关于jvm:jconsole和jstack定位死锁问题

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

> jps
56993 Jps
56636 Launcher
57066 DeadLock  // 这个就是死锁的过程

应用 jstack -l 57066 来定位死锁

> jstack -l 57066


Found 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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