Resumable exceptions #2

[Stephen Weeks]

Not long ago, Patrick R. Michaud proclaimed...
> In August [1] I posted some code to test the ability to
> resume execution after a thrown exception.  Here's a new
> version of that code, updated for other recent changes
> to Parrot's exceptions:
> 
>   .sub main :main
>       push_eh catcher
>       'foo'()
>       pop_eh
>       say 'ok 4'
>       .return ()
>     catcher:
>       .get_results ($P0)
>       $P1 = $P0['resume']
>       $P1()
>   .end
> 
>   .sub 'foo'
>       say 'ok 1'
>       $P0 = new 'Exception'
>       throw $P0
>       say 'ok 2'
>       $P0 = new 'Exception'
>       throw $P0
>       say 'ok 3'
>   .end
> 
> As before, I'm simply trying to test the ability to
> resume after exceptions thrown by C<foo>.
> 
> Currently Parrot disables exception handlers when they're
> invoked, thus the above results in "No exception handler"
> when the second exception is thrown.  What do we need to
> modify in Parrot so that the exception handler isn't
> automatically disabled?
> 
> (In response to my August message Allison noted that
> we needed to update "legacy" exception handlers for the 
> new model -- so I've begun the process of doing that update.
> But now I need to know the appropriate patch or change to
> make to Parrot so that it no longer disables handlers
> upon invocation, so that I can complete the updates of
> existing handlers.)

EHs are marked as "used" in src/scheduler.c:760

src/pmc/exceptionhandler.pmc:214-219 contain the logic for "If I am
marked as used, decline to handle the exception."  If you want to
preserve the idea of a disabled exception handler still in the list of
EHs in the context, you'll want to reorder the logic there so that it
declines before it checks to see if a type or severity filter is in
place.