[Seaside-dev] hot to not use continuations

[Sebastian Sastre]

Thanks for the clarification Julian.
I've pretty much did that notification handling to make things work as expected
(I mean instead of the ifCurtailed).
sebastian


  _____  

De: seaside-dev-bounces at lists.squeakfoundation.org
[mailto:seaside-dev-bounces at lists.squeakfoundation.org] En nombre de Julian
Fitzell
Enviado el: Thursday, April 09, 2009 07:35
Para: Seaside - developer list
Asunto: Re: [Seaside-dev] hot to not use continuations


On Thu, Apr 2, 2009 at 11:31 PM, Sebastian Sastre <ssastre at seaswork.com> wrote:


Folks, just for the record:
I've found a cause of problems unless you're prepared:

I was using a block with ifCurtailed: wrapping the process of action and
rendering. By wrapping I mean someting about a filter depends on it.

Incidentally, the ifCurtailed: was basically there to make a rollback and/or
unlock any locked objects of a non flawless transaction.
So, to prevent surprises, developers must expect WAResponseNotification at any
time. This means that a non resumable notification will be triggered at any
moment when the action/render block is evaluated.


Well, #handleFiltered: *may* return normally; WAResponseNotification is used to
indicate that a RequestHandler wants to *immediately* abort processing and
return a response. In practice though, when using RenderLoop, we pretty much
always signal a notification.




As it's not resumable, the block will be evaluating the ifCurtailed even when
all is perfectly fine.



The fact that the notification is non-resumeable is not really the issue. The
notification will always be caught by the ServerAdaptor and that will cause the
stack to be unwound, which causes your #ifCurtailed: to be called. Your code
*is* being abnormally terminated by a request to immediately return a response.

Try executing this (which uses a resumeable notification) in a workspace, for
example:

[[nil notify: 1] ifCurtailed: [Transcript show: 'curtailed']]
    on: Notification do: []

Filters or request handlers can, of course, intercept the WAResponseNotification
and modify the Response as they see fit.

Julian



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