My program will not stop after run() method in main thread finishes

I am using Java. The main thread sends data, while a worker thread listens to responses. I also have Timer in case timeout occurs. In main(), I am calling run(), which can finish, according to the output. Here is what it looks like:

class Send {
    Worker w;

    run() {
        // w was initialized in constructor
        w.start();
        ....
        w.join();
    }

    main(args) {
        Send s = new Send();
        s.run();
    }
    private class Worker extend Thread {
        public void run() {
            ....
        }
    }
} 

In s.run(), every time I need to cancel the Timer or restart the Timer, I would do

timer.cancel();
timer.purge();
timer = new Timer();
timer.schdule(...);

The TimerTask is simply calling a static method in Send to handle the timeout. So what did I do wrong to cause my program hanging after the main thread finishes? Thank you.

EDIT: the out put of kill -3 process-id:

Full thread dump OpenJDK 64-Bit Server VM (19.0-b09 mixed mode):

"DestroyJavaVM" prio=10 tid=0x00007f9f20035000 nid=0x73f1 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Timer-10" prio=10 tid=0x0000000001a7d800 nid=0x740f in Object.wait() [0x00007f9f1e39c000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x000000075833fe78> (a java.util.TaskQueue)
    at java.lang.Object.wait(Object.java:502)
    at java.util.TimerThread.mainLoop(Timer.java:505)
    - locked <0x000000075833fe78> (a java.util.TaskQueue)
    at java.util.TimerThread.run(Timer.java:484)

"Low Memory Detector" daemon prio=10 tid=0x00007f9f20004800 nid=0x7402 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"CompilerThread1" daemon prio=10 tid=0x0000000001a70000 nid=0x7401 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"CompilerThread0" daemon prio=10 tid=0x00007f9f20001000 nid=0x7400 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" daemon prio=10 tid=0x0000000001a6e800 nid=0x73ff waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" daemon prio=10 tid=0x0000000001a49000 nid=0x73fe in Object.wait() [0x00007f9f1f3f2000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x00000007580b1310> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:133)
    - locked <0x00000007580b1310> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:149)
    at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:177)

"Reference Handler" daemon prio=10 tid=0x0000000001a47000 nid=0x73fd in Object.wait() [0x00007f9f1f4f3000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x00000007580b11e8> (a java.lang.ref.Reference$Lock)
    at java.lang.Object.wait(Object.java:502)
    at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:133)
    - locked <0x00000007580b11e8> (a java.lang.ref.Reference$Lock)

"VM Thread" prio=10 tid=0x0000000001a40000 nid=0x73fc runnable 

"GC task thread#0 (ParallelGC)" prio=10 tid=0x00000000019d7000 nid=0x73f2 runnable 

"GC task thread#1 (ParallelGC)" prio=10 tid=0x00000000019d9000 nid=0x73f3 runnable 

"GC task thread#2 (ParallelGC)" prio=10 tid=0x00000000019da800 nid=0x73f4 runnable 

"GC task thread#3 (ParallelGC)" prio=10 tid=0x00000000019dc800 nid=0x73f5 runnable 

"GC task thread#4 (ParallelGC)" prio=10 tid=0x00000000019de800 nid=0x73f6 runnable 

"GC task thread#5 (ParallelGC)" prio=10 tid=0x00000000019e0000 nid=0x73f7 runnable 

"GC task thread#6 (ParallelGC)" prio=10 tid=0x00000000019e2000 nid=0x73f8 runnable 

"GC task thread#7 (ParallelGC)" prio=10 tid=0x00000000019e4000 nid=0x73f9 runnable 

"GC task thread#8 (ParallelGC)" prio=10 tid=0x00000000019e5800 nid=0x73fa runnable 

"GC task thread#9 (ParallelGC)" prio=10 tid=0x00000000019e7800 nid=0x73fb runnable 

"VM Periodic Task Thread" prio=10 tid=0x00007f9f20007800 nid=0x7403 waiting on condition 

JNI global references: 886

Heap
 PSYoungGen      total 150528K, used 7745K [0x00000007580b0000, 0x00000007628a0000, 0x0000000800000000)
  eden space 129088K, 6% used [0x00000007580b0000,0x00000007588405b8,0x000000075fec0000)
  from space 21440K, 0% used [0x00000007613b0000,0x00000007613b0000,0x00000007628a0000)
  to   space 21440K, 0% used [0x000000075fec0000,0x000000075fec0000,0x00000007613b0000)
 PSOldGen        total 343936K, used 0K [0x0000000608200000, 0x000000061d1e0开发者_运维知识库000, 0x00000007580b0000)
  object space 343936K, 0% used [0x0000000608200000,0x0000000608200000,0x000000061d1e0000)
 PSPermGen       total 21248K, used 3130K [0x00000005fdc00000, 0x00000005ff0c0000, 0x0000000608200000)
  object space 21248K, 14% used [0x00000005fdc00000,0x00000005fdf0ea30,0x00000005ff0c0000)

A Java program will exit after the last thread finishes.

To prevent that, mark the other threads as daemon threads.

Get a thread dump by running kill -3 <process id>. This will tell you which threads are hanging around & preventing the java process from exiting. Feel free to post (some of) the thread dump & folks can help you figure out what to do next.

It looks like you are creating several Timer threads. Check that all of them have exited properly, that is probably the problem.

If you check the Timer JavaDoc - http://download.oracle.com/javase/6/docs/api/java/util/Timer.html - you will notice the following note:

By default, the task execution thread does not run as a daemon thread

You can use a debugger (both Eclipse and NetBeans have excellent ones) to see which threads are still alive.