File: grefcount.c

package info (click to toggle)
glib2.0 2.58.3-2+deb10u2
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, buster, buster-backports, sid
  • size: 48,956 kB
  • sloc: ansic: 452,656; xml: 16,781; python: 6,149; makefile: 3,776; sh: 1,499; perl: 1,140; cpp: 9
file content (285 lines) | stat: -rw-r--r-- 6,842 bytes parent folder | download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
/* grefcount.c: Reference counting
 *
 * Copyright 2018  Emmanuele Bassi
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
 */

/**
 * SECTION:refcount
 * @Title: Reference counting
 * @Short_description: Reference counting types and functions
 *
 * Reference counting is a garbage collection mechanism that is based on
 * assigning a counter to a data type, or any memory area; the counter is
 * increased whenever a new reference to that data type is acquired, and
 * decreased whenever the reference is released. Once the last reference
 * is released, the resources associated to that data type are freed.
 *
 * GLib uses reference counting in many of its data types, and provides
 * the #grefcount and #gatomicrefcount types to implement safe and atomic
 * reference counting semantics in new data types.
 *
 * It is important to note that #grefcount and #gatomicrefcount should be
 * considered completely opaque types; you should always use the provided
 * API to increase and decrease the counters, and you should never check
 * their content directly, or compare their content with other values.
 *
 * Since: 2.58
 */

#include "config.h"

#include "grefcount.h"

#include "gatomic.h"
#include "gmessages.h"

/**
 * grefcount:
 *
 * A type for implementing non-atomic reference count semantics.
 *
 * Use g_ref_count_init() to initialize it; g_ref_count_inc() to
 * increase the counter, and g_ref_count_dec() to decrease it.
 *
 * It is safe to use #grefcount only if you're expecting to operate
 * on the reference counter from a single thread. It is entirely up
 * to you to ensure that all reference count changes happen in the
 * same thread.
 *
 * See also: #gatomicrefcount
 *
 * Since: 2.58
 */

/**
 * gatomicrefcount:
 *
 * A type for implementing atomic reference count semantics.
 *
 * Use g_atomic_ref_count_init() to initialize it; g_atomic_ref_count_inc()
 * to increase the counter, and g_atomic_ref_count_dec() to decrease it.
 *
 * It is safe to use #gatomicrefcount if you're expecting to operate on the
 * reference counter from multiple threads.
 *
 * See also: #grefcount
 *
 * Since: 2.58
 */

/**
 * g_ref_count_init:
 * @rc: the address of a reference count variable
 *
 * Initializes a reference count variable.
 *
 * Since: 2.58
 */
void
(g_ref_count_init) (grefcount *rc)
{
  g_return_if_fail (rc != NULL);

  /* Non-atomic refcounting is implemented using the negative range
   * of signed integers:
   *
   * G_MININT                 Z¯< 0 > Z⁺                G_MAXINT
   * |----------------------------|----------------------------|
   *
   * Acquiring a reference moves us towards MININT, and releasing a
   * reference moves us towards 0.
   */
  *rc = -1;
}

/**
 * g_ref_count_inc:
 * @rc: the address of a reference count variable
 *
 * Increases the reference count.
 *
 * Since: 2.58
 */
void
(g_ref_count_inc) (grefcount *rc)
{
  grefcount rrc;

  g_return_if_fail (rc != NULL);

  rrc = *rc;

  g_return_if_fail (rrc < 0);

  /* Check for saturation */
  if (rrc == G_MININT)
    {
      g_critical ("Reference count %p has reached saturation", rc);
      return;
    }

  rrc -= 1;

  *rc = rrc;
}

/**
 * g_ref_count_dec:
 * @rc: the address of a reference count variable
 *
 * Decreases the reference count.
 *
 * Returns: %TRUE if the reference count reached 0, and %FALSE otherwise
 *
 * Since: 2.58
 */
gboolean
(g_ref_count_dec) (grefcount *rc)
{
  grefcount rrc;

  g_return_val_if_fail (rc != NULL, FALSE);

  rrc = *rc;

  g_return_val_if_fail (rrc < 0, FALSE);

  rrc += 1;
  if (rrc == 0)
    return TRUE;

  *rc = rrc;

  return FALSE;
}

/**
 * g_ref_count_compare:
 * @rc: the address of a reference count variable
 * @val: the value to compare
 *
 * Compares the current value of @rc with @val.
 *
 * Returns: %TRUE if the reference count is the same
 *   as the given value
 *
 * Since: 2.58
 */
gboolean
(g_ref_count_compare) (grefcount *rc,
                       gint       val)
{
  grefcount rrc;

  g_return_val_if_fail (rc != NULL, FALSE);
  g_return_val_if_fail (val >= 0, FALSE);

  rrc = *rc;

  if (val == G_MAXINT)
    return rrc == G_MININT;

  return rrc == -val;
}

/**
 * g_atomic_ref_count_init:
 * @arc: the address of an atomic reference count variable
 *
 * Atomically initializes a reference count variable.
 *
 * Since: 2.58
 */
void
(g_atomic_ref_count_init) (gatomicrefcount *arc)
{
  g_return_if_fail (arc != NULL);

  /* Atomic refcounting is implemented using the positive range
   * of signed integers:
   *
   * G_MININT                 Z¯< 0 > Z⁺                G_MAXINT
   * |----------------------------|----------------------------|
   *
   * Acquiring a reference moves us towards MAXINT, and releasing a
   * reference moves us towards 0.
   */
  g_atomic_int_set (arc, 1);
}

/**
 * g_atomic_ref_count_inc:
 * @arc: the address of an atomic reference count variable
 *
 * Atomically increases the reference count.
 *
 * Since: 2.58
 */
void
(g_atomic_ref_count_inc) (gatomicrefcount *arc)
{
  g_return_if_fail (arc != NULL);
  g_return_if_fail (g_atomic_int_get (arc) > 0);

  if (g_atomic_int_get (arc) == G_MAXINT)
    {
      g_critical ("Reference count has reached saturation");
      return;
    }

  g_atomic_int_inc (arc);
}

/**
 * g_atomic_ref_count_dec:
 * @arc: the address of an atomic reference count variable
 *
 * Atomically decreases the reference count.
 *
 * Returns: %TRUE if the reference count reached 0, and %FALSE otherwise
 *
 * Since: 2.58
 */
gboolean
(g_atomic_ref_count_dec) (gatomicrefcount *arc)
{
  g_return_val_if_fail (arc != NULL, FALSE);
  g_return_val_if_fail (g_atomic_int_get (arc) > 0, FALSE);

  return g_atomic_int_dec_and_test (arc);
}

/**
 * g_atomic_ref_count_compare:
 * @arc: the address of an atomic reference count variable
 * @val: the value to compare
 *
 * Atomically compares the current value of @arc with @val.
 *
 * Returns: %TRUE if the reference count is the same
 *   as the given value
 *
 * Since: 2.58
 */
gboolean
(g_atomic_ref_count_compare) (gatomicrefcount *arc,
                              gint             val)
{
  g_return_val_if_fail (arc != NULL, FALSE);
  g_return_val_if_fail (val >= 0, FALSE);

  return g_atomic_int_get (arc) == val;
}