malloc_info(3) Library Functions Manual malloc_info(3)
NAME
malloc_info - export malloc state to a stream
LIBRARY
Standard C library (libc, -lc)
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 failure, it returns -1, and
errno is set to indicate the error.
ERRORS
EINVAL options was nonzero.
VERSIONS
malloc_info() was added in glibc 2.10.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│malloc_info() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
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 (ac-
cording 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 mal-
loc_info() directly into a buffer in memory, rather than to a file.
The malloc_info() function is designed to address deficiencies in mal-
loc_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 cre-
ation of one additional thread, and both the main thread and the addi-
tional thread allocate 10000 blocks of memory. After the blocks of
memory have been allocated, malloc_info() shows the state of two allo-
cation 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 <err.h>
#include <errno.h>
#include <malloc.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
static size_t blockSize;
static size_t numThreads;
static unsigned int numBlocks;
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 (unsigned int j = 0; j < numBlocks; j++)
if (malloc(blockSize * (2 + tn)) == NULL)
err(EXIT_FAILURE, "malloc-thread");
sleep(100); /* Sleep until main thread terminates. */
return NULL;
}
int
main(int argc, char *argv[])
{
int 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(*thr));
if (thr == NULL)
err(EXIT_FAILURE, "calloc");
printf("============ Before allocating blocks ============\n");
malloc_info(0, stdout);
/* Create threads that allocate different amounts of memory. */
for (size_t tn = 0; tn < numThreads; tn++) {
errno = pthread_create(&thr[tn], NULL, thread_func,
(void *) tn);
if (errno != 0)
err(EXIT_FAILURE, "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 (unsigned int j = 0; j < numBlocks; j++)
if (malloc(blockSize) == NULL)
err(EXIT_FAILURE, "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)
Linux man-pages 6.03 2023-02-05 malloc_info(3)
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