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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--                         S Y S T E M . M E M O R Y                        --

--                                                                          --

--                                 B o d y                                  --

--                                                                          --

--         Copyright (C) 2001-2009, 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.      --

--                                                                          --

------------------------------------------------------------------------------

--  This version provides ways to limit the amount of used memory for systems

--  that do not have OS support for that.

--  The amount of available memory available for dynamic allocation is limited

--  by setting the environment variable GNAT_MEMORY_LIMIT to the number of

--  kilobytes that can be used.

--

--  Windows is currently using this version.

with Ada.Exceptions;

with System.Soft_Links;

package body System.Memory is

   use Ada.Exceptions;

   use System.Soft_Links;

   function c_malloc (Size : size_t) return System.Address;

   pragma Import (C, c_malloc, "malloc");

   procedure c_free (Ptr : System.Address);

   pragma Import (C, c_free, "free");

   function c_realloc

     (Ptr : System.Address; Size : size_t) return System.Address;

   pragma Import (C, c_realloc, "realloc");

   function msize (Ptr : System.Address) return size_t;

   pragma Import (C, msize, "_msize");

   function getenv (Str : String) return System.Address;

   pragma Import (C, getenv);

   function atoi (Str : System.Address) return Integer;

   pragma Import (C, atoi);

   Available_Memory : size_t := 0;

   --  Amount of memory that is available for heap allocations.

   --  A value of 0 means that the amount is not yet initialized.

   Msize_Accuracy   : constant := 4096;

   --  Defines the amount of memory to add to requested allocation sizes,

   --  because malloc may return a bigger block than requested. As msize

   --  is used when by Free, it must be used on allocation as well. To

   --  prevent underflow of available_memory we need to use a reserve.

   procedure Check_Available_Memory (Size : size_t);

   --  This routine must be called while holding the task lock. When the

   --  memory limit is not yet initialized, it will be set to the value of

   --  the GNAT_MEMORY_LIMIT environment variable or to unlimited if that

   --  does not exist. If the size is larger than the amount of available

   --  memory, the task lock will be freed and a storage_error exception

   --  will be raised.

   -----------

   -- Alloc --

   -----------

   function Alloc (Size : size_t) return System.Address is

      Result      : System.Address;

      Actual_Size : size_t := Size;

   begin

      if Size = size_t'Last then

         Raise_Exception (Storage_Error'Identity, "object too large");

      end if;

      --  Change size from zero to non-zero. We still want a proper pointer

      --  for the zero case because pointers to zero length objects have to

      --  be distinct, but we can't just go ahead and allocate zero bytes,

      --  since some malloc's return zero for a zero argument.

      if Size = 0 then

         Actual_Size := 1;

      end if;

      Lock_Task.all;

      if Actual_Size + Msize_Accuracy >= Available_Memory then

         Check_Available_Memory (Size + Msize_Accuracy);

      end if;

      Result := c_malloc (Actual_Size);

      if Result /= System.Null_Address then

         Available_Memory := Available_Memory - msize (Result);

      end if;

      Unlock_Task.all;

      if Result = System.Null_Address then

         Raise_Exception (Storage_Error'Identity, "heap exhausted");

      end if;

      return Result;

   end Alloc;

   ----------------------------

   -- Check_Available_Memory --

   ----------------------------

   procedure Check_Available_Memory (Size : size_t) is

      Gnat_Memory_Limit : System.Address;

   begin

      if Available_Memory = 0 then

         --  The amount of available memory hasn't been initialized yet

         Gnat_Memory_Limit := getenv ("GNAT_MEMORY_LIMIT" & ASCII.NUL);

         if Gnat_Memory_Limit /= System.Null_Address then

            Available_Memory :=

              size_t (atoi (Gnat_Memory_Limit)) * 1024 + Msize_Accuracy;

         else

            Available_Memory := size_t'Last;

         end if;

      end if;

      if Size >= Available_Memory then

         --  There is a memory overflow

         Unlock_Task.all;

         Raise_Exception

           (Storage_Error'Identity, "heap memory limit exceeded");

      end if;

   end Check_Available_Memory;

   ----------

   -- Free --

   ----------

   procedure Free (Ptr : System.Address) is

   begin

      Lock_Task.all;

      if Ptr /= System.Null_Address then

         Available_Memory := Available_Memory + msize (Ptr);

      end if;

      c_free (Ptr);

      Unlock_Task.all;

   end Free;

   -------------

   -- Realloc --

   -------------

   function Realloc

     (Ptr  : System.Address;

      Size : size_t)

      return System.Address

   is

      Result      : System.Address;

      Actual_Size : constant size_t := Size;

      Old_Size    : size_t;

   begin

      if Size = size_t'Last then

         Raise_Exception (Storage_Error'Identity, "object too large");

      end if;

      Lock_Task.all;

      Old_Size := msize (Ptr);

      --  Conservative check - no need to try to be precise here

      if Size + Msize_Accuracy >= Available_Memory then

         Check_Available_Memory (Size + Msize_Accuracy);

      end if;

      Result := c_realloc (Ptr, Actual_Size);

      if Result /= System.Null_Address then

         Available_Memory := Available_Memory + Old_Size - msize (Result);

      end if;

      Unlock_Task.all;

      if Result = System.Null_Address then

         Raise_Exception (Storage_Error'Identity, "heap exhausted");

      end if;

      return Result;

   end Realloc;

end System.Memory;