How to create a Daemon thread

create a new thread from your main thread and use setDaemon(true) method...

if you are in nt environment you can use the javaw to launch you app without console, you'll be able to stop your app only from Windows NT Task Manager

if you are on UNIX platform you can launch you app with an & after the name of the app and you'll be able to stop it only with kill command

the use of the Windows NT Task Manager or kill method to stop your application was mentioned for
servers/daemons that are build to run infinitly

Hi, I had played with daemon thread and didn't find any problem.
What I did is the same as you...

//Create the thread class
public class MyDaemon extends Thread {
    //define some variables
      ....
    //the constructor
    public MyDaemon(String id,...) {
          super(id);
          ....
    }

    //the run method
    public void run() {
          //do the things you want
    }

    //any methods needed..
    .....
}

//declare a thread of type MyDaemon
private MyDaemon myDaemon;

//Start and stop the thread ..
public void startMyDaemon() {
    if(myDaemon==null) {
        myDaemon = new MyDaemon("1",...);//"1" is the thread id
        myDaemon.setDaemon(true);
        myDaemon.start();
    }
}

//Stop the thread..
public void stopMyDaemon() {
    if(myDaemon!=null) {
        myDaemon.stop();
        myDaemon = null;
    }
}


Should work for you if nothing's gone mad:)

Good luck!

How do you check that the thread did not start? The start method doesn't necessarily cause the new thread to begin execution. It only schedules it for execution. Typically, and this is JVM dependent, any code following Thread.start() in the thread performing the start will continue to be executed. This may make it appear, for an indeterminate period of time, that the other thread is not running.

Are you sure that the daemon thread didn't start and run to completion before you checked? The run method of the Runnable or Thread object called by the JVM controls the lifetime of the thread. When the run method finishes, so does the thread. Check that your run method does not exit.

Best regards,
Jim Cakalic

In Java, I don't think there is a way to check whether a scheduled Thread has started or not. Correct me if I'm wrong.

Thanks for all the answers. I had confused a Daemon thread with a Daemon process in Unix. Basically if I am not mistaken the JVM exits when the only threads are Daemon threads. Once the JVM exits there is no way by which the thread can continue execution. If I am mistaken please correct me. I have a doubt. Could someone give me an example of where a Daemon thread can be used in an application(other than GC).

Hi Rajiv,
   I tried what you said. But an IllegalThreadState exception is thrown. In fact if what I remember is right the documentation says that the setDaemon should be called before starting the thread. I used Java 1.2.2 and Windows NT.

Krishnan

Just check it whether u have written setDaemon(true); in constructor of the class or not... if not add it to constructor...

Rajiv

Hi Rajiv,
  You have asked me to put the setDaemon(true) in the constructor. This implies that it will be called before the thread is started. But in your first message you asked me to call it after starting the thread. Could you please explain.

Thanks

Krishnan.

Hi Rajiv,
  You have asked me to put the setDaemon(true) in the constructor. This implies that it will be called before the thread is started. But in your first message you asked me to call it after starting the thread. Could you please explain.

Thanks

Krishnan.

Hi Rajeev,
  You have asked me to put the setDaemon(true) statement in the constructor. This means that it will be called before the thread is started, but in the previous message you asked me to call it after the thread is started. Could you please explain.

Thanks
Krishnan

Yes Yaar I m Sorry for the First Statement... It has to be called before the Thread starts...

Im very very Sorry...
But did u tried that?

Rajiv

Hi Rajeev,
   I tried it. The run of the daemon thread executes if the main thread does not die. On the other hand if the main method just creates a daemon thread and starts it then the run is not executed.

public static void main(String args[])
{
  MyThread t = new MyThread();
   /*This creates a thread and also calls setDaemon(true) */
  t.start();
}

I guess the reason for this is that the JVM exits since it finds the only thread to be a Daemon. Once the JVM has exited there is no way by which the thread can run. Please tell me if what I have understood is correct.

Thanks
Krishnan