[racket-dev] [plt] Push #22421: master branch updated

At Sat, 9 Apr 2011 19:00:20 -0500, Robby Findler wrote:
> On Sat, Apr 9, 2011 at 6:46 PM,  <mflatt at racket-lang.org> wrote:
> > 8570033 Matthew Flatt <mflatt at racket-lang.org> 2011-04-09 17:10
> > :
> > | futures: more bug fixes, make `touch' safe
> > |  - bug fixes are related to allocation and runstack space
> > |  - a `touch' within a future can complete before the `touch'ing
> > |    future is itself `touch'ed
> 
> Just to make sure I understand: this is only in the case that the
> touch within the future is touching some finished future or a future
> that is going to finish without being unsafe, right?

Yes.

If a future is touched by more than once (I doubt we have such
programs, so far), then there's a slight generalization: If the touched
future involves an unsafe operation, but it is also touched via the
runtime thread, then the touching future can run after the runtime
touch completes.

There's probably room for improvement in the scheduler. Specifically,
if a future is touched and it's far back in the queue, it might be
better to move it to the front of the queue, so that the original
future can continue sooner.


Meanwhile, my explorations for `touch' uncovered the real sources (I
think) of crashes on my machine yesterday:

 * Lightweight continuations were sometimes captured during an attempt
   to synchronize for allocation (not useful, and not supported by the
   JIT).

 * Application of a lightweight continuation needed to make sure that
   the new runstack has enough extra space (i.e., the original host of
   the continuation checked to make sure it had enough space, so the
   new host needs to have at least as much space).

Fixing those bugs was probably more useful than the `touch' changes.