Re: Ada Tasking & LRM

Re: Ada Tasking & LRM

[Robert I. Eachus]

     Section 9.4(1) says "Each task depends on at least one master.
A master is a construct that is either a task, a currently executing
block statement or subprogram, or a library package ( a package
declared within another program unit is not a master)."

     The key is the words "at least one".  If a task is declared
within a unit that is enclosed by (one or more) outer units, the outer
units will be masters (if they are not nested packages) whether or not
the innermost enclosing unit is a master.  So the master of My_Task in
the first example is package One and there is no problem.

     The reason the second example raises PROGRAM_ERROR has nothing to
do with this rule.  The type a_task has not been and cannot be
elaborated before the creation of My_Task.  (The elaboration of A_Type
happens in the body of One the ellaboration of My_Task in the spec.)

      Note that one of the advantages of child packages in Ada 9X will
be that it will be possible to have a package which exports both a
task type and a child package containing an object of that type.
The usual Ada 83 solution for this sort of problem (in particular a
need to export both a private type and an object of that type) is to
use generics.

--

					Robert I. Eachus

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