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/*
* Copyright (C) 2001 Sistina Software (UK) Limited.
*
* This file is released under the LGPL.
*/
#ifndef _LVM_POOL_H
#define _LVM_POOL_H
#include <string.h>
#include <stdlib.h>
/*
* The pool allocator is useful when you are going to allocate
* lots of memory, use the memory for a bit, and then free the
* memory in one go. A surprising amount of code has this usage
* profile.
*
* You should think of the pool as an infinite, contiguous chunk
* of memory. The front of this chunk of memory contains
* allocated objects, the second half is free. pool_alloc grabs
* the next 'size' bytes from the free half, in effect moving it
* into the allocated half. This operation is very efficient.
*
* pool_free frees the allocated object *and* all objects
* allocated after it. It is important to note this semantic
* difference from malloc/free. This is also extremely
* efficient, since a single pool_free can dispose of a large
* complex object.
*
* pool_destroy frees all allocated memory.
*
* eg, If you are building a binary tree in your program, and
* know that you are only ever going to insert into your tree,
* and not delete (eg, maintaining a symbol table for a
* compiler). You can create yourself a pool, allocate the nodes
* from it, and when the tree becomes redundant call pool_destroy
* (no nasty iterating through the tree to free nodes).
*
* eg, On the other hand if you wanted to repeatedly insert and
* remove objects into the tree, you would be better off
* allocating the nodes from a free list; you cannot free a
* single arbitrary node with pool.
*/
struct pool;
/* constructor and destructor */
struct pool *pool_create(size_t chunk_hint);
void pool_destroy(struct pool *p);
/* simple allocation/free routines */
void *pool_alloc(struct pool *p, size_t s);
void *pool_alloc_aligned(struct pool *p, size_t s, unsigned alignment);
void pool_empty(struct pool *p);
void pool_free(struct pool *p, void *ptr);
/*
* Object building routines:
*
* These allow you to 'grow' an object, useful for
* building strings, or filling in dynamic
* arrays.
*
* It's probably best explained with an example:
*
* char *build_string(struct pool *mem)
* {
* int i;
* char buffer[16];
*
* if (!pool_begin_object(mem, 128))
* return NULL;
*
* for (i = 0; i < 50; i++) {
* snprintf(buffer, sizeof(buffer), "%d, ", i);
* if (!pool_grow_object(mem, buffer, strlen(buffer)))
* goto bad;
* }
*
* // add null
* if (!pool_grow_object(mem, "\0", 1))
* goto bad;
*
* return pool_end_object(mem);
*
* bad:
*
* pool_abandon_object(mem);
* return NULL;
*}
*
* So start an object by calling pool_begin_object
* with a guess at the final object size - if in
* doubt make the guess too small.
*
* Then append chunks of data to your object with
* pool_grow_object. Finally get your object with
* a call to pool_end_object.
*
*/
int pool_begin_object(struct pool *p, size_t hint);
int pool_grow_object(struct pool *p, const void *extra, size_t delta);
void *pool_end_object(struct pool *p);
void pool_abandon_object(struct pool *p);
/* utilities */
char *pool_strdup(struct pool *p, const char *str);
static inline void *pool_zalloc(struct pool *p, size_t s) {
void *ptr = pool_alloc(p, s);
if (ptr)
memset(ptr, 0, s);
return ptr;
}
#endif
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