How to create a thread that runs all the time my application is running

Question

EDIT: I'm now sure that the problem is related to the while (true) loop holding all other commands as I've commented it out and the application deploys without the attached exception. I'm not sure how much it is important but my ServletContextListener implementation looks like this:

public class BidPushService implements ServletContextListener{

public void contextInitialized(ServletContextEvent sce) {   
//Some init code not relevant, omitted for clarity
      BidPushThread t= new BidPushThread();
      t.setServletContext(sce.getServletContext());
      t.run();
}

So now the thread is run when the app is deployed but because the while loop is commented it has no real meaning.

I need to have a thread run in the background when my application loads and constantly (without a timeout) check a certain queue for objects. Of course, once there are objects, it "takes care of them" and then continues to check the queue.

Currently, I'm implementing the ServletContextListener interface and I'm being called when the app loads. In it, I do a few maintenance things and start a thread which I inherited from java.lang.Thread.

Here is where my problem begins (or so I think). In my run() method, I have a

while (true) {
    //some code which doesn't put the thread to sleep ever
}

When I try to deploy my app to the server I get a java.util.concurrent.TimeOutException. What am I doing wrong?

Can't I have a thread which is always running? When the app is removed, that thread is stopped by the corresponding event in my ServletContextListener.

I really do need something that keeps on checking the queue without delay.

Thanks a lot for any help!

Edit: This is the stack trace

GlassFish: deploy is failing=
    java.util.concurrent.TimeoutException
    at java.util.concurrent.FutureTask$Sync.innerGet(Unknown Source)
    at java.util.concurrent.FutureTask.get(Unknown Source)
    at com.sun.enterprise.jst.server.sunappsrv.SunAppServerBehaviour.publishDeployedDirectory(SunAppServerBehaviour.java:710)
    at com.sun.enterprise.jst.server.sunappsrv.SunAppServerBehaviour.publishModuleForGlassFishV3(SunAppServerBehaviour.java:569)
    at com.sun.enterprise.jst.server.sunappsrv.SunAppServerBehaviour.publishModule(SunAppServerBehaviour.java:266)
    at org.eclipse.wst.server.core.model.ServerBehaviourDelegate.publishModule(ServerBehaviourDelegate.java:948)
    at org.eclipse.wst.server.core.model.ServerBehaviourDelegate.publishModules(ServerBehaviourDelegate.java:1038)
    at org.eclipse.wst.server.core.model.ServerBehaviourDelegate.publish(ServerBehaviourDelegate.java:872)
    at org.eclipse.wst.server.core.model.ServerBehaviourDelegate.publish(ServerBehaviourDelegate.java:708)
    at org.eclipse.wst.server.core.internal.Server.publishImpl(Server.java:2690)
    at org.eclipse.wst.server.core.internal.Server$PublishJob.run(Server.java:272)
    at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)

My Code:

public class BidPushThread extends Thread {
    private ServletContext sc=null;
    @Override
    public void run() {
        if (sc!=null){
            final Map<String, List<AsyncContext>> aucWatchers = (Map<String, List<AsyncContext>>) sc.getAttribute("aucWatchers");
            BlockingQueue<Bid> aucBids = (BlockingQueue<Bid>) sc.getAttribute("aucBids");

              Executor bidExecutor = Executors.newCachedThreadPool(); 
              final Executor watcherExecutor = Executors.newCachedThreadPool();
              while(true)
              {  
                 try // There are unpublished new bid events.
                 {
                    final Bid bid = aucBids.take();
                    bidExecutor.execute(new Runnable(){
                       public void run() {
                          List<AsyncContext> watchers = aucWatchers.get(bid.getAuctionId()); 
                          for(final AsyncContext aCtx : watchers)
                          {
                             watcherExecutor.execute(new Runnable(){
                                public void run() {
                                   // publish a new bid event to a watcher
                                   try {
                                    aCtx.getResponse().getWriter().print("A new bid on the item was placed. The current price "+bid.getBid()+" , next bid price is "+(bid.getBid()+1));
                                } catch (IOException e) {
                                    // TODO Auto-generated catch block
                                    e.printStackTrace();
                                }
                                };
                             });
                          }                           
                       }
                    });
                 } catch(InterruptedException e){}
              }

        }
    }
    public void setServletContext(ServletContext sc){
        this.sc=sc;
    }
}

Sorry for the formatting mess but for the life of my "indent code by 4 spaces" just does not work for me Edit: Read about 'BlockingQueue' and implemented it, but I'm still getting the exact same exception and stack trace. changed the above code to reflect the use of 'BlockingQueue'

Answer 1

setDaemon

SUMMARY:

• Marks this thread as either a daemon thread or a user thread. The Java Virtual Machine exits when the only threads running are all daemon threads.
• This method must be called before the thread is started.
• This method first calls the checkAccess method of this thread
  with no arguments. This may result in throwing a SecurityException (in the
  current thread).

Threads

SUMMARY: In many cases, what we really want is to create background threads that do simple, periodic tasks in an application. The setDaemon() method can be used to mark a Thread as a daemon thread that should be killed and discarded when no other application threads remain. Normally, the Java interpreter continues to run until all threads have completed. But when daemon threads are the only threads still alive, the interpreter will exit.

Answer 2

Your code does not start a new thread, it runs the loop in the same thread and this is why you are getting a timeout error when deployed.

To start a thread you must call the start method, not the run method.

public void contextInitialized(ServletContextEvent sce) {   
//Some init code not relevant, omitted for clarity
  BidPushThread t= new BidPushThread();
  t.setServletContext(sce.getServletContext());
  t.start();// run();
}