[RFC][icedtea-web] Fix NPE thrown when applets in the plugin fail.

[Danesh Dadachanji]

Hi,

Any applet run by the plugin that throws an exception while loading 
(before init() is called) will output an NPE. This is because we have 
sent 3 events to the queue when the plugin is setup, APPLET_LOAD, 
APPLET_INIT and APPLET_START. This was causing problems when 
AppletInstance was not being set, and specifically when AppletInstance's 
Applet var was left as null.

AppletPanel's run thread continues to the next event, APPLET_INIT even 
if in APPLET_LOAD, the applet var was not set (exception occurred in the 
constructor of the applet, Launcher#createApplet() crashed etc). Then, 
the applet var is set to null so when it is referenced in APPLET_INIT's 
execution, the NPE is thrown.

There is no way of removing an event from the queue in our given 
situation. I tried finding a method that would do this so that I could 
empty the queue if either AppletInstance or Applet vars were null but I 
could not find one. The queue is also private to AppletPanel and since 
we cannot modify that, the only resolution I saw was to conditionally 
add the events to the queue later on down the line.

The changes I've made in the attached patch simply remove sending the 
init and start event when initializing the panel and send these signals 
once NetxPanel confirms a non-null applet. NetxPanel's runLoader is only 
executed in consequence to APPLET_LOAD so I believe it is safe to add 
these events here. The patch also sends an APPLET_DISPOSE event if it 
fails to run, which is just cleanup.

Reproducer is somewhat in the works (depending on limitations of running 
it in a browser). For your testing, just make an applet that throws 
something and you should see an NPE in NetxPanel and an NPE in AppletPanel.

ChangeLog:
+2012-02-29  Danesh Dadachanji  <ddadacha at redhat.com>
+
+	Fix NPE thrown when applets run by the plugin fail to initialize.
+	* netx/net/sourceforge/jnlp/NetxPanel.java
+	(runLoader): Check for null applet instance, if it is then send a dispose
+	event. If it is not, continue as before. If the applet is not null, send
+	an init and start event to the AppletPanel queue.
+	* plugin/icedteanp/java/sun/applet/PluginAppletViewer.java
+	(initEventQueue): Removed sending of APPLET_INIT and APPLET_START events.
+

I'd like to push this to HEAD, are there any comments?

Cheers,
Danesh
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