Gauche has been mutexing realization of a promise, but srfi-226 is the
right thing; evaluation of the body may communicate to another thread that
may take the value of the promise. Current Gauche deadlocks in that case.
By the way, in the reference implementation, 'force' has this code:
(if (promise-done? p)
((promise-thunk p))
(call-with-immediate-continuation-mark ....))
And:
(promise-lock! p)
...
(promise-done?-set! p (promise-done? q))
(promise-thunk-set! p (promise-thunk q)))
...
(promise-unlock! p)
First I thought you need to lock promise to check promise-done? and
retrieve promise-thunk, otherwise you may read the old value of
promise-thunk and reevaluate the body. However, it is allowed that the
body is evaluated multiple times, it's ok. Am I understanding it right?
On Sat, Mar 11, 2023 at 3:02 AM Marc Nieper-Wißkirchen <
marc.nie...@gmail.com> wrote:
> Am Sa., 11. März 2023 um 11:11 Uhr schrieb Shiro Kawai <
> shiro.ka...@gmail.com>:
> >
> > From the srfi text, it is allowed that the delay's body to be evaluated
> by more than one thread simultaneously; only that the result of force is
> the result of the first delivered result. Am I right?
>
> Indeed. This is analogous to promises being forced while their "body"
> is evaluated, even in the same thread.
>
> >
>
