man3/malloc_info.3

   1 .\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com>
   2 .\"
   3 .\" %%%LICENSE_START(VERBATIM)
   4 .\" Permission is granted to make and distribute verbatim copies of this
   5 .\" manual provided the copyright notice and this permission notice are
   6 .\" preserved on all copies.
   7 .\"
   8 .\" Permission is granted to copy and distribute modified versions of this
   9 .\" manual under the conditions for verbatim copying, provided that the
  10 .\" entire resulting derived work is distributed under the terms of a
  11 .\" permission notice identical to this one.
  12 .\"
  13 .\" Since the Linux kernel and libraries are constantly changing, this
  14 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  15 .\" responsibility for errors or omissions, or for damages resulting from
  16 .\" the use of the information contained herein.  The author(s) may not
  17 .\" have taken the same level of care in the production of this manual,
  18 .\" which is licensed free of charge, as they might when working
  19 .\" professionally.
  20 .\"
  21 .\" Formatted or processed versions of this manual, if unaccompanied by
  22 .\" the source, must acknowledge the copyright and authors of this work.
  23 .\" %%%LICENSE_END
  24 .\"
  25 .TH MALLOC_INFO 3  2015-01-22 "GNU" "Linux Programmer's Manual"
  26 .SH NAME
  27 malloc_info \- export malloc state to a stream
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <malloc.h>
  31 .sp
  32 .BI "int malloc_info(int " options ", FILE *" stream );
  33 .fi
  34 .SH DESCRIPTION
  35 The
  36 .BR malloc_info ()
  37 function exports an XML string that describes the current state
  38 of the memory-allocation
  39 implementation in the caller.
  40 The string is printed on the file stream
  41 .IR stream .
  42 The exported string includes information about all arenas (see
  43 .BR malloc (3)).
  44
  45 As currently implemented,
  46 .I options
  47 must be zero.
  48 .SH RETURN VALUE
  49 On success,
  50 .BR malloc_info ()
  51 returns 0;
  52 on error, it returns \-1, with
  53 .I errno
  54 set to indicate the cause.
  55 .SH ERRORS
  56 .TP
  57 .B EINVAL
  58 .I options
  59 was nonzero.
  60 .SH VERSIONS
  61 .BR malloc_info ()
  62 was added to glibc in version 2.10.
  63 .SH CONFORMING TO
  64 This function is a GNU extension.
  65 .SH NOTES
  66 The memory-allocation information is provided as an XML string
  67 (rather than a C structure)
  68 because the information may change over time
  69 (according to changes in the underlying implementation).
  70 The output XML string includes a version field.
  71
  72 The
  73 .BR open_memstream (3)
  74 function can be used to send the output of
  75 .BR malloc_info ()
  76 directly into a buffer in memory, rather than to a file.
  77
  78 The
  79 .BR malloc_info ()
  80 function is designed to address deficiencies in
  81 .BR malloc_stats (3)
  82 and
  83 .BR mallinfo (3).
  84 .SH EXAMPLE
  85 The program below takes up to four command-line arguments,
  86 of which the first three are mandatory.
  87 The first argument specifies the number of threads that
  88 the program should create.
  89 All of the threads, including the main thread,
  90 allocate the number of blocks of memory specified by the second argument.
  91 The third argument controls the size of the blocks to be allocated.
  92 The main thread creates blocks of this size,
  93 the second thread created by the program allocates blocks of twice this size,
  94 the third thread allocates blocks of three times this size, and so on.
  95
  96 The program calls
  97 .BR malloc_info ()
  98 twice to display the memory-allocation state.
  99 The first call takes place before any threads
 100 are created or memory allocated.
 101 The second call is performed after all threads have allocated memory.
 102
 103 In the following example,
 104 the command-line arguments specify the creation of one additional thread,
 105 and both the main thread and the additional thread
 106 allocate 10000 blocks of memory.
 107 After the blocks of memory have been allocated,
 108 .BR malloc_info ()
 109 shows the state of two allocation arenas.
 110 .in +4
 111 .nf
 112
 113 .RB "$ " "getconf GNU_LIBC_VERSION"
 114 glibc 2.13
 115 .RB "$ " "./a.out 1 10000 100"
 116 ============ Before allocating blocks ============
 117 <malloc version="1">
 118 <heap nr="0">
 119 <sizes>
 120 </sizes>
 121 <total type="fast" count="0" size="0"/>
 122 <total type="rest" count="0" size="0"/>
 123 <system type="current" size="135168"/>
 124 <system type="max" size="135168"/>
 125 <aspace type="total" size="135168"/>
 126 <aspace type="mprotect" size="135168"/>
 127 </heap>
 128 <total type="fast" count="0" size="0"/>
 129 <total type="rest" count="0" size="0"/>
 130 <system type="current" size="135168"/>
 131 <system type="max" size="135168"/>
 132 <aspace type="total" size="135168"/>
 133 <aspace type="mprotect" size="135168"/>
 134 </malloc>
 135
 136 ============ After allocating blocks ============
 137 <malloc version="1">
 138 <heap nr="0">
 139 <sizes>
 140 </sizes>
 141 <total type="fast" count="0" size="0"/>
 142 <total type="rest" count="0" size="0"/>
 143 <system type="current" size="1081344"/>
 144 <system type="max" size="1081344"/>
 145 <aspace type="total" size="1081344"/>
 146 <aspace type="mprotect" size="1081344"/>
 147 </heap>
 148 <heap nr="1">
 149 <sizes>
 150 </sizes>
 151 <total type="fast" count="0" size="0"/>
 152 <total type="rest" count="0" size="0"/>
 153 <system type="current" size="1032192"/>
 154 <system type="max" size="1032192"/>
 155 <aspace type="total" size="1032192"/>
 156 <aspace type="mprotect" size="1032192"/>
 157 </heap>
 158 <total type="fast" count="0" size="0"/>
 159 <total type="rest" count="0" size="0"/>
 160 <system type="current" size="2113536"/>
 161 <system type="max" size="2113536"/>
 162 <aspace type="total" size="2113536"/>
 163 <aspace type="mprotect" size="2113536"/>
 164 </malloc>
 165 .fi
 166 .in
 167 .SS Program source
 168 .nf
 169
 170 #include <unistd.h>
 171 #include <stdlib.h>
 172 #include <pthread.h>
 173 #include <malloc.h>
 174 #include <errno.h>
 175
 176 static size_t blockSize;
 177 static int numThreads, numBlocks;
 178
 179 #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \\
 180                         } while (0)
 181
 182 static void *
 183 thread_func(void *arg)
 184 {
 185     int j;
 186     int tn = (int) arg;
 187
 188     /* The multiplier \(aq(2 + tn)\(aq ensures that each thread (including
 189        the main thread) allocates a different amount of memory */
 190
 191     for (j = 0; j < numBlocks; j++)
 192         if (malloc(blockSize * (2 + tn)) == NULL)
 193             errExit("malloc\-thread");
 194
 195     sleep(100);         /* Sleep until main thread terminates */
 196     return NULL;
 197 }
 198
 199 int
 200 main(int argc, char *argv[])
 201 {
 202     int j, tn, sleepTime;
 203     pthread_t *thr;
 204
 205     if (argc < 4) {
 206         fprintf(stderr,
 207                 "%s num\-threads num\-blocks block\-size [sleep\-time]\\n",
 208                 argv[0]);
 209         exit(EXIT_FAILURE);
 210     }
 211
 212     numThreads = atoi(argv[1]);
 213     numBlocks = atoi(argv[2]);
 214     blockSize = atoi(argv[3]);
 215     sleepTime = (argc > 4) ? atoi(argv[4]) : 0;
 216
 217     thr = calloc(numThreads, sizeof(pthread_t));
 218     if (thr == NULL)
 219         errExit("calloc");
 220
 221     printf("============ Before allocating blocks ============\\n");
 222     malloc_info(0, stdout);
 223
 224     /* Create threads that allocate different amounts of memory */
 225
 226     for (tn = 0; tn < numThreads; tn++) {
 227         errno = pthread_create(&thr[tn], NULL, thread_func,
 228                                (void *) tn);
 229         if (errno != 0)
 230             errExit("pthread_create");
 231
 232         /* If we add a sleep interval after the start\-up of each
 233            thread, the threads likely won\(aqt contend for malloc
 234            mutexes, and therefore additional arenas won\(aqt be
 235            allocated (see malloc(3)). */
 236
 237         if (sleepTime > 0)
 238             sleep(sleepTime);
 239     }
 240
 241     /* The main thread also allocates some memory */
 242
 243     for (j = 0; j < numBlocks; j++)
 244         if (malloc(blockSize) == NULL)
 245             errExit("malloc");
 246
 247     sleep(2);           /* Give all threads a chance to
 248                            complete allocations */
 249
 250     printf("\\n============ After allocating blocks ============\\n");
 251     malloc_info(0, stdout);
 252
 253     exit(EXIT_SUCCESS);
 254 }
 255 .fi
 256 .SH SEE ALSO
 257 .BR mallinfo (3),
 258 .BR malloc (3),
 259 .BR malloc_stats (3),
 260 .BR mallopt (3),
 261 .BR open_memstream (3)