Applets not being garbage collected

[Robert Larsen]

Hi

I am developing Java applet games and have come across a problem that
seems to exist in the VM from Sun. I have tested in Mozilla and Firefox
on Windows and Linux and IE (several versions) on Windows.

When I run a game applet and then reload the page, two instances of the
game are running in the same VM. I have verified this with JMP
(http://www.khelekore.org/jmp/), and as the more recent games use lots
of memory (up to 42 megs), they run out of memory and throws a:

Exception in thread "Image Fetcher 0" java.lang.OutOf MemoryError: Java
heap space
java.lang.OutOf MemoryError: Java heap space

If not on the first reload then on the second or third. This also
happens if I close down the window and open the game again. The only
thing that works is closing down all windows.

I have the following in the applets destroy() method:

public void destroy() {
System.out.prin tln("Applet destroyed");
applet = null;
appletAdapter = null;

if (engine != null) {
engine.destroy( );
engine = null;
}
System.gc();
}

'applet' is a reference to the applet itself.
'appletAdapter' is a proxy for calling methods on the applet (games can
also run as an application so this object implements methods for getting
"host", "applet parameters" and calling JavaScript without the need for
an actual applet).
The engine object is the actual game and the applet does not have any
other references to anything, so this should clean up everything.
I also have this in the applet:

public void finalize() {
super.finalize( );
System.out.prin tln("Applet finalized");
}
....and this in the game engine:
protected void finalize() throws Throwable{
super.finalize( );
System.out.prin tln ("Engine finalized");
}


When I refresh the page I get "Applet destroyed" in my console but
neither "Applet finalized" nor "Engine finalized" + I can see in JMP
that there are two instances of both the GameEngine (the 'engine'
reference) object and the applet.

One (obj. id.: 0x8b384ae0) is owned by sun.plugin.Appl etViewer (obj.
id.: 0x8b382e40) which is owned by
sun.plugin.view er.MNetscapePlu ginObject (obj. id.: 0x8b382a70) which is
owned by sun.plugin.Appl etViewer (obj. id.: 0x8b382e40).

The other (obj. id.: 0x88f33000) is owned by java.lang.ref.F inalizer
(obj. id.: 0x88f33118).
And it seems that it is never actually finalized. I hit the System.gc
button in JMP and it frees lots of stuff, but not the applet and not the
game engine. I have had it running for hours and the finalizer never
seem to free the old reference.

I have tried inserting a delay for one minute before instanciating the
game engine so the garbage collecter has lots of time to free something
but that didn't help.


Do you guys know why this is ?
Can anything be done about it ?

Best regards,
Robert

[Andrew Thompson]

Re: Applets not being garbage collected

Robert Larsen wrote:
..
(applet browser memory problem)

>Do you guys know why this is ?

No (and I personally, am beyond caring about
applet/browser/VM interaction problems).

>Can anything be done about it ?

Launch the applet using web start. Here is an
example of an applet launched using web start.
<http://www.physci.org/jws/#jtest>

--
Andrew Thompson

http://www.athompson.info/andrew/

Message posted via JavaKB.com

http://www.javakb.com/Uwe/Forums.aspx/java-general/200704/1

[Robert Larsen]

Re: Applets not being garbage collected

Andrew Thompson wrote:

Robert Larsen wrote:
.
(applet browser memory problem)

>Do you guys know why this is ?

>
No (and I personally, am beyond caring about
applet/browser/VM interaction problems).

Oh how I wish I lived in your world :-)
Browsers are nothing but trouble.

>

>Can anything be done about it ?

>
Launch the applet using web start. Here is an
example of an applet launched using web start.
<http://www.physci.org/jws/#jtest>
>

This has crossed my mind. Problem is that actually two applets run on
the same page (a game and a chat applet) and running two separate
windows would...well... suck.
This may be the path I take if no other solution is found, but then I
will build a new application with both the game and the chat in one. But
I would really like to avoid that extra work so if anybody else has a
solution I would dance a happy dance and buy you a beer :-)