MuldeR's Utilities for Qt: include/MUtils/Lazy.h Source File

MuldeR's Utilities for Qt MUtilities

Lazy.h
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1 // MuldeR's Utilities for Qt
3 // Copyright (C) 2004-2019 LoRd_MuldeR <MuldeR2@GMX.de>
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, write to the Free Software
17 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
18 //
19 // http://www.gnu.org/licenses/lgpl-2.1.txt
21
27 #pragma once
28
29 //MUtils
30 #include <MUtils/Global.h>
31 #include <MUtils/Exception.h>
32
33 //Qt
34 #include <QThread>
35 #include <QAtomicPointer>
36 #include <QAtomicInt>
37
38 //CRT
39 #include <functional>
40
41 namespace MUtils
42 {
50 template<typename T> class Lazy
51 {
52 public:
53 Lazy(std::function<T*(void)> &&initializer) : m_initializer(initializer) { }
54
55 T& operator*(void)
56 {
57 return (*getValue());
58 }
59
60 T* operator->(void)
61 {
62 return getValue();
63 }
64
65 bool initialized()
66 {
67 return (m_state > 1);
68 }
69
70 ~Lazy(void)
71 {
72 if(T *const value = m_value)
73 {
74 delete value;
75 }
76 }
77
78 protected:
79 __forceinline T* getValue()
80 {
81 T *value;
82 while (!(value = m_value))
83 {
84 if (m_state.testAndSetOrdered(0, 1))
85 {
86 if (value = m_initializer())
87 {
88 m_value.fetchAndStoreOrdered(value);
89 m_state.fetchAndStoreOrdered(2);
90 break; /*success*/
91 }
92 m_state.fetchAndStoreOrdered(0);
93 MUTILS_THROW("Initializer returned NULL pointer!");
94 }
95 QThread::yieldCurrentThread();
96 }
97 return value;
98 }
99
100 private:
101 QAtomicPointer<T> m_value;
102 QAtomicInt m_state;
103 const std::function<T*(void)> m_initializer;
104 };
105 }
Global.h
This file contains miscellaneous functions that are generally useful for Qt-based applications...
MUtils::Lazy
Lazy initialization template class.
Definition: Lazy.h:50
MUtils
Global MUtils namespace.
Definition: CPUFeatures.h:37