glib/garcbox.c

   1 /* garcbox.c: Atomically reference counted data
   2  *
   3  * Copyright 2018  Emmanuele Bassi
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2.1 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public
  16  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  17  */
  18
  19 #include "config.h"
  20
  21 #include "grcbox.h"
  22
  23 #include "gmessages.h"
  24 #include "grcboxprivate.h"
  25 #include "grefcount.h"
  26
  27 #ifdef ENABLE_VALGRIND
  28 #include "valgrind.h"
  29 #endif
  30
  31 #include <string.h>
  32
  33 #define G_ARC_BOX(p)            (GArcBox *) (((char *) (p)) - G_ARC_BOX_SIZE)
  34
  35 /**
  36  * SECTION:arcbox
  37  * @Title: Atomically reference counted data
  38  * @Short_description: Allocated memory with atomic reference counting semantics
  39  *
  40  * An "atomically reference counted box", or "ArcBox", is an opaque wrapper
  41  * data type that is guaranteed to be as big as the size of a given data type,
  42  * and which augments the given data type with thread safe reference counting
  43  * semantics for its memory management.
  44  *
  45  * ArcBox is useful if you have a plain old data type, like a structure
  46  * typically placed on the stack, and you wish to provide additional API
  47  * to use it on the heap, without necessarily implementing copy/free
  48  * semantics, or your own reference counting.
  49  *
  50  * The typical use is:
  51  *
  52  * |[<!-- language="C" -->
  53  * typedef struct {
  54  *   float x, y;
  55  * } Point;
  56  *
  57  * Point *
  58  * point_new (float x, float y)
  59  * {
  60  *   Point *res = g_arc_box_new (Point);
  61  *
  62  *   res->x = x;
  63  *   res->y = y;
  64  *
  65  *   return res;
  66  * }
  67  * ]|
  68  *
  69  * Every time you wish to acquire a reference on the memory, you should
  70  * call g_arc_box_acquire(); similarly, when you wish to release a reference
  71  * you should call g_arc_box_release():
  72  *
  73  * |[<!-- language="C" -->
  74  * Point *
  75  * point_ref (Point *p)
  76  * {
  77  *   return g_arc_box_acquire (p);
  78  * }
  79  *
  80  * void
  81  * point_unref (Point *p)
  82  * {
  83  *   g_arc_box_release (p);
  84  * }
  85  * ]|
  86  *
  87  * If you have additional memory allocated inside the structure, you can
  88  * use g_arc_box_release_full(), which takes a function pointer, which
  89  * will be called if the reference released was the last:
  90  *
  91  * |[<!-- language="C" -->
  92  * typedef struct {
  93  *   char *name;
  94  *   char *address;
  95  *   char *city;
  96  *   char *state;
  97  *   int age;
  98  * } Person;
  99  *
 100  * void
 101  * person_clear (Person *p)
 102  * {
 103  *   g_free (p->name);
 104  *   g_free (p->address);
 105  *   g_free (p->city);
 106  *   g_free (p->state);
 107  * }
 108  *
 109  * void
 110  * person_unref (Person *p)
 111  * {
 112  *   g_arc_box_release_full (p, (GDestroyNotify) person_clear);
 113  * }
 114  * ]|
 115  *
 116  * If you wish to transfer the ownership of a reference counted data
 117  * type without increasing the reference count, you can use g_steal_pointer():
 118  *
 119  * |[<!-- language="C" -->
 120  *   Person *p = g_arc_box_new (Person);
 121  *
 122  *   fill_person_details (p);
 123  *
 124  *   add_person_to_database (db, g_steal_pointer (&p));
 125  * ]|
 126  *
 127  * The reference counting operations on data allocated using g_arc_box_alloc(),
 128  * g_arc_box_new(), and g_arc_box_dup() are guaranteed to be atomic, and thus
 129  * can be safely be performed by different threads. It is important to note that
 130  * only the reference acquisition and release are atomic; changes to the content
 131  * of the data are your responsibility.
 132  *
 133  * Since: 2.58.
 134  */
 135
 136 /**
 137  * g_arc_box_alloc:
 138  * @block_size: the size of the allocation
 139  *
 140  * Allocates @block_size bytes of memory, and adds atomic
 141  * reference counting semantics to it.
 142  *
 143  * The data will be freed when its reference count drops to
 144  * zero.
 145  *
 146  * Returns: a pointer to the allocated memory
 147  *
 148  * Since: 2.58
 149  */
 150 gpointer
 151 g_arc_box_alloc (gsize block_size)
 152 {
 153   g_return_val_if_fail (block_size > 0, NULL);
 154
 155   return g_rc_box_alloc_full (block_size, TRUE, FALSE);
 156 }
 157
 158 /**
 159  * g_arc_box_alloc0:
 160  * @block_size: the size of the allocation
 161  *
 162  * Allocates @block_size bytes of memory, and adds atomic
 163  * referenc counting semantics to it.
 164  *
 165  * The contents of the returned data is set to 0's.
 166  *
 167  * The data will be freed when its reference count drops to
 168  * zero.
 169  *
 170  * Returns: a pointer to the allocated memory
 171  *
 172  * Since: 2.58
 173  */
 174 gpointer
 175 g_arc_box_alloc0 (gsize block_size)
 176 {
 177   g_return_val_if_fail (block_size > 0, NULL);
 178
 179   return g_rc_box_alloc_full (block_size, TRUE, TRUE);
 180 }
 181
 182 /**
 183  * g_arc_box_new:
 184  * @type: the type to allocate, typically a structure name
 185  *
 186  * A convenience macro to allocate atomically reference counted
 187  * data with the size of the given @type.
 188  *
 189  * This macro calls g_arc_box_alloc() with `sizeof (@type)` and
 190  * casts the returned pointer to a pointer of the given @type,
 191  * avoiding a type cast in the source code.
 192  *
 193  * This macro cannot return %NULL, as the minimum allocation
 194  * size from `sizeof (@type)` is 1 byte.
 195  *
 196  * Returns: (not nullable): a pointer to the allocated memory,
 197  *   cast to a pointer for the given @type
 198  *
 199  * Since: 2.58
 200  */
 201
 202 /**
 203  * g_arc_box_new0:
 204  * @type: the type to allocate, typically a structure name
 205  *
 206  * A convenience macro to allocate atomically reference counted
 207  * data with the size of the given @type, and set its contents
 208  * to 0.
 209  *
 210  * This macro calls g_arc_box_alloc0() with `sizeof (@type)` and
 211  * casts the returned pointer to a pointer of the given @type,
 212  * avoiding a type cast in the source code.
 213  *
 214  * This macro cannot return %NULL, as the minimum allocation
 215  * size from `sizeof (@type)` is 1 byte.
 216  *
 217  * Returns: (not nullable): a pointer to the allocated memory,
 218  *   cast to a pointer for the given @type
 219  *
 220  * Since: 2.58
 221  */
 222
 223 /**
 224  * g_arc_box_dup:
 225  * @block_size: the number of bytes to copy
 226  * @mem_block: (not nullable): the memory to copy
 227  *
 228  * Allocates a new block of data with atomit reference counting
 229  * semantics, and copies @block_size bytes of @mem_block
 230  * into it.
 231  *
 232  * Returns: (not nullable): a pointer to the allocated memory
 233  *
 234  * Since: 2.58
 235  */
 236 gpointer
 237 (g_arc_box_dup) (gsize         block_size,
 238                  gconstpointer mem_block)
 239 {
 240   gpointer res;
 241
 242   g_return_val_if_fail (block_size > 0, NULL);
 243   g_return_val_if_fail (mem_block != NULL, NULL);
 244
 245   res = g_rc_box_alloc_full (block_size, TRUE, FALSE);
 246   memcpy (res, mem_block, block_size);
 247
 248   return res;
 249 }
 250
 251 /**
 252  * g_arc_box_acquire:
 253  * @mem_block: (not nullable): a pointer to reference counted data
 254  *
 255  * Atomically acquires a reference on the data pointed by @mem_block.
 256  *
 257  * Returns: (not nullabl): a pointer to the data, with its reference
 258  *   count increased
 259  *
 260  * Since: 2.58
 261  */
 262 gpointer
 263 (g_arc_box_acquire) (gpointer mem_block)
 264 {
 265   GArcBox *real_box = G_ARC_BOX (mem_block);
 266
 267   g_return_val_if_fail (mem_block != NULL, NULL);
 268 #ifndef G_DISABLE_ASSERT
 269   g_return_val_if_fail (real_box->magic == G_BOX_MAGIC, NULL);
 270 #endif
 271
 272   g_atomic_ref_count_inc (&real_box->ref_count);
 273
 274   return mem_block;
 275 }
 276
 277 /**
 278  * g_arc_box_release:
 279  * @mem_block: (not nullable): a pointer to reference counted data
 280  *
 281  * Atomically releases a reference on the data pointed by @mem_block.
 282  *
 283  * If the reference was the last one, it will free the
 284  * resources allocated for @mem_block.
 285  *
 286  * Since: 2.58
 287  */
 288 void
 289 g_arc_box_release (gpointer mem_block)
 290 {
 291   GArcBox *real_box = G_ARC_BOX (mem_block);
 292
 293   g_return_if_fail (mem_block != NULL);
 294 #ifndef G_DISABLE_ASSERT
 295   g_return_if_fail (real_box->magic == G_BOX_MAGIC);
 296 #endif
 297
 298   if (g_atomic_ref_count_dec (&real_box->ref_count))
 299     g_free (real_box);
 300 }
 301
 302 /**
 303  * g_arc_box_release_full:
 304  * @mem_block: (not nullable): a pointer to reference counted data
 305  * @clear_func: (not nullable): a function to call when clearing the data
 306  *
 307  * Atomically releases a reference on the data pointed by @mem_block.
 308  *
 309  * If the reference was the last one, it will call @clear_func
 310  * to clear the contents of @mem_block, and then will free the
 311  * resources allocated for @mem_block.
 312  *
 313  * Since: 2.58
 314  */
 315 void
 316 g_arc_box_release_full (gpointer       mem_block,
 317                         GDestroyNotify clear_func)
 318 {
 319   GArcBox *real_box = G_ARC_BOX (mem_block);
 320
 321   g_return_if_fail (mem_block != NULL);
 322   g_return_if_fail (clear_func != NULL);
 323 #ifndef G_DISABLE_ASSERT
 324   g_return_if_fail (real_box->magic == G_BOX_MAGIC);
 325 #endif
 326
 327   if (g_atomic_ref_count_dec (&real_box->ref_count))
 328     {
 329       clear_func (mem_block);
 330       g_free (real_box);
 331     }
 332 }