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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 attributes(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 (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 <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)