1 files changed, 86 insertions, 0 deletions
diff --git a/src/corelib/kernel/qapplicationstatic.h b/src/corelib/kernel/qapplicationstatic.h
new file mode 100644
index 0000000000..bf5e79b8bf
--- /dev/null
+++ b/src/corelib/kernel/qapplicationstatic.h
@@ -0,0 +1,86 @@
+// Copyright (C) 2021 The Qt Company Ltd.
+// Copyright (C) 2021 Intel Corporation.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef QAPPLICATIONSTATIC_H
+#define QAPPLICATIONSTATIC_H
+
+#include <QtCore/QMutex>
+#include <QtCore/qcoreapplication.h>
+#include <QtCore/qglobalstatic.h>
+
+#include <new>
+
+QT_BEGIN_NAMESPACE
+
+namespace QtGlobalStatic {
+template <typename QAS> struct ApplicationHolder
+{
+    using Type = typename QAS::QAS_Type;
+    using PlainType = std::remove_cv_t<Type>;
+
+    Q_CONSTINIT static inline struct { alignas(Type) unsigned char data[sizeof(Type)]; } storage = {};
+    Q_CONSTINIT static inline QBasicAtomicInteger<qint8> guard = { QtGlobalStatic::Uninitialized };
+    Q_CONSTINIT static inline QBasicMutex mutex {};
+
+    static constexpr bool MutexLockIsNoexcept = noexcept(mutex.lock());
+    static constexpr bool ConstructionIsNoexcept = noexcept(QAS::innerFunction(nullptr));
+
+    ApplicationHolder() = default;
+    Q_DISABLE_COPY_MOVE(ApplicationHolder)
+    ~ApplicationHolder()
+    {
+        if (guard.loadAcquire() == QtGlobalStatic::Initialized) {
+            // No mutex! Up to external code to ensure no race happens.
+            guard.storeRelease(QtGlobalStatic::Destroyed);
+            realPointer()->~PlainType();
+        }
+    }
+
+    static PlainType *realPointer()
+    {
+        return std::launder(reinterpret_cast<PlainType *>(&storage));
+    }
+
+    // called from QGlobalStatic::instance()
+    PlainType *pointer() noexcept(MutexLockIsNoexcept && ConstructionIsNoexcept)
+    {
+        if (guard.loadAcquire() == QtGlobalStatic::Initialized)
+            return realPointer();
+        QMutexLocker locker(&mutex);
+        if (guard.loadRelaxed() == QtGlobalStatic::Uninitialized) {
+            QAS::innerFunction(&storage);
+            const auto *app = QCoreApplication::instance();
+            Q_ASSERT_X(app, Q_FUNC_INFO,
+                       "The application static was used without a QCoreApplication instance");
+            QObject::connect(app, &QObject::destroyed, app, reset, Qt::DirectConnection);
+            guard.storeRelease(QtGlobalStatic::Initialized);
+        }
+        return realPointer();
+    }
+
+    static void reset()
+    {
+        // we only synchronize using the mutex here, not the guard
+        QMutexLocker locker(&mutex);
+        realPointer()->~PlainType();
+        guard.storeRelaxed(QtGlobalStatic::Uninitialized);
+    }
+};
+} // namespace QtGlobalStatic
+
+#define Q_APPLICATION_STATIC(TYPE, NAME, ...) \
+    namespace { struct Q_QAS_ ## NAME {                                     \
+        typedef TYPE QAS_Type;                                              \
+        static void innerFunction(void *pointer)                            \
+            noexcept(noexcept(std::remove_cv_t<QAS_Type>(__VA_ARGS__)))     \
+        {                                                                   \
+            new (pointer) QAS_Type(__VA_ARGS__);                            \
+        }                                                                   \
+    }; }                                                                    \
+    static QGlobalStatic<QtGlobalStatic::ApplicationHolder<Q_QAS_ ## NAME>> NAME;\
+    /**/
+
+QT_END_NAMESPACE
+
+#endif // QAPPLICATIONSTATIC_H