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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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MALLOC_INFO(3) Linux Programmer's Manual MALLOC_INFO(3)
malloc_info - export malloc state to a stream
#include <malloc.h>
int malloc_info(int options, FILE *stream);
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.
On success, malloc_info() returns 0; on error, it returns -1,
with errno set to indicate the cause.
EINVAL options was nonzero.
malloc_info() was added to glibc in version 2.10.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────┼───────────────┼─────────┤
│malloc_info() │ Thread safety │ MT-Safe │
└──────────────┴───────────────┴─────────┘
This function is a GNU extension.
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).
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);
}
mallinfo(3), malloc(3), malloc_stats(3), mallopt(3),
open_memstream(3)
This page is part of release 5.10 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)
Pages that refer to this page: mallinfo(3), malloc(3), malloc_stats(3), mallopt(3)
Copyright and license for this manual page
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