1MALLOC_INFO(3) Linux Programmer's Manual MALLOC_INFO(3)
2
6 malloc_info - export malloc state to a stream
7
9 #include <malloc.h>
10 int malloc_info(int options, FILE *stream);
12
14 The malloc_info() function exports an XML string that describes the
15 current state of the memory-allocation implementation in the caller.
16 The string is printed on the file stream stream. The exported string
17 includes information about all arenas (see malloc(3)).
18 As currently implemented, options must be zero.
20
22 On success, malloc_info() returns 0; on error, it returns -1, with
23 errno set to indicate the cause.
24
26 EINVAL options was nonzero.
27
29 malloc_info() was added to glibc in version 2.10.
30
32 For an explanation of the terms used in this section, see
33 attributes(7).
34 ┌──────────────┬───────────────┬─────────┐
36 │Interface │ Attribute │ Value │
37 ├──────────────┼───────────────┼─────────┤
38 │malloc_info() │ Thread safety │ MT-Safe │
39 └──────────────┴───────────────┴─────────┘
40
42 This function is a GNU extension.
43
45 The memory-allocation information is provided as an XML string (rather
46 than a C structure) because the information may change over time
47 (according to changes in the underlying implementation). The output
48 XML string includes a version field.
49 The open_memstream(3) function can be used to send the output of mal‐
51 loc_info() directly into a buffer in memory, rather than to a file.
52 The malloc_info() function is designed to address deficiencies in mal‐
54 loc_stats(3) and mallinfo(3).
55
57 The program below takes up to four command-line arguments, of which the
58 first three are mandatory. The first argument specifies the number of
59 threads that the program should create. All of the threads, including
60 the main thread, allocate the number of blocks of memory specified by
61 the second argument. The third argument controls the size of the
62 blocks to be allocated. The main thread creates blocks of this size,
63 the second thread created by the program allocates blocks of twice this
64 size, the third thread allocates blocks of three times this size, and
65 so on.
66 The program calls malloc_info() twice to display the memory-allocation
68 state. The first call takes place before any threads are created or
69 memory allocated. The second call is performed after all threads have
70 allocated memory.
71 In the following example, the command-line arguments specify the cre‐
73 ation of one additional thread, and both the main thread and the addi‐
74 tional thread allocate 10000 blocks of memory. After the blocks of
75 memory have been allocated, malloc_info() shows the state of two allo‐
76 cation arenas.
77 $ getconf GNU_LIBC_VERSION
79 glibc 2.13
80 $ ./a.out 1 10000 100
81 ============ Before allocating blocks ============
82 <malloc version="1">
83 <heap nr="0">
84 <sizes>
85 </sizes>
86 <total type="fast" count="0" size="0"/>
87 <total type="rest" count="0" size="0"/>
88 <system type="current" size="135168"/>
89 <system type="max" size="135168"/>
90 <aspace type="total" size="135168"/>
91 <aspace type="mprotect" size="135168"/>
92 </heap>
93 <total type="fast" count="0" size="0"/>
94 <total type="rest" count="0" size="0"/>
95 <system type="current" size="135168"/>
96 <system type="max" size="135168"/>
97 <aspace type="total" size="135168"/>
98 <aspace type="mprotect" size="135168"/>
99 </malloc>
100 ============ After allocating blocks ============
102 <malloc version="1">
103 <heap nr="0">
104 <sizes>
105 </sizes>
106 <total type="fast" count="0" size="0"/>
107 <total type="rest" count="0" size="0"/>
108 <system type="current" size="1081344"/>
109 <system type="max" size="1081344"/>
110 <aspace type="total" size="1081344"/>
111 <aspace type="mprotect" size="1081344"/>
112 </heap>
113 <heap nr="1">
114 <sizes>
115 </sizes>
116 <total type="fast" count="0" size="0"/>
117 <total type="rest" count="0" size="0"/>
118 <system type="current" size="1032192"/>
119 <system type="max" size="1032192"/>
120 <aspace type="total" size="1032192"/>
121 <aspace type="mprotect" size="1032192"/>
122 </heap>
123 <total type="fast" count="0" size="0"/>
124 <total type="rest" count="0" size="0"/>
125 <system type="current" size="2113536"/>
126 <system type="max" size="2113536"/>
127 <aspace type="total" size="2113536"/>
128 <aspace type="mprotect" size="2113536"/>
129 </malloc>
130 Program source
132 #include <unistd.h>
133 #include <stdlib.h>
134 #include <pthread.h>
135 #include <malloc.h>
136 #include <errno.h>
137 static size_t blockSize;
139 static int numThreads, numBlocks;
140 #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
142 } while (0)
143 static void *
145 thread_func(void *arg)
146 {
147 int j;
148 int tn = (int) arg;
149 /* The multiplier '(2 + tn)' ensures that each thread (including
151 the main thread) allocates a different amount of memory */
152 for (j = 0; j < numBlocks; j++)
154 if (malloc(blockSize * (2 + tn)) == NULL)
155 errExit("malloc-thread");
156 sleep(100); /* Sleep until main thread terminates */
158 return NULL;
159 }
160 int
162 main(int argc, char *argv[])
163 {
164 int j, tn, sleepTime;
165 pthread_t *thr;
166 if (argc < 4) {
168 fprintf(stderr,
169 "%s num-threads num-blocks block-size [sleep-time]\n",
170 argv[0]);
171 exit(EXIT_FAILURE);
172 }
173 numThreads = atoi(argv[1]);
175 numBlocks = atoi(argv[2]);
176 blockSize = atoi(argv[3]);
177 sleepTime = (argc > 4) ? atoi(argv[4]) : 0;
178 thr = calloc(numThreads, sizeof(pthread_t));
180 if (thr == NULL)
181 errExit("calloc");
182 printf("============ Before allocating blocks ============\n");
184 malloc_info(0, stdout);
185 /* Create threads that allocate different amounts of memory */
187 for (tn = 0; tn < numThreads; tn++) {
189 errno = pthread_create(&thr[tn], NULL, thread_func,
190 (void *) tn);
191 if (errno != 0)
192 errExit("pthread_create");
193 /* If we add a sleep interval after the start-up of each
195 thread, the threads likely won't contend for malloc
196 mutexes, and therefore additional arenas won't be
197 allocated (see malloc(3)). */
198 if (sleepTime > 0)
200 sleep(sleepTime);
201 }
202 /* The main thread also allocates some memory */
204 for (j = 0; j < numBlocks; j++)
206 if (malloc(blockSize) == NULL)
207 errExit("malloc");
208 sleep(2); /* Give all threads a chance to
210 complete allocations */
211 printf("\n============ After allocating blocks ============\n");
213 malloc_info(0, stdout);
214 exit(EXIT_SUCCESS);
216 }
217
219 mallinfo(3), malloc(3), malloc_stats(3), mallopt(3), open_memstream(3)
220
222 This page is part of release 4.16 of the Linux man-pages project. A
223 description of the project, information about reporting bugs, and the
224 latest version of this page, can be found at
225 https://www.kernel.org/doc/man-pages/.
226GNU 2017-09-15 MALLOC_INFO(3)