malloc_info(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | 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 *stream);

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 stream.  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 failure, it returns -1,
       and errno is set to indicate the error.

ERRORS         top

       EINVAL options was nonzero.

VERSIONS         top

       malloc_info() was added to glibc in version 2.10.

ATTRIBUTES         top

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

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

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).

EXAMPLES         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 tn = (int) arg;

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

           for (int 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 sleepTime;

           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;

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

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

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

           for (int 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 (int 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 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

GNU                            2021-03-22                 MALLOC_INFO(3)

Pages that refer to this page: mallinfo(3)malloc(3)malloc_stats(3)mallopt(3)