1、使用JMH做Java微基准测试：JMH简介

2、使用JMH做Java微基准测试（一）测试入门

3、使用JMH做Java微基准测试（二）Hello2020！

测试参数状态State

@Setup

方法级注解，这个注解的作用就是我们需要在测试之前进行一些准备工作，比如对一些数据的初始化之类的。

@State

当使用@Setup参数的时候，必须在类上加这个参数，不然会提示无法运行。

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 主要分为三种。

Thread: 该状态为每个线程独享。
Group: 该状态为同一个组里面所有线程共享。

Benchmark: 该状态在所有线程间共享。测试代码：


/** * Licensed to the Apache Software Foundation (ASF) under one or more* contributor license agreements.  See the NOTICE file distributed with* this work for additional information regarding copyright ownership.* The ASF licenses this file to You under the Apache License, Version 2.0* (the "License"); you may not use this file except in compliance with* the License.  You may obtain a copy of the License at**     http://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.**/
package com.tompai.test;
import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;
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;
/**
* @desc: demo
* @name: JMHSample_03_States.java
* @author: tompai
* @email：liinux@qq.com
* @createTime: 2020年1月3日 上午12:13:24
* @history:
* @version: v1.0
*/public class JMHSample_03_States {/** Most of the time, you need to maintain some state while the benchmark is* running. Since JMH is heavily used to build concurrent benchmarks, we* opted for an explicit notion of state-bearing objects.** Below are two state objects. Their class names are not essential, it* matters they are marked with @State. These objects will be instantiated* on demand, and reused during the entire benchmark trial.** The important property is that state is always instantiated by one of* those benchmark threads which will then have the access to that state.* That means you can initialize the fields as if you do that in worker* threads (ThreadLocals are yours, etc).*///默认状态。实例将分配给运行给定测试的每个线程（共享）。@State(Scope.Benchmark)public static class BenchmarkState {volatile double x = Math.PI;}//运行相同测试的所有线程将不共享实例。可以用来测试状态对象的多线程性能(或者仅标记该范围的基准)。@State(Scope.Thread)public static class ThreadState {volatile double x = Math.PI;}/** Benchmark methods can reference the states, and JMH will inject the* appropriate states while calling these methods. You can have no states at* all, or have only one state, or have multiple states referenced. This* makes building multi-threaded benchmark a breeze.** For this exercise, we have two methods.*/@Benchmarkpublic void measureUnshared(ThreadState state) {// All benchmark threads will call in this method.//// However, since ThreadState is the Scope.Thread, each thread// will have it's own copy of the state, and this benchmark// will measure unshared case.state.x++;}@Benchmarkpublic void measureShared(BenchmarkState state) {// All benchmark threads will call in this method.//// Since BenchmarkState is the Scope.Benchmark, all threads// will share the state instance, and we will end up measuring// shared case.state.x++;}/** ============================== HOW TO RUN THIS TEST: ====================================** You are expected to see the drastic difference in shared and unshared cases,* because you either contend for single memory location, or not. This effect* is more articulated on large machines.** You can run this test:** a) Via the command line:*    $ mvn clean install*    $ java -jar target/benchmarks.jar JMHSample_03 -t 4 -f 1*    (we requested 4 threads, single fork; there are also other options, see -h)** b) Via the Java API:*    (see the JMH homepage for possible caveats when running from IDE:*      http://openjdk.java.net/projects/code-tools/jmh/)*/public static void main(String[] args) throws RunnerException {Options opt = new OptionsBuilder().include(JMHSample_03_States.class.getSimpleName()).output("./Benchmark.log").threads(4).forks(1).build();new Runner(opt).run();}
}

测试结果：

# JMH version: 1.22
# VM version: JDK 1.8.0_221, Java HotSpot(TM) 64-Bit Server VM, 25.221-b11
# VM invoker: E:\Java\jdk\jdk1.8.0_221\jre\bin\java.exe
# VM options: -Dfile.encoding=UTF-8
# Warmup: 5 iterations, 10 s each
# Measurement: 5 iterations, 10 s each
# Timeout: 10 min per iteration
# Threads: 4 threads, will synchronize iterations
# Benchmark mode: Throughput, ops/time
# Benchmark: com.tompai.test.JMHSample_03_States.measureShared# Run progress: 0.00% complete, ETA 00:03:20
# Fork: 1 of 1
# Warmup Iteration   1: 67298896.997 ops/s
# Warmup Iteration   2: 68308485.750 ops/s
# Warmup Iteration   3: 69882743.315 ops/s
# Warmup Iteration   4: 69891149.623 ops/s
# Warmup Iteration   5: 67506135.646 ops/s
Iteration   1: 67391729.777 ops/s
Iteration   2: 66734187.576 ops/s
Iteration   3: 67945688.033 ops/s
Iteration   4: 70228301.275 ops/s
Iteration   5: 70063976.328 ops/sResult "com.tompai.test.JMHSample_03_States.measureShared":68472776.598 ±(99.9%) 6113605.121 ops/s [Average](min, avg, max) = (66734187.576, 68472776.598, 70228301.275), stdev = 1587683.835CI (99.9%): [62359171.477, 74586381.719] (assumes normal distribution)# JMH version: 1.22
# VM version: JDK 1.8.0_221, Java HotSpot(TM) 64-Bit Server VM, 25.221-b11
# VM invoker: E:\Java\jdk\jdk1.8.0_221\jre\bin\java.exe
# VM options: -Dfile.encoding=UTF-8
# Warmup: 5 iterations, 10 s each
# Measurement: 5 iterations, 10 s each
# Timeout: 10 min per iteration
# Threads: 4 threads, will synchronize iterations
# Benchmark mode: Throughput, ops/time
# Benchmark: com.tompai.test.JMHSample_03_States.measureUnshared# Run progress: 50.00% complete, ETA 00:01:41
# Fork: 1 of 1
# Warmup Iteration   1: 267075988.556 ops/s
# Warmup Iteration   2: 272251667.492 ops/s
# Warmup Iteration   3: 274444908.147 ops/s
# Warmup Iteration   4: 277804069.510 ops/s
# Warmup Iteration   5: 278807440.060 ops/s
Iteration   1: 287512303.825 ops/s
Iteration   2: 283023773.358 ops/s
Iteration   3: 281720730.780 ops/s
Iteration   4: 263154214.935 ops/s
Iteration   5: 287522409.968 ops/sResult "com.tompai.test.JMHSample_03_States.measureUnshared":280586686.573 ±(99.9%) 38850733.584 ops/s [Average](min, avg, max) = (263154214.935, 280586686.573, 287522409.968), stdev = 10089412.136CI (99.9%): [241735952.989, 319437420.158] (assumes normal distribution)# Run complete. Total time: 00:03:22REMEMBER: The numbers below are just data. To gain reusable insights, you need to follow up on
why the numbers are the way they are. Use profilers (see -prof, -lprof), design factorial
experiments, perform baseline and negative tests that provide experimental control, make sure
the benchmarking environment is safe on JVM/OS/HW level, ask for reviews from the domain experts.
Do not assume the numbers tell you what you want them to tell.Benchmark                             Mode  Cnt          Score          Error  Units
JMHSample_03_States.measureShared    thrpt    5   68472776.598 ±  6113605.121  ops/s
JMHSample_03_States.measureUnshared  thrpt    5  280586686.573 ± 38850733.584  ops/s

结论：不共享【@State(Scope.Thread)】情况下吞吐量很高！！！

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