Java死锁范例以及如何分析死锁-Java开发Java经验技巧

1、java死锁范例以及如何分析死锁-编程 开发技术java死锁范例以及如何分析死锁木文由importnew范琦琦翻译自journaldevo欢迎加入翻译小组。转载请见文末要求。死锁是两个甚至多个线程被永久阻塞时的一种运行局面，这种局面的生成伴随着 至少两个线程和两个或者多个资源。在这里我已写好一个简单的程序，它将会引 起死锁方案然后我们就会明白如何分析它。java死锁范例threaddeadlock. javapackage com. journaldcv. threads;public class threaddeadlock public static void main(string ar

2、gs) throws tnterruptedexceptionobject objlobject obj2object obj3new object (); new object (); new object ();thread tl二newthread(newsyncthrcad(objl,obj2),tl);thread t2=newthread(newsyncthread (obj2,obj3),"t2");thread t3=newthread (newsyncthread (obj3,objl),"t3");tl. st art (); thr

3、ead, sleep(5000);t2. start ();thread, sleep(5000); t3. start ();class syncthread implernents runnable private object objl;private object obj2;public syncthread(object ol, object o2) this. objl=ol;this obj2=o2;©overridepublic void nan() st ring name = thread. currentthread (). getnameo ;system.o

4、ut. println(nanie + acquiring lock on +objl); synchronized (objl) system. out. println(name + " acquired lock on +objl); work ();system, out. println(name + acquiring lock on +obj2); synchronized (obj2) system, out. printin(name + acquired lock on +obj2); work ();system, out. println(namc + &qu

5、ot; released lock on +obj2);system.out. println(nanie + released lock on +objl); system, out. pr in tin (name + finished execution. /z); private void work() try thread, sleep(30000); catch 仃nterruptedexcept ion e) e. printstacktrace ();在上面的程序中同步线程正完成runnable的接口，它工作的是两个对象，这两 个对象向对方寻求死锁而且都在使用同步阻塞。在主函数

6、中，我使用了三个为同步线程运行的线程，而且在其中每个线程中都有 一个可共享的资源。这些线程以向笫一个对彖获取封锁这种方式运行。但是当它试着像第二个对彖获 取封锁吋，它就会进入等待状态，因为它已经被另一个线程封锁住了。这样，在 线程引起死锁的过程中，就形成了一个依赖于资源的循环。当我执行上而的程序时，就产生了输出，但是程序却因为死锁无法停止。tl acquiring lock on java.lang.0bject6d9dd520tl acquired lock on java.lang. 0bject6d9dd520t2 acquiring lock on java. lang. 0bject

7、22aed3a5t2 acquired lock on java, lang. object223ed3a5t3 acquiring lock on java.lang.0bject218c2661t3 acquired lock on java. lang. 0bject218c266111 acquiring lock on java.lang. 0bject22aed3a5t2 acquiring lock on java, lang. object218c2661t3 acquiring lock on java. lang. object6d9dd520在此我们可以清楚地在输岀结果屮

8、辨认岀死锁局面，但是在我们实际生活所用的 应用中，发现死锁并将它排除是非常难的。分析死锁为了分析一个死锁，我们需要关注下应用中的java线程转存，在上一节中我已 经解释了如何使用visualvm收集资料或者jstack应用程序产生线程转存。以下就是上述程序的线程转存。2012-12-27 19:08:34full thread dump java hotspot (tm) 64bit server vm (23. 5b02 mixed mode):"attach listener'7 dacmon prio=5 tid=0x00007fb0a2814000 nid=0x400

9、7 waiting on condition 0x0000000000000000java. lang. thread. state: runnable"destroyjaveivm" prio=5 tid=0x00007fb0a2801000 nid二0x1703 waiting on condition 0x0000000000000000java.lang.thread. state: runnablet3 prio=5 tid=0x00007fb0a204b000 nid=0x4d07 waiting for monitor entry 0x000000015d97

10、1000java.lang. thread .state: blocked (on object monitor)at com. journaldev. threads syncthread run(threaddeadlock java:41)-waiting to lock <0x000000013df2f658> (a java.lang.object)- locked <0x000000013df2f678> (a java. lang. object)at java. lang. thread, run (thread. java:722)t2 prio=5

11、tid=0x00007fb0a 1073000 nid=0x4207 waiting for monitor entry 0x000000015d209000java.lang. thread. state: blocked (on object monitor)at com. journal dev. threads. syncthread. run(threaddeadlock. java:41)- waiting to lock <0x000000013df2f678> (a java. lang. object)- locked <0x000000013df2f668

12、> (a java. lang. object)at java. lang. thread, run (thread.java:722)tl prio=5 tid=0x00007fb0a 1072000 nid=0x5503 waiting for monitor entry 0x000000015d86e000java.lang. thread. state: blocked (on object monitor)at com. journal dev. threads. syncthread. run(threaddeadlock. java:41)- waiting to lock

13、 <0x000000013df2f668> (a java. lang. object)- locked <0x000000013df2f658> (a java. lang. object) at java. lang. thread, run (thread.java:722)"service thread" daemon prio=5 tid=0x00007fboa1038000 nid二0x5303 runnable 0x0000000000000000java.lang. thread. state: runnable"c2 co

14、mpi 1 erthread 1daemon prio=5 tid=0x00007fb0al037000 nid=0x5203 waiting on condition 0x0000000000000000java. lang. thread. state: runnable"c2 compi 1 erthread0，z daemon prio=5 tid=0x00007fb0a 1016000 nid=0x5103 waiting on condition 0x0000000000000000java. lang. thread. state: runnable"sign

15、al dispatcher'7 dacmon prio=5 tid=0x00007fb0a4003000 nid=0x5003 runnable 0x0000000000000000java. lang. thread. state: runnable"finalizer" daemon prio=5 tid=0x00007fb0a4800000 nid=0x3f03 in object, wait () 0x000000015d0c0000java.1ang.thread.state: waiting (on object monitor)at java. lan

16、g. object, wait(native method)- waiting on <0x000000013de75798> (a java. lang. ref. referencequeue$lock)at java lerng. ref.refercnccqueuc. remove(refercnccqueuc. java:135) -locked <0x000000013de75798> (a java. lang. ref. referencequeue$lock) at java. lang. ref. referencequeue. remove(ref

17、erencequeue.java:151) atjava. lang. ref. finalizer$finalizerthread. run(finalizer. java:177)"reference handler" daemon prio=5 tid=0x00007fb0a4002000 nid=0x3e03 in object, wait() 0x000000015cfbd000java, lang. thread.state: waiting (on object monitor)at java. lang. object, wai t (native meth

18、od)-waiting on <0x000000013dc75320> (a java. lang. ref. rcfcrcncc$lock) at java lang.0bject.wait(object java:503)atjava.lang.ref. reference$referencehandler. run(referenee. java:133)- locked <0x000000013de75320> (a java. lang. ref. reference$lock)vm thread" prio=5 tid=0x00007fb0a204

19、9800 nid二0x3d03 runnable"gc task thrcadso (parallclgc)z，prio=5 tid=0x00007fb0a300d800 nid=0x3503 runnablegc task thread# 1 (parallelgc)prio=5 tid=0x00007fb0a2001800 nid二0x3603runnablegc task thread#2 (parallelgc)z，prio=5 tid=0x00007fb0a2003800 nid二0x3703 runnablegc task thread#3 (parallelgc)

20、9; prio=5 tid=0x00007fb0a2004000 nid二0x3803 runnablegc task thread#4 (parallelgc)z，prio=5 tid=0x00007fb0a2005000 nid二0x3903 runnablegc task thread#5 (paral 1 elgc)' prio=5 tid=0x00007fb0a2005800 nid=0x3a03 nmn ablegc task thread#6 (parallelgc)z，prio=5 tid=0x00007fb0a2006000 nid=0x3b03 runnable&q

21、uot;gc task thrcad#7 (parallclgc)z，prio=5 tid=0x00007fb0a2006800 nid=0x3c03runnablevm periodic task thread" prio=5 tid=0x00007fboa1015000 nid二0x5403waiting on conditionjn1 global references: 114found one java-level deadlock:气3：waiting to lock monitor 0x00007fb0al074b08 (object 0x000000013df2f65

22、8, a java. lang. object),which is held by tltl： waiting to lock monitor 0x00007fb0al010f08 (object 0x000000013df2f668,a java lang. 0bject),which is held by "t2气2:waiting to lock monitor 0x00007fb0al012360 (object 0x000000013df2f678, a java. lang. object),which is held by t3java stack informatio

23、n for the threads listed above:at com. journaldev. threads. syncthread. run(threaddeadlock. java:41)- waiting to lock <0x000000013df2f658> (a java.lang. object)- locked <0x000000013df2f678> (a java.lang. object)at java lang .thread run( thread java:722)tl：at com. journaldev. threads. syn

24、cthread. run(threaddeadlock. java:41)- waiting to lock <0x000000013df2f668> (a java. lang. object)- locked <0x000000013df2f658> (a java. lang. object)at java lang. thread nin(thread java:722)气2：at com. journaldev. threads. syncthread. run(threaddeadlock. java:41)- waiting to lock <0x0

25、00000013df2f678> (a java. lang. object)- locked <0x000000013df2f668> (a java. lang. object) at java lang. thread nin(thread java:722)found 1 deadlock.这三个线程转存的输岀清处地说明了死锁环境和线程，以及包含死锁环境的资 源。为了分析死锁，我们需要关注死锁状态的线程，然后资源再等待去封锁，每一个 资源都冇一个独特的1d,冇了这个1d我们就能发现是哪一个进程已经封锁住对 彖。举个例子，线程 气3”正在等待封锁0x000000013df2f658,但是它己经被线 程气1”封锁住了。当我们分析死锁环境的时候，如果发现线程正在引起死锁，这是我们就要改变代 码來避免死锁的产生。避免死锁有很多方针可供我们使用来避免死锁的局面。避免嵌套封锁：这是死锁最主要的原因的，如果你已经有一个资源了就要避免封锁 另一个资源。如果你运行时只有一个对象封锁，那是儿乎不可能出现