【开发篇】十六、线程耗尽与死锁检测

痛定思痛。 2024-04-23 15:45 1阅读 0赞

#### 文章目录 ####

*  1、背景
 *  2、模拟
 *  3、死锁的检测
 *  4、处理

## 1、背景 ##

程序在启动运行一段时间之后，就无法接受任何请求了。  
解决：

*  检查是否有死锁发生，无法自动解除的死锁，会把线程永远阻塞
 *  没有死锁，则打印线程栈，分析慢方法

## 2、模拟 ##

@RestController
    @RequestMapping("/performance")
    public class PerformanceController {
        
    
        private Object obj1 = new Object();
        private Object obj2 = new Object();
    
        @GetMapping("/deadlock1")
        public String test1() throws InterruptedException {
        
            synchronized (obj1){
        
                Thread.sleep(5000);
                synchronized (obj2){
        
                    return "返回成功";
                }
            }
         }
    
    	@GetMapping("/deadlock2")
        public String test2() throws InterruptedException {
        
            synchronized (obj2){
        
                Thread.sleep(5000);
                synchronized (obj1){
        
                    return "返回成功";
                }
            }
         }
    }

Jmeter并发调一下上面两个模拟死锁的接口，再调其他正常的接口，也不能正常响应和返回了。

![在这里插入图片描述][944f47a637d1451fa08266253aaed7a4.png]  
因为tomcat线程池里设置的500个线程被耗尽了。

## 3、死锁的检测 ##

> 方法一：线程转储，搜索deadlock

jstack -l 进程ID > 文件名

![在这里插入图片描述][1e7d507c28594f4f9c47458f6321817f.png]  
查看详情，找到死锁发生的行号

> 方法二：Visual VM

一般用于开发环境或者本地复现，生产环境无连接权限  
![在这里插入图片描述][24b3b3c744cb449e82c06e963b751715.png]

> 方法三：使用fastthread自动检测线程问题

[https://fastthread.io/][https_fastthread.io]

![在这里插入图片描述][978a63be9f9e4aa0a6833c5565160aff.png]

## 4、处理 ##

上面死锁的处理：

@RestController
    @RequestMapping("/performance")
    public class PerformanceController {
        
    
        private Object obj1 = new Object();
        private Object obj2 = new Object();
        private Lock lock1 = new ReentrantLock();
        private Lock lock2 = new ReentrantLock();
        private Random random = new Random();
    
        @GetMapping("/1")
        public void test1(){
        
            while (true){
        
    
            }
        }
    
        @GetMapping("/deadlock1")
        public String test2() throws InterruptedException {
        
            boolean b1 = lock1.tryLock(1, TimeUnit.SECONDS);
            if(b1){
        
                try {
        
                    Thread.sleep(5000);
                    boolean b2 = lock2.tryLock(1, TimeUnit.SECONDS);
                    if(b2){
        
                        try{
        
                            return "返回成功";
                        }
                        finally {
        
                            lock2.unlock();
                        }
                    }
                }finally {
        
                    lock1.unlock();
                }
            }
            return "处理失败";
        }
    
        @GetMapping("/deadlock2")
        public String test3() throws InterruptedException {
        
            boolean b1 = lock2.tryLock(1, TimeUnit.SECONDS);
            if(b1){
        
                try {
        
                    Thread.sleep(5000);
                    boolean b2 = lock1.tryLock(1, TimeUnit.SECONDS);
                    if(b2){
        
                        try{
        
                            return "返回成功";
                        }
                        finally {
        
                            lock1.unlock();
                        }
                    }
                }finally {
        
                    lock2.unlock();
                }
            }
            return "处理失败";
        }
    
    }

[944f47a637d1451fa08266253aaed7a4.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/23/d73fc7df0bbd4ac78a4edc8a55d1671b.png
[1e7d507c28594f4f9c47458f6321817f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/23/e82e46139f3346e08f365c09b5aaa014.png
[24b3b3c744cb449e82c06e963b751715.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/23/6d3d29f18bce4955a0e03cb013210e03.png
[https_fastthread.io]: https://fastthread.io/
[978a63be9f9e4aa0a6833c5565160aff.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/23/a4f2e7617ca5415f8ab64542fcf4c6cf.png