Re: [Chicken-users] Continuations in C

[Daniel B. Faken]

On Fri, 9 Sep 2005, felix winkelmann wrote:
> On 9/9/05, Daniel B. Faken <address@hidden> wrote:
> >   From http://luajit.luaforge.net/coco.html:
> > "Coco is a small extension to get True C Coroutine semantics for Lua 5.1.
> > 
> 
> Yes this is clever. I thought about using makecontext/setcontext
> (patching setjmp
> isn't that nice, really) myself a while ago. Another nice property of this
> would be that C frames have dynamic extent (they could be garbage
> collected).

Actually I just noticed that, according to the manual, Chicken already 
kind of supports the "Coroutines in C" idea:
"When multiple threads are running concurrently, and control switches from 
one thread to another, then the continuation of the current thread is 
captured and saved. Any pending C stack frame still active from a callback 
will remain on the stack until the threads is re-activated again."

[and, since CHICKEN_yield() is just a callback to (thread-yield!), this 
should work from C]

-- right?  I have NOT tried this yet!

I guess in this sense Chicken has something like Lua's "One-shot 
continuations", for C.

[though I should include the qualifications in the manual: the 
continuation (ha) of the above quote is:
  "This means that in a multithreading situation, when C callbacks are 
involved, the available nursery space can be smaller than expected. So 
doing many nested Scheme->C->Scheme calls can reduce the available memory 
up to the point of thrashing. It is advisable to have only a single thread 
with pending C stack-frames at any given time."]

 - Daniel