Add a new Q_GLOBAL_STATIC implementation

Unlike the previous implementation, this implementation is locked:
only one initialisation is ever run at the same time. It is
exception-safe, meaning that a throwing constructor will restart the
process.

Also, start using the thread-safe behaviour that GCC has offered for a
long time and C++11 requires.

Change-Id: I20db44f57d258923df64c0051358fd0d9a5ccd51
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: David Faure (KDE) <faure@kde.org>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>

3 files changed, 161 insertions, 119 deletions

diff --git a/src/corelib/global/global.pri b/src/corelib/global/global.pri
index 01756c8419..491464621c 100644
--- a/src/corelib/global/global.pri
+++ b/src/corelib/global/global.pri
@@ -9,6 +9,7 @@ HEADERS +=  \
         global/qendian.h \
         global/qnumeric_p.h \
         global/qnumeric.h \
+        global/qglobalstatic.h \
         global/qlibraryinfo.h \
         global/qlogging.h \
         global/qtypeinfo.h \
diff --git a/src/corelib/global/qglobal.h b/src/corelib/global/qglobal.h
index 03cd3dc591..60b6e32522 100644
--- a/src/corelib/global/qglobal.h
+++ b/src/corelib/global/qglobal.h
@@ -664,125 +664,6 @@ typedef void (*QFunctionPointer)();
 #  define Q_UNIMPLEMENTED() qWarning("%s:%d: %s: Unimplemented code.", __FILE__, __LINE__, Q_FUNC_INFO)
 #endif
 
-#if defined(QT_NO_THREAD)
-
-template <typename T>
-class QGlobalStatic
-{
-public:
-    T *pointer;
-    inline QGlobalStatic(T *p) : pointer(p) { }
-    inline ~QGlobalStatic() { pointer = 0; }
-};
-
-#define Q_GLOBAL_STATIC(TYPE, NAME)                                  \
-    static TYPE *NAME()                                              \
-    {                                                                \
-        static TYPE thisVariable;                                    \
-        static QGlobalStatic<TYPE > thisGlobalStatic(&thisVariable); \
-        return thisGlobalStatic.pointer;                             \
-    }
-
-#define Q_GLOBAL_STATIC_WITH_ARGS(TYPE, NAME, ARGS)                  \
-    static TYPE *NAME()                                              \
-    {                                                                \
-        static TYPE thisVariable ARGS;                               \
-        static QGlobalStatic<TYPE > thisGlobalStatic(&thisVariable); \
-        return thisGlobalStatic.pointer;                             \
-    }
-
-#define Q_GLOBAL_STATIC_WITH_INITIALIZER(TYPE, NAME, INITIALIZER)    \
-    static TYPE *NAME()                                              \
-    {                                                                \
-        static TYPE thisVariable;                                    \
-        static QGlobalStatic<TYPE > thisGlobalStatic(0);             \
-        if (!thisGlobalStatic.pointer) {                             \
-            TYPE *x = thisGlobalStatic.pointer = &thisVariable;      \
-            INITIALIZER;                                             \
-        }                                                            \
-        return thisGlobalStatic.pointer;                             \
-    }
-
-#else
-
-// forward declaration, since qatomic.h needs qglobal.h
-template <typename T> class QBasicAtomicPointer;
-
-// POD for Q_GLOBAL_STATIC
-template <typename T>
-class QGlobalStatic
-{
-public:
-    QBasicAtomicPointer<T> pointer;
-    bool destroyed;
-};
-
-// Created as a function-local static to delete a QGlobalStatic<T>
-template <typename T>
-class QGlobalStaticDeleter
-{
-public:
-    QGlobalStatic<T> &globalStatic;
-    QGlobalStaticDeleter(QGlobalStatic<T> &_globalStatic)
-        : globalStatic(_globalStatic)
-    { }
-
-    inline ~QGlobalStaticDeleter()
-    {
-        delete globalStatic.pointer.load();
-        globalStatic.pointer.store(0);
-        globalStatic.destroyed = true;
-    }
-};
-
-#define Q_GLOBAL_STATIC(TYPE, NAME)                                           \
-    static TYPE *NAME()                                                       \
-    {                                                                         \
-        static QGlobalStatic<TYPE > thisGlobalStatic                          \
-                            = { Q_BASIC_ATOMIC_INITIALIZER(0), false };       \
-        if (!thisGlobalStatic.pointer.load() && !thisGlobalStatic.destroyed) { \
-            TYPE *x = new TYPE;                                               \
-            if (!thisGlobalStatic.pointer.testAndSetOrdered(0, x))            \
-                delete x;                                                     \
-            else                                                              \
-                static QGlobalStaticDeleter<TYPE > cleanup(thisGlobalStatic); \
-        }                                                                     \
-        return thisGlobalStatic.pointer.load();                               \
-    }
-
-#define Q_GLOBAL_STATIC_WITH_ARGS(TYPE, NAME, ARGS)                           \
-    static TYPE *NAME()                                                       \
-    {                                                                         \
-        static QGlobalStatic<TYPE > thisGlobalStatic                          \
-                            = { Q_BASIC_ATOMIC_INITIALIZER(0), false };       \
-        if (!thisGlobalStatic.pointer.load() && !thisGlobalStatic.destroyed) {       \
-            TYPE *x = new TYPE ARGS;                                          \
-            if (!thisGlobalStatic.pointer.testAndSetOrdered(0, x))            \
-                delete x;                                                     \
-            else                                                              \
-                static QGlobalStaticDeleter<TYPE > cleanup(thisGlobalStatic); \
-        }                                                                     \
-        return thisGlobalStatic.pointer.load();                               \
-    }
-
-#define Q_GLOBAL_STATIC_WITH_INITIALIZER(TYPE, NAME, INITIALIZER)             \
-    static TYPE *NAME()                                                       \
-    {                                                                         \
-        static QGlobalStatic<TYPE > thisGlobalStatic                          \
-                            = { Q_BASIC_ATOMIC_INITIALIZER(0), false };       \
-        if (!thisGlobalStatic.pointer.load() && !thisGlobalStatic.destroyed) {       \
-            QScopedPointer<TYPE > x(new TYPE);                                \
-            INITIALIZER;                                                      \
-            if (thisGlobalStatic.pointer.testAndSetOrdered(0, x.data())) {    \
-                static QGlobalStaticDeleter<TYPE > cleanup(thisGlobalStatic); \
-                x.take();                                                     \
-            }                                                                 \
-        }                                                                     \
-        return thisGlobalStatic.pointer.load();                               \
-    }
-
-#endif
-
 Q_DECL_CONSTEXPR static inline bool qFuzzyCompare(double p1, double p2)
 {
     return (qAbs(p1 - p2) <= 0.000000000001 * qMin(qAbs(p1), qAbs(p2)));
@@ -1089,6 +970,9 @@ template <typename T> struct QEnableIf<true, T> { typedef T Type; };
 QT_END_NAMESPACE
 QT_END_HEADER
 
+// Q_GLOBAL_STATIC
+#include <QtCore/qglobalstatic.h>
+
 // qDebug and friends
 #include <QtCore/qlogging.h>
 #include <QtCore/qflags.h>
diff --git a/src/corelib/global/qglobalstatic.h b/src/corelib/global/qglobalstatic.h
new file mode 100644
index 0000000000..78a4acff12
--- /dev/null
+++ b/src/corelib/global/qglobalstatic.h
@@ -0,0 +1,157 @@
+/****************************************************************************
+**
+** Copyright (C) 2012 Intel Corporation
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtCore/qglobal.h>
+
+#ifndef QGLOBALSTATIC_H
+#define QGLOBALSTATIC_H
+
+#include <QtCore/qatomic.h>
+
+QT_BEGIN_HEADER
+QT_BEGIN_NAMESPACE
+
+/*
+ * QGlobalStatic internals:
+ *
+ * The pointer is initialized to 0.
+ * The guard is initialized to 0.
+ * The guard can assume the following values:
+ *   -2:      object initialized and already destroyed
+ *   -1:      object initialized and is still valid
+ *    0:      not initialized, the value of the pointer should be null
+ *   +1:      initializing, must wait until a state change happens
+ *            (not used in the current implementation)
+ */
+
+namespace QtGlobalStatic {
+enum GuardValues {
+    Destroyed = -2,
+    Initialized = -1,
+    Uninitialized = 0,
+    Initializing = 1
+};
+}
+
+#if defined(QT_NO_THREAD) || defined(Q_CC_GNU)
+// some compilers support thread-safe statics
+// The IA-64 C++ ABI requires this, so we know that all GCC versions since 3.4
+// support it. C++11 also requires this behavior.
+// Clang and Intel CC masquerade as GCC when compiling on Linux and Mac OS X.
+
+#define Q_GLOBAL_STATIC_INTERNAL(ARGS)                          \
+    Q_DECL_HIDDEN inline Type *innerFunction()                  \
+    {                                                           \
+        struct HolderBase {                                     \
+            ~HolderBase() Q_DECL_NOTHROW                        \
+            { guard.store(QtGlobalStatic::Destroyed); }         \
+        };                                                      \
+        static struct Holder : public HolderBase {              \
+            Type value;                                         \
+            Holder()                                            \
+                Q_DECL_NOEXCEPT_EXPR(noexcept(Type ARGS))       \
+                : value ARGS                                    \
+            { guard.store(QtGlobalStatic::Initialized); }       \
+        } holder;                                               \
+        return &holder.value;                                   \
+    }
+#else
+// We don't know if this compiler supports thread-safe global statics
+// so use our own locked implementation
+
+QT_END_NAMESPACE
+#include <QtCore/qmutex.h>
+QT_BEGIN_NAMESPACE
+
+#define Q_GLOBAL_STATIC_INTERNAL(ARGS)                                  \
+    Q_DECL_HIDDEN inline Type *innerFunction()                          \
+    {                                                                   \
+        static Type *d;                                                 \
+        static QBasicMutex mutex;                                       \
+        int x = guard.loadAcquire();                                    \
+        if (Q_UNLIKELY(x >= QtGlobalStatic::Uninitialized)) {           \
+            QMutexLocker locker(&mutex);                                \
+            if (guard.load() == QtGlobalStatic::Uninitialized) {        \
+                d = new Type ARGS;                                      \
+                static struct Cleanup {                                 \
+                    ~Cleanup() {                                        \
+                        delete d;                                       \
+                        guard.store(QtGlobalStatic::Destroyed);         \
+                    }                                                   \
+                } cleanup;                                              \
+                guard.store(QtGlobalStatic::Initialized);               \
+            }                                                           \
+        }                                                               \
+        return d;                                                       \
+    }
+#endif
+
+// this class must be POD, unless the compiler supports thread-safe statics
+template <typename T, T *(&innerFunction)(), QBasicAtomicInt &guard>
+struct QGlobalStatic
+{
+    typedef T Type;
+
+    bool isDestroyed() const { return guard.load() <= QtGlobalStatic::Destroyed; }
+    bool exists() const { return guard.load() == QtGlobalStatic::Initialized; }
+    operator Type *() { if (isDestroyed()) return 0; return innerFunction(); }
+    Type *operator()() { if (isDestroyed()) return 0; return innerFunction(); }
+    Type *operator->() { return innerFunction(); }
+    Type &operator*() { return *innerFunction(); }
+};
+
+#define Q_GLOBAL_STATIC_WITH_ARGS(TYPE, NAME, ARGS)                         \
+    namespace { namespace Q_QGS_ ## NAME {                                  \
+        typedef TYPE Type;                                                  \
+        QBasicAtomicInt guard = Q_BASIC_ATOMIC_INITIALIZER(QtGlobalStatic::Uninitialized); \
+        Q_GLOBAL_STATIC_INTERNAL(ARGS)                                      \
+    } }                                                                     \
+    static QGlobalStatic<TYPE,                                              \
+                         Q_QGS_ ## NAME::innerFunction,                     \
+                         Q_QGS_ ## NAME::guard> NAME;
+
+#define Q_GLOBAL_STATIC(TYPE, NAME)                                         \
+    Q_GLOBAL_STATIC_WITH_ARGS(TYPE, NAME, ())
+
+QT_END_NAMESPACE
+QT_END_HEADER
+
+#endif // QGLOBALSTATIC_H