[Openmcl-devel] binding with threads

David L. Rager ragerdl at gmail.com
Thu Mar 21 07:27:56 PDT 2013

Hi Vijay,

Welcome to the world of CCL threads!

I don't yet know the answer to your first question.  However, maybe
you can figure it out with this debugging hint:  I have my own
multi-threading package, so this will look like pseudo-code.  The most
common thing I do is interrupt a thread and view its backtrace, which
should help you in this instance.

(all-threads)  ; or :proc, or (ccl:all-processes) iirc
(interrupt-thread (nth <n> (all-threads)) #'break)
:y <thread-number-to-yield-to>
:b ; for backtrace
<other common debugging features>

Is your futures library available?  There are various Lisp libraries
that provide parallel execution.  For example, Vladamir Sedach
provides an eager futures library [
http://common-lisp.net/project/eager-future/ ].  Also, I provide a
"plet" primitive (and others, like "spec-mv-let") for ACL2, which is
built on top of CL [
http://www.cs.utexas.edu/users/moore/acl2/current/PLET.html ].  If
you'd like more information about the latter, feel free to inquire
(probably off the list-serve).


PS -- setf can be different than just using let.  Maybe using or not
using special variables is part of the issue?
PPS -- are you on CCL 1.9 or later?  There was a bug for a little bit
right before the 1.9 release, but I'd be surprised if you were hitting
it in this simple test case.

On Thu, Mar 21, 2013 at 5:41 AM, Vijay Mathew
<vijay.the.lisper at gmail.com> wrote:
> Consider this code snippet which demonstrates a "futures" package for
> executing computations asynchronously:
> (setf e (futures:make-pool-executor 2))
> (setf f1 (futures:executor-submit e #'(lambda (x) (* x 2)) 100))
> (setf f2 (futures:executor-submit e #'(lambda (x y) (+ x y)) 200 300))
> (format t "~A~%" (futures:future-result f1))
> (format t "~A~%" (futures:future-result f2))
> (futures:executor-shutdown e nil)
> `pool-executor' internally uses a pool of ccl threads for executing the jobs
> submitted to it. Now if I rewrite the same sample using `let' bindings, the
> call to `future-result' just hangs. The threads actually run, but it seems
> `future-result' somehow do not see the updated value of the internal
> `result' slot.
> If I load this script, it just hangs the CCL REPL:
> (let ((e (futures:make-pool-executor 2)))
>   (let ((f1 (futures:executor-submit e #'(lambda (x) (* x 2)) 100))
>         (f2 (futures:executor-submit e #'(lambda (x y) (+ x y)) 200 300)))
>     (format t "~A~%" (futures:future-result f1))
>     (format t "~A~%" (futures:future-result f2))
>     (futures:executor-shutdown e nil)))
> Also I would like to learn about the best way to debug programs that use CCL
> threads.
> I am new to Common Lisp and the kind of support I am getting from this
> mailing list is very encouraging!
> Thank you,
> --Vijay
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> Openmcl-devel at clozure.com
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