[Ada] Automatic deallocation of task upon termination

[Arnaud Charlet <charlet at adacore dot com>]

This change implements a new feature in the tasking runtime library: if
Unchecked_Deallocation is called on a non-terminated task (which was
previously a no-op), the task is now marked to be freed automatically when
it terminates.

The following test case demonstrates the feature:

$ gnatmake -q -z free_nonterm_task

When executing free_nonterm_task under valgrind, no memory leak corresponding
to the creation of task T (in System.Tasking.Stages.Create_Task) shall be
reported.

package Free_Nonterm_Task is
   pragma Elaborate_Body;
end Free_Nonterm_Task;

with Ada.Unchecked_Deallocation;
with Ada.Text_IO; use Ada.Text_IO;

package body Free_Nonterm_Task is

   type T;
   type A is access T;

   task type T is
      entry Term (Self : in out A);
   end T;

   procedure Free is new Ada.Unchecked_Deallocation (T, A);

   task body T is
   begin
      Put_Line ("T: enter");

      accept Term (Self : in out A) do
         Free (Self);
      end Term;
      Put_Line ("T: exit");
   end T;
   My_Task : A;
begin
   Put_Line ("Create task");
   My_Task := new T;
   Put_Line ("Call Term");
   My_Task.Term (My_Task);
end Free_Nonterm_Task;

Tested on x86_64-pc-linux-gnu, committed on trunk

2011-09-06  Thomas Quinot  <quinot@adacore.com>

	* s-tassta.adb, s-taskin.ads (Free_Task): If the task is not
	terminated, mark it for deallocation upon termination.
	(Terminate_Task): Call Free_Task again if the task is marked
	for automatic deallocation upon termination.

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