1.7.26/jul-to-slf4j-1.7.26.jar:/Users/sgcx251/.m2/repository/javax/annotation/javax.annotation-api/1.3.2/javax.annotation-api-1.3.2.jar:/Users/sgcx251/.m2/repository/org/yaml/snakeyaml/1.23/snakeyaml-1.23.jar:/Users/sgcx251/.m2/repository/org/springframework/boot/spring-boot-starter-json/2.1.7.RELEASE/spring-boot-starter-json-2.1.7.RELEASE.jar:/Users/sgcx251/.m2/repository/com/fasterxml/jackson/core/jackson-databind/2.9.9/jackson-databind-2.9.9.jar:/Users/sgcx251/.m2/repository/com/fasterxml/jackson/core/jackson-annotations/2.9.0/jackson-annotations-2.9.0.jar:/Users/sgcx251/.m2/repository/com/fasterxml/jackson/core/jackson-core/2.9.9/jackson-core-2.9.9.jar:/Users/sgcx251/.m2/repository/com/fasterxml/jackson/datatype/jackson-datatype-jdk8/2.9.9/jackson-datatype-jdk8-2.9.9.jar:/Users/sgcx251/.m2/repository/com/fasterxml/jackson/datatype/jackson-datatype-jsr310/2.9.9/jackson-datatype-jsr310-2.9.9.jar:/Users/sgcx251/.m2/repository/com/fasterxml/jackson/module/jackson-module-parameter-names/2.9.9/jackson-module-parameter-names-2.9.9.jar:/Users/sgcx251/.m2/repository/org/springframework/boot/spring-boot-starter-tomcat/2.1.7.RELEASE/spring-boot-starter-tomcat-2.1.7.RELEASE.jar:/Users/sgcx251/.m2/repository/org/apache/tomcat/embed/tomcat-embed-core/9.0.22/tomcat-embed-core-9.0.22.jar:/Users/sgcx251/.m2/repository/org/apache/tomcat/embed/tomcat-embed-el/9.0.22/tomcat-embed-el-9.0.22.jar:/Users/sgcx251/.m2/repository/org/apache/tomcat/embed/tomcat-embed-websocket/9.0.22/tomcat-embed-websocket-9.0.22.jar:/Users/sgcx251/.m2/repository/org/hibernate/validator/hibernate-validator/6.0.17.Final/hibernate-validator-6.0.17.Final.jar:/Users/sgcx251/.m2/repository/javax/validation/validation-api/2.0.1.Final/validation-api-2.0.1.Final.jar:/Users/sgcx251/.m2/repository/org/jboss/logging/jboss-logging/3.3.2.Final/jboss-logging-3.3.2.Final.jar:/Users/sgcx251/.m2/repository/com/fasterxml/classmate/1.4.0/classmate-1.4.0.jar:/Users/sgcx251/.m2/repository/org/springframework/spring-web/5.1.9.RELEASE/spring-web-5.1.9.RELEASE.jar:/Users/sgcx251/.m2/repository/org/springframework/spring-beans/5.1.9.RELEASE/spring-beans-5.1.9.RELEASE.jar:/Users/sgcx251/.m2/repository/org/springframework/spring-webmvc/5.1.9.RELEASE/spring-webmvc-5.1.9.RELEASE.jar:/Users/sgcx251/.m2/repository/org/springframework/spring-aop/5.1.9.RELEASE/spring-aop-5.1.9.RELEASE.jar:/Users/sgcx251/.m2/repository/org/springframework/spring-context/5.1.9.RELEASE/spring-context-5.1.9.RELEASE.jar:/Users/sgcx251/.m2/repository/org/springframework/spring-expression/5.1.9.RELEASE/spring-expression-5.1.9.RELEASE.jar:/Users/sgcx251/.m2/repository/mysql/mysql-connector-java/8.0.17/mysql-connector-java-8.0.17.jar:/Users/sgcx251/.m2/repository/org/slf4j/slf4j-api/1.7.26/slf4j-api-1.7.26.jar:/Users/sgcx251/.m2/repository/org/springframework/spring-core/5.1.9.RELEASE/spring-core-5.1.9.RELEASE.jar:/Users/sgcx251/.m2/repository/org/springframework/spring-jcl/5.1.9.RELEASE/spring-jcl-5.1.9.RELEASE.jar:/Users/sgcx251/.m2/repository/org/openjdk/jmh/jmh-core/1.19/jmh-core-1.19.jar:/Users/sgcx251/.m2/repository/net/sf/jopt-simple/jopt-simple/4.6/jopt-simple-4.6.jar:/Users/sgcx251/.m2/repository/org/apache/commons/commons-math3/3.2/commons-math3-3.2.jar com.songguo.jmhtest.JMH.JMHFirstBenchmark
# JMH version: 1.19
# VM version: JDK 1.8.0_201, VM 25.201-b09
# VM invoker: /Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre/bin/java
# VM options: -javaagent:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=53834:/Applications/IntelliJ IDEA.app/Contents/bin -Dfile.encoding=UTF-8
# Warmup: 3 iterations, 1 s each
# Measurement: 3 iterations, 1 s each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Average time, time/op
# Benchmark: com.songguo.jmhtest.JMH.JMHFirstBenchmark.sleepAWhile

# Run progress: 0.00% complete, ETA 00:00:06
# Fork: 1 of 1
# Warmup Iteration   1: 51319.974 us/op
# Warmup Iteration   2: 51825.236 us/op
# Warmup Iteration   3: 52087.356 us/op
Iteration   1: 51217.424 us/op
Iteration   2: 52467.070 us/op
Iteration   3: 52034.209 us/op


Result "com.songguo.jmhtest.JMH.JMHFirstBenchmark.sleepAWhile":
  51906.234 ±(99.9%) 11577.038 us/op [Average]
  (min, avg, max) = (51217.424, 51906.234, 52467.070), stdev = 634.577
  CI (99.9%): [40329.197, 63483.272] (assumes normal distribution)


# Run complete. Total time: 00:00:10

Benchmark                          Mode  Cnt      Score       Error  Units
JMH.JMHFirstBenchmark.sleepAWhile  avgt    3  51906.234 ± 11577.038  us/op

Process finished with exit code 0

我们用的sleep的时间是·平均约为50毫秒，所以我们最终的结果
51906.234 ±(99.9%) 11577.038 us/op [Average]

基本概念
Mode
Mode 表示 JMH 进行 Benchmark 时所使用的模式。通常是测量的维度不同，或是测量的方式不同。目前 JMH 共有四种模式：
(1).Throughput: 整体吞吐量，例如“1秒内可以执行多少次调用”。
(2).AverageTime: 调用的平均时间，例如“每次调用平均耗时xxx毫秒”。
(3).SampleTime: 随机取样，最后输出取样结果的分布，例如“99%的调用在xxx毫秒以内，99.99%的调用在xxx毫秒以内”
(4).SingleShotTime: 以上模式都是默认一次 iteration 是 1s，唯有 SingleShotTime 是只运行一次。往往同时把 warmup 次数设为0，用于测试冷启动时的性能。

Iteration
Iteration是JMH进行测试的最小单位。大部分模式下，iteration代表的是一秒，JMH会在这一秒内不断调用需要benchmark的方法，然后根据模式对其采样，计算吞吐量，计算平均执行时间等。
Warmup
Warmup是指在实际进行Benchmark前先进行预热的行为。因为JVM的JIT机制的存在，如果某个函数被调用多次以后，JVM会尝试将其编译成为机器码从而提高执行速度。所以为了让benchmark的结果更加接近真实情况就需要进行预热。

注解整理

@Benchmark
表示该方法是需要进行 benchmark 的对象，用法和 JUnit 的 @Test 类似。
@Mode
Mode 如之前所说，表示 JMH 进行 Benchmark 时所使用的模式。
@State
State 用于声明某个类是一个“状态”，然后接受一个 Scope 参数用来表示该状态的共享范围。因为很多 benchmark 会需要一些表示状态的类，JMH 允许你把这些类以依赖注入的方式注入到 benchmark 函数里。Scope 主要分为两种。
(1).Thread: 该状态为每个线程独享。
(2).Benchmark: 该状态在所有线程间共享。
关于State的用法，官方的 code sample 里有比较好的例子。
@OutputTimeUnit
benchmark 结果所使用的时间单位。

启动选项

JMH 在启动前设置的参数。

    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(JMHFirstBenchmark.class.getSimpleName())
                .forks(1)
                .warmupIterations(3)
                .measurementIterations(3)
                .build();

        new Runner(opt).run();
    }

include
benchmark 所在的类的名字，注意这里是使用正则表达式对所有类进行匹配的。
fork
进行 fork 的次数。如果 fork 数是2的话，则 JMH 会 fork 出两个进程来进行测试。
warmupIterations
预热的迭代次数。
measurementIterations
实际测量的迭代次数。

JMH的使用和代码

概述

使用场景

配置

注解整理

启动选项

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JMH的使用和代码

概述

使用场景

配置

注解 整理

启动选项

注解整理