man3/malloc_info.3

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  23 .TH MALLOC_INFO 3  2012-04-28 "GNU" "Linux Programmer's Manual"
  24 .SH NAME
  25 malloc_info \- export malloc state to a stream
  26 .SH SYNOPSIS
  27 .nf
  28 .B #include <malloc.h>
  29 .sp
  30 .BI "int malloc_info(int " options ", FILE *" fp );
  31 .fi
  32 .SH DESCRIPTION
  33 The
  34 .BR malloc_info ()
  35 function exports an XML string that describes the current state
  36 of the memory-allocation
  37 implementation in the caller.
  38 The string is printed on the file stream
  39 .IR fp .
  40 The exported string includes information about all arenas (see
  41 .BR malloc (3)).
  42
  43 As currently implemented,
  44 .I options
  45 must be zero.
  46 .SH RETURN VALUE
  47 On success,
  48 .BR malloc_info ()
  49 returns 0;
  50 on error, it returns \-1.
  51 .SH ERRORS
  52 .TP
  53 .B EINVAL
  54 .I options
  55 was nonzero.
  56 .SH VERSIONS
  57 .BR malloc_info (3)
  58 was added to glibc in version 2.10.
  59 .SH CONFORMING TO
  60 This function is a GNU extension.
  61 .SH NOTES
  62 The memory-allocation information is provided as an XML string
  63 (rather than a C structure)
  64 because the information may change over time
  65 (according to changes in the underlying implementation).
  66 The output XML string includes a version field.
  67
  68 The
  69 .BR open_memstream (3)
  70 function can be used to send the output of
  71 .BR malloc_info ()
  72 directly into a buffer in memory, rather than to a file.
  73
  74 The
  75 .BR malloc_info ()
  76 function is designed to address deficiencies in
  77 .BR malloc_stats (3)
  78 and
  79 .BR mallinfo (3).
  80 .SH EXAMPLE
  81 The program below takes up to four command-line arguments,
  82 of which the first three are mandatory.
  83 The first argument specifies the number of threads that
  84 the program should create.
  85 All of the threads, including the main thread,
  86 allocate the number of blocks of memory specified by the second argument.
  87 The third argument controls the size of the blocks to be allocated.
  88 The main thread creates blocks of this size,
  89 the second thread created by the program allocates blocks of twice this size,
  90 the third thread allocates blocks of three times this size, and so on.
  91
  92 The program calls
  93 .BR malloc_info ()
  94 twice to display the memory-allocation state.
  95 The first call takes place before any threads
  96 are created or memory allocated.
  97 The second call is performed after all threads have allocated memory.
  98
  99 In the following example,
 100 the command-line arguments specify the creation of one additional thread,
 101 and both the main thread and the additional thread
 102 allocate 10000 blocks of memory.
 103 After the blocks of memory have been allocated,
 104 .BR malloc_info ()
 105 shows the state of two allocation arenas.
 106 .in +4
 107 .nf
 108
 109 .RB "$ " "getconf GNU_LIBC_VERSION"
 110 glibc 2.13
 111 .RB "$ " "./a.out 1 10000 100"
 112 ============ Before allocating blocks ============
 113 <malloc version="1">
 114 <heap nr="0">
 115 <sizes>
 116 </sizes>
 117 <total type="fast" count="0" size="0"/>
 118 <total type="rest" count="0" size="0"/>
 119 <system type="current" size="135168"/>
 120 <system type="max" size="135168"/>
 121 <aspace type="total" size="135168"/>
 122 <aspace type="mprotect" size="135168"/>
 123 </heap>
 124 <total type="fast" count="0" size="0"/>
 125 <total type="rest" count="0" size="0"/>
 126 <system type="current" size="135168"/>
 127 <system type="max" size="135168"/>
 128 <aspace type="total" size="135168"/>
 129 <aspace type="mprotect" size="135168"/>
 130 </malloc>
 131
 132 ============ After allocating blocks ============
 133 <malloc version="1">
 134 <heap nr="0">
 135 <sizes>
 136 </sizes>
 137 <total type="fast" count="0" size="0"/>
 138 <total type="rest" count="0" size="0"/>
 139 <system type="current" size="1081344"/>
 140 <system type="max" size="1081344"/>
 141 <aspace type="total" size="1081344"/>
 142 <aspace type="mprotect" size="1081344"/>
 143 </heap>
 144 <heap nr="1">
 145 <sizes>
 146 </sizes>
 147 <total type="fast" count="0" size="0"/>
 148 <total type="rest" count="0" size="0"/>
 149 <system type="current" size="1032192"/>
 150 <system type="max" size="1032192"/>
 151 <aspace type="total" size="1032192"/>
 152 <aspace type="mprotect" size="1032192"/>
 153 </heap>
 154 <total type="fast" count="0" size="0"/>
 155 <total type="rest" count="0" size="0"/>
 156 <system type="current" size="2113536"/>
 157 <system type="max" size="2113536"/>
 158 <aspace type="total" size="2113536"/>
 159 <aspace type="mprotect" size="2113536"/>
 160 </malloc>
 161 .fi
 162 .in
 163 .SS Program source
 164 .nf
 165
 166 #include <unistd.h>
 167 #include <stdlib.h>
 168 #include <pthread.h>
 169 #include <malloc.h>
 170 #include <errno.h>
 171
 172 static size_t blockSize;
 173 static int numThreads, numBlocks;
 174
 175 #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \\
 176                         } while (0)
 177
 178 static void *
 179 thread_func(void *arg)
 180 {
 181     int j;
 182     int tn = (int) arg;
 183
 184     /* The multiplier \(aq(2 + tn)\(aq ensures that each thread (including
 185        the main thread) allocates a different amount of memory */
 186
 187     for (j = 0; j < numBlocks; j++)
 188         if (malloc(blockSize * (2 + tn)) == NULL)
 189             errExit("malloc\-thread");
 190
 191     sleep(100);         /* Sleep until main thread terminates */
 192     return NULL;
 193 }
 194
 195 int
 196 main(int argc, char *argv[])
 197 {
 198     int j, tn, sleepTime;
 199     pthread_t *thr;
 200
 201     if (argc < 4) {
 202         fprintf(stderr,
 203                 "%s num\-threads num\-blocks block\-size [sleep\-time]\\n",
 204                 argv[0]);
 205         exit(EXIT_FAILURE);
 206     }
 207
 208     numThreads = atoi(argv[1]);
 209     numBlocks = atoi(argv[2]);
 210     blockSize = atoi(argv[3]);
 211     sleepTime = (argc > 4) ? atoi(argv[4]) : 0;
 212
 213     thr = calloc(numThreads, sizeof(pthread_t));
 214     if (thr == NULL)
 215         errExit("calloc");
 216
 217     printf("============ Before allocating blocks ============\\n");
 218     malloc_info(0, stdout);
 219
 220     /* Create threads that allocate different amounts of memory */
 221
 222     for (tn = 0; tn < numThreads; tn++) {
 223         errno = pthread_create(&thr[tn], NULL, thread_func,
 224                                (void *) tn);
 225         if (errno != 0)
 226             errExit("pthread_create");
 227
 228         /* If we add a sleep interval after the start\-up of each
 229            thread, the threads likely won\(aqt contend for malloc
 230            mutexes, and therefore additional arenas won\(aqt be
 231            allocated (see malloc(3)). */
 232
 233         if (sleepTime > 0)
 234             sleep(sleepTime);
 235     }
 236
 237     /* The main thread also allocates some memory */
 238
 239     for (j = 0; j < numBlocks; j++)
 240         if (malloc(blockSize) == NULL)
 241             errExit("malloc");
 242
 243     sleep(2);           /* Give all threads a chance to
 244                            complete allocations */
 245
 246     printf("\\n============ After allocating blocks ============\\n");
 247     malloc_info(0, stdout);
 248
 249     exit(EXIT_SUCCESS);
 250 }
 251 .fi
 252 .SH SEE ALSO
 253 .BR mallinfo (3),
 254 .BR malloc (3),
 255 .BR malloc_stats (3),
 256 .BR mallopt (3),
 257 .BR open_memstream (3)