Static Singleton instance reference gets cleaned memory!

OK, it's one of the strangest things I've ever seen.

I am currently working on a project where I use a singleton like this:

public class SingletonExample {  private static SingletonExample instance; private Vector listeners; private PhoneListener phoneListener;

  private SingletonExample(){       listeners = new Vector();     phoneListener = new PhoneListenerImpl();  }

  public static synchronized SingletonExample getInstance(){        if(instance == null){         instance = new SingletonExample();        }     return instance;  }

  public synchronized void addListener(SomeListener listener){      if(listener != null){         synchronized(listeners){              listeners.addElement(listener);               if(listeners.size() == 1){                    Phone.addPhoneListener(phoneListener);                }         }                 } }

  public synchronized void removeListener(SomeListener listener){       if(listener != null){         synchronized(listeners){              if(listeners.contains(listener)){                 listeners.removeElement(listener);                }                 if(listeners.isEmpty()){                  Phone.removePhoneListener(phoneListener);             }         }                 } }

  private void reportListeners(){       synchronized(listeners){          int sz = listeners.size();            for(int i = 0; i < sz; i++){               final SomeListener sl = (SomeListener) listeners.elementAt(i);                new Thread(){                 public void run(){                        sl.onListenerReported();                  }             }.start();            }     } }

  private class PhoneListenerImpl implements PhoneListener {        public void callAdded(int arg0) {}

      public void callAnswered(int arg0) {}

       public void callConferenceCallEstablished(int arg0) {}

      public void callConnected(int arg0) {     }

       public void callDirectConnectConnected(int arg0) {}

     public void callDirectConnectDisconnected(int arg0) {}

      public void callDisconnected(int arg0) {          reportListeners();            }

       public void callEndedByUser(int arg0) {           reportListeners();                }

       public void callFailed(int arg0, int arg1) {          reportListeners();                    }

       public void callHeld(int callId) {}

     public void callIncoming(int callId) {}

     public void callInitiated(int callid) {}

        public void callRemoved(int callId) {}

      public void callResumed(int callId) {}

      public void callWaiting(int callid) {}

      public void conferenceCallDisconnected(int callId) {} }}

(Not the best singleton, but very safe and is the one I usually use).

Want to-be-singleton class contains a collection of the listener (I have not included SomeListener interface, but it is very simple, only an onListenerReported of the method). Also contains an instance of PhoneListener. When a call is disconnected, the class of SingletonExample should report each listener on a new Thread.

Now the collections on static variables is subject to leaks memory, but this class is intended to contain only one or two listeners at a time, so there is not much. And as we are about to see, the static integer variable 'instance' is going to be garbage collected between "consecutive" calls to getInstance.

Now, I have a method like this, taken from a menu action:

public void someMethodFiredFromMenu() {  new Thread(){     public void run(){

          SomeListener listener = new SomeListener(){               public void onListenerReported() {                    System.out.println(">>>>>>> Call disconnected!");

                  //FIXME: Singleton static member is null at this point,                   // so it is constructed again!!!                  SingletonExample.getInstance().removeListener(this);

                  //Do other things here                                    }                                     };

          //First call to getInstance, static member is constructed as expected         SingletonExample.getInstance().addListener(listener);     } }.start();}

If test you it on a 4.7 Simulator I (BlackBerry 9530 Simulator, v4.7.0.75) you can see that the static variable singleton (named 'instance' within class SingletonExample) is collected between calls to someMethodFiredFromMenu.

It never happened to me before. Somehow, that there are two threads involved, the JAVA virtual machine (if we can call it ) determines that the variable is more accessible and collects, thus screwing my design.

Interesting things:

Make two consecutive getInstance calls in the same thread works.

Holding a last reference to the SingletonExample within the method of the menu and its use (even in different threads) also works.

* Note: I've changed a few names from my original code, so there are compilation errors, but at least you know what the code meant.

It is a feature of the BlackBerry JVM and what others have stumbled on before, including me.

The best way to summarize the problem is that a static is only a Singleton when the static object references are in the same instance of the Application.

Another way to say it is that each instance of the Application has its own set of static variables.

The problem here is that you code earphone is running an application, which will have a set of difference of static variables for your Application.

Here the best way to create a Singleton in a BlackBerry

http://supportforums.BlackBerry.com/T5/Java-development/create-a-singleton-using-the-RuntimeStore/TA...

That said, I would recommend that you avoid treatment on the earpiece - if you can only use global event to convey the information for your Application, then it can be handled in your Application and static object is a Singleton!

A bit off-topic and just because I'm here, but what's the point of the Thread in this treatment?

public void someMethodFiredFromMenu() {}
New Thread() {}
public void run() {}

SomeListener listener = new SomeListener() {}
public void onListenerReported() {}
System.out.println ("> call disconnected!");

FIXME: Singleton static member is NULL at this point,
Thus, it is built again!
SingletonExample.getInstance () .removeListener (this);
Do other things here
}
};

First call to getInstance static member is built as planned
SingletonExample.getInstance () .addListener (listener);
}
}. start();
}

Tags: BlackBerry Developers

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Step 1: Disconnect all external devices (printers, scanner, USB (universal serial bus) readers, etc...) Except the keyboard and mouse and then start.

If this solves the problem, then add back devices at a time until you discover the piece of hardware causing the issue. Then get any drivers\software update for the device.

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Remember: if I delete records, do I get the memory they used?

I have large files which I copied on my externalhard drive. If I have SupprimerLa files, I get the memory back, they used.

If you delete the original folders you copied, find you the hard disk space, called secondary memory.

See you soon.

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How can I get more memory on my laptop?

Uh, buy it

Care to be more specific?

I get virtual memory is low opinion.

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I got this computer with Windows XP since 2004 & never really drained all the old programs / unused.

I went to the Control Panel, add/remove programs and deleted what I know, that I don't use, but I don't want to spoil anything.

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Hello Tracy,.

This means that you have little free disk space on your C volume that is limiting the scope of the size of the pagefgile can develop.

What is the processor and RAM how much your computer have? Make a right-click on the icon my computer on your desktop and select properties for this information.

Try Ctrl + Alt + Delete, select Task Manager, and then click the performance tab. Under Commit Charge, which is the Total, limit, and the pic?

You can create more free space in C in carrying one of the measures suggested below.

The default allocation for the restoration of the system is 12% on your C partition is more generous. I have them would be reduced by 700 MB. Make my computer right click on your icon, and select System Restore. Place the cursor on your C drive select settings but this time find the slider and drag it to the left until it shows 700 MB and output. When you get to the settings screen, click on apply and OK and leave.

A flaw that might be useless which is for temporary internet files, especially if you keep no copies on the disk offline. Setting the default value is 3% of the walk. Depending on your attitude to copies offline, you could bring it to 1% or 2%. In Internet Explorer, select Tools, Internet Options, general, temporary Internet files, settings to make the change. At the same time, look at the number of days, the story stands.

The default allocation for the basket is 10% of the disk. Change to 5%, which should be enough. In Windows Explorer hover over your Recycle Bin, right click and select Properties, Global and move the slider from 10% to 5%. However, try to let you become so complete that if it is complete and you delete a file by mistake it will bypass the Recycle Bin and have gone forever.

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http://www.CCleaner.com/download

Kind regards

Chauvet J.

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Space and memory are two different things.

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I think you're confusing terms and certainly confuse us.

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