[Python-Dev] continuations and C extensions?

[Aaron Watters]

the immutable GvR intones:
> Continuations involving only Python stack frames might be supported,
> if we can agree on the the sharing / copying semantics.  This is where

> I don't know enough see questions at #2 above).

What if there are native C calls mixed in (eg, list.sort calls back to
myclass.__cmp__ which decides to do a call/cc).  One of the really
big advantages of Python in my book is the relative simplicity of
embedding
and extensions, and this is generally one of the failings of lisp
implementations.
I understand lots of scheme implementations purport
to be extendible and embeddable, but in practice you can't do it with
*existing* code -- there is always a show stopper involving having to
change the way some Oracle library which you don't have the source for
does memory management or something... I've known several grad students
who have been bitten by this...  I think having to unroll the C stack
safely
might be one problem area.

With, eg, a netscape nsapi embedding you can actually get into netscape
code calls my code calls netscape code calls my code... suspends in a
continuation?  How would that work?  [my ignorance is torment!]

Threading and extensions are probably also problematic, but at least
it's
better understood, I think.  Just kvetching.  Sorry.
   -- Aaron Watters

ps: Of course there are valid reasons and excellent advantages
  to having continuations, but it's also interesting to consider the
possible cost.
  There ain't no free lunch.