1 /**************************************************************************** 2 ** 3 ** Copyright (C) 2016 Intel Corporation. 4 ** Contact: https://www.qt.io/licensing/ 5 ** 6 ** This file is part of the QtCore module of the Qt Toolkit. 7 ** 8 ** $QT_BEGIN_LICENSE:LGPL$ 9 ** Commercial License Usage 10 ** Licensees holding valid commercial Qt licenses may use this file in 11 ** accordance with the commercial license agreement provided with the 12 ** Software or, alternatively, in accordance with the terms contained in 13 ** a written agreement between you and The Qt Company. For licensing terms 14 ** and conditions see https://www.qt.io/terms-conditions. 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The licenses are as published by the Free Software 30 ** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3 31 ** included in the packaging of this file. Please review the following 32 ** information to ensure the GNU General Public License requirements will 33 ** be met: https://www.gnu.org/licenses/gpl-2.0.html and 34 ** https://www.gnu.org/licenses/gpl-3.0.html. 35 ** 36 ** $QT_END_LICENSE$ 37 ** 38 ****************************************************************************/ 39 40 #include <QtCore/qglobal.h> 41 42 #ifndef QGLOBALSTATIC_H 43 #define QGLOBALSTATIC_H 44 45 #include <QtCore/qatomic.h> 46 47 QT_BEGIN_NAMESPACE 48 49 namespace QtGlobalStatic { 50 enum GuardValues { 51 Destroyed = -2, 52 Initialized = -1, 53 Uninitialized = 0, 54 Initializing = 1 55 }; 56 } 57 58 #if !QT_CONFIG(thread) || defined(Q_COMPILER_THREADSAFE_STATICS) 59 // some compilers support thread-safe statics 60 // The IA-64 C++ ABI requires this, so we know that all GCC versions since 3.4 61 // support it. C++11 also requires this behavior. 62 // Clang and Intel CC masquerade as GCC when compiling on Linux. 63 // 64 // Apple's libc++abi however uses a global lock for initializing local statics, 65 // which will block other threads also trying to initialize a local static 66 // until the constructor returns ... 67 // We better avoid these kind of problems by using our own locked implementation. 68 69 #if defined(Q_OS_UNIX) && defined(Q_CC_INTEL) 70 // Work around Intel issue ID 6000058488: 71 // local statics inside an inline function inside an anonymous namespace are global 72 // symbols (this affects the IA-64 C++ ABI, so OS X and Linux only) 73 # define Q_GLOBAL_STATIC_INTERNAL_DECORATION Q_DECL_HIDDEN 74 #else 75 # define Q_GLOBAL_STATIC_INTERNAL_DECORATION Q_DECL_HIDDEN inline 76 #endif 77 78 #define Q_GLOBAL_STATIC_INTERNAL(ARGS) \ 79 Q_GLOBAL_STATIC_INTERNAL_DECORATION Type *innerFunction() \ 80 { \ 81 struct HolderBase { \ 82 ~HolderBase() noexcept \ 83 { if (guard.loadRelaxed() == QtGlobalStatic::Initialized) \ 84 guard.storeRelaxed(QtGlobalStatic::Destroyed); } \ 85 }; \ 86 static struct Holder : public HolderBase { \ 87 Type value; \ 88 Holder() \ 89 noexcept(noexcept(Type ARGS)) \ 90 : value ARGS \ 91 { guard.storeRelaxed(QtGlobalStatic::Initialized); } \ 92 } holder; \ 93 return &holder.value; \ 94 } 95 #else 96 // We don't know if this compiler supports thread-safe global statics 97 // so use our own locked implementation 98 99 QT_END_NAMESPACE 100 #include <QtCore/qmutex.h> 101 #include <mutex> 102 QT_BEGIN_NAMESPACE 103 104 #define Q_GLOBAL_STATIC_INTERNAL(ARGS) \ 105 Q_DECL_HIDDEN inline Type *innerFunction() \ 106 { \ 107 static Type *d; \ 108 static QBasicMutex mutex; \ 109 int x = guard.loadAcquire(); \ 110 if (Q_UNLIKELY(x >= QtGlobalStatic::Uninitialized)) { \ 111 const std::lock_guard<QBasicMutex> locker(mutex); \ 112 if (guard.loadRelaxed() == QtGlobalStatic::Uninitialized) { \ 113 d = new Type ARGS; \ 114 static struct Cleanup { \ 115 ~Cleanup() { \ 116 delete d; \ 117 guard.storeRelaxed(QtGlobalStatic::Destroyed); \ 118 } \ 119 } cleanup; \ 120 guard.storeRelease(QtGlobalStatic::Initialized); \ 121 } \ 122 } \ 123 return d; \ 124 } 125 #endif 126 127 // this class must be POD, unless the compiler supports thread-safe statics 128 template <typename T, T *(&innerFunction)(), QBasicAtomicInt &guard> 129 struct QGlobalStatic 130 { 131 typedef T Type; 132 isDestroyedQGlobalStatic133 bool isDestroyed() const { return guard.loadRelaxed() <= QtGlobalStatic::Destroyed; } existsQGlobalStatic134 bool exists() const { return guard.loadRelaxed() == QtGlobalStatic::Initialized; } 135 operator Type *() { if (isDestroyed()) return nullptr; return innerFunction(); } operatorQGlobalStatic136 Type *operator()() { if (isDestroyed()) return nullptr; return innerFunction(); } 137 Type *operator->() 138 { 139 Q_ASSERT_X(!isDestroyed(), "Q_GLOBAL_STATIC", "The global static was used after being destroyed"); 140 return innerFunction(); 141 } 142 Type &operator*() 143 { 144 Q_ASSERT_X(!isDestroyed(), "Q_GLOBAL_STATIC", "The global static was used after being destroyed"); 145 return *innerFunction(); 146 } 147 }; 148 149 #define Q_GLOBAL_STATIC_WITH_ARGS(TYPE, NAME, ARGS) \ 150 namespace { namespace Q_QGS_ ## NAME { \ 151 typedef TYPE Type; \ 152 QBasicAtomicInt guard = Q_BASIC_ATOMIC_INITIALIZER(QtGlobalStatic::Uninitialized); \ 153 Q_GLOBAL_STATIC_INTERNAL(ARGS) \ 154 } } \ 155 static QGlobalStatic<TYPE, \ 156 Q_QGS_ ## NAME::innerFunction, \ 157 Q_QGS_ ## NAME::guard> NAME; 158 159 #define Q_GLOBAL_STATIC(TYPE, NAME) \ 160 Q_GLOBAL_STATIC_WITH_ARGS(TYPE, NAME, ()) 161 162 QT_END_NAMESPACE 163 #endif // QGLOBALSTATIC_H 164