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NAME

       malloc_info - export malloc state to a stream

SYNOPSIS

       #include <malloc.h>

       int malloc_info(int options, FILE *stream);

DESCRIPTION

       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
       stream.  The exported string includes information about all arenas (see malloc(3)).

       As currently implemented, options must be zero.

RETURN VALUE

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

ERRORS

       EINVAL options was nonzero.

VERSIONS

       malloc_info() was added to glibc in version 2.10.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├──────────────┼───────────────┼─────────┤
       │malloc_info() │ Thread safety │ MT-Safe │
       └──────────────┴───────────────┴─────────┘

CONFORMING TO

       This function is a GNU extension.

NOTES

       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

       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

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

COLOPHON

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       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at https://www.kernel.org/doc/man-pages/.