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update codes and docs
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‎codes/javacore-jvm/README.md

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‎codes/javacore-jvm/src/main/java/io/github/dunwu/javacore/jvm/memory/ConstantPoolOutOfMemoryDemo.java

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* <li>(JDK8 及以后)-XX:MetaspaceSize=10m -XX:MaxMetaspaceSize=10m</li>
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* </ul>
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* <p>
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* Linux Test Cli: java -verbose:gc -XX:PermSize=10m -XX:MaxPermSize=10m -cp target/javacore-jvm-1.0.1.jar io.github.dunwu.javacore.jvm.memory.ConstantPoolOutOfMemoryDemo
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* Linux Test Cli: nohup java -verbose:gc -XX:MetaspaceSize=10m -XX:MaxMetaspaceSize=10m -XX:+HeapDumpOnOutOfMemoryError -classpath "target/javacore-jvm-1.0.1.jar:target/lib/*" io.github.dunwu.javacore.jvm.memory.ConstantPoolOutOfMemoryDemo >> output.log 2>&1 &
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*
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2019-06-25

‎codes/javacore-jvm/src/main/java/io/github/dunwu/javacore/jvm/memory/DeadloopDemo.java

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package io.github.dunwu.javacore.jvm.memory;
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import java.util.UUID;
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import java.util.concurrent.TimeUnit;
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import java.util.stream.Collectors;
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import java.util.stream.IntStream;
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/**
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* Linux Test Cli: nohup java -verbose:gc -Xms256M -Xmx512M
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* -XX:+PrintGCDetails -XX:+PrintGCTimeStamps
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* -XX:+PrintGCDateStamps -XX:-OmitStackTraceInFastThrow -XX:+HeapDumpOnOutOfMemoryError
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* -Dcom.sun.management.jmxremote=true
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* -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.authenticate=false
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* -Djava.rmi.server.hostname=${ip} -Dcom.sun.management.jmxremote.port=18888
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* -Xdebug -Xnoagent -Djava.compiler=NONE
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* -Xrunjdwp:transport=dt_socket,address=28888,server=y,suspend=n
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* -classpath "target/javacore-jvm-1.0.1.jar:target/lib/*" io.github.dunwu.javacore.jvm.memory.DeadloopDemo
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* >> output.log 2>&1 &
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*
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2020-08-07
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*/
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public class DeadloopDemo {
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public static void main(String[] args) throws InterruptedException {
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//启动10个线程
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IntStream.rangeClosed(1, 10).mapToObj(i -> new Thread(() -> {
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while (true) {
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//每一个线程都是一个死循环，休眠10秒，打印10M数据
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String payload = IntStream.rangeClosed(1, 10000000)
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.mapToObj(__ -> "a")
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.collect(Collectors.joining("")) + UUID.randomUUID().toString();
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try {
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TimeUnit.SECONDS.sleep(10);
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} catch (InterruptedException e) {
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e.printStackTrace();
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}
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System.out.println(payload.length());
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}
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})).forEach(Thread::start);
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TimeUnit.HOURS.sleep(1);
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}
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}

‎codes/javacore-jvm/src/main/java/io/github/dunwu/javacore/jvm/memory/DirectOutOfMemoryDemo.java

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* 错误现象：java.lang.OutOfMemoryError
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* <p>
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* VM Args：-verbose:gc -Xmx20M -XX:MaxDirectMemorySize=10M
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* <p>
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* Linux Test Cli: nohup java -verbose:gc -Xmx20M -XX:MaxDirectMemorySize=10M -classpath "target/javacore-jvm-1.0.1.jar:target/lib/*"
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* io.github.dunwu.javacore.jvm.memory.DirectOutOfMemoryDemo >> output.log 2>&1 &
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*
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2019-06-25

‎codes/javacore-jvm/src/main/java/io/github/dunwu/javacore/jvm/memory/GcOverheadLimitExceededDemo.java

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* 官方对此的定义：超过98%的时间用来做GC并且回收了不到2%的堆内存时会抛出此异常。
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* <p>
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* VM Args: -Xms10M -Xmx10M
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*
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* Linux Test Cli: java -verbose:gc -Xms10M -Xmx10M -cp target/javacore-jvm-1.0.1.jar io.github.dunwu.javacore.jvm.memory.GcOverheadLimitExceededDemo
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* <p>
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* Linux Test Cli: nohup java -verbose:gc -Xms10M -Xmx10M -XX:+HeapDumpOnOutOfMemoryError -classpath
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* "target/javacore-jvm-1.0.1.jar:target/lib/*" io.github.dunwu.javacore.jvm.memory.GcOverheadLimitExceededDemo >>
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* output.log 2>&1 &
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*
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2019-06-25

‎codes/javacore-jvm/src/main/java/io/github/dunwu/javacore/jvm/memory/HeapMemoryLeakMemoryErrorDemo.java

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* 错误现象：java.lang.OutOfMemoryError: Java heap space
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* <p>
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* VM Args：-verbose:gc -Xms10M -Xmx10M -XX:+HeapDumpOnOutOfMemoryError
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* <p>
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* Linux Test Cli: nohup java -verbose:gc -Xms10M -Xmx10M -XX:+HeapDumpOnOutOfMemoryError -classpath
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* "target/javacore-jvm-1.0.1.jar:target/lib/*" io.github.dunwu.javacore.jvm.memory.HeapMemoryLeakMemoryErrorDemo >>
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* output.log 2>&1 &
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*
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2019-06-25

‎codes/javacore-jvm/src/main/java/io/github/dunwu/javacore/jvm/memory/HeapMemoryLeakMemoryErrorDemo2.java

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import java.util.Random;
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/**
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* Linux Test Cli: nohup java -verbose:gc -Xms10M -Xmx10M -XX:+HeapDumpOnOutOfMemoryError -classpath
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* "target/javacore-jvm-1.0.1.jar:target/lib/*" io.github.dunwu.javacore.jvm.memory.HeapMemoryLeakMemoryErrorDemo2 >>
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* output.log 2>&1 &
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*
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2020-03-09
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*/

‎codes/javacore-jvm/src/main/java/io/github/dunwu/javacore/jvm/memory/MethodAreaOutOfMemoryDemo.java

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* 方法区出现 OutOfMemoryError
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* <li>(JDK8 以前)-XX:PermSize=10m -XX:MaxPermSize=10m</li>
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* <li>(JDK8 及以后)-XX:MetaspaceSize=10m -XX:MaxMetaspaceSize=10m</li>
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*
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* Linux Test Cli: nohup java -verbose:gc -XX:MetaspaceSize=10m -XX:MaxMetaspaceSize=10m -cp target/javacore-jvm-1.0.1.jar io.github.dunwu.javacore.jvm.memory.MethodAreaOutOfMemoryDemo >> output.log 2>&1 &
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* <p>
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* Linux Test Cli: nohup java -verbose:gc -XX:MetaspaceSize=10m -XX:MaxMetaspaceSize=10m -XX:+HeapDumpOnOutOfMemoryError
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* -classpath "target/javacore-jvm-1.0.1.jar:target/lib/*" io.github.dunwu.javacore.jvm.memory.MethodAreaOutOfMemoryDemo
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* >> output.log 2>&1 &
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*
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2019-06-26

‎codes/javacore-jvm/src/main/java/io/github/dunwu/javacore/jvm/memory/PermOutOfMemoryErrorDemo.java

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import javassist.ClassPool;
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/**
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* 永久代内存空间不足示例
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* <p>
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* 错误现象：
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* 永久代内存空间不足示例 错误现象：
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* <ul>
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* <li>java.lang.OutOfMemoryError: PermGen space (JDK8 以前版本)</li>
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* <li>java.lang.OutOfMemoryError: Metaspace (JDK8 及以后版本)</li>
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* <li>-Xmx100M -XX:MaxPermSize=16M (JDK8 以前版本)</li>
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* <li>-Xmx100M -XX:MaxMetaspaceSize=16M (JDK8 及以后版本)</li>
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* </ul>
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* Linux Test Cli: nohup java -verbose:gc -Xmx100M -XX:MaxMetaspaceSize=16M -XX:+HeapDumpOnOutOfMemoryError -classpath "target/javacore-jvm-1.0.1.jar:target/lib/*" io.github.dunwu.javacore.jvm.memory.PermOutOfMemoryErrorDemo >> output.log 2>&1 &
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*
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* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
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* @since 2020-03-08

‎docs/jvm/jvm-cli-tools.md

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| `jmap` | JVM 堆内存分析工具。用于打印 JVM 进程对象直方图、类加载统计。并且可以生成堆转储快照（一般称为 heapdump 或 dump 文件）。 |
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| `jstack` | JVM 栈查看工具。用于打印 JVM 进程的线程和锁的情况。并且可以生成线程快照（一般称为 threaddump 或 javacore 文件）。 |
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| `jhat` | 用来分析 jmap 生成的 dump 文件。 |
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| `jinfo` | 用于实时查看和调整虚拟机运行参数。 |
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| `jinfo` | JVM 信息查看工具。用于实时查看和调整 JVM 进程参数。 |
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| `jcmd` | JVM 命令行调试 工具。用于向 JVM 进程发送调试命令。 |
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<!-- TOC depthFrom:2 depthTo:3 -->
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