刚才用jstack解决了一个进程死锁的问题——其实早就解决了，也知道原因，只是一直没找到死锁的位置，不太甘心而已。
流程大致如下：
(0)环境要求，JDK1.6及以上
(1)先找到进程的PID，Windows下，打开进程管理器，按照名字排序，可以找到叫做javaw.exe的进程(java虚拟机进程一律叫做javaw.exe)，要找出哪个是你的进程，记住当前进程列表，然后重启你的进程，PID刷新过的那个即是你的进程。
(2)在CMD下运行：jstack pid，jstack会在console上打出一系列信息
(3)分析上述信息
实例：
我这个问题的的jstack信息如下：
C:\Documents and Settings\user>jstack 6652
2012-06-07 21:32:02
Full thread dump Java HotSpot(TM) Client VM (16.3-b01 mixed mode, sharing):
"Thread-1" daemon prio=6 tid=0x03010c00 nid=0xcdc waiting for monitor entry [0x0
339f000]
java.lang.Thread.State: BLOCKED (on object monitor)
at org.apache.commons.net.telnet.TelnetInputStream.__read(TelnetInputStr
eam.java:122)
- waiting to lock <0x22942280> (a org.apache.commons.net.ftp.FTPClient)
at org.apache.commons.net.telnet.TelnetInputStream.run(TelnetInputStream
.java:535)
at java.lang.Thread.run(Thread.java:619)
"Framework Event Dispatcher" daemon prio=6 tid=0x03010400 nid=0x998 in Object.wa
it() [0x0334f000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x228fa800> (a org.eclipse.osgi.framework.eventmgr.EventMa
nager$EventThread)
at java.lang.Object.wait(Object.java:485)
at org.eclipse.osgi.framework.eventmgr.EventManager$EventThread.getNextE
vent(EventManager.java:400)
- locked <0x228fa800> (a org.eclipse.osgi.framework.eventmgr.EventManage
r$EventThread)
at org.eclipse.osgi.framework.eventmgr.EventManager$EventThread.run(Even
tManager.java:336)
"Start Level Event Dispatcher" daemon prio=6 tid=0x02fcf400 nid=0x2638 in Object
.wait() [0x032de000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x2295db48> (a [I)
at java.lang.Object.wait(Object.java:485)
at org.apache.commons.net.telnet.TelnetInputStream.read(TelnetInputStrea
m.java:339)
- locked <0x2295db48> (a [I)
at org.apache.commons.net.telnet.TelnetInputStream.read(TelnetInputStrea
m.java:466)
at java.io.BufferedInputStream.read1(BufferedInputStream.java:256)
at java.io.BufferedInputStream.read(BufferedInputStream.java:317)
- locked <0x2295fe18> (a java.io.BufferedInputStream)
at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:264)
at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:306)
at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:158)
- locked <0x22961f88> (a java.io.InputStreamReader)
at java.io.InputStreamReader.read(InputStreamReader.java:167)
at java.io.BufferedReader.fill(BufferedReader.java:136)
at java.io.BufferedReader.readLine(BufferedReader.java:299)
- locked <0x22961f88> (a java.io.InputStreamReader)
at java.io.BufferedReader.readLine(BufferedReader.java:362)
at org.apache.commons.net.ftp.FTP.__getReply(FTP.java:264)
at org.apache.commons.net.ftp.FTP._connectAction_(FTP.java:335)
at org.apache.commons.net.ftp.FTPClient._connectAction_(FTPClient.java:5
50)
at org.apache.commons.net.SocketClient.connect(SocketClient.java:163)
at com.mycompany.dc.ftp.client.FTPClientImpl.connect(FTPClientImpl.java:7
5)
- locked <0x22942280> (a org.apache.commons.net.ftp.FTPClient)
at com.mycompany.dc.ftp.client.FTPClientFactoryImpl.getClient(FTPClientFa
ctoryImpl.java:35)
- locked <0x228f9310> (a java.lang.Object)
at ftpclienttest.Activator.start(Activator.java:43)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl$1.run(Bund
leContextImpl.java:711)
at java.security.AccessController.doPrivileged(Native Method)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl.startActiv
ator(BundleContextImpl.java:702)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl.start(Bund
leContextImpl.java:683)
at org.eclipse.osgi.framework.internal.core.BundleHost.startWorker(Bundl
eHost.java:381)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.resume(Abstra
ctBundle.java:389)
at org.eclipse.osgi.framework.internal.core.Framework.resumeBundle(Frame
work.java:1131)
at org.eclipse.osgi.framework.internal.core.StartLevelManager.resumeBund
les(StartLevelManager.java:559)
at org.eclipse.osgi.framework.internal.core.StartLevelManager.resumeBund
les(StartLevelManager.java:544)
at org.eclipse.osgi.framework.internal.core.StartLevelManager.incFWSL(St
artLevelManager.java:457)
at org.eclipse.osgi.framework.internal.core.StartLevelManager.doSetStart
Level(StartLevelManager.java:243)
- locked <0x27e68d70> (a java.lang.Object)
at org.eclipse.osgi.framework.internal.core.StartLevelManager.dispatchEv
ent(StartLevelManager.java:438)
at org.eclipse.osgi.framework.internal.core.StartLevelManager.dispatchEv
ent(StartLevelManager.java:1)
at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventM
anager.java:230)
at org.eclipse.osgi.framework.eventmgr.EventManager$EventThread.run(Even
tManager.java:340)
"Framework Active Thread" prio=6 tid=0x02ff1800 nid=0x1fbc in Object.wait() [0x0
328f000]
java.lang.Thread.State: TIMED_WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x27e65770> (a org.eclipse.osgi.framework.internal.core.Fr
amework)
at org.eclipse.osgi.framework.internal.core.Framework.run(Framework.java
:1817)
- locked <0x27e65770> (a org.eclipse.osgi.framework.internal.core.Framew
ork)
at java.lang.Thread.run(Thread.java:619)
"OSGi Console" prio=6 tid=0x03005400 nid=0x225c waiting on condition [0x0323f000
]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at org.eclipse.osgi.framework.internal.core.FrameworkConsole.runConsole(
FrameworkConsole.java:125)
at org.eclipse.osgi.framework.internal.core.FrameworkConsole.run(Framewo
rkConsole.java:104)
at java.lang.Thread.run(Thread.java:619)
"Low Memory Detector" daemon prio=6 tid=0x02c09800 nid=0x1d68 runnable [0x000000
00]
java.lang.Thread.State: RUNNABLE
"CompilerThread0" daemon prio=10 tid=0x02c03000 nid=0x24c4 waiting on condition
[0x00000000]
java.lang.Thread.State: RUNNABLE
"Attach Listener" daemon prio=10 tid=0x02c01800 nid=0x1138 waiting on condition
[0x00000000]
java.lang.Thread.State: RUNNABLE
"Signal Dispatcher" daemon prio=10 tid=0x02c20c00 nid=0x18ac runnable [0x0000000
0]
java.lang.Thread.State: RUNNABLE
"Finalizer" daemon prio=8 tid=0x02bc0400 nid=0x11ac in Object.wait() [0x02d8f000
]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x27d5e5c8> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:118)
- locked <0x27d5e5c8> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:134)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)
"Reference Handler" daemon prio=10 tid=0x02bbb800 nid=0x9cc in Object.wait() [0x
02d3f000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x27d5e650> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:485)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116)
- locked <0x27d5e650> (a java.lang.ref.Reference$Lock)
"main" prio=6 tid=0x008a6c00 nid=0x22ec in Object.wait() [0x0098f000]
java.lang.Thread.State: TIMED_WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x22c303c8> (a org.eclipse.core.runtime.internal.adaptor.S
emaphore)
at org.eclipse.core.runtime.internal.adaptor.Semaphore.acquire(Semaphore
.java:55)
- locked <0x22c303c8> (a org.eclipse.core.runtime.internal.adaptor.Semap
hore)
at org.eclipse.core.runtime.adaptor.EclipseStarter.updateSplash(EclipseS
tarter.java:1251)
at org.eclipse.core.runtime.adaptor.EclipseStarter.setStartLevel(Eclipse
Starter.java:1213)
at org.eclipse.core.runtime.adaptor.EclipseStarter.startup(EclipseStarte
r.java:288)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.ja
va:175)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:622)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:577)
at org.eclipse.equinox.launcher.Main.run(Main.java:1410)
at org.eclipse.equinox.launcher.Main.main(Main.java:1386)
"VM Thread" prio=10 tid=0x02bba000 nid=0xdb4 runnable
"VM Periodic Task Thread" prio=10 tid=0x02c0e400 nid=0x24ac waiting on condition
JNI global references: 677
分析：
根据提示，有两个线程都用到了ftpClient这个对象作为锁，而且前一个得到锁的要等待后一个需要这个锁的返回结果，造成死锁。这两处分别为：
(1) at org.apache.commons.net.telnet.TelnetInputStream.__read(TelnetInputStr
eam.java:122)
(2) - locked <0x22942280> (a org.apache.commons.net.ftp.FTPClient)
at com.sagemcom.dc.ftp.client.FTPClientFactoryImpl.getClient(FTPClientFa
ctoryImpl.java:35)
- locked <0x228f9310> (a java.lang.Object)
前者是系统自己用的锁，后者是我代码里面加的。自己代码里面换一个对象做锁就解决了。
总结
jstack在解决问题上还是比较有帮助的，信息简洁有效，其实有很多图形化的分析工具是基于它的。但jstack需要jdk1.6以上的版本才支持。
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