Re: task synchronization and activation

[Jean-Pierre Rosen <rosen@adalog.fr>]

Evangelista Sami a �crit :
> Hello all
> 
> Why does a task have to wait that all the tasks it created are
> activated before
> executing? I am thinking of point 9.2.5 of the RM :
> 
> "The task that created the new tasks and initiated their activations
> (the activator) is blocked until all of these activations complete
> (successfully or not)."
> 
> I can understand that a master has to wait for the tasks he created
> before finalizing since in the other case it could "free" some memory
> needed by its children.
> But i cannot see why this synchronisation after activation is
> necessary. What is the technical reason?
> 
It has to do with exceptions at elaboration.

When a task is started, it first elaborates its declarative part. If 
exceptions are raised during this elaboration, they cannot be handled by 
the task itself, therefore it is necessary to notify *someone*, and the 
obvious "someone" is the activator. However, we don't want to have 
asynchronous exceptions, therefore the activator has to wait that all 
subtasks are (correctly) activated.

Differently said: when an activator reaches the first statement after 
the begin, it is guaranteed that all subtasks have been correctly 
activated; otherwise, Tasking_Error is raised after begin (so it can be 
handled locally), but before the first statement.

-- 
---------------------------------------------------------
            J-P. Rosen (rosen@adalog.fr)
Visit Adalog's web site at http://www.adalog.fr