gcc/ada/libgnat/s-memory__mingw.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                         S Y S T E M . M E M O R Y                        --
   6 --                                                                          --
   7 --                                 B o d y                                  --
   8 --                                                                          --
   9 --         Copyright (C) 2001-2017, Free Software Foundation, Inc.          --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  This version provides ways to limit the amount of used memory for systems
  33 --  that do not have OS support for that.
  34
  35 --  The amount of available memory available for dynamic allocation is limited
  36 --  by setting the environment variable GNAT_MEMORY_LIMIT to the number of
  37 --  kilobytes that can be used.
  38 --
  39 --  Windows is currently using this version.
  40
  41 with Ada.Exceptions;
  42 with System.Soft_Links;
  43
  44 package body System.Memory is
  45
  46    use Ada.Exceptions;
  47    use System.Soft_Links;
  48
  49    function c_malloc (Size : size_t) return System.Address;
  50    pragma Import (C, c_malloc, "malloc");
  51
  52    procedure c_free (Ptr : System.Address);
  53    pragma Import (C, c_free, "free");
  54
  55    function c_realloc
  56      (Ptr : System.Address; Size : size_t) return System.Address;
  57    pragma Import (C, c_realloc, "realloc");
  58
  59    function msize (Ptr : System.Address) return size_t;
  60    pragma Import (C, msize, "_msize");
  61
  62    function getenv (Str : String) return System.Address;
  63    pragma Import (C, getenv);
  64
  65    function atoi (Str : System.Address) return Integer;
  66    pragma Import (C, atoi);
  67
  68    Available_Memory : size_t := 0;
  69    --  Amount of memory that is available for heap allocations.
  70    --  A value of 0 means that the amount is not yet initialized.
  71
  72    Msize_Accuracy   : constant := 4096;
  73    --  Defines the amount of memory to add to requested allocation sizes,
  74    --  because malloc may return a bigger block than requested. As msize
  75    --  is used when by Free, it must be used on allocation as well. To
  76    --  prevent underflow of available_memory we need to use a reserve.
  77
  78    procedure Check_Available_Memory (Size : size_t);
  79    --  This routine must be called while holding the task lock. When the
  80    --  memory limit is not yet initialized, it will be set to the value of
  81    --  the GNAT_MEMORY_LIMIT environment variable or to unlimited if that
  82    --  does not exist. If the size is larger than the amount of available
  83    --  memory, the task lock will be freed and a storage_error exception
  84    --  will be raised.
  85
  86    -----------
  87    -- Alloc --
  88    -----------
  89
  90    function Alloc (Size : size_t) return System.Address is
  91       Result      : System.Address;
  92       Actual_Size : size_t := Size;
  93
  94    begin
  95       if Size = size_t'Last then
  96          Raise_Exception (Storage_Error'Identity, "object too large");
  97       end if;
  98
  99       --  Change size from zero to non-zero. We still want a proper pointer
 100       --  for the zero case because pointers to zero length objects have to
 101       --  be distinct, but we can't just go ahead and allocate zero bytes,
 102       --  since some malloc's return zero for a zero argument.
 103
 104       if Size = 0 then
 105          Actual_Size := 1;
 106       end if;
 107
 108       Lock_Task.all;
 109
 110       if Actual_Size + Msize_Accuracy >= Available_Memory then
 111          Check_Available_Memory (Size + Msize_Accuracy);
 112       end if;
 113
 114       Result := c_malloc (Actual_Size);
 115
 116       if Result /= System.Null_Address then
 117          Available_Memory := Available_Memory - msize (Result);
 118       end if;
 119
 120       Unlock_Task.all;
 121
 122       if Result = System.Null_Address then
 123          Raise_Exception (Storage_Error'Identity, "heap exhausted");
 124       end if;
 125
 126       return Result;
 127    end Alloc;
 128
 129    ----------------------------
 130    -- Check_Available_Memory --
 131    ----------------------------
 132
 133    procedure Check_Available_Memory (Size : size_t) is
 134       Gnat_Memory_Limit : System.Address;
 135
 136    begin
 137       if Available_Memory = 0 then
 138
 139          --  The amount of available memory hasn't been initialized yet
 140
 141          Gnat_Memory_Limit := getenv ("GNAT_MEMORY_LIMIT" & ASCII.NUL);
 142
 143          if Gnat_Memory_Limit /= System.Null_Address then
 144             Available_Memory :=
 145               size_t (atoi (Gnat_Memory_Limit)) * 1024 + Msize_Accuracy;
 146          else
 147             Available_Memory := size_t'Last;
 148          end if;
 149       end if;
 150
 151       if Size >= Available_Memory then
 152
 153          --  There is a memory overflow
 154
 155          Unlock_Task.all;
 156          Raise_Exception
 157            (Storage_Error'Identity, "heap memory limit exceeded");
 158       end if;
 159    end Check_Available_Memory;
 160
 161    ----------
 162    -- Free --
 163    ----------
 164
 165    procedure Free (Ptr : System.Address) is
 166    begin
 167       Lock_Task.all;
 168
 169       if Ptr /= System.Null_Address then
 170          Available_Memory := Available_Memory + msize (Ptr);
 171       end if;
 172
 173       c_free (Ptr);
 174
 175       Unlock_Task.all;
 176    end Free;
 177
 178    -------------
 179    -- Realloc --
 180    -------------
 181
 182    function Realloc
 183      (Ptr  : System.Address;
 184       Size : size_t)
 185       return System.Address
 186    is
 187       Result      : System.Address;
 188       Actual_Size : constant size_t := Size;
 189       Old_Size    : size_t;
 190
 191    begin
 192       if Size = size_t'Last then
 193          Raise_Exception (Storage_Error'Identity, "object too large");
 194       end if;
 195
 196       Lock_Task.all;
 197
 198       Old_Size := msize (Ptr);
 199
 200       --  Conservative check - no need to try to be precise here
 201
 202       if Size + Msize_Accuracy >= Available_Memory then
 203          Check_Available_Memory (Size + Msize_Accuracy);
 204       end if;
 205
 206       Result := c_realloc (Ptr, Actual_Size);
 207
 208       if Result /= System.Null_Address then
 209          Available_Memory := Available_Memory + Old_Size - msize (Result);
 210       end if;
 211
 212       Unlock_Task.all;
 213
 214       if Result = System.Null_Address then
 215          Raise_Exception (Storage_Error'Identity, "heap exhausted");
 216       end if;
 217
 218       return Result;
 219    end Realloc;
 220
 221 end System.Memory;