什么是死锁

死锁问题是多线程特有的问题，它能够被认为是线程间切换耗费零碎性能的一种极其状况。 在死锁时，线程间互相期待资源，而又不开释本身的资源，导致无穷无尽的期待，其后果是零碎工作永远无奈执行实现。 死锁问题是在多线程开发中应该坚定防止和杜绝的问题.

死锁示例代码

package com.rumenz.learn.deadLock;public class RumenzThread implements Runnable{    int a,b;    public RumenzThread(int a, int b) {        this.a = a;        this.b = b;    }    @Override    public void run() {       //Integer.valueOf(a) 包装成对象        synchronized (Integer.valueOf(a)){            try{                //睡眠3秒,减少死锁的几率                Thread.sleep(3000);            }catch (Exception e){                e.printStackTrace();            }            synchronized (Integer.valueOf(b)){                System.out.println("a+b="+(a+b));            }        }    }}package com.rumenz.learn.deadLock;public class DeadLock {    public static void main(String[] args) {        new Thread(new RumenzThread(1, 2)).start();        new Thread(new RumenzThread(2, 1)).start();    }}

运行程序应用jstack -l pid来定位死锁

先找到死锁程序的过程id

> jps56993 Jps56636 Launcher57066 DeadLock  //这个就是死锁的过程

应用jstack -l 57066来定位死锁

> jstack -l 57066Found one Java-level deadlock:============================="Thread-1":  waiting to lock monitor 0x00007fbe6d80de18 (object 0x000000076ab33988, a java.lang.Integer),  which is held by "Thread-0""Thread-0":  waiting to lock monitor 0x00007fbe6d8106a8 (object 0x000000076ab33998, a java.lang.Integer),  which is held by "Thread-1"Java stack information for the threads listed above:==================================================="Thread-1":    at com.rumenz.learn.deadLock.RumenzThread.run(RumenzThread.java:27)    - waiting to lock <0x000000076ab33988> (a java.lang.Integer)    - locked <0x000000076ab33998> (a java.lang.Integer)    at java.lang.Thread.run(Thread.java:748)"Thread-0":    at com.rumenz.learn.deadLock.RumenzThread.run(RumenzThread.java:27)    - waiting to lock <0x000000076ab33998> (a java.lang.Integer)    - locked <0x000000076ab33988> (a java.lang.Integer)    at java.lang.Thread.run(Thread.java:748)Found 1 deadlock. //发现一个死锁
RumenzThread.java:27 定位到大略的代码文件地位。

jconsole定位死锁问题

  • 找到死锁过程

  • 链接,不平安的链接

  • 抉择线程

  • 点击检测死锁

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