[visad] finally solved Visad offscreen mode memory problems

[Stuart Maclean]

Curtis Rueden wrote:
> Hi Stuart,
> 
> Thanks for pointing this out. I'll take a look at it in more detail
> later this week, but initially I do have one comment. Rather than
> using interrupts, a slightly cleaner way would be to use monitors with
> wait and notifyAll, like the code is already doing. It might take
> slightly longer than interrupt in certain cases (I'm not sure), but it
> gives you more control over the flow of the code. For example, the
> graphics context will always get properly disposed.
> 
> 

Hi Curtis, good point.  I think I chose interrupts since they are not 'lost' like notifies can be.  Thread.interrupt sets the 
interrupt status on a Thread, a definite change in program state.  Calls like Object.wait check this status (and reset it!), and 
throw InterruptedException (IE) before/during the wait.  I found the problem with just wait/notify is that using notify to halt 
a thread relies on the wait having happened earlier, if not, you are stuck.  So its a race condition.  The interrupt approach is 
actually similar to the CountdownLatch set to one, used as an  'event'.

But I do see your point re other objects in a bad state in the app.  But is it not the responsibility of say a Graphics object 
user to catch any IE, dispose of objects correctly and maybe re-throw the IE.

Your comments welcomed

Stuart