jstack实战

迈不过友情╰ 2022-09-14 00:08 145阅读 0赞

**目录**

一、jstack死锁检测

①死锁代码：

②、linux编译执行java程序

③、jstack+pid 分析死锁

二、jstack实战之高cpu占用率排查

①代码：

②编译(javac DeadWhile.java)、运行(java DeadWhile)：

③排查——更多详见：jstack

--------------------

# 一、jstack死锁检测 #

### ①死锁代码： ###

/**
     * 死锁 
     * Created by hgg on 2019/9/24.
     */
    public class DeadLockWait {
    
        public static void main(String[] args) {
            Runnable r1 = () ->{
                synchronized ("A"){
                    System.out.println("|持有A锁，等待B");
                    synchronized ("B"){
                        System.out.println("|线程同时持有A、B");
                    }
                }
            };
            Runnable r2 = () ->{
                synchronized ("B"){
                    System.out.println("||持有B锁，等待A");
                    synchronized ("A"){
                        System.out.println("||线程同时持有A、B");
                    }
                }
            };
    
            Thread t1 = new Thread(r1);
            Thread t2 = new Thread(r2);
    
            t1.start();
            t2.start();
        }
    }

### ②、linux编译执行java程序 ###

编译：javac DeadLockWait.java        （生成DeadLockWait.class）

执行：java DeadLockWait

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5aSa5p2l5ZOI57Gz_size_20_color_FFFFFF_t_70_g_se_x_16][]

多执行几次，直至进入如下死锁状态：

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5aSa5p2l5ZOI57Gz_size_14_color_FFFFFF_t_70_g_se_x_16][]

### ③、jstack+pid 分析死锁 ###

说明：**jps**获取java进程pid

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5aSa5p2l5ZOI57Gz_size_20_color_FFFFFF_t_70_g_se_x_16 1][]

# 二、jstack实战之高cpu占用率排查 #

### ①代码： ###

import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    
    /**
     * 死循环——堆溢出
     * Created by hgg on 2021年9月30日11:23:32
     */
    public class DeadWhile {
    
        private static ExecutorService fixedThreadPool = Executors.newFixedThreadPool(3);
    
        private static Object lock = new Object();
    
        public static void main(String[] args) {
            MyRunner my1 = new MyRunner();
            MyRunner my2 = new MyRunner();
    
            fixedThreadPool.execute(my1);
            fixedThreadPool.execute(my2);
    
            fixedThreadPool.shutdown();
        }
    
        static class MyRunner implements Runnable{
            @Override
            public void run() {
                synchronized (lock){
                    Long i =1L;
                    Boolean flag = true;
                    Long start = System.currentTimeMillis();
                    System.out.println(i + "：start：" + (start));
                    while (flag){
                        i++;
                        if (i > 9999999999L){
                            flag = false;
                            System.out.println(i + "：over：" + (System.currentTimeMillis() - start));
                        }
                    }
                }
            }
        }
    }

### ②编译(javac DeadWhile.java)、运行(java DeadWhile)： ###

### ③排查——更多详见：[jstack][] ###

**top**                                                ————定位CPU占用较高的进程

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5aSa5p2l5ZOI57Gz_size_20_color_FFFFFF_t_70_g_se_x_16 2][]

**top -H -p \[高耗**CPU-PID**\]             **————指定进程下各个线程的情况

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5aSa5p2l5ZOI57Gz_size_20_color_FFFFFF_t_70_g_se_x_16 3][]

**printf "%x" \[上面高CPU-PID\]     **————将pid转换为16进制**    **

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5aSa5p2l5ZOI57Gz_size_11_color_FFFFFF_t_70_g_se_x_16][]

**jstack \[PID\]| grep -10 \[上面16进制\]**        ————定位程序中问题线程(前后十行)**   **

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5aSa5p2l5ZOI57Gz_size_20_color_FFFFFF_t_70_g_se_x_16 4][]

友情链接：

[jstack实战点睛][jstack 1]

[jstack 命令学习笔记][jstack 2]

[jstack(较详细)][jstack]

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[jstack]: https://blog.csdn.net/justry_deng/article/details/90447410
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[jstack 1]: https://buqutianya.blog.csdn.net/article/details/78895141
[jstack 2]: https://blog.csdn.net/weixin_30700977/article/details/99012798