1 ------------------------------------------------------------------------------
3 -- GNAT RUN-TIME COMPONENTS --
5 -- S Y S T E M . M E M O R Y --
9 -- Copyright (C) 2001-2003 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 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, 51 Franklin Street, Fifth Floor, --
20 -- Boston, MA 02110-1301, USA. --
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. --
29 -- GNAT was originally developed by the GNAT team at New York University. --
30 -- Extensive contributions were provided by Ada Core Technologies Inc. --
32 ------------------------------------------------------------------------------
34 -- This version provides ways to limit the amount of used memory for systems
35 -- that do not have OS support for that.
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.
41 -- Windows is currently using this version.
44 with System.Soft_Links;
46 package body System.Memory is
49 use System.Soft_Links;
51 function c_malloc (Size : size_t) return System.Address;
52 pragma Import (C, c_malloc, "malloc");
54 procedure c_free (Ptr : System.Address);
55 pragma Import (C, c_free, "free");
58 (Ptr : System.Address; Size : size_t) return System.Address;
59 pragma Import (C, c_realloc, "realloc");
61 function msize (Ptr : System.Address) return size_t;
62 pragma Import (C, msize, "_msize");
64 function getenv (Str : String) return System.Address;
65 pragma Import (C, getenv);
67 function atoi (Str : System.Address) return Integer;
68 pragma Import (C, atoi);
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.
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.
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
92 function Alloc (Size : size_t) return System.Address is
93 Result : System.Address;
94 Actual_Size : size_t := Size;
97 if Size = size_t'Last then
98 Raise_Exception (Storage_Error'Identity, "object too large");
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.
112 if Actual_Size + Msize_Accuracy >= Available_Memory then
113 Check_Available_Memory (Size + Msize_Accuracy);
116 Result := c_malloc (Actual_Size);
118 if Result /= System.Null_Address then
119 Available_Memory := Available_Memory - msize (Result);
124 if Result = System.Null_Address then
125 Raise_Exception (Storage_Error'Identity, "heap exhausted");
131 ----------------------------
132 -- Check_Available_Memory --
133 ----------------------------
135 procedure Check_Available_Memory (Size : size_t) is
136 Gnat_Memory_Limit : System.Address;
139 if Available_Memory = 0 then
141 -- The amount of available memory hasn't been initialized yet
143 Gnat_Memory_Limit := getenv ("GNAT_MEMORY_LIMIT" & ASCII.NUL);
145 if Gnat_Memory_Limit /= System.Null_Address then
147 size_t (atoi (Gnat_Memory_Limit)) * 1024 + Msize_Accuracy;
149 Available_Memory := size_t'Last;
153 if Size >= Available_Memory then
155 -- There is a memory overflow
159 (Storage_Error'Identity, "heap memory limit exceeded");
161 end Check_Available_Memory;
167 procedure Free (Ptr : System.Address) is
171 if Ptr /= System.Null_Address then
172 Available_Memory := Available_Memory + msize (Ptr);
185 (Ptr : System.Address;
187 return System.Address
189 Result : System.Address;
190 Actual_Size : constant size_t := Size;
194 if Size = size_t'Last then
195 Raise_Exception (Storage_Error'Identity, "object too large");
200 Old_Size := msize (Ptr);
202 -- Conservative check - no need to try to be precise here
204 if Size + Msize_Accuracy >= Available_Memory then
205 Check_Available_Memory (Size + Msize_Accuracy);
208 Result := c_realloc (Ptr, Actual_Size);
210 if Result /= System.Null_Address then
211 Available_Memory := Available_Memory + Old_Size - msize (Result);
216 if Result = System.Null_Address then
217 Raise_Exception (Storage_Error'Identity, "heap exhausted");