1 /*
2 * Copyright (c) 2006 Cyrille Berger <cberger@cberger.net>
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
17 */
18
19 #include "kis_shared.h"
20 #include "kis_debug.h"
21
22
23 /**
24 * NOTE: The description of how Weak shared pointers system works:
25 *
26 * Every KisShared object has his own _sharedWeakReference pointer.
27 * This pointer holds QAtomicInt counter. When KisShared constructs
28 * itself, it increments _sharedWeakReference by one. When it dies -
29 * it decrements it. This is the only way how the number in the
30 * counter can become odd. Obviously, when the number falls to zero,
31 * the counter object is deleted.
32 *
33 * When a weak shared pointer is created, it gets the pointer and
34 * increments the counter by 2, so the parity of the number is kept
35 * unchanged. Now the counter is shared between the KisShared and
36 * KisWeakSharedPtr and the latter one can check the correctness
37 * of the pointer by checking parity!
38 */
39
KisShared()40 KisShared::KisShared()
41 {
42 /**
43 * We can defer creation of a weak reference until
44 * better days... It gives us 41% better performance. ;)
45 */
46 _sharedWeakReference = 0;
47 }
48
~KisShared()49 KisShared::~KisShared()
50 {
51 /**
52 * Check no-one references us
53 */
54 Q_ASSERT(_ref == 0);
55
56 if(_sharedWeakReference && !_sharedWeakReference->deref())
57 delete _sharedWeakReference;
58 }
59