package com.msb;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * @description:
 * @date : 2020/8/12 21:12
 * @author: zwz
 */
public class T15_FullGC_Problem01 {

    private static class CardInfo {
        BigDecimal price = new BigDecimal(0.0);
        String name = "张三";
        int age = 5;
        Date birthdate = new Date();

        public void m() {
        }
    }

    private static ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(50,
            new ThreadPoolExecutor.DiscardOldestPolicy());

    public static void main(String[] args) throws Exception {
        executor.setMaximumPoolSize(50);

        for (; ; ) {
            modelFit();
            Thread.sleep(100);
        }
    }

    private static void modelFit() {
        List<CardInfo> taskList = getAllCardInfo();
        taskList.forEach(info -> {
            // do something
            executor.scheduleWithFixedDelay(() -> {
                //do sth with info
                info.m();

            }, 2, 3, TimeUnit.SECONDS);
        });
    }

    private static List<CardInfo> getAllCardInfo() {
        List<CardInfo> taskList = new ArrayList<>();

        for (int i = 0; i < 100; i++) {
            CardInfo ci = new CardInfo();
            taskList.add(ci);
        }

        return taskList;
    }


}

GC日志

1. JPS定位到PID

2. jstack

jstack 定位线程状况，重点关注：WAITING BLOCKED
eg.
waiting on <0x0000000088ca3310> (a java.lang.Object)
假如有一个进程中100个线程，很多线程都在waiting on <xx> ，一定要找到是哪个线程持有这把锁
怎么找？搜索jstack dump的信息，找<xx> ，看哪个线程持有这把锁RUNNABLE

死锁检测

package com.lg;

/**
 * @description: 互斥条件、请求与保持条件、不剥夺条件、循环等待条件
 * @date : 2020/7/27 11:31
 * @author: zwz
 */
public class MustDeadLock implements Runnable {

    public int flag;
    static final Object o1 = new Object();
    static final Object o2 = new Object();

    @Override
    public void run() {
        System.out.println("线程" + Thread.currentThread().getName() + "的flag为" + flag);
        if (flag == 1) {
            synchronized (o1) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                synchronized (o2) {
                    System.out.println("线程1获得了两把锁");
                }
            }
        }

        if (flag == 2) {
            synchronized (o2) {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                synchronized (o1) {
                    System.out.println("线程2获得了两把锁");
                }
            }
        }
    }

    public static void main(String[] args) {
        MustDeadLock lock = new MustDeadLock();
        MustDeadLock lock2 = new MustDeadLock();
        lock.flag = 1;
        lock2.flag = 2;

        Thread t1 = new Thread(lock, "t1");
        Thread t2 = new Thread(lock2, "t2");
        t1.start();
        t2.start();
    }
}

3 jinfo PID

4. arthas

• JVM

  
  

• 确定jar包加载路径

  
  

• 代码反编译

  
  

• 线上debug：watch

  
  
  

  watch demo.MathGame primeFactors "{params,target,returnObj,throwExp}" -x 2 -n 2

  
  

• sm 查找方法

  
  

• sc 查找类

  
  

• readline 重新写java并编译成class。运行时替换class

  
  

• 原理：
  字节码 AOP spring aop jvm级别 java agent 热部署jrebel

jmap 查找有多少对象产生

• 线上系统，内存特别大，jmap执行期间会对进程产生很大影响，甚至卡顿（电商不适合）
  1：设定了参数HeapDump，OOM的时候会自动产生堆转储文件（不是很专业，因为多有监控，内存增长就会报警）
  2：<font color='red'>很多服务器备份（高可用），停掉这台服务器对其他服务器不影响</font>
  3：在线定位(一般小点儿公司用不到)
  4：在测试环境中压测（产生类似内存增长问题，在堆还不是很大的时候进行转储）

• 堆转储文件

  
  
  
  

jstat

jhat