死锁编码及定位分析（故障排查）

深碍√TFBOYSˉ_ 2023-06-29 05:53 35阅读 0赞

什么是死锁？  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczNjA4NA_size_16_color_FFFFFF_t_70]  
在Java中使用多线程，就会有可能导致死锁问题。死锁会让程序一直卡住，不再程序往下执行。我们只能通过中止并重启的方式来让程序重新执行。

#### 造成死锁的原因： ####

*  当前线程拥有其他线程需要的资源
 *  当前线程等待其他线程已拥有的资源
 *  都不放弃自己拥有的资源

class HoldLockThread implements Runnable{ 
        private String lockA;
        private String lockB;
    
        public HoldLockThread(String lockA, String lockB) { 
            this.lockA = lockA;
            this.lockB = lockB;
        }
    
        @Override
        public void run() { 
    
            synchronized (lockA){ 
                System.out.println(Thread.currentThread().getName() + "\t持有："+lockA + "\t尝试获得" + lockB);
                try { 
                    TimeUnit.SECONDS.sleep(2);
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
                synchronized (lockB){ 
                    System.out.println(Thread.currentThread().getName() + "\t持有："+lockB + "\t尝试获得" + lockA);
                }
    
            }
    
        }
    }
    public class DeadLockDemo { 
        public static void main(String[] args) { 
            String lockA = "lockA";
            String lockB = "lockB";
            new Thread(new HoldLockThread(lockA,lockB),"AAA").start();
            new Thread(new HoldLockThread(lockB,lockA),"BBB").start();
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczNjA4NA_size_16_color_FFFFFF_t_70 1]

### 那么怎么判断是死锁，为什么不是死循环 ###

/**
         * linux ps -ef|grep xxxx
         * windows下的java程序   也有类似ps的查看进程的命令，但是目前我们需要查看的只是java
         *            jps = java ps     jps -l
         */

在命令行下输入`jps -l`，查看到当前的JUC.DeadLockDemo进程号10440  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczNjA4NA_size_16_color_FFFFFF_t_70 2]  
然后用jstack 10440来查看  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczNjA4NA_size_16_color_FFFFFF_t_70 3]  
很长就不全部截图了，最后有个**Found 1 deadlock**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzczNjA4NA_size_16_color_FFFFFF_t_70 4]

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