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+/****************************************************************************
+**
+** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
+** Contact: Qt Software Information (qt-info@nokia.com)
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** No Commercial Usage
+** This file contains pre-release code and may not be distributed.
+** You may use this file in accordance with the terms and conditions
+** contained in the either Technology Preview License Agreement or the
+** Beta Release License Agreement.
+**
+** 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, Nokia gives you certain
+** additional rights. These rights are described in the Nokia Qt LGPL
+** Exception version 1.0, 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.
+**
+** If you are unsure which license is appropriate for your use, please
+** contact the sales department at qt-sales@nokia.com.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qsharedpointer.h"
+
+// to be sure we aren't causing a namespace clash:
+#include "qshareddata.h"
+
+/*!
+    \class QSharedPointer
+    \brief The QSharedPointer class holds a strong reference to a shared pointer
+    \since 4.5
+
+    \reentrant
+    \ingroup misc
+
+    The QSharedPointer is an automatic, shared pointer in C++. It
+    behaves exactly like a normal pointer for normal purposes,
+    including respect for constness.
+
+    QSharedPointer will delete the pointer it is holding when it goes
+    out of scope, provided no other QSharedPointer objects are
+    referencing it.
+
+    A QSharedPointer object can be created from a normal pointer,
+    another QSharedPointer object or by promoting a
+    QWeakPointer object to a strong reference.
+
+    \section1 Thread-Safety
+
+    QSharedPointer and QWeakPointer are thread-safe and operate
+    atomically on the pointer value. Different threads can also access
+    the same QSharedPointer or QWeakPointer object at the same time
+    without need for locking mechanisms.
+
+    It should be noted that, while the pointer value can be accessed
+    in this manner, QSharedPointer and QWeakPointer provide no
+    guarantee about the object being pointed to. Thread-safety and
+    reentrancy rules for that object still apply.
+
+    \section1 Other Pointer Classes
+
+    Qt also provides two other pointer wrapper classes: QPointer and
+    QSharedDataPointer. They are incompatible with one another, since
+    each has its very different use case.
+
+    QSharedPointer holds a shared pointer by means of an external
+    reference count (i.e., a reference counter placed outside the
+    object). Like its name indicates, the pointer value is shared
+    among all instances of QSharedPointer and QWeakPointer. The
+    contents of the object pointed to by the pointer should not
+    considered shared, however: there is only one object. For that
+    reason, QSharedPointer does not provide a way to detach or make
+    copies of the pointed object.
+
+    QSharedDataPointer, on the other hand, holds a pointer to shared
+    data (i.e., a class derived from QSharedData). It does so by means
+    of an internal reference count, placed in the QSharedData base
+    class. This class can, therefore, detach based on the type of
+    access made to the data being guarded: if it's a non-const access,
+    it creates a copy atomically for the operation to complete.
+
+    QExplicitlySharedDataPointer behaves like QSharedDataPointer,
+    except that it only detaches if
+    QExplicitlySharedDataPointer::detach() is explicitly called.
+
+    Finally, QPointer holds a pointer to a QObject-derived object, but
+    it does so weakly. QPointer is similar, in that behaviour, to
+    QWeakPointer: it does not allow you to prevent the object from
+    being destroyed. All you can do is query whether it has been
+    destroyed or not.
+
+    \sa QSharedDataPointer, QWeakPointer
+*/
+
+/*!
+    \class QWeakPointer
+    \brief The QWeakPointer class holds a weak reference to a shared pointer
+    \since 4.5
+    \reentrant
+    \ingroup misc
+
+    The QWeakPointer is an automatic weak reference to a
+    pointer in C++. It cannot be used to dereference the pointer
+    directly, but it can be used to verify if the pointer has been
+    deleted or not in another context.
+
+    QWeakPointer objects can only be created by assignment
+    from a QSharedPointer.
+
+    To access the pointer that QWeakPointer is tracking, you
+    must first create a QSharedPointer object and verify if the pointer
+    is null or not.
+
+    \sa QSharedPointer
+*/
+
+/*!
+    \fn QSharedPointer::QSharedPointer()
+
+    Creates a QSharedPointer that points to null (0).
+*/
+
+/*!
+    \fn QSharedPointer::~QSharedPointer()
+
+    Destroys this QSharedPointer object. If it is the last reference to
+    the pointer stored, this will delete the pointer as well.
+*/
+
+/*!
+    \fn QSharedPointer::QSharedPointer(T *ptr)
+
+    Creates a QSharedPointer that points to \a ptr. The pointer \a ptr
+    becomes managed by this QSharedPointer and must not be passed to
+    another QSharedPointer object or deleted outside this object.
+*/
+
+/*!
+    \fn QSharedPointer::QSharedPointer(T *ptr, Deleter deleter)
+
+    Creates a QSharedPointer that points to \a ptr. The pointer \a ptr
+    becomes managed by this QSharedPointer and must not be passed to
+    another QSharedPointer object or deleted outside this object.
+
+    The \a deleter paramter specifies the custom deleter for this
+    object. The custom deleter is called when the strong reference
+    count drops to 0 instead of the operator delete(). This is useful,
+    for instance, for calling deleteLater() in a QObject instead:
+
+    \code
+    static void doDeleteLater(MyObject *obj)
+    {
+        obj->deleteLater();
+    }
+
+    void otherFunction()
+    {
+        QSharedPointer<MyObject> obj =
+            QSharedPointer<MyObject>(new MyObject, doDeleteLater);
+
+        // continue using obj
+        obj.clear();    // calls obj->deleteLater();
+    }
+    \endcode
+
+    It is also possible to specify a member function directly, as in:
+    \code
+        QSharedPointer<MyObject> obj =
+            QSharedPointer<MyObject>(new MyObject, &QObject::deleteLater);
+    \endcode
+
+    \sa clear()
+*/
+
+/*!
+    \fn QSharedPointer::QSharedPointer(const QSharedPointer<T> &other)
+
+    Creates a QSharedPointer object that shares \a other's pointer.
+
+    If \tt T is a derived type of the template parameter of this class,
+    QSharedPointer will perform an automatic cast. Otherwise, you will
+    get a compiler error.
+*/
+
+/*!
+    \fn QSharedPointer::QSharedPointer(const QWeakPointer<T> &other)
+
+    Creates a QSharedPointer by promoting the weak reference \a other
+    to strong reference and sharing its pointer.
+
+    If \tt T is a derived type of the template parameter of this
+    class, QSharedPointer will perform an automatic cast. Otherwise,
+    you will get a compiler error.
+*/
+
+/*!
+    \fn QSharedPointer &QSharedPointer::operator=(const QSharedPointer<T> &other)
+
+    Makes this object share \a other's pointer. The current pointer
+    reference is discarded and, if it was the last, the pointer will
+    be deleted.
+
+    If \tt T is a derived type of the template parameter of this
+    class, QSharedPointer will perform an automatic cast. Otherwise,
+    you will get a compiler error.
+*/
+
+/*!
+    \fn QSharedPointer &QSharedPointer::operator=(const QWeakPointer<T> &other)
+
+    Promotes \a other to a strong reference and makes this object
+    share a reference to the pointer referenced by it. The current pointer
+    reference is discarded and, if it was the last, the pointer will
+    be deleted.
+
+    If \tt T is a derived type of the template parameter of this
+    class, QSharedPointer will perform an automatic cast. Otherwise,
+    you will get a compiler error.
+*/
+
+/*!
+    \fn T *QSharedPointer::data() const
+
+    Returns the value of the pointer referenced by this object.
+
+    Note: do not delete the pointer returned by this function or pass
+    it to another function that could delete it, including creating
+    QSharedPointer or QWeakPointer objects.
+*/
+
+/*!
+    \fn T &QSharedPointer::operator *() const
+
+    Provides access to the shared pointer's members.
+
+    \sa isNull()
+*/
+
+/*!
+    \fn T *QSharedPointer::operator ->() const
+
+    Provides access to the shared pointer's members.
+
+    \sa isNull()
+*/
+
+/*!
+    \fn bool QSharedPointer::isNull() const
+
+    Returns true if this object is holding a reference to a null
+    pointer.
+*/
+
+/*!
+    \fn QSharedPointer::operator bool() const
+
+    Returns true if this object is not null. This function is suitable
+    for use in \tt if-constructs, like:
+
+    \code
+        if (sharedptr) { ... }
+    \endcode
+
+    \sa isNull()
+*/
+
+/*!
+    \fn bool QSharedPointer::operator !() const
+
+    Returns true if this object is null. This function is suitable
+    for use in \tt if-constructs, like:
+
+    \code
+        if (!sharedptr) { ... }
+    \endcode
+
+    \sa isNull()
+*/
+
+/*!
+    \fn QSharedPointer<X> QSharedPointer::staticCast() const
+
+    Performs a static cast from this pointer's type to \tt X and returns
+    a QSharedPointer that shares the reference. This function can be
+    used for up- and for down-casting, but is more useful for
+    up-casting.
+
+    Note: the template type \c X must have the same const and volatile
+    qualifiers as the template of this object, or the cast will
+    fail. Use constCast() if you need to drop those qualifiers.
+
+    \sa dynamicCast(), constCast(), qSharedPointerCast()
+*/
+
+/*!
+    \fn QSharedPointer<X> QSharedPointer::dynamicCast() const
+
+    Performs a dynamic cast from this pointer's type to \tt X and
+    returns a QSharedPointer that shares the reference. If this
+    function is used to up-cast, then QSharedPointer will perform a \tt
+    dynamic_cast, which means that if the object being pointed by this
+    QSharedPointer is not of type \tt X, the returned object will be
+    null.
+
+    Note: the template type \c X must have the same const and volatile
+    qualifiers as the template of this object, or the cast will
+    fail. Use constCast() if you need to drop those qualifiers.
+
+    \sa qSharedPointerDynamicCast()
+*/
+
+/*!
+    \fn QSharedPointer<X> QSharedPointer::constCast() const
+
+    Performs a \tt const_cast from this pointer's type to \tt X and returns
+    a QSharedPointer that shares the reference. This function can be
+    used for up- and for down-casting, but is more useful for
+    up-casting.
+
+    \sa isNull(), qSharedPointerConstCast()
+*/
+
+/*!
+    \fn QWeakPointer<T> QSharedPointer::toWeakRef() const
+
+    Returns a weak reference object that shares the pointer referenced
+    by this object.
+*/
+
+/*!
+    \fn void QSharedPointer::clear()
+
+    Clears this QSharedPointer object, dropping the reference that it
+    may have had to the pointer. If this was the last reference, then
+    the pointer itself will be deleted.
+*/
+
+/*!
+    \fn QWeakPointer::QWeakPointer()
+
+    Creates a QWeakPointer that points to nothing.
+*/
+
+/*!
+    \fn QWeakPointer::~QWeakPointer()
+
+    Destroys this QWeakPointer object. The pointer referenced
+    by this object will not be deleted.
+*/
+
+/*!
+    \fn QWeakPointer::QWeakPointer(const QWeakPointer<T> &other)
+
+    Creates a QWeakPointer that holds a weak reference to the
+    pointer referenced by \a other.
+
+    If \tt T is a derived type of the template parameter of this
+    class, QWeakPointer will perform an automatic cast. Otherwise,
+    you will get a compiler error.
+*/
+
+/*!
+    \fn QWeakPointer::QWeakPointer(const QSharedPointer<T> &other)
+
+    Creates a QWeakPointer that holds a weak reference to the
+    pointer referenced by \a other.
+
+    If \tt T is a derived type of the template parameter of this
+    class, QWeakPointer will perform an automatic cast. Otherwise,
+    you will get a compiler error.
+*/
+
+/*!
+    \fn QWeakPointer &QWeakPointer::operator=(const QWeakPointer<T> &other)
+
+    Makes this object share \a other's pointer. The current pointer
+    reference is discarded but is not deleted.
+
+    If \tt T is a derived type of the template parameter of this
+    class, QWeakPointer will perform an automatic cast. Otherwise,
+    you will get a compiler error.
+*/
+
+/*!
+    \fn QWeakPointer &QWeakPointer::operator=(const QSharedPointer<T> &other)
+
+    Makes this object share \a other's pointer. The current pointer
+    reference is discarded but is not deleted.
+
+    If \tt T is a derived type of the template parameter of this
+    class, QWeakPointer will perform an automatic cast. Otherwise,
+    you will get a compiler error.
+*/
+
+/*!
+    \fn bool QWeakPointer::isNull() const
+
+    Returns true if this object is holding a reference to a null
+    pointer.
+
+    Note that, due to the nature of weak references, the pointer that
+    QWeakPointer references can become null at any moment, so
+    the value returned from this function can change from false to
+    true from one call to the next.
+*/
+
+/*!
+    \fn QWeakPointer::operator bool() const
+
+    Returns true if this object is not null. This function is suitable
+    for use in \tt if-constructs, like:
+
+    \code
+        if (weakref) { ... }
+    \endcode
+
+    Note that, due to the nature of weak references, the pointer that
+    QWeakPointer references can become null at any moment, so
+    the value returned from this function can change from true to
+    false from one call to the next.
+
+    \sa isNull()
+*/
+
+/*!
+    \fn bool QWeakPointer::operator !() const
+
+    Returns true if this object is null. This function is suitable
+    for use in \tt if-constructs, like:
+
+    \code
+        if (!weakref) { ... }
+    \endcode
+
+    Note that, due to the nature of weak references, the pointer that
+    QWeakPointer references can become null at any moment, so
+    the value returned from this function can change from false to
+    true from one call to the next.
+
+    \sa isNull()
+*/
+
+/*!
+    \fn QSharedPointer<T> QWeakPointer::toStrongRef() const
+
+    Promotes this weak reference to a strong one and returns a
+    QSharedPointer object holding that reference.
+*/
+
+/*!
+    \fn void QWeakPointer::clear()
+
+    Clears this QWeakPointer object, dropping the reference that it
+    may have had to the pointer.
+*/
+
+/*!
+    \fn bool operator==(const QSharedPointer<T> &ptr1, const QSharedPointer<X> &ptr2)
+    \relates QSharedPointer
+
+    Returns true if the pointer referenced by \a ptr1 is the
+    same pointer as that referenced by \a ptr2.
+
+    If \a ptr2's template parameter is different from \a ptr1's,
+    QSharedPointer will attempt to perform an automatic \tt static_cast
+    to ensure that the pointers being compared are equal. If \a ptr2's
+    template parameter is not a base or a derived type from
+    \a ptr1's, you will get a compiler error.
+*/
+
+/*!
+    \fn bool operator!=(const QSharedPointer<T> &ptr1, const QSharedPointer<X> &ptr2)
+    \relates QSharedPointer
+
+    Returns true if the pointer referenced by \a ptr1 is not the
+    same pointer as that referenced by \a ptr2.
+
+    If \a ptr2's template parameter is different from \a ptr1's,
+    QSharedPointer will attempt to perform an automatic \tt static_cast
+    to ensure that the pointers being compared are equal. If \a ptr2's
+    template parameter is not a base or a derived type from
+    \a ptr1's, you will get a compiler error.
+*/
+
+/*!
+    \fn bool operator==(const QSharedPointer<T> &ptr1, const X *ptr2)
+    \relates QSharedPointer
+
+    Returns true if the pointer referenced by \a ptr1 is the
+    same pointer as \a ptr2.
+
+    If \a ptr2's type is different from \a ptr1's,
+    QSharedPointer will attempt to perform an automatic \tt static_cast
+    to ensure that the pointers being compared are equal. If \a ptr2's
+    type is not a base or a derived type from this
+    \a ptr1's, you will get a compiler error.
+*/
+
+/*!
+    \fn bool operator!=(const QSharedPointer<T> &ptr1, const X *ptr2)
+    \relates QSharedPointer
+
+    Returns true if the pointer referenced by \a ptr1 is not the
+    same pointer as \a ptr2.
+
+    If \a ptr2's type is different from \a ptr1's,
+    QSharedPointer will attempt to perform an automatic \tt static_cast
+    to ensure that the pointers being compared are equal. If \a ptr2's
+    type is not a base or a derived type from this
+    \a ptr1's, you will get a compiler error.
+*/
+
+/*!
+    \fn bool operator==(const T *ptr1, const QSharedPointer<X> &ptr2)
+    \relates QSharedPointer
+
+    Returns true if the pointer \a ptr1 is the
+    same pointer as that referenced by \a ptr2.
+
+    If \a ptr2's template parameter is different from \a ptr1's type,
+    QSharedPointer will attempt to perform an automatic \tt static_cast
+    to ensure that the pointers being compared are equal. If \a ptr2's
+    template parameter is not a base or a derived type from
+    \a ptr1's type, you will get a compiler error.
+*/
+
+/*!
+    \fn bool operator!=(const T *ptr1, const QSharedPointer<X> &ptr2)
+    \relates QSharedPointer
+
+    Returns true if the pointer \a ptr1 is not the
+    same pointer as that referenced by \a ptr2.
+
+    If \a ptr2's template parameter is different from \a ptr1's type,
+    QSharedPointer will attempt to perform an automatic \tt static_cast
+    to ensure that the pointers being compared are equal. If \a ptr2's
+    template parameter is not a base or a derived type from
+    \a ptr1's type, you will get a compiler error.
+*/
+
+/*!
+    \fn bool operator==(const QSharedPointer<T> &ptr1, const QWeakPointer<X> &ptr2)
+    \relates QWeakPointer
+
+    Returns true if the pointer referenced by \a ptr1 is the
+    same pointer as that referenced by \a ptr2.
+
+    If \a ptr2's template parameter is different from \a ptr1's,
+    QSharedPointer will attempt to perform an automatic \tt static_cast
+    to ensure that the pointers being compared are equal. If \a ptr2's
+    template parameter is not a base or a derived type from
+    \a ptr1's, you will get a compiler error.
+*/
+
+/*!
+    \fn bool operator!=(const QSharedPointer<T> &ptr1, const QWeakPointer<X> &ptr2)
+    \relates QWeakPointer
+
+    Returns true if the pointer referenced by \a ptr1 is not the
+    same pointer as that referenced by \a ptr2.
+
+    If \a ptr2's template parameter is different from \a ptr1's,
+    QSharedPointer will attempt to perform an automatic \tt static_cast
+    to ensure that the pointers being compared are equal. If \a ptr2's
+    template parameter is not a base or a derived type from
+    \a ptr1's, you will get a compiler error.
+*/
+
+/*!
+    \fn bool operator==(const QWeakPointer<T> &ptr1, const QSharedPointer<X> &ptr2)
+    \relates QWeakPointer
+
+    Returns true if the pointer referenced by \a ptr1 is the
+    same pointer as that referenced by \a ptr2.
+
+    If \a ptr2's template parameter is different from \a ptr1's,
+    QSharedPointer will attempt to perform an automatic \tt static_cast
+    to ensure that the pointers being compared are equal. If \a ptr2's
+    template parameter is not a base or a derived type from
+    \a ptr1's, you will get a compiler error.
+*/
+
+/*!
+    \fn bool operator!=(const QWeakPointer<T> &ptr1, const QSharedPointer<X> &ptr2)
+    \relates QWeakPointer
+
+    Returns true if the pointer referenced by \a ptr1 is not the
+    same pointer as that referenced by \a ptr2.
+
+    If \a ptr2's template parameter is different from \a ptr1's,
+    QSharedPointer will attempt to perform an automatic \tt static_cast
+    to ensure that the pointers being compared are equal. If \a ptr2's
+    template parameter is not a base or a derived type from
+    \a ptr1's, you will get a compiler error.
+*/
+
+/*!
+    \fn QSharedPointer<X> qSharedPointerCast(const QSharedPointer<T> &other)
+    \relates QSharedPointer
+
+    Returns a shared pointer to the pointer held by \a other, cast to
+    type \tt X.  The types \tt T and \tt X must belong to one
+    hierarchy for the \tt static_cast to succeed.
+
+    Note that \tt X must have the same cv-qualifiers (\tt const and
+    \tt volatile) that \tt T has, or the code will fail to
+    compile. Use qSharedPointerConstCast to cast away the constness.
+
+    \sa QSharedPointer::staticCast(), qSharedPointerDynamicCast(), qSharedPointerConstCast()
+*/
+
+/*!
+    \fn QSharedPointer<X> qSharedPointerCast(const QWeakPointer<T> &other)
+    \relates QSharedPointer
+    \relates QWeakPointer
+
+    Returns a shared pointer to the pointer held by \a other, cast to
+    type \tt X.  The types \tt T and \tt X must belong to one
+    hierarchy for the \tt static_cast to succeed.
+
+    The \a other object is converted first to a strong reference. If
+    that conversion fails (because the object it's pointing to has
+    already been deleted), this function returns a null
+    QSharedPointer.
+
+    Note that \tt X must have the same cv-qualifiers (\tt const and
+    \tt volatile) that \tt T has, or the code will fail to
+    compile. Use qSharedPointerConstCast to cast away the constness.
+
+    \sa QWeakPointer::toStrongRef(), qSharedPointerDynamicCast(), qSharedPointerConstCast()
+*/
+
+/*!
+    \fn QSharedPointer<X> qSharedPointerDynamicCast(const QSharedPointer<T> &other)
+    \relates QSharedPointer
+
+    Returns a shared pointer to the pointer held by \a other, using a
+    dynamic cast to type \tt X to obtain an internal pointer of the
+    appropriate type. If the \tt dynamic_cast fails, the object
+    returned will be null.
+
+    Note that \tt X must have the same cv-qualifiers (\tt const and
+    \tt volatile) that \tt T has, or the code will fail to
+    compile. Use qSharedPointerConstCast to cast away the constness.
+
+    \sa QSharedPointer::dynamicCast(), qSharedPointerCast(), qSharedPointerConstCast()
+*/
+
+/*!
+    \fn QSharedPointer<X> qSharedPointerDynamicCast(const QWeakPointer<T> &other)
+    \relates QSharedPointer
+    \relates QWeakPointer
+
+    Returns a shared pointer to the pointer held by \a other, using a
+    dynamic cast to type \tt X to obtain an internal pointer of the
+    appropriate type. If the \tt dynamic_cast fails, the object
+    returned will be null.
+
+    The \a other object is converted first to a strong reference. If
+    that conversion fails (because the object it's pointing to has
+    already been deleted), this function also returns a null
+    QSharedPointer.
+
+    Note that \tt X must have the same cv-qualifiers (\tt const and
+    \tt volatile) that \tt T has, or the code will fail to
+    compile. Use qSharedPointerConstCast to cast away the constness.
+
+    \sa QWeakPointer::toStrongRef(), qSharedPointerCast(), qSharedPointerConstCast()
+*/
+
+/*!
+    \fn QSharedPointer<X> qSharedPointerConstCast(const QSharedPointer<T> &other)
+    \relates QSharedPointer
+
+    Returns a shared pointer to the pointer held by \a other, cast to
+    type \tt X.  The types \tt T and \tt X must belong to one
+    hierarchy for the \tt const_cast to succeed. The \tt const and \tt
+    volatile differences between \tt T and \tt X are ignored.
+
+    \sa QSharedPointer::constCast(), qSharedPointerCast(), qSharedPointerDynamicCast()
+*/
+
+/*!
+    \fn QSharedPointer<X> qSharedPointerConstCast(const QWeakPointer<T> &other)
+    \relates QSharedPointer
+    \relates QWeakPointer
+
+    Returns a shared pointer to the pointer held by \a other, cast to
+    type \tt X. The types \tt T and \tt X must belong to one
+    hierarchy for the \tt const_cast to succeed. The \tt const and
+    \tt volatile differences between \tt T and \tt X are ignored.
+
+    The \a other object is converted first to a strong reference. If
+    that conversion fails (because the object it's pointing to has
+    already been deleted), this function returns a null
+    QSharedPointer.
+
+    \sa QWeakPointer::toStrongRef(), qSharedPointerCast(), qSharedPointerDynamicCast()
+*/
+
+/*!
+    \fn QWeakPointer<X> qWeakPointerCast(const QWeakPointer<T> &other)
+    \relates QWeakPointer
+
+    Returns a weak pointer to the pointer held by \a other, cast to
+    type \tt X. The types \tt T and \tt X must belong to one
+    hierarchy for the \tt static_cast to succeed.
+
+    Note that \tt X must have the same cv-qualifiers (\tt const and
+    \tt volatile) that \tt T has, or the code will fail to
+    compile. Use qSharedPointerConstCast to cast away the constness.
+*/
+
+#include <qset.h>
+#include <qmutex.h>
+
+#if !defined(QT_NO_MEMBER_TEMPLATES)
+
+//#  define QT_SHARED_POINTER_BACKTRACE_SUPPORT
+#  ifdef QT_SHARED_POINTER_BACKTRACE_SUPPORT
+#    if defined(__GLIBC__) && (__GLIBC__ >= 2) && !defined(__UCLIBC__) && !defined(QT_LINUXBASE)
+#      define BACKTRACE_SUPPORTED
+#    elif defined(Q_OS_MACX)
+#      define BACKTRACE_SUPPORTED
+#    endif
+#  endif
+
+#  if !defined(BACKTRACE_SUPPORTED)
+// Dummy implementation of the functions.
+// Using QHashDummyValue also means that the QHash below is actually a QSet
+typedef QT_PREPEND_NAMESPACE(QHashDummyValue) Backtrace;
+
+static inline Backtrace saveBacktrace() { return Backtrace(); }
+static inline void printBacktrace(Backtrace) { }
+
+#  else
+#    include <sys/types.h>
+#    include <execinfo.h>
+#    include <stdio.h>
+#    include <unistd.h>
+#    include <sys/wait.h>
+
+typedef QT_PREPEND_NAMESPACE(QByteArray) Backtrace;
+
+static inline Backtrace saveBacktrace() __attribute__((always_inline));
+static inline Backtrace saveBacktrace()
+{
+    static const int maxFrames = 32;
+
+    Backtrace stacktrace;
+    stacktrace.resize(sizeof(void*) * maxFrames);
+    int stack_size = backtrace((void**)stacktrace.data(), maxFrames);
+    stacktrace.resize(sizeof(void*) * stack_size);
+
+    return stacktrace;
+}
+
+static void printBacktrace(Backtrace stacktrace)
+{
+    void *const *stack = (void *const *)stacktrace.constData();
+    int stack_size = stacktrace.size() / sizeof(void*);
+    char **stack_symbols = backtrace_symbols(stack, stack_size);
+
+    int filter[2];
+    pid_t child = -1;
+    if (pipe(filter) != -1)
+        child = fork();
+    if (child == 0) {
+        // child process
+        dup2(fileno(stderr), fileno(stdout));
+        dup2(filter[0], fileno(stdin));
+        close(filter[0]);
+        close(filter[1]);
+        execlp("c++filt", "c++filt", "-n", NULL);
+
+        // execlp failed
+        execl("/bin/cat", "/bin/cat", NULL);
+        _exit(127);
+    }
+
+    // parent process
+    close(filter[0]);
+    FILE *output;
+    if (child == -1) {
+        // failed forking
+        close(filter[1]);
+        output = stderr;
+    } else {
+        output = fdopen(filter[1], "w");
+    }
+
+    fprintf(stderr, "Backtrace of the first creation (most recent frame first):\n");
+    for (int i = 0; i < stack_size; ++i) {
+        if (strlen(stack_symbols[i]))
+            fprintf(output, "#%-2d %s\n", i, stack_symbols[i]);
+        else
+            fprintf(output, "#%-2d %p\n", i, stack[i]);
+    }
+
+    if (child != -1) {
+        fclose(output);
+        waitpid(child, 0, 0);
+    }
+}
+#  endif  // BACKTRACE_SUPPORTED
+
+namespace {
+    QT_USE_NAMESPACE
+    class KnownPointers
+    {
+    public:
+        QMutex mutex;
+        QHash<void *, Backtrace> values;
+    };
+}
+
+Q_GLOBAL_STATIC(KnownPointers, knownPointers)
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \internal
+*/
+void QtSharedPointer::internalSafetyCheckAdd(const volatile void *ptr)
+{
+    QMutexLocker lock(&knownPointers()->mutex);
+    void *actual = const_cast<void*>(ptr);
+    if (knownPointers()->values.contains(actual)) {
+        printBacktrace(knownPointers()->values.value(actual));
+        qFatal("QSharedPointerData: internal self-check failed: pointer %p was already tracked "
+               "by another QSharedPointerData object", actual);
+    }
+
+    knownPointers()->values.insert(actual, saveBacktrace());
+}
+
+/*!
+    \internal
+*/
+void QtSharedPointer::internalSafetyCheckRemove(const volatile void *ptr)
+{
+    QMutexLocker lock(&knownPointers()->mutex);
+    void *actual = const_cast<void*>(ptr);
+    knownPointers()->values.remove(actual);
+}
+
+QT_END_NAMESPACE
+
+#endif