bordeaux threads return value

[Jim Newton]

I'm looking at the documentation https://trac.common-lisp.net/bordeaux-threads/wiki/ApiDocumentation
And I see that I can start a thread with make-thread given a 0-ary function,
and I can wait on the thread with join-thread. But the documentation does not say how
to get the return value of the 0-ary function. I would have expected that join-thread would
return the value, but the documentation explicitly does not say that.

There does not seem to be a documented way in this version of the API to get the return value.
Can someone help?

Thanks
Jim

[Jim Newton]

> But the documentation does not say how
> to get the return value of the 0-ary function.

It does seem that the sbcl implementation of join-thread returns the value of the function.

;;;; sbcl -----
(defun join-thread (thread)
(sb-thread:join-thread thread))

[Nicolas Neuss]

Usually these threads will work on some shared datastructure where
access is controlled via mutices etc.

If you want to distribute calculations depending on parameters and
obtain the return values, take a look at lparallel which provides a nice
interface for that: pmap, precuce etc.

Nicolas

[Jim Newton]

I took a look at the implementation of join-thread on several lisp implementations (sbcl, cmicl, ecl), and in each case join-thread returns the value which the 0-ary function returns. My suspicion is that that is the intent. It's just omitted from the documentation.

[Nicolas Neuss]

Yes, and in my version of the SBCL manual it is documented:

Function: join-thread [sb-thread] thread &key default timeout

Suspend current thread until thread exits. Return the result values of the thread function.
[...]

Nevertheless, you should take a look at lparallel.

Nicolas

[Jim Newton]

For example, the lipspworks version very explicitly returns the return value(s) of the function.

;; lispworks
(defun join-thread (thread)
(%join-thread thread)
(let ((return-values
(mp:process-property 'return-values thread)))
(values-list return-values)))