Using local storage pools...

[Brian Drummond <brian_drummond@btconnect.com>]

I am trying to learn a little about storage pools, with a view to (hopefully)
using local pools to improve the Binary_Trees benchmark in the same way as some
of the faster C benchmarks.

Arguably they cheat : they do not explicitly free each tree node (the "free"
call has been deleted!) but free the entire pool at the end of the loop.
But if that's valid, Ada should be able to do the same.

http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gnat_ugn_unw/Some-Useful-Memory-Pools.html
suggests System.Pool_Local offers a way to do likewise - a pool that is
automatically reclaimed when it goes out of scope.

This turns out to have its own performance problem, but that is another story...

The question(or four)  for now is ... should the following really raise
Storage_Error, i.e. am I doing something silly, and if so, what? 
Or is this a bug in Gnat?

NOTE - using System.Pool_Global.Unbounded_No_Reclaim_Pool 
(commented out) instead of the pool shown, works as expected.

(Tested on GCC4.5.0 and Libre 2010)

- Brian

------------------------------------------------------------------------------------
with System.Pool_Local;
with System.Pool_Global;
with Ada.Unchecked_Deallocation;

procedure pooltest is

   type Node;
   type Treenode is access Node;
   type Node is record
      Left  : Treenode := null;
      Right : Treenode := null;
      Item  : Integer  := 0; 
   end record;

   P : System.Pool_Local.Unbounded_Reclaim_Pool;    
   --P : System.Pool_Global.Unbounded_No_Reclaim_Pool;
   for Treenode'Storage_Pool use P;

   procedure free is new Ada.Unchecked_Deallocation(Node, Treenode);

   TestNode : Treenode;

begin
   Testnode := new Node'(null, null, 1);
   free(Testnode);   
end pooltest;
------------------------------------------------------------------------------------