Re: hacking on 1.7 threads

[Mikael Djurfeldt]

Julian Graham <address@hidden> writes:

> That is, if I'm storing a list SCM in an scm_thread struct that's
> allocated on the heap, and I cons stuff onto it, do I have to do
> anything special to prevent the GC from collecting the SCM contents
> of the struct?

Yes.  As Rob already has explained, any Scheme object stored in a data
structure allocated outside the stack must be explicitly protected.

The way to do it in this case is to add a line in
threads.c:thread_mark:

static SCM
thread_mark (SCM obj)
{
  scm_thread *t = SCM_THREAD_DATA (obj);
  scm_gc_mark (t->result);
  scm_gc_mark (t->cancellation_handler_list); /* <--- */
  return t->root->handle; /* mark root-state of this thread */
}

Note, though, that this is the easy part.  I do expect that there also
could arise nasty complications having to do with the order in which
things are done at cancellation.  It's for example important that the
scm_thread data structure isn't deallocated before the handlers are
invoked.  It's also important that the GC is still aware of the thread
at that point in time.  It's important that the thread *is* properly
deallocated *after* the handlers have run---that kind of stuff.  But
maybe there's no problem at all.

M