Re: Please help me kill this java thread..... code example

Eric Sosman <esosman@comcast-dot-net.invalid>
Thu, 15 Nov 2012 13:33:17 -0500
On 11/15/2012 1:16 PM, wrote:

Thank you for your help! Sorry, I did have many more printouts to stdout, but stripped them to make it easier to read.... It is interesting that you said the System.exit should should down everything, now I am stumped...but here are my responses:

      1) The shutdown() method is never called. You haven't shown
         us any of the arrangements you've made to have it called,
         so we can't tell whether they're correct (or even whether
         they exist). Try `System.out.println("Kilroy was here");'
         at the start of shutdown(), just to find out whether you
         do or do not ever get there.
      2) A security manager forbids exit() from doing anything.
         If this happens a SecurityException will be thrown, and
         that might (or might not) be what stops the GUI. Perhaps
         your habit of catching and ignoring exceptions has blinded
         you to what's going on here.

I am sure shutdown is being called, because I can see that the GUI does shutdown/closes.

     There are many things that might stop the GUI, so the fact
that it vanished does not prove shutdown() was called. Have you
tried the suggested println()?

      3) You're wrong: The worker thread does in fact stop. You've
         not explained why you think it's still running, so we can't
         tell whether your conclusion is correct.

I do not believe the worker thread is stopping because AFTER I click on the shutdown button, I then see the GUI shutdown/close, BUT I still see the netbeans JMV stdout window say the jvm is running still, AND I can perform ONE LAST scan, AND THEN I see the netbean jvm window close, and the scanner beam is then silent.

     Okay: I've come up with a fourth guess. Perhaps exit() has in
fact been called (and allowed), and the JVM is in the process of
shutting down. But perhaps shutdown cannot complete while the scanner
code holds a lock or other resource (JNI?) that the JVM's shutdown
needs before shutdown can complete. Firing the scanner one last time
might jar things loose. (Remember: This is still just a guess.)

     The scanner code (in another thread you called it "the motorola
sample program") is not known to me, so I can't say what it might be
hanging on to. Knute Johnson's suggestion of interrupting the thread
might work, if the code is well-behaved (and doesn't, for example,
just catch and ignore exceptions); I'd suggest giving it a try. If
that doesn't help -- well, you say you're using NetBeans, which means
you have a debugger available; have you used it to find out what the
threads are doing instead of exiting?

Eric Sosman

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