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28 | |
29 | |
30 | #include "qplatformdefs.h" |
31 | #include "qthreadonce.h" |
32 | |
33 | #include "qmutex.h" |
34 | |
35 | Q_GLOBAL_STATIC(QRecursiveMutex, onceInitializationMutex) |
36 | |
37 | enum { |
38 | MustRunCode = 0x01, |
39 | MustUnlockMutex = 0x02 |
40 | }; |
41 | |
42 | /*! |
43 | \internal |
44 | Initialize the Q_ONCE structure. |
45 | |
46 | Q_ONCE consists of two variables: |
47 | - a static POD QOnceControl::ControlVariable (it's a QBasicAtomicInt) |
48 | - an automatic QOnceControl that controls the former |
49 | |
50 | The POD is initialized to 0. |
51 | |
52 | When QOnceControl's constructor starts, it'll lock the global |
53 | initialization mutex. It'll then check if it's the first to up |
54 | the control variable and will take note. |
55 | |
56 | The QOnceControl's destructor will unlock the global |
57 | initialization mutex. |
58 | */ |
59 | QOnceControl::QOnceControl(QBasicAtomicInt *control) |
60 | { |
61 | d = 0; |
62 | gv = control; |
63 | // check if code has already run once |
64 | if (gv->loadAcquire() == 2) { |
65 | // uncontended case: it has already initialized |
66 | // no waiting |
67 | return; |
68 | } |
69 | |
70 | // acquire the path |
71 | onceInitializationMutex()->lock(); |
72 | extra = MustUnlockMutex; |
73 | |
74 | if (gv->testAndSetAcquire(expectedValue: 0, newValue: 1)) { |
75 | // path acquired, we're the first |
76 | extra |= MustRunCode; |
77 | } |
78 | } |
79 | |
80 | QOnceControl::~QOnceControl() |
81 | { |
82 | if (mustRunCode()) |
83 | // code wasn't run! |
84 | gv->testAndSetRelease(expectedValue: 1, newValue: 0); |
85 | else |
86 | gv->testAndSetRelease(expectedValue: 1, newValue: 2); |
87 | if (extra & MustUnlockMutex) |
88 | onceInitializationMutex()->unlock(); |
89 | } |
90 | |
91 | /*! |
92 | \internal |
93 | Returns true if the initialization code must be run. |
94 | |
95 | Obviously, the initialization code must be run only once... |
96 | */ |
97 | bool QOnceControl::mustRunCode() |
98 | { |
99 | return extra & MustRunCode; |
100 | } |
101 | |
102 | void QOnceControl::done() |
103 | { |
104 | extra &= ~MustRunCode; |
105 | } |
106 | |