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