[racket] plot-frame does not wait at end of process

For this specific program, it would behave the same way. In general what
yield means is "block on this evt, but while you're blocked handle GUI
events". So you call it from the eventspace handler thread of some
eventspace, then that eventspace can still handle events while the evt
passed to yield is not ready.

FWIW, in general using yield properly is hard because you have to call it
from inside some event handler and then you get into a nested situation,
something that it is easy to get wrong. That is, GUIs tend to work well and
be not too hard to implement if you maintain the "handle one event
completely before starting to handle another one" discipline. But that
isn't right sometimes (modal dialogs are the classic example: when you
choose the File|Open... menu item in DrRacket, for example, it has to get
half-way into the handling of that event and then start handling other
events (clicks on the file dialog) before returning. So what you usually do
here is just lock every other thing in your app ...).

hth,
Robby




On Sun, Mar 17, 2013 at 8:33 AM, Laurent <laurent.orseau at gmail.com> wrote:

> In his second version (see below), Matthew was basically encapsulating
> what you have written inside (yield ...).
> Would you mind to explain what differences that makes? I've read the docs
> but I'm still confused about `yield'.
>
> >> >> >   #lang at-exp racket
> >> >> >   (require plot
> >> >> >            racket/gui/base)
> >> >> >   (plot-new-window? #t)
> >> >> >   (yield
> >> >> >    (thread
> >> >> >     (lambda ()
>
> >> >> >       (let loop ()
> >> >> >         (let ((dummy (read)))
> >> >> >           (if (and (number? dummy) (zero? dummy))
> >> >> >               (void)
> >> >> >               (begin
> >> >> >                 ;; queue a callback instead of `plot' directly:
> >> >> >                 (queue-callback
> >> >> >                  (lambda ()
> >> >> >                    (plot (function (λ(x) (* x x)) -2 2))))
> >> >> >                 (loop))))))))
>
> Thanks,
> Laurent
>
>
> On Sun, Mar 17, 2013 at 2:13 PM, Robby Findler <
> robby at eecs.northwestern.edu> wrote:
>
>> That way has the property that each plot window has its own thread of
>> execution, which is probably not necessary (I don't know if plot windows
>> communicate or if that matters), but if it were me, I'd probably just make
>> one extra thread, not N, and I'd put the reading into the extra thread not
>> the GUI, like the below.
>>
>> #lang racket/gui
>> (require plot)
>> (plot-new-window? #t)
>> (define (do-one)
>>   (define dummy (read))
>>   (cond
>>     [(and (number? dummy) (zero? dummy))
>>      #f]
>>     [else
>>      (queue-callback
>>       (λ ()
>>         (plot (function (λ (x) (* x x)) -2 2))))
>>      #t]))
>>
>> (when (do-one)
>>   (void
>>    (thread
>>     (λ ()
>>       (let loop ()
>>         (when (do-one)
>>           (loop)))))))
>>
>>
>>
>>
>> On Sun, Mar 17, 2013 at 4:42 AM, Laurent <laurent.orseau at gmail.com>wrote:
>>
>>> So, does this means that Deren's program from
>>> http://lists.racket-lang.org/users/archive/2012-April/051490.html
>>> would then look like that:
>>>
>>> #lang racket
>>> (require plot)
>>> (plot-new-window? #t)
>>> (let loop ()
>>>   (let ((dummy (read)))
>>>     (if (and (number? dummy) (zero? dummy))
>>>         (void)
>>>         (begin
>>>           (parameterize ([current-eventspace (make-eventspace)])
>>>             (plot (function (λ(x) (* x x)) -2 2)))
>>>           (loop)))))
>>>
>>> ?
>>>
>>> Laurent
>>>
>>>
>>> On Sun, Mar 17, 2013 at 7:15 AM, Eli Barzilay <eli at barzilay.org> wrote:
>>>
>>>> On Thursday, Robby Findler wrote:
>>>> > Also: I don't think that you need a parameter for this default. the
>>>> > current-eventspace parameter would already do this job.
>>>>
>>>> IOW, Robby wants no keyword or parameter, just the default behavior,
>>>> and if there's a problem with that then people would deal with it like
>>>> with any other gui code.  FWIW, I'm on that side too.
>>>>
>>>> --
>>>>           ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
>>>>                     http://barzilay.org/                   Maze is
>>>> Life!
>>>> ____________________
>>>>   Racket Users list:
>>>>   http://lists.racket-lang.org/users
>>>>
>>>
>>>
>>
>
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