[Erp5-dev] Activity semaphoring/locking mechanisms, was: activate_kw for activities - how to use?

[Pelletier Vincent]

Le Mardi 11 Mars 2008 11:39, Łukasz Nowak a écrit :
> Some guessing - putting activity-like statements in activate_kw *might*
> be supported by scripts and methods invoked in activities, which shall
> pass those parameters into activate method call.

I think it should be:
  [...]scripts and methods invokING activities[...]
The content of activate_kw should be in turn used by the called method when 
generating new activities.

> Eg, calling:
>
> object.activate().edit(activate_kw={'tag':'my_tag'})
> object.activate(after_tag='my_tag').doSomethingElse()
>
> will do:
>  - invoke edit with with activities
>  - edit will invoke all its subsequents methods with activities and tag
> set to 'my_tag'
>  - invoking doSomethingElse will wait as long, as all scripts/methods
> generated by edit with this tag will be finished
>
> Am I right? Is that what activate_kw is for?

With more details, it will:
- create 2 activities (edit and doSomethingElse). Note that  "edit" activity
  has no tag.
- assuming that there is no existing activity (or at least, none with
  tag='my_tag'), either can execute. So they are 2 cases:
Case 1: edit is invoked strcictly first (doSomethingElse is not called untill 
edit call is over)
  - edit is invoked and generates an activity (most probably a
    "reindexObject") with tag='my_tag'
  - now, the only processable activity is "reindexObject", since
    doSomethingElse depends on its tag: reindexObject is invoked
  - doSomethingElse is invoked
Case 2: doSomethingElse is invoked before edit is over (includes being invoked 
before or simultaneously by another node - if any other)
  - doSomethingElse is invoked
  - edit is invoked and generate a reindexObject activity with tag="my_tag"
  - reindexObject is invoked

I guess you only want Case 1 to be possible. If so, you should issue something 
like:
 object.activate(tag='my_tag').edit(activate_kw={'tag':'my_tag'})
 object.activate(after_tag='my_tag').doSomethingElse()
So that edit activity itself also gets the tag doSomethinElse depends on.
edit activity will only be removed strictly after completion, so there will 
already be an activity with 'my_tag' present, so doSomethingElse has no 
chance to be executed at that time.

Note that those scenarii depends on "edit" to generate activities properly, 
with given tag.
In the case of "edit", I guess it is because it does not need to generate 
complex activities. But some method might want to use their own tags, which 
makes dependancy handling at their level a tiny bit more complex (they need 
to create dummy activities with provided tag and depending on the tags they 
internaly use).

-- 
Vincent Pelletier