[Wxsqueak] Re: Putting halts in event handlers

[Rob Gayvert]

dan wrote:
> 
> If you get an exception in the callback, it seems like you catch it and 
> ignore it, right?

It's not entirely ignored -- the callback is "completed" by restoring 
the C stack, and then it opens a debugger on the Squeak callback 
process. If it's a one-shot deal, this can be useful. But in a case like 
this tree item comparison, it can be a mess. The bottom line is that you 
  have to be very careful with what goes on in a callback.

> We have been discussing callbacks in the general squeak list. It looks 
> like you have done some interesting stuff regarding putting callback 
> support into the VM. Is that right?

I can't claim to have invented anything new (the ideas are all from 
Andreas), but the end result is interesting. In the 0.4 release, the 
callbacks were handled entirely within WxPlugin, without any core VM 
support. The downside of this was that the callback processes were hard 
to control, so any API call that might result in a nested callback had 
to be guarded with a special semaphore. In 0.5, I'm using Andreas' new 
VM modifications, which makes the calls much cleaner, and should be more 
stable as well.

.. Rob