NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

MALLOC_INFO(3)            Linux Programmer's Manual           MALLOC_INFO(3)

NAME         top

       malloc_info - export malloc state to a stream

SYNOPSIS         top

       #include <malloc.h>

       int malloc_info(int options, FILE *fp);

DESCRIPTION         top

       The malloc_info() function exports an XML string that describes the
       current state of the memory-allocation implementation in the caller.
       The string is printed on the file stream fp.  The exported string
       includes information about all arenas (see malloc(3)).

       As currently implemented, options must be zero.

RETURN VALUE         top

       On success, malloc_info() returns 0; on error, it returns -1, with
       errno set to indicate the cause.

ERRORS         top

       EINVAL options was nonzero.

VERSIONS         top

       malloc_info() was added to glibc in version 2.10.

CONFORMING TO         top

       This function is a GNU extension.

NOTES         top

       The memory-allocation information is provided as an XML string
       (rather than a C structure) because the information may change over
       time (according to changes in the underlying implementation).  The
       output XML string includes a version field.

       The open_memstream(3) function can be used to send the output of
       malloc_info() directly into a buffer in memory, rather than to a
       file.

       The malloc_info() function is designed to address deficiencies in
       malloc_stats(3) and mallinfo(3).

EXAMPLE         top

       The program below takes up to four command-line arguments, of which
       the first three are mandatory.  The first argument specifies the
       number of threads that the program should create.  All of the
       threads, including the main thread, allocate the number of blocks of
       memory specified by the second argument.  The third argument controls
       the size of the blocks to be allocated.  The main thread creates
       blocks of this size, the second thread created by the program
       allocates blocks of twice this size, the third thread allocates
       blocks of three times this size, and so on.

       The program calls malloc_info() twice to display the memory-
       allocation state.  The first call takes place before any threads are
       created or memory allocated.  The second call is performed after all
       threads have allocated memory.

       In the following example, the command-line arguments specify the
       creation of one additional thread, and both the main thread and the
       additional thread allocate 10000 blocks of memory.  After the blocks
       of memory have been allocated, malloc_info() shows the state of two
       allocation arenas.

           $ getconf GNU_LIBC_VERSION
           glibc 2.13
           $ ./a.out 1 10000 100
           ============ Before allocating blocks ============
           <malloc version="1">
           <heap nr="0">
           <sizes>
           </sizes>
           <total type="fast" count="0" size="0"/>
           <total type="rest" count="0" size="0"/>
           <system type="current" size="135168"/>
           <system type="max" size="135168"/>
           <aspace type="total" size="135168"/>
           <aspace type="mprotect" size="135168"/>
           </heap>
           <total type="fast" count="0" size="0"/>
           <total type="rest" count="0" size="0"/>
           <system type="current" size="135168"/>
           <system type="max" size="135168"/>
           <aspace type="total" size="135168"/>
           <aspace type="mprotect" size="135168"/>
           </malloc>

           ============ After allocating blocks ============
           <malloc version="1">
           <heap nr="0">
           <sizes>
           </sizes>
           <total type="fast" count="0" size="0"/>
           <total type="rest" count="0" size="0"/>
           <system type="current" size="1081344"/>
           <system type="max" size="1081344"/>
           <aspace type="total" size="1081344"/>
           <aspace type="mprotect" size="1081344"/>
           </heap>
           <heap nr="1">
           <sizes>
           </sizes>
           <total type="fast" count="0" size="0"/>
           <total type="rest" count="0" size="0"/>
           <system type="current" size="1032192"/>
           <system type="max" size="1032192"/>
           <aspace type="total" size="1032192"/>
           <aspace type="mprotect" size="1032192"/>
           </heap>
           <total type="fast" count="0" size="0"/>
           <total type="rest" count="0" size="0"/>
           <system type="current" size="2113536"/>
           <system type="max" size="2113536"/>
           <aspace type="total" size="2113536"/>
           <aspace type="mprotect" size="2113536"/>
           </malloc>

   Program source
       #include <unistd.h>
       #include <stdlib.h>
       #include <pthread.h>
       #include <malloc.h>
       #include <errno.h>

       static size_t blockSize;
       static int numThreads, numBlocks;

       #define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                               } while (0)

       static void *
       thread_func(void *arg)
       {
           int j;
           int tn = (int) arg;

           /* The multiplier '(2 + tn)' ensures that each thread (including
              the main thread) allocates a different amount of memory */

           for (j = 0; j < numBlocks; j++)
               if (malloc(blockSize * (2 + tn)) == NULL)
                   errExit("malloc-thread");

           sleep(100);         /* Sleep until main thread terminates */
           return NULL;
       }

       int
       main(int argc, char *argv[])
       {
           int j, tn, sleepTime;
           pthread_t *thr;

           if (argc < 4) {
               fprintf(stderr,
                       "%s num-threads num-blocks block-size [sleep-time]\n",
                       argv[0]);
               exit(EXIT_FAILURE);
           }

           numThreads = atoi(argv[1]);
           numBlocks = atoi(argv[2]);
           blockSize = atoi(argv[3]);
           sleepTime = (argc > 4) ? atoi(argv[4]) : 0;

           thr = calloc(numThreads, sizeof(pthread_t));
           if (thr == NULL)
               errExit("calloc");

           printf("============ Before allocating blocks ============\n");
           malloc_info(0, stdout);

           /* Create threads that allocate different amounts of memory */

           for (tn = 0; tn < numThreads; tn++) {
               errno = pthread_create(&thr[tn], NULL, thread_func,
                                      (void *) tn);
               if (errno != 0)
                   errExit("pthread_create");

               /* If we add a sleep interval after the start-up of each
                  thread, the threads likely won't contend for malloc
                  mutexes, and therefore additional arenas won't be
                  allocated (see malloc(3)). */

               if (sleepTime > 0)
                   sleep(sleepTime);
           }

           /* The main thread also allocates some memory */

           for (j = 0; j < numBlocks; j++)
               if (malloc(blockSize) == NULL)
                   errExit("malloc");

           sleep(2);           /* Give all threads a chance to
                                  complete allocations */

           printf("\n============ After allocating blocks ============\n");
           malloc_info(0, stdout);

           exit(EXIT_SUCCESS);
       }

SEE ALSO         top

       mallinfo(3), malloc(3), malloc_stats(3), mallopt(3),
       open_memstream(3)

COLOPHON         top

       This page is part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU                              2013-04-19                   MALLOC_INFO(3)