Add an internal QRefCount class to QtCore

The class will be used by QString and possibly other
container classes to allow for the Data objects to be
created at compile time in read-only memory.

Change-Id: I9c7538bc97df637cc920e6e5ef23d67a93abac0d
Reviewed-on: http://codereview.qt.nokia.com/1216
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Olivier Goffart <olivier.goffart@nokia.com>

src/corelib/tools/qrefcount.cpp

@@ -0,0 +1,51 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** 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, Nokia gives you certain additional
+** rights. These rights are described in the Nokia 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.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+  \class QtPrivate::RefCount
+  \internal
+
+  QRefCount implements atomic ref counting for Qt's shared classes. It behaves very similar
+  to QAtomicInt, but ignores negative ref counts.
+
+  This can be used to allow to implement e.g. const read-only QStringData objects. QString::shared_null and
+  the qs(...) macro make use of this feature.
+*/

src/corelib/tools/qrefcount.h

@@ -0,0 +1,92 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** 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, Nokia gives you certain additional
+** rights. These rights are described in the Nokia 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.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QREFCOUNT_H
+#define QREFCOUNT_H
+
+#include <QtCore/qatomic.h>
+
+QT_BEGIN_HEADER
+
+QT_BEGIN_NAMESPACE
+
+QT_MODULE(Core)
+
+namespace QtPrivate
+{
+
+class RefCount
+{
+public:
+   inline void ref() {
+        if (atomic >= 0)
+            atomic.ref();
+    }
+
+    inline bool deref() {
+        if (atomic < 0)
+            return true;
+        return atomic.deref();
+    }
+
+    inline bool operator==(int value) const
+    { return atomic.operator ==(value); }
+    inline bool operator!=(int value) const
+    { return atomic.operator !=(value); }
+    inline bool operator!() const
+    { return atomic.operator !(); }
+    inline operator int() const
+    { return atomic.operator int(); }
+    inline RefCount &operator=(int value)
+    { atomic = value; return *this; }
+
+    QBasicAtomicInt atomic;
+};
+
+#define Q_REFCOUNT_INITIALIZER(a) { Q_BASIC_ATOMIC_INITIALIZER(a) }
+
+}
+
+QT_END_NAMESPACE
+
+QT_END_HEADER
+
+#endif

src/corelib/tools/tools.pri

@@ -30,6 +30,7 @@ HEADERS +=  \
         tools/qrect.h \
         tools/qregexp.h \
         tools/qringbuffer_p.h \
+        tools/qrefcount.h \
         tools/qscopedpointer.h \
         tools/qscopedpointer_p.h \
         tools/qscopedvaluerollback.h \
@@ -72,6 +73,7 @@ SOURCES += \
         tools/qcontiguouscache.cpp \
         tools/qrect.cpp \
         tools/qregexp.cpp \
+        tools/qrefcount.cpp \
         tools/qshareddata.cpp \
         tools/qsharedpointer.cpp \
         tools/qsimd.cpp \