Re: [Chicken-users] External representation for continuations

[Felix Winkelmann]

Thomas Chust wrote:
> Hello,
>
> I've come across a paper about Kali Scheme and so I started wondering 
> whether it would be possible to create a sensible external 
> representation of continuations / threads in CHICKEN -- something you 
> could transmit over a network channel and use at the other side, at 
> least if the other side was running the same Scheme program.
>
> Any good ideas are welcome!

Basically everything is possible... ;-)

I pondered about this quite a bit. Basic serialization of data is not
a big problem, but code is somewhat tricky. A closure (or continuation)
contains a code-pointer to some C routine. To properly serialize a closure,
the code-pointer would have to be converted into some unique id, which,
when deserialized back into a running process must be converted into
a code-pointer again (we can't just write the code-pointer directly:
in a process that deserializes a closure, the code-addresses may be at
completely different locations, or might even not be available, for
example if a library is not linked, which was used and referenced in
a serialized continuation/closure).

One possible solution would be to generate a function-table for each
compiled file that maps code-pointers to unique identifiers). On serialization
a code-pointer would be looked up in that table, the id written and on
deserialization the id is searched in all loaded/linked units/modules
and converted back into a code-pointer.

But serializing continuations is a tricky business: ports and foreign-
pointers have to handled specially and one has to make sure that a cont.
does not pull in the whole global environment.


cheers,
felix