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authorTon Voon <ton.voon@opsera.com>2010-06-24 09:02:31 (GMT)
committerTon Voon <ton.voon@opsera.com>2010-06-24 09:02:31 (GMT)
commit342f3b403e888800fb1b0502bf4e0d8268358573 (patch)
tree47a0031fcf01edae3131fc147304d14f6f2aee20 /gl/malloca.c
parentf789a37b057b6f34820ea4f95d63f53b5a84c980 (diff)
downloadmonitoring-plugins-342f3b403e888800fb1b0502bf4e0d8268358573.tar.gz
Added unsetenv and setenv from gnulib
Diffstat (limited to 'gl/malloca.c')
-rw-r--r--gl/malloca.c140
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1/* Safe automatic memory allocation.
2 Copyright (C) 2003, 2006-2007, 2009-2010 Free Software Foundation, Inc.
3 Written by Bruno Haible <bruno@clisp.org>, 2003.
4
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3, or (at your option)
8 any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, write to the Free Software Foundation,
17 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
18
19#include <config.h>
20
21/* Specification. */
22#include "malloca.h"
23
24/* Use the system functions, not the gnulib overrides in this file. */
25#undef malloc
26
27/* The speed critical point in this file is freea() applied to an alloca()
28 result: it must be fast, to match the speed of alloca(). The speed of
29 mmalloca() and freea() in the other case are not critical, because they
30 are only invoked for big memory sizes. */
31
32#if HAVE_ALLOCA
33
34/* Store the mmalloca() results in a hash table. This is needed to reliably
35 distinguish a mmalloca() result and an alloca() result.
36
37 Although it is possible that the same pointer is returned by alloca() and
38 by mmalloca() at different times in the same application, it does not lead
39 to a bug in freea(), because:
40 - Before a pointer returned by alloca() can point into malloc()ed memory,
41 the function must return, and once this has happened the programmer must
42 not call freea() on it anyway.
43 - Before a pointer returned by mmalloca() can point into the stack, it
44 must be freed. The only function that can free it is freea(), and
45 when freea() frees it, it also removes it from the hash table. */
46
47#define MAGIC_NUMBER 0x1415fb4a
48#define MAGIC_SIZE sizeof (int)
49/* This is how the header info would look like without any alignment
50 considerations. */
51struct preliminary_header { void *next; char room[MAGIC_SIZE]; };
52/* But the header's size must be a multiple of sa_alignment_max. */
53#define HEADER_SIZE \
54 (((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max)
55struct header { void *next; char room[HEADER_SIZE - sizeof (struct preliminary_header) + MAGIC_SIZE]; };
56/* Verify that HEADER_SIZE == sizeof (struct header). */
57typedef int verify1[2 * (HEADER_SIZE == sizeof (struct header)) - 1];
58/* We make the hash table quite big, so that during lookups the probability
59 of empty hash buckets is quite high. There is no need to make the hash
60 table resizable, because when the hash table gets filled so much that the
61 lookup becomes slow, it means that the application has memory leaks. */
62#define HASH_TABLE_SIZE 257
63static void * mmalloca_results[HASH_TABLE_SIZE];
64
65#endif
66
67void *
68mmalloca (size_t n)
69{
70#if HAVE_ALLOCA
71 /* Allocate one more word, that serves as an indicator for malloc()ed
72 memory, so that freea() of an alloca() result is fast. */
73 size_t nplus = n + HEADER_SIZE;
74
75 if (nplus >= n)
76 {
77 char *p = (char *) malloc (nplus);
78
79 if (p != NULL)
80 {
81 size_t slot;
82
83 p += HEADER_SIZE;
84
85 /* Put a magic number into the indicator word. */
86 ((int *) p)[-1] = MAGIC_NUMBER;
87
88 /* Enter p into the hash table. */
89 slot = (unsigned long) p % HASH_TABLE_SIZE;
90 ((struct header *) (p - HEADER_SIZE))->next = mmalloca_results[slot];
91 mmalloca_results[slot] = p;
92
93 return p;
94 }
95 }
96 /* Out of memory. */
97 return NULL;
98#else
99# if !MALLOC_0_IS_NONNULL
100 if (n == 0)
101 n = 1;
102# endif
103 return malloc (n);
104#endif
105}
106
107#if HAVE_ALLOCA
108void
109freea (void *p)
110{
111 /* mmalloca() may have returned NULL. */
112 if (p != NULL)
113 {
114 /* Attempt to quickly distinguish the mmalloca() result - which has
115 a magic indicator word - and the alloca() result - which has an
116 uninitialized indicator word. It is for this test that sa_increment
117 additional bytes are allocated in the alloca() case. */
118 if (((int *) p)[-1] == MAGIC_NUMBER)
119 {
120 /* Looks like a mmalloca() result. To see whether it really is one,
121 perform a lookup in the hash table. */
122 size_t slot = (unsigned long) p % HASH_TABLE_SIZE;
123 void **chain = &mmalloca_results[slot];
124 for (; *chain != NULL;)
125 {
126 if (*chain == p)
127 {
128 /* Found it. Remove it from the hash table and free it. */
129 char *p_begin = (char *) p - HEADER_SIZE;
130 *chain = ((struct header *) p_begin)->next;
131 free (p_begin);
132 return;
133 }
134 chain = &((struct header *) ((char *) *chain - HEADER_SIZE))->next;
135 }
136 }
137 /* At this point, we know it was not a mmalloca() result. */
138 }
139}
140#endif