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) 2001-2003 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 2,  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.  See the GNU General Public License --
17-- for  more details.  You should have  received  a copy of the GNU General --
18-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
19-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
20-- MA 02111-1307, USA.                                                      --
21--                                                                          --
22-- As a special exception,  if other files  instantiate  generics from this --
23-- unit, or you link  this unit with other files  to produce an executable, --
24-- this  unit  does not  by itself cause  the resulting  executable  to  be --
25-- covered  by the  GNU  General  Public  License.  This exception does not --
26-- however invalidate  any other reasons why  the executable file  might be --
27-- covered by the  GNU Public License.                                      --
28--                                                                          --
29-- GNAT was originally developed  by the GNAT team at  New York University. --
30-- Extensive contributions were provided by Ada Core Technologies Inc.      --
31--                                                                          --
32------------------------------------------------------------------------------
33
34--  This version provides ways to limit the amount of used memory for systems
35--  that do not have OS support for that.
36
37--  The amount of available memory available for dynamic allocation is limited
38--  by setting the environment variable GNAT_MEMORY_LIMIT to the number of
39--  kilobytes that can be used.
40--
41--  Windows is currently using this version.
42
43with Ada.Exceptions;
44with System.Soft_Links;
45
46package body System.Memory is
47
48   use Ada.Exceptions;
49   use System.Soft_Links;
50
51   function c_malloc (Size : size_t) return System.Address;
52   pragma Import (C, c_malloc, "malloc");
53
54   procedure c_free (Ptr : System.Address);
55   pragma Import (C, c_free, "free");
56
57   function c_realloc
58     (Ptr : System.Address; Size : size_t) return System.Address;
59   pragma Import (C, c_realloc, "realloc");
60
61   function msize (Ptr : System.Address) return size_t;
62   pragma Import (C, msize, "_msize");
63
64   function getenv (Str : String) return System.Address;
65   pragma Import (C, getenv);
66
67   function atoi (Str : System.Address) return Integer;
68   pragma Import (C, atoi);
69
70   Available_Memory : size_t := 0;
71   --  Amount of memory that is available for heap allocations.
72   --  A value of 0 means that the amount is not yet initialized.
73
74   Msize_Accuracy   : constant := 4096;
75   --  Defines the amount of memory to add to requested allocation sizes,
76   --  because malloc may return a bigger block than requested. As msize
77   --  is used when by Free, it must be used on allocation as well. To
78   --  prevent underflow of available_memory we need to use a reserve.
79
80   procedure Check_Available_Memory (Size : size_t);
81   --  This routine must be called while holding the task lock. When the
82   --  memory limit is not yet initialized, it will be set to the value of
83   --  the GNAT_MEMORY_LIMIT environment variable or to unlimited if that
84   --  does not exist. If the size is larger than the amount of available
85   --  memory, the task lock will be freed and a storage_error exception
86   --  will be raised.
87
88   -----------
89   -- Alloc --
90   -----------
91
92   function Alloc (Size : size_t) return System.Address is
93      Result      : System.Address;
94      Actual_Size : size_t := Size;
95
96   begin
97      if Size = size_t'Last then
98         Raise_Exception (Storage_Error'Identity, "object too large");
99      end if;
100
101      --  Change size from zero to non-zero. We still want a proper pointer
102      --  for the zero case because pointers to zero length objects have to
103      --  be distinct, but we can't just go ahead and allocate zero bytes,
104      --  since some malloc's return zero for a zero argument.
105
106      if Size = 0 then
107         Actual_Size := 1;
108      end if;
109
110      Lock_Task.all;
111
112      if Actual_Size + Msize_Accuracy >= Available_Memory then
113         Check_Available_Memory (Size + Msize_Accuracy);
114      end if;
115
116      Result := c_malloc (Actual_Size);
117
118      if Result /= System.Null_Address then
119         Available_Memory := Available_Memory - msize (Result);
120      end if;
121
122      Unlock_Task.all;
123
124      if Result = System.Null_Address then
125         Raise_Exception (Storage_Error'Identity, "heap exhausted");
126      end if;
127
128      return Result;
129   end Alloc;
130
131   ----------------------------
132   -- Check_Available_Memory --
133   ----------------------------
134
135   procedure Check_Available_Memory (Size : size_t) is
136      Gnat_Memory_Limit : System.Address;
137
138   begin
139      if Available_Memory = 0 then
140
141         --  The amount of available memory hasn't been initialized yet
142
143         Gnat_Memory_Limit := getenv ("GNAT_MEMORY_LIMIT" & ASCII.NUL);
144
145         if Gnat_Memory_Limit /= System.Null_Address then
146            Available_Memory :=
147              size_t (atoi (Gnat_Memory_Limit)) * 1024 + Msize_Accuracy;
148         else
149            Available_Memory := size_t'Last;
150         end if;
151      end if;
152
153      if Size >= Available_Memory then
154
155         --  There is a memory overflow
156
157         Unlock_Task.all;
158         Raise_Exception
159           (Storage_Error'Identity, "heap memory limit exceeded");
160      end if;
161   end Check_Available_Memory;
162
163   ----------
164   -- Free --
165   ----------
166
167   procedure Free (Ptr : System.Address) is
168   begin
169      Lock_Task.all;
170
171      if Ptr /= System.Null_Address then
172         Available_Memory := Available_Memory + msize (Ptr);
173      end if;
174
175      c_free (Ptr);
176
177      Unlock_Task.all;
178   end Free;
179
180   -------------
181   -- Realloc --
182   -------------
183
184   function Realloc
185     (Ptr  : System.Address;
186      Size : size_t)
187      return System.Address
188   is
189      Result      : System.Address;
190      Actual_Size : constant size_t := Size;
191      Old_Size    : size_t;
192
193   begin
194      if Size = size_t'Last then
195         Raise_Exception (Storage_Error'Identity, "object too large");
196      end if;
197
198      Lock_Task.all;
199
200      Old_Size := msize (Ptr);
201
202      --  Conservative check - no need to try to be precise here
203
204      if Size + Msize_Accuracy >= Available_Memory then
205         Check_Available_Memory (Size + Msize_Accuracy);
206      end if;
207
208      Result := c_realloc (Ptr, Actual_Size);
209
210      if Result /= System.Null_Address then
211         Available_Memory := Available_Memory + Old_Size - msize (Result);
212      end if;
213
214      Unlock_Task.all;
215
216      if Result = System.Null_Address then
217         Raise_Exception (Storage_Error'Identity, "heap exhausted");
218      end if;
219
220      return Result;
221   end Realloc;
222
223end System.Memory;
224