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>
#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);
}
mallinfo(3),
malloc(3),
malloc_stats(3),
mallopt(3),
open_memstream(3)