检查死锁与Locked ownable synchronizers(转载)

2018/07/13 01:09
阅读数 948

通过jstack可快速检查线程的死锁信息,用法如下:

# 获取JVM ID(JAVA 进程ID),通过参数lv可以获取更详细的JAVA方法调用信息
jps -lv
# 得到JVM ID后,执行jstack命令,这里假定为123
# 将结果重定向到文件,更便于查看
jstack -l 123 >> d:/123.txt
  • 1
  • 2
  • 3
  • 4
  • 5

翻到页底,可发现明显的死锁信息:

Java stack information for the threads listed above:
===================================================
"Thread-1":
    at com.mirana.concurrent.LockedOwnThread.run(LockedOwnThread.java:47) - waiting to lock <0x000000076c5806f8> (a java.lang.Class for java.lang.Object) - locked <0x000000076c636568> (a java.lang.Class for com.mirana.concurrent.LockedOwnThread) - locked <0x000000076c6392f0> (a com.mirana.concurrent.LockedOwnThread) "Thread-0": at com.mirana.concurrent.LockedOwnThread$AThread.run(LockedOwnThread.java:27) - waiting to lock <0x000000076c636568> (a java.lang.Class for com.mirana.concurrent.LockedOwnThread) - locked <0x000000076c5806f8> (a java.lang.Class for java.lang.Object) Found 1 deadlock.
  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13

从输出信息中,可明显发觉两个线程彼此锁定了对方需要的锁(0x000000076c636568与0x000000076c5806f8)。

在打印的堆栈信息中,我们还发现了如下信息:

"Thread-0" #11 prio=5 os_prio=0 tid=0x000000001e902000 nid=0x5b34c waiting for monitor entry [0x000000001f5bf000]
   java.lang.Thread.State: BLOCKED (on object monitor) at com.mirana.concurrent.LockedOwnThread$AThread.run(LockedOwnThread.java:27) - waiting to lock <0x000000076c636538> (a java.lang.Class for com.mirana.concurrent.LockedOwnThread) - locked <0x000000076c5806f8> (a java.lang.Class for java.lang.Object) Locked ownable synchronizers: - None
  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8

Locked ownable synchronizers是个什么东东?按照官方定义

一个可持有的同步器多半是线程独有并且使用了AbstractOwnableSynchronizer(或是其子类)去实现它的同步特性,ReentrantLock与ReentrantReadWriteLock就是JAVA平台提供的两个例子。

我们将程序改为如下形式,依旧为死锁形式:
```java
static class AThread extends Thread { private ReentrantLock lock1; private ReentrantLock lock2; /** * @param lock1 * @param lock2 */ public AThread(ReentrantLock lock1, ReentrantLock lock2) { super(); this.lock1 = lock1; this.lock2 = lock2; } public void run() { try { lock1.lock(); Thread.sleep(3000); // 必须获取两个锁后才执行操作 lock2.lock(); System.out.println("A: I have all Locks!"); } catch (InterruptedException e) { e.printStackTrace(); } finally { lock2.unlock(); lock1.unlock(); } } } static class BThread extends Thread { private ReentrantLock lock1; private ReentrantLock lock2; /** * @param lock1 * @param lock2 */ public BThread(ReentrantLock lock1, ReentrantLock lock2) { super(); this.lock1 = lock1; this.lock2 = lock2; } public void run() { try { lock2.lock(); Thread.sleep(1000); // 必须获取两个锁后才执行操作 lock1.lock(); System.out.println("B: I have all Locks!"); } catch (InterruptedException e) { e.printStackTrace(); } finally { lock1.unlock(); lock2.unlock(); } } } // 测试程序主函数 public static void main(String[] args) throws InterruptedException { final ReentrantLock lock1 = new ReentrantLock(); final ReentrantLock lock2 = new ReentrantLock(); new AThread(lock1, lock2).start(); new BThread(lock1, lock2).start(); } <div class="se-preview-section-delimiter"></div> 
  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14
  • 15
  • 16
  • 17
  • 18
  • 19
  • 20
  • 21
  • 22
  • 23
  • 24
  • 25
  • 26
  • 27
  • 28
  • 29
  • 30
  • 31
  • 32
  • 33
  • 34
  • 35
  • 36
  • 37
  • 38
  • 39
  • 40
  • 41
  • 42
  • 43
  • 44
  • 45
  • 46
  • 47
  • 48
  • 49
  • 50
  • 51
  • 52
  • 53
  • 54
  • 55
  • 56
  • 57
  • 58
  • 59
  • 60
  • 61
  • 62
  • 63
  • 64
  • 65
  • 66
  • 67
  • 68
  • 69
  • 70
  • 71
  • 72
  • 73
  • 74
  • 75
  • 76
  • 77
  • 78
  • 79
  • 80
  • 81
  • 82
  • 83
  • 84
  • 85

最后打印线程的堆栈信息,出现的内容如下:

"Thread-1" #12 prio=5 os_prio=0 tid=0x000000001ef5a000 nid=0x1c2c waiting on condition [0x000000001fcbf000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x000000076c637ca0> (a java.util.concurrent.locks.ReentrantLock$NonfairSync) at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175) at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870) at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199) at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209) at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285) at com.mirana.concurrent.LockedOwnThread$BThread.run(LockedOwnThread.java:70) Locked ownable synchronizers: - <0x000000076c637cd0> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14

发现ReentrantLock与内置锁有如下3点不同: 
1. 等待的对象不同,内置锁是“monitor entry”(监视器进入点),而ReentrantLock是“condition”(条件); 
2. 线程的状态不同,内置锁是“BLOCKED”,而ReentrantLock是“WAITING”; 
3. 锁定的同步器不同,内置锁没有,而ReentrantLock则指向持有的同步器;

结论

通过jstack可快速检查到死锁情况,并能给出冲突的锁与监测对象,另外,内置锁对象与ReentrantLock在运行中表现出截然不同的状态。

 

原文地址:https://blog.csdn.net/yiifaa/article/details/76013837

展开阅读全文
打赏
0
0 收藏
分享
加载中
更多评论
打赏
0 评论
0 收藏
0
分享
返回顶部
顶部