Content-type: text/html Man page of amalloc


Section: C Library Functions (3)
Index Return to Main Contents


acalloc, acreate, adelete, afree, amallinfo, amalloc, amallopt, amallocblksize, arealloc - arena memory allocator  


Standard C Library (, libc.a)  


#include <sys/types.h> #include <malloc.h>

void *acreate (
        void *addr, size_t len, int flags, void *ushdr,
        void *(*grow_func)(size_t, void *)); int adelete (void *ap); void *amalloc (
        size_t size, void *ap); void afree (
        void *ptr, void *ap); void *arealloc (
        void *ptr, size_t size, void *ap); void *acalloc (
        size_t nelem, size_t elsize, void *ap); size_t amallocblksize (
        void *ptr, void *ap);

The following function definitions are provided only for System V compatibility:

int amallopt (
        int cmd, int value, void *ap); struct mallinfo amallinfo (
        void *ap);  


The amalloc family of functions provides a main memory allocator based on the malloc memory allocator. This allocator has been extended so that an arbitrary memory space (``arena'') can be set up as an area from which to allocate memory.

Calls to the amalloc family of functions differ from calls to the standard malloc only in that an arena pointer must be supplied. This arena pointer is returned by a call to acreate.

The following functions are in the amalloc family: Sets up an area defined as starting at virtual address addr and extending for len bytes. Arenas can be either growing or non-growing.

An arena that is non-growing is constrained to use only up to len bytes of memory. The grow_func parameter should be NULL in this case.
If the arena is ``growable'', len specifies the original size (minimum of 1K bytes) and the grow_func parameter specifies a function that will be called when the allocator requires more memory. Note that the original buffer address addr will be used only for the arena header; the first time more memory is required, the ``grow'' function will be called. This suggests that a minimal (1K) original buffer should be used when setting up a growable arena.
The grow function will be called with two parameters: the number of bytes required and a pointer to the arena requiring the space. The number of bytes requested will always be a multiple of M_BLKSZ (see <malloc.h> header file). The function should return the address of a suitably large block of memory. This block does not need to be contiguous with the original arena memory. This block could be obtained from a number of sources, such as by mapping in another file (by means of mmap) or by calling malloc to enlarge the program's data space. If the grow function decides that it cannot provide any more space, it must return (void*)-1.
The ushdr function is currently unused and must be NULL. Causes any resources allocated for the arena (for example, mutexes) to be freed. Nothing is done with the arena memory itself. No additional calls to any arena functions can be made after calling adelete. Returns a pointer to a block of at least size bytes suitably aligned for any use. Destroys the contents of a block previously allocated by amalloc, arealloc, or acalloc and makes this space available for future allocation. The argument to afree is a pointer to the block previously allocated by amalloc, arealloc, or acalloc.
Undefined results will occur if the space assigned by any of the three arena allocator functions is overrun or if some random number is handed to afree. It is always permitted to pass NULL to afree. Changes the size of the block pointed to by ptr to size bytes and returns a pointer to the (possibly moved) block. The contents will be unchanged, up to the lesser of the new and old sizes. In the special case of a null ptr, arealloc degenerates to amalloc. A zero size causes the passed block to be freed. Allocates space for an array of nelem elements of size elsize. The space is initialized to zeros. Returns the actual size of the block pointed to by ptr. The returned size may be greater than the original requested size. Provides for control over the allocation algorithm. The available values for cmd are defined in the <malloc.h> header file.
The amallopt function can be called repeatedly but, for most commands, not after the first small block is allocated. Provides instrumentation describing space usage. It returns the mallinfo structure defined in the <malloc.h> header file. The structure is zero until after the first space has been allocated from the arena.

Each of the allocation functions returns a pointer to space suitably aligned for storage of any type of object.

The behaviors of these functions can be tuned to optimize their performance in a particular application. For descriptions of the variables that control how the functions operate, see malloc(3).  


The acreate function returns NULL and sets errno if either len is less than 1K or the MEM_SHARED flag is passed.

The amalloc, arealloc, and acalloc functions return a NULL pointer if there is not enough available memory. When arealloc returns NULL, the block pointed to by ptr is left intact. If amallopt is called after any allocation (for most cmd arguments) or if cmd or value is invalid, non-zero is returned. Otherwise, it returns zero.  


Functions: malloc(3), mmap(2) delim off




This document was created by man2html, using the manual pages.
Time: 02:42:16 GMT, October 02, 2010