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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). ┌──────────────┬───────────────┬─────────┐ │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).
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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