external/gpl2/lvm2/dist/libdm/mm/pool.h

   1 /*      $NetBSD$        */
   2
   3 /*
   4  * Copyright (C) 2001-2004 Sistina Software, Inc. All rights reserved.
   5  * Copyright (C) 2004-2007 Red Hat, Inc. All rights reserved.
   6  *
   7  * This file is part of the device-mapper userspace tools.
   8  *
   9  * This copyrighted material is made available to anyone wishing to use,
  10  * modify, copy, or redistribute it subject to the terms and conditions
  11  * of the GNU Lesser General Public License v.2.1.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public License
  14  * along with this program; if not, write to the Free Software Foundation,
  15  * Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  16  */
  17
  18 #ifndef _DM_POOL_H
  19 #define _DM_POOL_H
  20
  21 #include <string.h>
  22 #include <stdlib.h>
  23
  24 /*
  25  * The pool allocator is useful when you are going to allocate
  26  * lots of memory, use the memory for a bit, and then free the
  27  * memory in one go.  A surprising amount of code has this usage
  28  * profile.
  29  *
  30  * You should think of the pool as an infinite, contiguous chunk
  31  * of memory.  The front of this chunk of memory contains
  32  * allocated objects, the second half is free.  pool_alloc grabs
  33  * the next 'size' bytes from the free half, in effect moving it
  34  * into the allocated half.  This operation is very efficient.
  35  *
  36  * pool_free frees the allocated object *and* all objects
  37  * allocated after it.  It is important to note this semantic
  38  * difference from malloc/free.  This is also extremely
  39  * efficient, since a single pool_free can dispose of a large
  40  * complex object.
  41  *
  42  * pool_destroy frees all allocated memory.
  43  *
  44  * eg, If you are building a binary tree in your program, and
  45  * know that you are only ever going to insert into your tree,
  46  * and not delete (eg, maintaining a symbol table for a
  47  * compiler).  You can create yourself a pool, allocate the nodes
  48  * from it, and when the tree becomes redundant call pool_destroy
  49  * (no nasty iterating through the tree to free nodes).
  50  *
  51  * eg, On the other hand if you wanted to repeatedly insert and
  52  * remove objects into the tree, you would be better off
  53  * allocating the nodes from a free list; you cannot free a
  54  * single arbitrary node with pool.
  55  */
  56
  57 struct pool;
  58
  59 /* constructor and destructor */
  60 struct pool *pool_create(const char *name, size_t chunk_hint);
  61 void pool_destroy(struct pool *p);
  62
  63 /* simple allocation/free routines */
  64 void *pool_alloc(struct pool *p, size_t s);
  65 void *pool_alloc_aligned(struct pool *p, size_t s, unsigned alignment);
  66 void pool_empty(struct pool *p);
  67 void pool_free(struct pool *p, void *ptr);
  68
  69 /*
  70  * Object building routines:
  71  *
  72  * These allow you to 'grow' an object, useful for
  73  * building strings, or filling in dynamic
  74  * arrays.
  75  *
  76  * It's probably best explained with an example:
  77  *
  78  * char *build_string(struct pool *mem)
  79  * {
  80  *      int i;
  81  *      char buffer[16];
  82  *
  83  *      if (!pool_begin_object(mem, 128))
  84  *              return NULL;
  85  *
  86  *      for (i = 0; i < 50; i++) {
  87  *              snprintf(buffer, sizeof(buffer), "%d, ", i);
  88  *              if (!pool_grow_object(mem, buffer, strlen(buffer)))
  89  *                      goto bad;
  90  *      }
  91  *
  92  *      // add null
  93  *      if (!pool_grow_object(mem, "\0", 1))
  94  *              goto bad;
  95  *
  96  *      return pool_end_object(mem);
  97  *
  98  * bad:
  99  *
 100  *      pool_abandon_object(mem);
 101  *      return NULL;
 102  *}
 103  *
 104  * So start an object by calling pool_begin_object
 105  * with a guess at the final object size - if in
 106  * doubt make the guess too small.
 107  *
 108  * Then append chunks of data to your object with
 109  * pool_grow_object.  Finally get your object with
 110  * a call to pool_end_object.
 111  *
 112  */
 113 int pool_begin_object(struct pool *p, size_t hint);
 114 int pool_grow_object(struct pool *p, const void *extra, size_t delta);
 115 void *pool_end_object(struct pool *p);
 116 void pool_abandon_object(struct pool *p);
 117
 118 /* utilities */
 119 char *pool_strdup(struct pool *p, const char *str);
 120 char *pool_strndup(struct pool *p, const char *str, size_t n);
 121 void *pool_zalloc(struct pool *p, size_t s);
 122
 123 #endif