[Seaside] Re: Task Escape

[Philippe Marschall]

2008/1/10, Zulq Alam <me at zulq.net>:
> I have created a superclass for all my tasks, CancelAwareTask to work in
> conjunction with a Notification subclass CancelNotification. In response
> to a notification, the task will reset its state and then answer (if
> possible).
>
> CancelAwareTask>>#go
>      " Subclasses should implement #run instead. "
>      [self run]
>          on: CancelNotification
>          do: [self handleCancel]
>
> CancelAwareTask>>#cancel
>      CancelNotification signal
>
> CancelAwareTask>>#handleCancel
>      self reset.
>      self answer
>
> CancelAwareTask>>#reset
>      " Reset any state. "
>      self subclassResponsibility
>
> CancelAwareTask>>#run
>      " Implement instead of #go. "
>      self subclassResponsibility
>
>
> A run method might then be:
>
> MyCancelAwareTask>>#run
>      self stepOne
>      self stepTwo
>      ...
>      self stepN
>
> MyCancelAwareTask>>#stepN
>      (self call: MyComponent new) ifFalse: [self cancel]
>
> MyCancelAwareTask>>#reset
>      iVarOne := nil.
>      iVarTwo := nil.
>      ...
>      iVarN := nil
>
> This seems to work and I like it because I don't have to change very
> much to make it work. I suspect it's not very efficient though.

Given all the overhead like sending stuff over the internet this
shouldn't be noticable.

Cheers
Philippe

> Would be
> interested in your comments.
>
> Thanks,
> Zulq.
>
> Zulq Alam wrote:
> > I have a task with N steps:
> >
> > MyTask>>#go
> >     self stepOne.
> >     self stepTwo.
> >     ...
> >     self stepN.
> >
> > Each step calls one or more components. Each component offer a Cancel
> > link / button. If clicked, the component answers false. If a component
> > answers false, the task should stop. I currently do this by checking the
> > answer value and then answering if the value is false.
> >
> > MyTask>>#stepN
> >     (self call: MyComponent new)
> >         ifFalse: [self answer: false]
> >
> > This seems to work OK but only if the task has been called. If it is the
> > root component, then the answer is a no-op.
> >
> > I don't intend for such tasks to be used as root components and
> > practically this isn't a problem but it doesn't feel right. The task
> > should work no matter how it is being used.
> >
> > I suppose I could check after each step (yuk):
> >
> > MyTask>>#go
> >     ((self stepOne
> >         ifTrue: [self stepTwo])
> >             ifTrue: [self stepThree])
> >     ...
> >             ifTrue: [self stepN]
> >
> > Or, I could check at the beginning of each step (*slightly* less yuk):
> >
> > MyTask>>#stepN
> >     shouldRun ifFalse: [^ self].
> >     ...
> >
> > Or:
> >
> > MyTask>>#stepN
> >     self stepNMinusOne ifFalse: [^ self]
> >     ...
> >
> > Or I could use a signal:
> >
> > MyTask>>#stepN
> >     (self call: MyComponent new) ifFalse: [MyCancellation signal]
> >
> > MyTask>>#go
> >     [self stepOne.
> >     self stepTwo.
> >     ...
> >     self stepThree]
> >         on: MyCancellation
> >         do: [self answer: false]
> >
> > To me the signal looks the best, but feels like an abuse of the
> > exception handling framework.
> >
> > What have others done? It's very possible I still don't know how to use
> > tasks properly, so please feel free to correct me!
> >
> > Thanks,
> > Zulq.
>
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