RE: [Rcosjava-general] Threading in the applet

[Peggy N. <pe...@ip...>]

Hi Andrew

thanks. just a couple of questions....

> It goes init(), start(), run(), and stop().  init() does the basic
> initialisation.  start() calls startThread() (from
> setupAnimatorLayouts()).  

umm, isn't startThread() called from init()? Not that I think it makes 
a lot of difference, by the looks of it both init() and start() are called 
again when the page/applet is "refreshed".

> If startThread() is not called by start()
> then the running variable is always false.  So when it gets to run()
> the thread waits and is never notified.  

In what cases would this happen? 

Possibly stupid question: 
Are the methods isRunning() and startThread() in the applet 
accessible (or indeed accessed) from other classes?

thanks,
Peggy

When startThread() is called
> by the ProgramManager (from another thread) then it's notified and
> keeps running.  So if you comment out that call, go to "Program
> Manager" and hit "Run" and it will work!
> 
> It was also done for minimize/maximize/entering/leaving/reloading
> pages.  This was done for largely historic reasons.  When RCOS.java
> was a 1.1 applet sitting in IE 3/4 and Netscape 3/4 the
> init/start/stop/destroy calls were called at different times for
> different browser versions.
> 
> If you want information about it check out:
> http://support.microsoft.com/support/kb/articles/Q227/2/10.ASP
> http://developer.netscape.com/support/faqs/champions/java.html
> 
> In the end, you're probably wondering why I did it this way.  Me too. 
> I don't think this is the best way but I hate threads and it does work
> okay but it needs improvement (see below).
> 
> >Q. This 'running' variable - deemed volatile - I understand this to
> >mean that it might be changed from an external source ie another
> >thread. To compliment my other questions - when does 'running' become
> >false, aside from its initialisation?
> >
> 
> This is just following Sun's documentation about "Why Thread.stop,
> Thread.suspend and Runtime.runFinalizersOnExit is deprecated".
> 
> http://java.sun.com/products/jdk/1.2/docs/guide/misc/threadPrimitiveDe
> precation.html
> 
> It's to "ensure prompt communication of the stop-request, the 
> variable must be volatile (or access to the variable must be 
> synchronized)."  The startThread() method is synchronized but 
> the isRunning() is not.
> 
> In previous version there was this method:
> 
> public synchronized void stepThread()
> {
>   running = false;
>   notify();
> }
> 
> This was part of the implementation to step through an instruction at
> a time.  The bug for this is here:
> 
> http://sourceforge.net/tracker/index.php?func=detail&aid=452014&group_
> id=5762&atid=105762
> 
> >
> >Also, I see that the kernelThread loops around for its existence,
> >calling performInstructionExecutionCycle(). Why does the thread then
> >sleep?
> >
> 
> This is just to allow other threads to run.  The animator thread gets
> pretty starved when the sleep is removed.
> 
> 
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