Since processing.core.PApplet.main(String[], PApplet) registers
System.exit(0); as the event-handler for shutting down, it is not possible
to add any shutdown code in Processing, to e.g. release system-resources
like serial interfaces.

A better solution is to replace System.exit(0); with applet.destroy(); in
processing.core.PApplet.main(...).new MouseAdapter()
{...}.mousePressed(MouseEvent) (line 7249 in PApplet.java in svn-tag 1.1)
and in processing.core.PApplet.main(...).new WindowAdapter()
{...}.windowClosing(WindowEvent) (line 7330 in same version).

If done so, the user could easily override PApplet.destroy() to add
shutdown-code.

In fact System.exit(int) should NEVER be called! I think there are more
occurences. Theses should also be checked.

That's what stop() is for, in part because not everything (perhaps not even
most things anymore) created with Processing are applets. Though stop()
still has its problems, seen in bug #183.

Fry, the Problem is, that stop() is ONLY called by the ESCAPE-Key listener.
Instead, when closing the applet either by closing the window or by
clicking the "close"-label, the VM is forced to shut down whith no chance
to perform anything.

Furthermore, bug #183 should read as

"start() is called by the appletviewer, but destroy() is guaranteed to
be NOT called. "


Thus, I advice to replace it with applet.destroy() which only calls
applet.stop(). So these would be equivalent.
Another way would be to use exit() instead.

*** This bug has been marked as a duplicate of 183 ***