[Pharo-project] About testing that ensure works

Stéphane Ducasse stephane.ducasse at inria.fr
Wed Apr 27 11:16:12 CEST 2011

I see. Subtle. May be a solution not slowing everything but more limited is the way to go.

>>>> i am puzzled. You wanna to be sure that ensure block are executed?
>>>> It is.
>>> I want to write a test that shows and tests the withOrganizer:do:
>>> semantics.
>>> In particular that the ensure is executed and that the context set by the
>>> withOrganizer: is only present
>>> in the do: block.
>> In other words, another use case probably written more cleanly using the
>> non-existing
>> Announcer >> #suspend: subscriber while: aBlock
> What is potential implementation?
> Announcer >>suspend: subscriber while: aBlock
> | subscriptions |
> subscriptions := OrderedCollection new.
> registry subscriptionsOf: subscriber do: [:each |
>  subscriptions add: each
> ].
> registry removeSubscriber: subscriber.
> ^ aBlock ensure: [ subscriptions do: [:ea | registry add: ea ] ]
> The problem is that its not doing exactly what is said:
> - it suspends existing subscriptions instead of suspending subscriber.
> The difference between those are subtle but important:
>  a suspended subscriber should not receive any announcements during
> block evaluation,
> even if it may want to subscribe to new ones during given block evaluation.
> And the code above not handling this case , as well as it doesn't
> handling the case when subscriber may want
> to occasionally unsubscribe from some announcements during block evaluation.
> So, for doing this correctly, a subscription registry should keep a
> list of suspended subscribers somewhere,
> and then in #deliver:
> it should check if subscription's subscriber are not in that list, and
> only then let it deliver an announcement.
> The problem is that delivery time will slowdown considerably, because
> for every subscription you should check
> if it's subscriber are not in 'suspended subscribers' list.
> So, it is really depends on intent. Suspending a concrete subscription
> will require adding 'suspended' flag to subscription state.
> But suspending a concrete subscriber and to guarantee that it won't
> receive any announcements (even if it will subscribe for
> a new ones during suspension time), can't be solved by having
> 'suspended' ivar on subscription. You have to manage suspended
> subscribers list separately.
> -- 
> Best regards,
> Igor Stasenko AKA sig.

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