[RFC] plugin: use an AppContext to support applets running with different look and feels

[Omair Majid]

Hi,

The attached patch is an (updated) attempt to fix PR565 [1]. The patch 
does two things:

1. It creates a ThreadGroup for the applet earlier in the initialization 
phase.

The applet's intialization code (currently) creates 3 threads (most of 
this code is in NetxPanel, AppletPanel and Launcher). The first thread 
is what calls applet.init(), applet.start() etc. It creates the second 
thread to load the applet (so loading can be interrupted). This second 
thread is what calls Launcher.launch() which ends up creating the third 
thread to actually load the applet. This third thread is created in a 
new ThreadGroup and has the JNLPClassLoader set as the 
ContextClassLoader. The patch makes sure that all three threads are 
created in the same ThreadGroup and the appropriate context class loader 
is set for all of them. This part of the patch is attached to the bug 
report. With this patch, all the threads of an applet can load the 
classes for the custom look and feel.

2. Allows different applets to use different look and feels.

The patch creates a new AppContext for each applet ThreadGroup. This 
means that each applet instance can set its own look and feel and not 
affect any other applet (which might lead to visual inconsistency as 
well as errors in loading custom look and feels). The AppContext class 
(part of sun.awt package) contains a map from ThreadGroup to AppContext 
that Swing and AWT can use to make sure they have the AppContext, which 
they can then use to index ThreadGroup-specific things like EventQueues 
and LookAndFeels. ApplicationInstance stores the AppContext for each 
applet instance, so the correct type of AppContext can be returned by 
JNLPSecuritymanager when AppContext.getAppContext() calls it to find the 
current AppContext.

I would greatly appreciate it if people can try this patch out. While I 
have tested with a large number of jnlp files and many applets, it could 
certainly use more testing.

Any and all feedback is welcome!

Thanks,
Omair

[1] http://icedtea.classpath.org/bugzilla/show_bug.cgi?id=565
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