[Seaside] Questions about double (or more) request

[Philippe Marschall]

2009/8/6 Mariano Martinez Peck <marianopeck at gmail.com>:
>
>
> On Thu, Aug 6, 2009 at 4:16 AM, Philippe Marschall
> <philippe.marschall at gmail.com> wrote:
>>
>> 2009/8/5 Mariano Martinez Peck <marianopeck at gmail.com>:
>> > Hi! I am trying to understand how seaside handle double or more,
>> > request. I
>> > started with the simpler example: WACounter, which has:
>> >
>> > renderContentOn: html
>> >     Transcript show: 'renderContentOn'; cr.
>> >     html heading: count.
>> >     html anchor
>> >         callback: [ self increase ];
>> >         with: '++'.
>> >     html space.
>> >     html anchor
>> >         callback: [ self decrease ];
>> >         with: '--'
>> >
>> >
>> > increase
>> >     Transcript show: 'increase'; cr.
>> >     count := count + 1.
>> >     (Delay forSeconds: 3) wait.
>> >
>> >
>> > Now, suppose the counter is in 0. I click one time on '++' and wait and
>> > I
>> > see in the transcipt:
>> >
>> > increase
>> > renderContentOn
>> >
>> > Ok, perfect. New session, 0 again. Now I click on '++' but before it
>> > finish,
>> > I click 3 times more (very quickly). I can see this in the transcipt:
>> >
>> > increase
>> > increase
>> > increase
>> > increase
>> > renderContentOn
>> >
>> > So, as I can see:
>> >
>> > 1) the callback (self increase in this case) is called for every click.
>> > 2) the renderContentOn isn't call until all of the self increase of that
>> > session finish.
>> > 3) when renderContentOn  is called, the webpage shows the number 1
>> > (which is
>> > correct instead of 4).
>> >
>> > Now the questions are:
>> >
>> > a) how does seaside can do that? every request has its own variables? I
>> > think this has to be with continuations but I want to be sure.
>>
>> I order of you observations:
>> 1) You (your browser) makes three callback requests and discards the
>> redirect to render for the first two
>
> Ok, but which is the "condition" to be discarded? if the callback request is
> finished but there are others callbacks request then it is discarded?

Seaside doesn't discard anything, the browser has to. Here's a rough
sketch of what happens:
- You initiate a content exchange for the "callbacks page".
- The browser sends a request.
- The Seaside callback machinery kicks in.
- Before Seaside can send a response you initiate three more requests
resulting in three more requests.

Seaside doesn't really have a problem with this, it will process these
requests one after another, meaning "executing" the same "callback
page" several times and send the redirect response to the render page
for each one. However the browser has, he has just one pane where he
can render the resonse. So he'll have to discard all but one of the
responses. The least bad thing is to discard all but the last one.

>>
>> 2) There is a lock that allows only one request per session at a time,
>> otherwise your components would have to be thread safe
>> 3) state backtracking, before every request the state of the counter
>> is reverted to 0
>
> that's because there was the method states ?

Yes

>>
>> > b) which of all of the self increase is the one that is finally
>> > rendered?
>> > the first one?
>>
>> That should be the last one. The browser should discard processing the
>> previous requests. Disable backtracking to be sure.
>
> what do you mean with Disable backtracking ? remove the method states from
> the component?

Yes

Cheers
Philippe