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.OutOfMemoryError: Java
heap space
java.lang.OutOfMemoryError: 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.println("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.println("Applet finalized");
}
....and this in the game engine:
protected void finalize() throws Throwable{
super.finalize();
System.out.println ("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.AppletViewer (obj.
id.: 0x8b382e40) which is owned by
sun.plugin.viewer.MNetscapePluginObject (obj. id.: 0x8b382a70) which is
owned by sun.plugin.AppletViewer (obj. id.: 0x8b382e40).
The other (obj. id.: 0x88f33000) is owned by java.lang.ref.Finalizer
(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
Applets not being garbage collected 
