dump线程让死锁无处可逃

昨天看到有人问：”一个程序在运行的时候，如何知道它是否发生死锁，如果发生死锁，如何找到发生死锁的位置？“；便贴了一段dump线程的数据，今天又有人问我怎么从dump文件中分析死锁，随做此文：

1、首先构造死锁，代码如下：

 

 

public class Deadlocker {

    private static Object lock_1 = new int[1];
    private static Object lock_2 = new int[1];

    public class Thread1 extends Thread {

        @Override
        public void run() {
            System.out.println("thread 1 start");
            synchronized (lock_1) {
                try {
                    Thread.sleep(5000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("thread 1 get lock 1 need lock 2");
                synchronized (lock_2) {
                }
            }
            System.out.println("thread 1 end");
        }
    }

    public class Thread2 extends Thread {

        @Override
        public void run() {
            System.out.println("thread 2 start");
            synchronized (lock_2) {
                try {
                    Thread.sleep(5000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("thread 2 get lock 2 need lock 1");
                synchronized (lock_1) {
                }
            }
            System.out.println("thread 2 end");
        }
    }

    public static void main(String[] args) {
        Thread1 thread1 = new Deadlocker().new Thread1();
        Thread2 thread2 = new Deadlocker().new Thread2();
        thread1.start();
        thread2.start();
    }
}

 

 

2、运行结果如下：

 

 

thread 1 start

thread 2 start

thread 1 get lock 1 need lock 2

thread 2 get lock 2 need lock 1

 

 

3、分析：

从打印的结果很容易分析线程1 和线程2 处于死锁。相互需要对方的持有的锁；

 

4、使用：jps 查看线程id，再使用：jstack 线程id  > dumpthread 命令。部分结果如下（去除各种gc线程。。。）：

 

第一部分：

 

 

"Thread-1" prio=10 tid=0x0000000040a49800 nid=0x2d1e waiting for monitor entry [0x00007f50eda98000]

   java.lang.Thread.State: BLOCKED (on object monitor)

at Deadlocker$Thread2.run(Deadlocker.java:47)

- waiting to lock <0x00000007d6f97ec8> (a [I)

- locked <0x00000007d6f97ee0> (a [I)

 

"Thread-0" prio=10 tid=0x0000000040a47800 nid=0x2d1d waiting for monitor entry [0x00007f50edb99000]

   java.lang.Thread.State: BLOCKED (on object monitor)

at Deadlocker$Thread1.run(Deadlocker.java:28)

- waiting to lock <0x00000007d6f97ee0> (a [I)

- locked <0x00000007d6f97ec8> (a [I)

 

。。。。。各种其他线程

 

这里可以看出两个线程处于BLOCKED  状态，各自在等待各自的锁（ 0x00000007d6f97ec8 和0x00000007d6f97ee0 ）

 

第二部分：

 

 

Found one Java-level deadlock:

=============================

"Thread-1":

  waiting to lock monitor 0x0000000040a33dd8 (object 0x00000007d6f97ec8, a [I),

  which is held by "Thread-0"

"Thread-0":

  waiting to lock monitor 0x0000000040a365e0 (object 0x00000007d6f97ee0, a [I),

  which is held by "Thread-1"

 

这个一看就更明白了。。说发现一个java死锁，Thread-1在等待一个lock，而这个锁被Thread-0 持有，

而 Thread-0在等待另外一个lock，而这个锁被Thread-1 持有

 

Java stack information for the threads listed above:

===================================================

"Thread-1":

at Deadlocker$Thread2.run(Deadlocker.java:47)

- waiting to lock <0x00000007d6f97ec8> (a [I)

- locked <0x00000007d6f97ee0> (a [I)

"Thread-0":

at Deadlocker$Thread1.run(Deadlocker.java:28)

- waiting to lock <0x00000007d6f97ee0> (a [I)

- locked <0x00000007d6f97ec8> (a [I)

 

Found 1 deadlock.

 

上面的红色部分便也可以清楚查询到死锁的位置了；

 

当然据说第二部分只有java5 以上版本才有的（未验证）。 dump数据见附件

 

 

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评论

1 楼 chenzhou123520 2012-10-13  

楼主分析很细致，感谢分享