# malloc_info

## 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.
    


## ATTRIBUTES



           For an explanation of the terms used in this section, see
           attributes(7).
           ┌──────────────────────────────────────┬───────────────┬─────────┐
           │ **Interface** │ **Attribute** │ **Value** │
           ├──────────────────────────────────────┼───────────────┼─────────┤
           │ **malloc_info**()                        │ Thread safety │ MT-Safe │
           └──────────────────────────────────────┴───────────────┴─────────┘
    


## STANDARDS



           GNU.
    


## 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);
           }
    


* * *