浅谈 Java 多线程环境下 如何跟踪死锁 （例子）

1）源代码如下：

package ThreadDeadLockTrial;

import java.util.*;   

  

class Thread1 extends Thread {  

        @Override  

        public void run() {  

            System.out.println("thread 1 start");  

            synchronized (ThreadDeadTrial.lock_1) {

            System.out.println("thread 1 locked lock1");  

                try {  

                    Thread.sleep(5000);  

                } catch (InterruptedException e) {  

                    e.printStackTrace();  

                }  

                System.out.println("thread 1 wait for lock2");  

                synchronized (ThreadDeadTrial.lock_2) {  

                System.out.println("thread 1 locked lock2");  

                }  

            }  

        System.out.println("thread 1 end");  

        }  

    }  

  

class Thread2 extends Thread {

        @Override  

        public void run() {  

            System.out.println("thread 2 start");  

            synchronized (ThreadDeadTrial.lock_2) {  

            System.out.println("thread 2 locked lock2");  

                try {  

                    Thread.sleep(5000);  

                } catch (InterruptedException e) {  

                    e.printStackTrace();  

                }  

                System.out.println("thread 2 wait for lock1");  

                synchronized (ThreadDeadTrial.lock_1) {  

                System.out.println("thread 2 locked lock1");  

                }  

            }  

         System.out.println("thread 2 end");   

        }  

   }  

 

 

public class ThreadDeadTrial {

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

    
public static void main(String[] args) {
// TODO Auto-generated method stub
Thread1 thread1 = new Thread1();  

        Thread2 thread2 = new Thread2(); 

        thread1.start();

        thread2.start();

        System.out.println("Main thread exit");

        
}

}

当运行这个程序时，program就会死循环，等在这里了。

如何check ? (jps and jstack 都事jdk自己带的）

1)  jps

10340 ThreadDeadTrial

7124

7668 Jps

2)  jstack 10340  > .\deaddump.data

 

3) open deaddump.data，就能看到下面的信息了，注意红字和蓝色字。够明显的了吧

2016-01-19 16:48:28

Full thread dump Java HotSpot(TM) Client VM (25.40-b25 mixed mode, sharing):

"DestroyJavaVM" #10 prio=5 os_prio=0 tid=0x0239c400 nid=0x25d4 waiting on condition [0x00000000]

   java.lang.Thread.State: RUNNABLE

"Thread-1" #9 prio=5 os_prio=0 tid=0x01e8f800 nid=0x3dc waiting for monitor entry [0x05fbf000]

   java.lang.Thread.State: BLOCKED (on object monitor)
at ThreadDeadLockTrial.Thread2.run(ThreadDeadTrial.java:37)
- waiting to lock <0x102b85c8> (a [I)
- locked <0x102b85d8> (a [I)

"Thread-0" #8 prio=5 os_prio=0 tid=0x01e8d400 nid=0x1f3c waiting for monitor entry [0x0514f000]

   java.lang.Thread.State: BLOCKED (on object monitor)
at ThreadDeadLockTrial.Thread1.run(ThreadDeadTrial.java:17)
- waiting to lock <0x102b85d8> (a [I)
- locked <0x102b85c8> (a [I)

"Service Thread" #7 daemon prio=9 os_prio=0 tid=0x01e57000 nid=0x2250 runnable [0x00000000]

   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread0" #6 daemon prio=9 os_prio=2 tid=0x01e4fc00 nid=0x17c4 waiting on condition [0x00000000]

   java.lang.Thread.State: RUNNABLE

"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x01e4ec00 nid=0x2ac0 waiting on condition [0x00000000]

   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x01e3c400 nid=0x20c8 runnable [0x00000000]

   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x01dd3400 nid=0x248c in Object.wait() [0x0570f000]

   java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x10206dd0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
- locked <0x10206dd0> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)

"Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x01dd1800 nid=0x2a9c in Object.wait() [0x04fcf000]

   java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x102068c8> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:502)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:157)
- locked <0x102068c8> (a java.lang.ref.Reference$Lock)

"VM Thread" os_prio=2 tid=0x01dd0400 nid=0x2a34 runnable 

"VM Periodic Task Thread" os_prio=2 tid=0x01e58400 nid=0x2898 waiting on condition 

JNI global references: 6

Found one Java-level deadlock:

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

"Thread-1":

  waiting to lock monitor 0x01dd5d14 (object 0x102b85c8, a [I),

  which is held by "Thread-0"

"Thread-0":

  waiting to lock monitor 0x01dd8244 (object 0x102b85d8, a [I),

  which is held by "Thread-1"

Java stack information for the threads listed above:

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

"Thread-1":
at ThreadDeadLockTrial.Thread2.run(ThreadDeadTrial.java:37)
- waiting to lock <0x102b85c8> (a [I)
- locked <0x102b85d8> (a [I)

"Thread-0":
at ThreadDeadLockTrial.Thread1.run(ThreadDeadTrial.java:17)
- waiting to lock <0x102b85d8> (a [I)
- locked <0x102b85c8> (a [I)

Found 1 deadlock.