Example of Creating and Using a User Heap

The program below shows how you might create and use a heap.

Assuming that the program file is called t.c, compile it with the following command:

/usr/ibmcxx/bin/cc -qheapdebug t.c -lhu

#include <stdlib.h>
#include <stdio.h>
#include <umalloc.h>

static void *get_fn(Heap_t usrheap, size_t *length, int *clean)
{
   void *p;

   /* Round up to the next chunk size */
   *length = ((*length) / 65536) * 65536 + 65536;
   *clean = _BLOCK_CLEAN;
   p = calloc(*length,1);
   return (p);
}

static void release_fn(Heap_t usrheap, void *p, size_t size)
{
   free( p );
   return;
}

int main(void)
{
   void    *initial_block;
   long   rc;
   Heap_t  myheap;
   char    *ptr;
   int     initial_sz;

   /* Get initial area to start heap */
   initial_sz = 65536;
   initial_block = malloc(initial_sz);
   if(initial_block == NULL) return (1);

   /* create a user heap */
   myheap = _ucreate(initial_block, initial_sz, _BLOCK_CLEAN,
                     _HEAP_REGULAR, get_fn, release_fn);
   if (myheap == NULL) return(2);


   /* allocate from user heap and cause it to grow */
   ptr = _umalloc(myheap, 100000);
   _ufree(ptr);

   /* destroy user heap */
   if (_udestroy(myheap, _FORCE)) return(3);

   /* return initial block used to create heap */

   free(initial_block);
   return 0;
}

Memory Management Functions
Managing Memory with Multiple Memory Heaps
Types of Memory
Debugging Memory Heaps

Creating and Using a Fixed Size Heap
Creating and Using an Expandable Heap
Debugging Problems with Heap Memory
Changing the Default Heap Used in a Program
Example of Creating and Using a Shared-Memory User Heap