Java Thread run some day then death ,use jstack check it,it run again, is

Question

hi all;
I write a java program run as linux daemon,
command line is >nohup java myclass &>/dev/null
it run some day ,then death, ,look like death lock ,but thread not exit
if i use jstack checke it ,it run again!
my env is
Linux version 2.4.20 ,redhat linux
jstack 14616
Attaching to process ID 14616, please wait...
Debugger attached successfully.
Client compiler detected.
JVM version is 1.5.0_02-b09
my program like
commandline nohuo java StartUp >/dev/null &
public Class StartUp{
public static void main(String[] argv){
   Connection con = getDBConnection
     Thread t1 = new Thread(new MyRun(con));
  t1.start();
     Thread t2 = new Thread(new MyRun(con));
  t2.start();
  for(;;){
  Thread.sleep(100);
public class MyRun implements Runnable{
Connection con;
public MyRun(Connection c){con = c;}
public void run(){
     for(;;){
     object = readData(con);
     process(object);
     log.info("watch info ....");
     Thread.sleep(500);
}

Answer 1

Today i found my program hang, i use kill -SIGQUIT to print thead trace
but i can't find the bug,after send singal ,the thread run again!
another question
how to detect a thread is hang?and use another thread restart it?
thread dump
Full thread dump Java HotSpot(TM) Client VM (1.5.0_02-b09 mixed mode, sharing):
"pool-1-thread-2" prio=1 tid=0x08447858 nid=0x5aa6 waiting on condition [0x4680f000..0x4681021c]
at sun.misc.Unsafe.park(Native Method)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:118)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1772)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:359)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:470)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:674)
at java.lang.Thread.run(Thread.java:595)
"pool-1-thread-1" prio=1 tid=0x08392740 nid=0x5aa5 waiting on condition [0x4678f000..0x4678ff1c]
at sun.misc.Unsafe.park(Native Method)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:118)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1772)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:359)
at com.ejet.mms.MmsSend.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
at java.lang.Thread.run(Thread.java:595)
"Low Memory Detector" daemon prio=1 tid=0x080a18b0 nid=0x5a9f runnable [0x00000000..0x00000000]
"CompilerThread0" daemon prio=1 tid=0x080a0360 nid=0x5a9e waiting on condition [0x00000000..0x417e2c04]
"Signal Dispatcher" daemon prio=1 tid=0x0809f478 nid=0x5a9d waiting on condition [0x00000000..0x00000000]
"Finalizer" daemon prio=1 tid=0x080989e8 nid=0x5a9c in Object.wait() [0x413e4000..0x413e441c]
at java.lang.Object.wait(Native Method)
- waiting on <0x66c18420> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:116)
- locked <0x66c18420> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:132)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)
"Reference Handler" daemon prio=1 tid=0x08097cf8 nid=0x5a9b in Object.wait() [0x41364000..0x4136451c]
at java.lang.Object.wait(Native Method)
- waiting on <0x66c184a0> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:474)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116)
- locked <0x66c184a0> (a java.lang.ref.Reference$Lock)
"main" prio=1 tid=0x0805ae68 nid=0x5a98 waiting on condition [0xbfffc000..0xbfffc4f8]
at java.lang.Thread.sleep(Native Method)
at com.ejet.mms.MmsStartup.main(Unknown Source)
"VM Thread" prio=1 tid=0x08095218 nid=0x5a9a runnable
"VM Periodic Task Thread" prio=1 tid=0x080a2d40 nid=0x5aa0 waiting on condition