1 ------------------------------------------------------------------------------
3 -- GNAT RUN-TIME COMPONENTS --
5 -- S Y S T E M . M E M O R Y --
11 -- Copyright (C) 2001 Free Software Foundation, Inc. --
13 -- This specification is derived from the Ada Reference Manual for use with --
14 -- GNAT. The copyright notice above, and the license provisions that follow --
15 -- apply solely to the contents of the part following the private keyword. --
17 -- GNAT is free software; you can redistribute it and/or modify it under --
18 -- terms of the GNU General Public License as published by the Free Soft- --
19 -- ware Foundation; either version 2, or (at your option) any later ver- --
20 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
21 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
22 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
23 -- for more details. You should have received a copy of the GNU General --
24 -- Public License distributed with GNAT; see file COPYING. If not, write --
25 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
26 -- MA 02111-1307, USA. --
28 -- As a special exception, if other files instantiate generics from this --
29 -- unit, or you link this unit with other files to produce an executable, --
30 -- this unit does not by itself cause the resulting executable to be --
31 -- covered by the GNU General Public License. This exception does not --
32 -- however invalidate any other reasons why the executable file might be --
33 -- covered by the GNU Public License. --
35 -- GNAT was originally developed by the GNAT team at New York University. --
36 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
38 ------------------------------------------------------------------------------
40 -- This version provides ways to limit the amount of used memory for systems
41 -- that do not have OS support for that.
43 -- The amount of available memory available for dynamic allocation is limited
44 -- by setting the environment variable GNAT_MEMORY_LIMIT to the number of
45 -- kilobytes that can be used.
47 -- Windows is currently using this version.
50 with System.Soft_Links;
52 package body System.Memory is
55 use System.Soft_Links;
57 function c_malloc (Size : size_t) return System.Address;
58 pragma Import (C, c_malloc, "malloc");
60 procedure c_free (Ptr : System.Address);
61 pragma Import (C, c_free, "free");
64 (Ptr : System.Address; Size : size_t) return System.Address;
65 pragma Import (C, c_realloc, "realloc");
67 function msize (Ptr : System.Address) return size_t;
68 pragma Import (C, msize, "_msize");
70 function getenv (Str : String) return System.Address;
71 pragma Import (C, getenv);
73 function atoi (Str : System.Address) return Integer;
74 pragma Import (C, atoi);
76 Available_Memory : size_t := 0;
77 -- Amount of memory that is available for heap allocations.
78 -- A value of 0 means that the amount is not yet initialized.
80 Msize_Accuracy : constant := 4096;
81 -- Defines the amount of memory to add to requested allocation sizes,
82 -- because malloc may return a bigger block than requested. As msize
83 -- is used when by Free, it must be used on allocation as well. To
84 -- prevent underflow of available_memory we need to use a reserve.
86 procedure Check_Available_Memory (Size : size_t);
87 -- This routine must be called while holding the task lock. When the
88 -- memory limit is not yet initialized, it will be set to the value of
89 -- the GNAT_MEMORY_LIMIT environment variable or to unlimited if that
90 -- does not exist. If the size is larger than the amount of available
91 -- memory, the task lock will be freed and a storage_error exception
98 function Alloc (Size : size_t) return System.Address is
99 Result : System.Address;
100 Actual_Size : size_t := Size;
103 if Size = size_t'Last then
104 Raise_Exception (Storage_Error'Identity, "object too large");
107 -- Change size from zero to non-zero. We still want a proper pointer
108 -- for the zero case because pointers to zero length objects have to
109 -- be distinct, but we can't just go ahead and allocate zero bytes,
110 -- since some malloc's return zero for a zero argument.
118 if Actual_Size + Msize_Accuracy >= Available_Memory then
119 Check_Available_Memory (Size + Msize_Accuracy);
122 Result := c_malloc (Actual_Size);
124 if Result /= System.Null_Address then
125 Available_Memory := Available_Memory - msize (Result);
130 if Result = System.Null_Address then
131 Raise_Exception (Storage_Error'Identity, "heap exhausted");
137 ----------------------------
138 -- Check_Available_Memory --
139 ----------------------------
141 procedure Check_Available_Memory (Size : size_t) is
142 Gnat_Memory_Limit : System.Address;
145 if Available_Memory = 0 then
147 -- The amount of available memory hasn't been initialized yet
149 Gnat_Memory_Limit := getenv ("GNAT_MEMORY_LIMIT" & ASCII.NUL);
151 if Gnat_Memory_Limit /= System.Null_Address then
153 size_t (atoi (Gnat_Memory_Limit)) * 1024 + Msize_Accuracy;
155 Available_Memory := size_t'Last;
159 if Size >= Available_Memory then
161 -- There is a memory overflow
165 (Storage_Error'Identity, "heap memory limit exceeded");
167 end Check_Available_Memory;
173 procedure Free (Ptr : System.Address) is
177 if Ptr /= System.Null_Address then
178 Available_Memory := Available_Memory + msize (Ptr);
191 (Ptr : System.Address;
193 return System.Address
195 Result : System.Address;
196 Actual_Size : size_t := Size;
200 if Size = size_t'Last then
201 Raise_Exception (Storage_Error'Identity, "object too large");
206 Old_Size := msize (Ptr);
208 -- Conservative check - no need to try to be precise here
210 if Size + Msize_Accuracy >= Available_Memory then
211 Check_Available_Memory (Size + Msize_Accuracy);
214 Result := c_realloc (Ptr, Actual_Size);
216 if Result /= System.Null_Address then
217 Available_Memory := Available_Memory + Old_Size - msize (Ptr);
222 if Result = System.Null_Address then
223 Raise_Exception (Storage_Error'Identity, "heap exhausted");