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From: Vratislav Podzimek <vratislav.podzimek@gmail.com>
Newsgroups: comp.lang.ada
Subject: Bug in GNAT? - Max_size_in_storage_elements insufficient
Date: Tue, 18 Oct 2016 11:17:37 +0000 (UTC)
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Xref: news.eternal-september.org comp.lang.ada:32116
Date: 2016-10-18T11:17:37+00:00
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When trying to set Storage_Size for tasks or records I'm getting a crash 
indicating that the Max_size_in_storage_elements attribute doesn't seem 
to provide the correct value. Here are the simple reproducers:

1) task type

with Ada.Text_Io; use Ada.Text_Io;

procedure Task_Storage_Size is
   task type My_Task (Id : Natural);    --  works just fine without the 
discriminant
   task body My_Task is
      X : Natural := Id;
   begin
      X := X ** 10;

      Put_Line ("ID : " & Natural'Image (Id));
   end;

   type My_Task_Access is access My_Task
     with Storage_Size => 4 * My_Task'Max_size_in_storage_elements; --  
Crashes
--     with Storage_Size => 6 * My_Task'Max_size_in_storage_elements; -- 
Doesn't crash.

   type My_Task_Array is array (Natural range <>) of My_Task_Access;
   Tasks : My_Task_Array (1..4);
begin
   --  raises STORAGE_ERROR : s-poosiz.adb:259 explicit raise
   for I in Tasks'Range loop
      Tasks (I) := new My_Task (I);
   end loop;
end;


2) record type:

procedure Record_Storage_Size is
   type My_Record is
      record
         X : Natural := 0;
      end record;

   type My_Record_Access is access My_Record
     with Storage_Size => 4 * My_Record'Max_size_in_storage_elements; -- 
crashes
     -- with Storage_Size => 8 * My_Record'Max_size_in_storage_elements; 
-- doesn't crash

   type My_Record_Array is array (Natural range <>) of My_Record_Access;
   Records : My_Record_Array (1..4);
begin
   --  raises STORAGE_ERROR : s-poosiz.adb:108 explicit raise
   for I in Records'Range loop
      Records (I) := new My_Record;
   end loop;
end;


To safe us from a potential discussion that has already happened on IRC, 
here's the related chunk from the RM:
"If Storage_Size is specified for an access type, then the Storage_Size 
of this pool is at least that requested, and the storage for the pool is 
reclaimed when the master containing the declaration of the access type 
is left"

So Storage_Size specification for an access type specifies the amount of 
space for the allocated objects of the accessed type. However, it can 
also be used for a task type (not access to a task type) to specify the 
amount of space for a task's stack.

Or am I missing something?