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28
29
30#ifndef QTHREADONCE_H
31#define QTHREADONCE_H
32
33#include <QtCore/qglobal.h>
34#include <QtCore/qatomic.h>
35
36
37class QOnceControl
38{
39public:
40 QOnceControl(QBasicAtomicInt *);
41 ~QOnceControl();
42
43 bool mustRunCode();
44 void done();
45
46private:
47 QBasicAtomicInt *gv;
48 union {
49 qint32 extra;
50 void *d;
51 };
52};
53
54#define Q_ONCE_GV_NAME2(prefix, line) prefix ## line
55#define Q_ONCE_GV_NAME(prefix, line) Q_ONCE_GV_NAME2(prefix, line)
56#define Q_ONCE_GV Q_ONCE_GV_NAME(_q_once_, __LINE__)
57
58#define Q_ONCE \
59 static QBasicAtomicInt Q_ONCE_GV = Q_BASIC_ATOMIC_INITIALIZER(0); \
60 if (0){} else \
61 for (QOnceControl _control_(&Q_ONCE_GV); _control_.mustRunCode(); _control_.done())
62
63template<typename T>
64class QSingleton
65{
66 // this is a POD-like class
67 struct Destructor
68 {
69 T *&pointer;
70 Destructor(T *&ptr) : pointer(ptr) {}
71 ~Destructor() { delete pointer; }
72 };
73
74public:
75 T *_q_value;
76 QBasicAtomicInt _q_guard;
77
78 inline T *value()
79 {
80 for (QOnceControl control(&_q_guard); control.mustRunCode(); control.done()) {
81 _q_value = new T();
82 static Destructor cleanup(_q_value);
83 }
84 return _q_value;
85 }
86
87 inline T& operator*() { return *value(); }
88 inline T* operator->() { return value(); }
89 inline operator T*() { return value(); }
90};
91
92#endif
93

source code of qtbase/tests/auto/corelib/thread/qthreadonce/qthreadonce.h