path: root/gcc/ada/a-fihema.adb

------------------------------------------------------------------------------
--                                                                          --
--                         GNAT COMPILER COMPONENTS                         --
--                                                                          --
--     A D A . F I N A L I Z A T I O N . H E A P _ M A N A G E M E N T      --
--                                                                          --
--                                B o d y                                   --
--                                                                          --
--          Copyright (C) 2008-2011, Free Software Foundation, Inc.         --
--                                                                          --
-- GNAT is free software;  you can  redistribute it  and/or modify it under --
-- terms of the  GNU General Public License as published  by the Free Soft- --
-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
--                                                                          --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception,   --
-- version 3.1, as published by the Free Software Foundation.               --
--                                                                          --
-- You should have received a copy of the GNU General Public License and    --
-- a copy of the GCC Runtime Library Exception along with this program;     --
-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
-- <http://www.gnu.org/licenses/>.                                          --
--                                                                          --
-- GNAT was originally developed  by the GNAT team at  New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc.      --
--                                                                          --
------------------------------------------------------------------------------

with Ada.Exceptions;          use Ada.Exceptions;
with Ada.Unchecked_Conversion;

with System;                  use System;
with System.Address_Image;
with System.IO;               use System.IO;
with System.Soft_Links;       use System.Soft_Links;
with System.Storage_Elements; use System.Storage_Elements;
with System.Storage_Pools;    use System.Storage_Pools;

package body Ada.Finalization.Heap_Management is

   Header_Size   : constant Storage_Count  := Node'Size / Storage_Unit;
   --  Size of the header in bytes. Added to Storage_Size requested by
   --  Allocate/Deallocate to determine the Storage_Size passed to the
   --  underlying pool.

   Header_Offset : constant Storage_Offset := Header_Size;
   --  Offset from the header to the actual object. Used to get from the
   --  address of a header to the address of the actual object, and vice-versa.

   function Address_To_Node_Ptr is
     new Ada.Unchecked_Conversion (Address, Node_Ptr);

   procedure Attach (N : Node_Ptr; L : Node_Ptr);
   --  Prepend a node to a list

   procedure Detach (N : Node_Ptr);
   --  Unhook a node from an arbitrary list

   ---------------------------
   -- Add_Offset_To_Address --
   ---------------------------

   function Add_Offset_To_Address
     (Addr   : System.Address;
      Offset : System.Storage_Elements.Storage_Offset) return System.Address
   is
   begin
      return System.Storage_Elements."+" (Addr, Offset);
   end Add_Offset_To_Address;

   --------------
   -- Allocate --
   --------------

   procedure Allocate
     (Collection   : in out Finalization_Collection;
      Addr         : out System.Address;
      Storage_Size : System.Storage_Elements.Storage_Count;
      Alignment    : System.Storage_Elements.Storage_Count;
      Needs_Header : Boolean := True)
   is
   begin
      --  Allocation of an object with controlled parts

      if Needs_Header then

         --  Do not allow the allocation of controlled objects while the
         --  associated collection is being finalized.

         if Collection.Finalization_Started then
            raise Program_Error with "allocation after finalization started";
         end if;

         declare
            N_Addr : Address;
            N_Ptr  : Node_Ptr;

         begin
            --  Use the underlying pool to allocate enough space for the object
            --  and the list header. The returned address points to the list
            --  header. If locking is necessary, it will be done by the
            --  underlying pool.

            Allocate
              (Collection.Base_Pool.all,
               N_Addr,
               Storage_Size + Header_Size,
               Alignment);

            --  Map the allocated memory into a Node record. This converts the
            --  top of the allocated bits into a list header.

            N_Ptr := Address_To_Node_Ptr (N_Addr);
            Attach (N_Ptr, Collection.Objects'Unchecked_Access);

            --  Move the address from Prev to the start of the object. This
            --  operation effectively hides the list header.

            Addr := N_Addr + Header_Offset;
         end;

      --  Allocation of a non-controlled object

      else
         Allocate
           (Collection.Base_Pool.all,
            Addr,
            Storage_Size,
            Alignment);
      end if;

      pragma Assert (Addr mod Alignment = 0);
   end Allocate;

   ------------
   -- Attach --
   ------------

   procedure Attach (N : Node_Ptr; L : Node_Ptr) is
   begin
      Lock_Task.all;

      L.Next.Prev := N;
      N.Next := L.Next;
      L.Next := N;
      N.Prev := L;

      Unlock_Task.all;
      --  Note: no need to unlock in case of exceptions; the above code cannot
      --  raise any.
   end Attach;

   ---------------
   -- Base_Pool --
   ---------------

   function Base_Pool
     (Collection : Finalization_Collection) return Any_Storage_Pool_Ptr
   is
   begin
      return Collection.Base_Pool;
   end Base_Pool;

   ----------------
   -- Deallocate --
   ----------------

   procedure Deallocate
     (Collection   : in out Finalization_Collection;
      Addr         : System.Address;
      Storage_Size : System.Storage_Elements.Storage_Count;
      Alignment    : System.Storage_Elements.Storage_Count;
      Has_Header   : Boolean := True)
   is
      pragma Assert (Addr mod Alignment = 0);
   begin
      --  Deallocation of an object with controlled parts

      if Has_Header then
         declare
            N_Addr : Address;
            N_Ptr  : Node_Ptr;

         begin
            --  Move the address from the object to the beginning of the list
            --  header.

            N_Addr := Addr - Header_Offset;

            --  Converts the bits preceding the object into a list header

            N_Ptr := Address_To_Node_Ptr (N_Addr);
            Detach (N_Ptr);

            --  Use the underlying pool to destroy the object along with the
            --  list header.

            Deallocate
              (Collection.Base_Pool.all,
               N_Addr,
               Storage_Size + Header_Size,
               Alignment);
         end;

      --  Deallocation of a non-controlled object

      else
         Deallocate
           (Collection.Base_Pool.all,
            Addr,
            Storage_Size,
            Alignment);
      end if;
   end Deallocate;

   ------------
   -- Detach --
   ------------

   procedure Detach (N : Node_Ptr) is
      pragma Assert (N.Next /= null and then N.Prev /= null);
      --  It must be attached to some list

      procedure Null_Out_Pointers;
      --  Set Next/Prev pointer of N to null (for debugging)

      ----------
      -- Head --
      ----------

      procedure Null_Out_Pointers is
      begin
         N.Next := null;
         N.Prev := null;
      end Null_Out_Pointers;

   begin
      Lock_Task.all;

      N.Prev.Next := N.Next;
      N.Next.Prev := N.Prev;

      Unlock_Task.all;
      --  Note: no need to unlock in case of exceptions; the above code cannot
      --  raise any.

      pragma Debug (Null_Out_Pointers);
      --  No need to null out the pointers, except that it makes pcol easier to
      --  understand.
   end Detach;

   --------------
   -- Finalize --
   --------------

   overriding procedure Finalize
     (Collection : in out Finalization_Collection)
   is
      Curr_Ptr : Node_Ptr := Collection.Objects.Next; -- skip dummy head
      Ex_Occur : Exception_Occurrence;
      Raised   : Boolean := False;

   --  Start of processing for Finalize

   begin
      --  Set Finalization_Started to prevent any allocations of objects with
      --  controlled parts during finalization. The associated access type is
      --  about to go out of scope; Finalization_Started is never again
      --  modified.

      Collection.Finalization_Started := True;

      --  Go through the Objects list, and finalize each one. There is no need
      --  to detach items from the list, because the whole collection is about
      --  to go away.

      while Curr_Ptr /= Collection.Objects'Unchecked_Access loop
         --  ??? Kludge: Don't do anything until the proper place to set
         --  primitive Finalize_Address has been determined.

         if Collection.Finalize_Address /= null then
            declare
               Object_Address : constant Address :=
                 Curr_Ptr.all'Address + Header_Offset;
               --  Get address of object from address of header

            begin
               Collection.Finalize_Address (Object_Address);

            exception
               when Fin_Except : others =>
                  if not Raised then
                     Raised := True;
                     Save_Occurrence (Ex_Occur, Fin_Except);
                  end if;
            end;
         end if;

         Curr_Ptr := Curr_Ptr.Next;
      end loop;

      --  If the finalization of a particular node raised an exception, reraise
      --  it after the remainder of the list has been finalized.

      if Raised then
         Reraise_Occurrence (Ex_Occur);
      end if;
   end Finalize;

   ----------------
   -- Initialize --
   ----------------

   overriding procedure Initialize
     (Collection : in out Finalization_Collection)
   is
   begin
      --  The dummy head must point to itself in both directions

      Collection.Objects.Next := Collection.Objects'Unchecked_Access;
      Collection.Objects.Prev := Collection.Objects'Unchecked_Access;
   end Initialize;

   ----------
   -- pcol --
   ----------

   procedure pcol (Collection : Finalization_Collection) is
      Head      : constant Node_Ptr := Collection.Objects'Unrestricted_Access;
      --  "Unrestricted", because we're evilly getting access-to-variable of a
      --  constant!  OK for debugging code.

      Head_Seen : Boolean := False;
      N_Ptr     : Node_Ptr;

   begin
      --  Output the basic contents of the collection

      --    Collection: 0x123456789
      --    Base_Pool : null <or> 0x123456789
      --    Fin_Addr  : null <or> 0x123456789
      --    Fin_Start : TRUE <or> FALSE

      Put ("Collection: ");
      Put_Line (Address_Image (Collection'Address));

      Put ("Base_Pool : ");
      if Collection.Base_Pool = null then
         Put_Line (" null");
      else
         Put_Line (Address_Image (Collection.Base_Pool'Address));
      end if;

      Put ("Fin_Addr  : ");
      if Collection.Finalize_Address = null then
         Put_Line ("null");
      else
         Put_Line (Address_Image (Collection.Finalize_Address'Address));
      end if;

      Put ("Fin_Start : ");
      Put_Line (Collection.Finalization_Started'Img);

      --  Output all chained elements. The format is the following:

      --    ^ <or> ? <or> null
      --    |Header: 0x123456789 (dummy head)
      --    |  Prev: 0x123456789
      --    |  Next: 0x123456789
      --    V

      --  ^ - the current element points back to the correct element
      --  ? - the current element points back to an erroneous element
      --  n - the current element points back to null

      --  Header - the address of the list header
      --  Prev   - the address of the list header which the current element
      --         - points back to
      --  Next   - the address of the list header which the current element
      --         - points to
      --  (dummy head) - present if dummy head

      N_Ptr := Head;

      while N_Ptr /= null loop -- Should never be null; we being defensive
         Put_Line ("V");

         --  We see the head initially; we want to exit when we see the head a
         --  SECOND time.

         if N_Ptr = Head then
            exit when Head_Seen;

            Head_Seen := True;
         end if;

         --  The current element is null. This should never happen since the
         --  list is circular.

         if N_Ptr.Prev = null then
            Put_Line ("null (ERROR)");

         --  The current element points back to the correct element

         elsif N_Ptr.Prev.Next = N_Ptr then
            Put_Line ("^");

         --  The current element points to an erroneous element

         else
            Put_Line ("? (ERROR)");
         end if;

         --  Output the header and fields

         Put ("|Header: ");
         Put (Address_Image (N_Ptr.all'Address));

         --  Detect the dummy head

         if N_Ptr = Head then
            Put_Line (" (dummy head)");
         else
            Put_Line ("");
         end if;

         Put ("|  Prev: ");
         if N_Ptr.Prev = null then
            Put_Line ("null");
         else
            Put_Line (Address_Image (N_Ptr.Prev.all'Address));
         end if;

         Put ("|  Next: ");
         if N_Ptr.Next = null then
            Put_Line ("null");
         else
            Put_Line (Address_Image (N_Ptr.Next.all'Address));
         end if;

         N_Ptr := N_Ptr.Next;
      end loop;
   end pcol;

   ------------------------------
   -- Set_Finalize_Address_Ptr --
   ------------------------------

   procedure Set_Finalize_Address_Ptr
     (Collection : in out Finalization_Collection;
      Proc_Ptr   : Finalize_Address_Ptr)
   is
   begin
      Collection.Finalize_Address := Proc_Ptr;
   end Set_Finalize_Address_Ptr;

   --------------------------
   -- Set_Storage_Pool_Ptr --
   --------------------------

   procedure Set_Storage_Pool_Ptr
     (Collection : in out Finalization_Collection;
      Pool_Ptr   : Any_Storage_Pool_Ptr)
   is
   begin
      Collection.Base_Pool := Pool_Ptr;
   end Set_Storage_Pool_Ptr;

end Ada.Finalization.Heap_Management;