1 ------------------------------------------------------------------------------
3 -- GNAT RUN-TIME COMPONENTS --
5 -- S Y S T E M . M E M O R Y --
9 -- Copyright (C) 2001-2009, Free Software Foundation, Inc. --
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. --
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. --
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/>. --
27 -- GNAT was originally developed by the GNAT team at New York University. --
28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
30 ------------------------------------------------------------------------------
32 -- This version provides ways to limit the amount of used memory for systems
33 -- that do not have OS support for that.
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.
39 -- Windows is currently using this version.
42 with System.Soft_Links;
44 package body System.Memory is
47 use System.Soft_Links;
49 function c_malloc (Size : size_t) return System.Address;
50 pragma Import (C, c_malloc, "malloc");
52 procedure c_free (Ptr : System.Address);
53 pragma Import (C, c_free, "free");
56 (Ptr : System.Address; Size : size_t) return System.Address;
57 pragma Import (C, c_realloc, "realloc");
59 function msize (Ptr : System.Address) return size_t;
60 pragma Import (C, msize, "_msize");
62 function getenv (Str : String) return System.Address;
63 pragma Import (C, getenv);
65 function atoi (Str : System.Address) return Integer;
66 pragma Import (C, atoi);
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.
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.
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
90 function Alloc (Size : size_t) return System.Address is
91 Result : System.Address;
92 Actual_Size : size_t := Size;
95 if Size = size_t'Last then
96 Raise_Exception (Storage_Error'Identity, "object too large");
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.
110 if Actual_Size + Msize_Accuracy >= Available_Memory then
111 Check_Available_Memory (Size + Msize_Accuracy);
114 Result := c_malloc (Actual_Size);
116 if Result /= System.Null_Address then
117 Available_Memory := Available_Memory - msize (Result);
122 if Result = System.Null_Address then
123 Raise_Exception (Storage_Error'Identity, "heap exhausted");
129 ----------------------------
130 -- Check_Available_Memory --
131 ----------------------------
133 procedure Check_Available_Memory (Size : size_t) is
134 Gnat_Memory_Limit : System.Address;
137 if Available_Memory = 0 then
139 -- The amount of available memory hasn't been initialized yet
141 Gnat_Memory_Limit := getenv ("GNAT_MEMORY_LIMIT" & ASCII.NUL);
143 if Gnat_Memory_Limit /= System.Null_Address then
145 size_t (atoi (Gnat_Memory_Limit)) * 1024 + Msize_Accuracy;
147 Available_Memory := size_t'Last;
151 if Size >= Available_Memory then
153 -- There is a memory overflow
157 (Storage_Error'Identity, "heap memory limit exceeded");
159 end Check_Available_Memory;
165 procedure Free (Ptr : System.Address) is
169 if Ptr /= System.Null_Address then
170 Available_Memory := Available_Memory + msize (Ptr);
183 (Ptr : System.Address;
185 return System.Address
187 Result : System.Address;
188 Actual_Size : constant size_t := Size;
192 if Size = size_t'Last then
193 Raise_Exception (Storage_Error'Identity, "object too large");
198 Old_Size := msize (Ptr);
200 -- Conservative check - no need to try to be precise here
202 if Size + Msize_Accuracy >= Available_Memory then
203 Check_Available_Memory (Size + Msize_Accuracy);
206 Result := c_realloc (Ptr, Actual_Size);
208 if Result /= System.Null_Address then
209 Available_Memory := Available_Memory + Old_Size - msize (Result);
214 if Result = System.Null_Address then
215 Raise_Exception (Storage_Error'Identity, "heap exhausted");