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Full Discussion: find size of heap allocated
Top Forums Programming find size of heap allocated Post 302520160 by Praveen_218 on Friday 6th of May 2011 03:46:05 AM
Old 05-06-2011
Quote:
This will not take memory from heap. This would be allocated from stack because this is a local variable and you aren't using malloc() / any alloc() functions.
How come????

The arrary is going to be on the heap of the process memory only.
However, it's the pointer variable 'a' is going to be over the stack frame of the function using that as it's local.

---------- Post updated at 01:16 PM ---------- Previous update was at 12:51 PM ----------

@aliter ,
Thanks for the information, that's definitely going to be a direction, I'll need to investigate a bit further for my own shake.

To sum up, do you mean to say, in other words, that it's the implementation of heap which is going to be different in different systems?

That's what I'm aware of and most logical thing to conclude of when two operating systems are developed altogether differently and separately.

Also its never the compiler which actually allocates these heap related object/variables rather the OS memory manager allocates them at the run time only.

Its perfectly okey to have different implementations of the actual resident memory area of a heap based variables. The running process (which owns these variables) just treat them at a memory location that's always upper bound and assumes such memory area altogether grows outwards (the stack grows in the direction opposite to the heap, which is inwards).

The whole thing could also be implemented as to simulate this behavior and that's what many virtual memory implementations do.

Not only that, the whole process memory area could altogether be implemented differently (over different platforms) but they give the same feeling to the running process by exposing similar interfaces and response from the operating platform the process is executing on.

Your information was important to me more because of the fact you have clubbed FreeBSD & Linux implementations together.

Might be Linux code implementing these behaviors find it's root in BSD repository tree only, but I'm just speculating here.

Last edited by Praveen_218; 05-06-2011 at 04:55 AM..
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MALLOC_INFO(3)						     Linux Programmer's Manual						    MALLOC_INFO(3)

NAME
malloc_info - export malloc state to a stream SYNOPSIS
#include <malloc.h> int malloc_info(int options, FILE *fp); 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 fp. 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. ERRORS
EINVAL options was nonzero. VERSIONS
malloc_info(3) was added to glibc in version 2.10. 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 speci- fied 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 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 <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] ", 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 ============ "); 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(" ============ After allocating blocks ============ "); malloc_info(0, stdout); exit(EXIT_SUCCESS); } SEE ALSO
mallinfo(3), malloc(3), malloc_stats(3), mallopt(3), open_memstream(3) COLOPHON
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. GNU
2012-04-28 MALLOC_INFO(3)
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