[Stackless] Patch to exception handler.

Gil Colgate gcolgate at gmail.com
Mon Apr 16 20:33:10 CEST 2012

Did this meet with anyone's approval?

On Mon, Apr 9, 2012 at 11:43 AM, Gil Colgate <gcolgate at gmail.com> wrote:

> Here is a fix for the exception handler, I included just the .patch.
>     This corrects the problems with python having a different exception
> the environment when the item is called again.
>     In the previous code, whenever a python tasklet was suspended the top
> of the exception chain was saved. This very well could be a pointer into
> code above the python stack into the main program. When the python tasklet
> is called again, it's stack is put back *in the same place*, but the
> environment above the stack *might be different*. This would cause the
> exception chain to screw up in the part where the exception chain points
> above the stack. This was the cause of the broken exception chain bug.
>     If a tasklet has none of it's own exception chains, we will discover
> this by reading the exception list and seeing that the address is above the
> stack, so we don't need to save or restore it it.
>     If, on the other hand, the tasklet has a chain we save it. When
> restoring it we look at the current chain and insert the chain from the
> restored stack into it at the appropriate spot, so that the tasklet's chain
> points correctly into it's parent's change.
>     Stack slicing: Stackless in general has a problem with stack slicing.
> This code will work in when the stack is sliced (I tested it with 2K stack
> slices and try-catches everywhere) but certain exceptions that belonged to
> inactive stack slices will not be executed since they are not currently
> linked into the chain.
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