[armedbear-devel] threads, join, clos

Tobias C. Rittweiler tcr at freebits.de
Sun Apr 25 00:21:06 UTC 2010

David Kirkman <dkirkman at ucsd.edu> writes:

> On Sat, Apr 24, 2010 at 3:43 PM, Tobias C. Rittweiler <tcr at freebits.de> wrote:
>> A thread can return multiple values. Will those be returned in list form
>> as primary return value?
> Well, in the original patch it just returned the first value, and the second
> value is the completed/interrupted flag.  That's on obvious error, so I'm
> attaching a new patch that returns all of the values, plus the completed
> interrupted flag (for a function returning (values 1 2) thread-join will now
> return 1, 2, T)

That strictly couples the caller with its return sites; pain that
multiple values are usually supposed to obliterate from.

> > SBCL returns the values as multiple values, and signals an error in case
> > it couldn't join. I'm not sure what interface I'd like more. On SBCL,
> > you pretty much always have to wrap HANDLER-CASE around join-thread
> > which makes it unappropriate to use with MAPC.
> >
> > At the project I'm currently working on, I added the following wrapper:
> >
> >  (defun join-thread (thread &key timeout
> >                                  (on-timeout :timeout)
> >                                  (on-failure :error))
> >    ...)
> >
> > The ON-TIMEOUT/FAILURE arguments are returned as primary results, making
> > it potentially ambiguous (does :error come from the return value of the
> > thread or because of a failure?); however the user can specify these
> > values -- and the user should almost always know in what range a
> > thread's return value is going to be -- so it's my humble opinion on how
> > I think JOIN-THREAD should look like. :-)
> >
> I'm not committed to any particular semantics, other than I want thread-join
> to exist in some form!  Naturally, I kind of like the attached patch :)  (and I
> don't know how to get at keyword arguments in a java implemented
> primitive!).

You'd have to parse the &rest args by hand. I suggest you implement a
%join-thread in Java which only takes required arguments, and implement

> Is there a proposed threading standard for common lisp, or a de facto
> standard?

Not really. You can look at other implementation's documentation.


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