使用jstack快速寻找死循环和死锁的原因

布满荆棘的人生 2023-06-27 08:53 8阅读 0赞

## 代码演示 ##

*  死循环
    
     *  使用步骤：
     *  1.运行服务器，使用浏览器多个窗口同时访问此路径（注意：因为多个死循环会导致电脑cpu高速运行，运行小心电脑会卡顿，测试完即可关闭）
     *  2.cmd输入jps -l命令查询服务器对应的pid
     *  3.cmd输入jstack pid > pid.txt命令，将进程运行过程存储在pid.txt中，查看此文件即可了解哪里发生了死循环
 *  死锁
    
     *  使用步骤：
     *  1.运行服务器，使用浏览器窗口访问此路径
     *  2.cmd输入jps -l命令查询服务器对应的pid
     *  3.cmd输入jstack pid > pid.txt命令，将进程运行过程存储在pid.txt中，查看此文件即可了解哪里发生了死锁
     *  4.查看pid.txt文件最后，发现如下内容：
     *  由此可知jstack对于发现死锁发挥着很好的效果与作用

> Found one Java-level deadlock:  
> =============================  
> “Thread-4”:  
> waiting to lock monitor 0x000000001a5913f8 (object 0x00000000da8e4788, a java.lang.Object),  
> which is held by “Thread-3”  
> “Thread-3”:  
> waiting to lock monitor 0x000000001a5925d8 (object 0x00000000da8e4798, a java.lang.Object),  
> which is held by “Thread-4”  
> Java stack information for the threads listed above:  
> ===================================================  
> “Thread-4”:  
> at com.zr.monitor\_tuning.chapter2.CpuController.lambda 1 ( C p u C o n t r o l l e r . j a v a : 120 ) − w a i t i n g t o l o c k < 0 x 00000000 d a 8 e 4788 > ( a j a v a . l a n g . O b j e c t ) − l o c k e d < 0 x 00000000 d a 8 e 4798 > ( a j a v a . l a n g . O b j e c t ) a t c o m . z r . m o n i t o r t u n i n g . c h a p t e r 2. C p u C o n t r o l l e r 1(CpuController.java:120) - waiting to lock <0x00000000da8e4788> (a java.lang.Object) - locked <0x00000000da8e4798> (a java.lang.Object) at com.zr.monitor\_tuning.chapter2.CpuController 1(CpuController.java:120)−waitingtolock<0x00000000da8e4788>(ajava.lang.Object)−locked<0x00000000da8e4798>(ajava.lang.Object)atcom.zr.monitortuning.chapter2.CpuController$Lambda$444/1678468958.run(Unknown Source)  
> at java.lang.Thread.run(Thread.java:748)  
> “Thread-3”:  
> at com.zr.monitor\_tuning.chapter2.CpuController.lambda 0 ( C p u C o n t r o l l e r . j a v a : 106 ) − w a i t i n g t o l o c k < 0 x 00000000 d a 8 e 4798 > ( a j a v a . l a n g . O b j e c t ) − l o c k e d < 0 x 00000000 d a 8 e 4788 > ( a j a v a . l a n g . O b j e c t ) a t c o m . z r . m o n i t o r t u n i n g . c h a p t e r 2. C p u C o n t r o l l e r 0(CpuController.java:106) - waiting to lock <0x00000000da8e4798> (a java.lang.Object) - locked <0x00000000da8e4788> (a java.lang.Object) at com.zr.monitor\_tuning.chapter2.CpuController 0(CpuController.java:106)−waitingtolock<0x00000000da8e4798>(ajava.lang.Object)−locked<0x00000000da8e4788>(ajava.lang.Object)atcom.zr.monitortuning.chapter2.CpuController$Lambda$443/582497331.run(Unknown Source)  
> at java.lang.Thread.run(Thread.java:748)  
> Found 1 deadlock.

package com.zr.monitor_tuning.chapter2;
    
    import java.util.ArrayList;
    import java.util.List;
    
    import org.hibernate.validator.internal.util.privilegedactions.NewInstance;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RestController;
    
    /** @version: 1.0.0 * @Description: 使用jstack快速寻找死循环和死锁的原因 * @author: ZR * @date: 2020年1月5日 下午10:01:19 */
    @RestController
    @RequestMapping("/cpu")
    public class CpuController { 
    
    	/** * 死循环 * 使用步骤： * 1.运行服务器，使用浏览器多个窗口同时访问此路径（注意：因为多个死循环会导致电脑cpu高速运行，运行小心电脑会卡顿，测试完即可关闭） * 2.cmd输入jps -l命令查询服务器对应的pid * 3.cmd输入jstack pid > pid.txt命令，将进程运行过程存储在pid.txt中，查看此文件即可了解哪里发生了死循环 * @return */
    	@RequestMapping("/loop")
    	public List<Long> loop() { 
    		//输如错误的json数据，让getPartneridsFromJson()方法发生死循环
    		String data="{\"data\":[{\"partnerid\":]";
    		return getPartneridsFromJson(data);
    	}
    	
    	/** * 从json数据中获取所有的partnerid * @param data * @return */
    	public static List<Long> getPartneridsFromJson(String data){   
    	    //{\"data\":[{\"partnerid\":982,\"count\":\"10000\",\"cityid\":\"11\"},{\"partnerid\":983,\"count\":\"10000\",\"cityid\":\"11\"},{\"partnerid\":984,\"count\":\"10000\",\"cityid\":\"11\"}]} 
    	    //上面是正常的数据,不会发生死循环，但是错误的json会发生死循环
    	    List<Long> list = new ArrayList<Long>(2);  
    	    if(data == null || data.length() <= 0){   
    	        return list;  
    	    }      
    	    int datapos = data.indexOf("data");  
    	    if(datapos < 0){   
    	        return list;  
    	    }  
    	    int leftBracket = data.indexOf("[",datapos);  
    	    int rightBracket= data.indexOf("]",datapos);  
    	    if(leftBracket < 0 || rightBracket < 0){   
    	        return list;  
    	    }  
    	    String partners = data.substring(leftBracket+1,rightBracket);  
    	    if(partners == null || partners.length() <= 0){   
    	        return list;  
    	    }  
    	    while(partners!=null && partners.length() > 0){   
    	        int idpos = partners.indexOf("partnerid");  
    	        if(idpos < 0){   
    	            break;  
    	        }  
    	        int colonpos = partners.indexOf(":",idpos);  
    	        int commapos = partners.indexOf(",",idpos);  
    	        if(colonpos < 0 || commapos < 0){   
    	            //partners = partners.substring(idpos+"partnerid".length());//1 
    	            continue;
    	        }  
    	        String pid = partners.substring(colonpos+1,commapos);  
    	        if(pid == null || pid.length() <= 0){   
    	            //partners = partners.substring(idpos+"partnerid".length());//2 
    	            continue;
    	        }  
    	        try{   
    	            list.add(Long.parseLong(pid));  
    	        }catch(Exception e){   
    	            //do nothing 
    	        }  
    	        partners = partners.substring(commapos);  
    	    }  
    	    return list;  
    	}
    	
    	/** * 死锁 * 使用步骤： * 1.运行服务器，使用浏览器窗口访问此路径 * 2.cmd输入jps -l命令查询服务器对应的pid * 3.cmd输入jstack pid > pid.txt命令，将进程运行过程存储在pid.txt中，查看此文件即可了解哪里发生了死锁 * 4.查看pid.txt文件最后，发现如下内容： Found one Java-level deadlock: ============================= "Thread-4": waiting to lock monitor 0x000000001a5913f8 (object 0x00000000da8e4788, a java.lang.Object), which is held by "Thread-3" "Thread-3": waiting to lock monitor 0x000000001a5925d8 (object 0x00000000da8e4798, a java.lang.Object), which is held by "Thread-4" Java stack information for the threads listed above: =================================================== "Thread-4": at com.zr.monitor_tuning.chapter2.CpuController.lambda$1(CpuController.java:120) - waiting to lock <0x00000000da8e4788> (a java.lang.Object) - locked <0x00000000da8e4798> (a java.lang.Object) at com.zr.monitor_tuning.chapter2.CpuController$$Lambda$444/1678468958.run(Unknown Source) at java.lang.Thread.run(Thread.java:748) "Thread-3": at com.zr.monitor_tuning.chapter2.CpuController.lambda$0(CpuController.java:106) - waiting to lock <0x00000000da8e4798> (a java.lang.Object) - locked <0x00000000da8e4788> (a java.lang.Object) at com.zr.monitor_tuning.chapter2.CpuController$$Lambda$443/582497331.run(Unknown Source) at java.lang.Thread.run(Thread.java:748) Found 1 deadlock. * 由此可知jstack对于发现死锁发挥着很好的效果与作用 * @return */
    	@RequestMapping("/deadLock")
    	public String deadLock() { 
    		Object object1=new Object();
    		Object object2=new Object();
    		new Thread(()->{ 
    			synchronized (object1) { 
    				try { 
    					Thread.sleep(1000);
    				} catch (InterruptedException e) { 
    					// TODO Auto-generated catch block
    					e.printStackTrace();
    				}
    				synchronized (object2) { 
    					System.out.println("object1 finish");
    				}
    			}
    		}).start();
    		
    		new Thread(()->{ 
    			synchronized (object2) { 
    				try { 
    					Thread.sleep(1000);
    				} catch (InterruptedException e) { 
    					// TODO Auto-generated catch block
    					e.printStackTrace();
    				}
    				synchronized (object1) { 
    					System.out.println("object2 finish");
    				}
    			}
    		}).start();
    		return "deadLock";
    	}
    	
    	
    }