jstack exception

[Li Li]

hi all
    jstack throws NullPointException.
    my jdk version:
 java version "1.6.0_27"
Java(TM) SE Runtime Environment (build 1.6.0_27-b07)
Java HotSpot(TM) 64-Bit Server VM (build 20.2-b06, mixed mode)


   the output of jstack command:

jstack -F 17296
Attaching to process ID 17296, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 20.2-b06
Deadlock Detection:

No deadlocks found.

Thread 17330: (state = BLOCKED)
 - java.lang.Object.wait(long) @bci=0 (Interpreted frame)
 - sun.misc.GC$Daemon.run() @bci=51, line=100 (Interpreted frame)


Thread 17325: (state = BLOCKED)


Thread 17324: (state = BLOCKED)


Thread 17323: (state = BLOCKED)
 - java.lang.Object.wait(long) @bci=0 (Interpreted frame)
 - java.lang.ref.ReferenceQueue.remove(long) @bci=44, line=118
(Interpreted frame)
 - java.lang.ref.ReferenceQueue.remove() @bci=2, line=134 (Interpreted frame)
 - java.lang.ref.Finalizer$FinalizerThread.run() @bci=3, line=159
(Interpreted frame)


Thread 17322: (state = BLOCKED)
 - java.lang.Object.wait(long) @bci=0 (Interpreted frame)
 - java.lang.Object.wait() @bci=2, line=485 (Interpreted frame)
 - java.lang.ref.Reference$ReferenceHandler.run() @bci=46, line=116
(Interpreted frame)


Thread 17296: (state = IN_JAVA)
Error occurred during stack walking:
java.lang.NullPointerException
	at sun.jvm.hotspot.tools.StackTrace.run(StackTrace.java:78)
	at sun.jvm.hotspot.tools.StackTrace.run(StackTrace.java:45)
	at sun.jvm.hotspot.tools.JStack.run(JStack.java:60)
	at sun.jvm.hotspot.tools.Tool.start(Tool.java:221)
	at sun.jvm.hotspot.tools.JStack.main(JStack.java:86)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at sun.tools.jstack.JStack.runJStackTool(JStack.java:118)
	at sun.tools.jstack.JStack.main(JStack.java:84)