malloc_info

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



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).

       ┌──────────────┬───────────────┬─────────┐
       │Interface     Attribute     Value   │
       ├──────────────┼───────────────┼─────────┤
       │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).

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

COLOPHON
       This page is part of release 5.09 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                                2020-11-01                     MALLOC_INFO(3)