JMH generator: Frequently Asked Questions Questions Questions in Java Class Library
JMH generator: Frequently Asked Questions Questions Questions in Java Class Library
The JMH generator is a powerful benchmark testing tool that can help developers evaluate and optimize the performance of Java code.Using the JMH generator, you can easily write the benchmark test, measure the operation time, throughput and resource utilization of the code.However, because the JMH generator will encounter some common problems during use, this article will provide some answers and Java code examples to help readers better understand and use the JMH generator.
Question 1: How to use the JMH generator to write the benchmark test?
answer:
To use the JMH generator to write the benchmark test, we need to add related dependencies to the project.In the Maven project, the JMH generator can be introduced by adding the following dependencies to the POM.XML file:
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-core</artifactId>
<Version> {jmh version number} </version>
</dependency>
<dependency>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-generator-annprocess</artifactId>
<Version> {jmh version number} </version>
</dependency>
Once the dependencies are added, you can use the JMH generator to write the benchmark test.First, create a Java class containing the benchmark test method, and use the method to evaluate the performance evaluation with the `@Benchmark` annotation mark.You can then configure and run the benchmark test with the annotation of the JMH generator.For example, you can use the specified time unit to use `@omputtimeunit`, and use the number of preheating iterations to specify the number of preheating iterations.
Below is an example code that uses the JMH generator to write the benchmark test:
import org.openjdk.jmh.annotations.*;
import java.util.concurrent.TimeUnit;
@State(Scope.Thread)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
public class MyBenchmark {
@Benchmark
public void myMethod() {
// The code that has been evaluated
}
}
In the example above, the `@State` annotation specifies the status range of the benchmark test,` `` `` ``@@OUTPUTTTIMEUNIT` specifies the time unit, `@warmup` specifies the number of pre -heated iterations,With time, `@Measurement` specify the actual measurement iteration and time.
Question 2: How to run the benchmark test generated by the JMH generator?
answer:
To run the benchmark test generated by the JMH generator, you can use the command line or perform a tool (such as Maven).When running the command line, you need to execute the following command:
java -jar {jmh generator generated jar file} {other options}
Among them, the jar file generated by `{jmh generator}` is a JAR file path generated by the benchmark test by the JMH generator.
If you run with the construction tool, you can configure the JMH plug -in in the pom.xml file of the project, and then use the plug -in target to run the benchmark test.For example, in the Maven project, you can configure the JMH plug -in like the following:
<build>
<plugins>
<plugin>
<groupId>org.openjdk.jmh</groupId>
<artifactId>jmh-maven-plugin</artifactId>
<Version> {jmh version number} </version>
<configuration>
<TARGET> {benchmark test full name} </target>
</configuration>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>generate-sources</goal>
<goal>test</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
In the above configuration, `{jmh version number}` is the version number of the JMH plug -in.Then, you can perform the following command to perform the benchmark test:
mvn clean install
Question 3: How to solve the problem of inaccurate test results?
answer:
In the benchmark test, there may be some inaccurate problems.There are several common solutions that can improve the accuracy of the benchmark test results:
1. Avoid interference: improve accuracy by reducing factors that may interfere with test results.For example, JVM compile test code can be prohibited, and JVM optimization can be closed.
2. Increasing the number of iterations: Increasing the number of iterations of the benchmark test can improve the accuracy of the results.You can adjust the number of iterations by setting the ITERATIONS attribute of the JMH generator's `@Measurement`.
3. Use the Blackhole class: In the benchmark test, you can use the Blackhole class provided by the JMH generator to avoid compiler optimization.The Blackhole class will receive the results and prevent further calculation.This can ensure that the test results are not optimized by the compiler.
Below is an example code using the Blackhole class:
import org.openjdk.jmh.infra.Blackhole;
@Benchmark
public void myMethod(Blackhole blackhole) {
// The code that has been evaluated
// Pass the result to the Blackhole object
blackhole.consume(result);
}
In the above example, `Result` is the result of the assessment code. Use the method to pass the result to the Blackhole object.
The above are a few common questions about JMH generators and examples of Java code.It is hoped that readers can better understand and use the JMH generator to improve the performance of the Java code.
