diff options
Diffstat (limited to 'src/corelib/tools/qsharedpointer.cpp')
| -rw-r--r-- | src/corelib/tools/qsharedpointer.cpp | 134 |
1 files changed, 29 insertions, 105 deletions
diff --git a/src/corelib/tools/qsharedpointer.cpp b/src/corelib/tools/qsharedpointer.cpp index be8b6a7aab..62b76c5bb7 100644 --- a/src/corelib/tools/qsharedpointer.cpp +++ b/src/corelib/tools/qsharedpointer.cpp @@ -379,7 +379,7 @@ You can inherit this class when you need to create a QSharedPointer from any instance of a class; for instance, from within the object itself. The key point is that the technique of - just returning QSharedPointer<T>(this) can not be used, because + just returning QSharedPointer<T>(this) cannot be used, because this winds up creating multiple distinct QSharedPointer objects with separate reference counts. For this reason you must never create more than one QSharedPointer from the same raw pointer. @@ -388,44 +388,14 @@ sharedFromThis() that return a QSharedPointer<T> and QSharedPointer<const T>, depending on constness, to \c this: - \code - class Y: public QEnableSharedFromThis<Y> - { - public: - QSharedPointer<Y> f() - { - return sharedFromThis(); - } - }; - - int main() - { - QSharedPointer<Y> p(new Y()); - QSharedPointer<Y> y = p->f(); - Q_ASSERT(p == y); // p and q must share ownership - } - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 0 It is also possible to get a shared pointer from an object outside of the class itself. This is especially useful in code that provides an interface to scripts, where it is currently not possible to use shared pointers. For example: - \code - class ScriptInterface : public QObject - { - \Q_OBJECT - - // ... - - public slots: - void slotCalledByScript(Y *managedBySharedPointer) - { - QSharedPointer<Y> yPtr = managedBySharedPointer->sharedFromThis(); - // Some other code unrelated to scripts that expects a QSharedPointer<Y> ... - } - }; - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 1 */ /*! @@ -466,30 +436,13 @@ when the strong reference count drops to 0. This is useful, for instance, for calling \l {QObject::}{deleteLater()} on 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 + \snippet code/src_corelib_tools_qsharedpointer.cpp 2 Note that the custom deleter function will be called with a pointer to type \c X, even if the QSharedPointer template parameter \c T is not the same. It is also possible to specify a member function directly, as in: - \code - QSharedPointer<MyObject> obj = - QSharedPointer<MyObject>(new MyObject, &QObject::deleteLater); - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 3 \sa clear() */ @@ -618,9 +571,7 @@ Returns \c true if this object is not null. This function is suitable for use in \tt if-constructs, like: - \code - if (sharedptr) { ... } - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 4 \sa isNull() */ @@ -628,12 +579,10 @@ /*! \fn template <class T> bool QSharedPointer<T>::operator !() const - Returns \c true if this object is null. This function is suitable - for use in \tt if-constructs, like: + Returns \c true if this object is \nullptr. This function is + suitable for use in \tt if-constructs, like: - \code - if (!sharedptr) { ... } - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 5 \sa isNull() */ @@ -766,9 +715,7 @@ Resets this QSharedPointer object to point to \a t instead. Equivalent to: - \code - QSharedPointer<T> other(t); this->swap(other); - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 6 */ /*! @@ -777,9 +724,7 @@ Resets this QSharedPointer object to point to \a t instead, with the Deleter \a deleter. Equivalent to: - \code - QSharedPointer<T> other(t, deleter); this->swap(other); - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 7 */ /*! @@ -896,9 +841,7 @@ Returns \c true if this object is not null. This function is suitable for use in \tt if-constructs, like: - \code - if (weakref) { ... } - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 8 Note that, due to the nature of weak references, the pointer that QWeakPointer references can become null at any moment, so @@ -911,12 +854,10 @@ /*! \fn template <class T> bool QWeakPointer<T>::operator !() const - Returns \c true if this object is null. This function is suitable - for use in \tt if-constructs, like: + Returns \c true if this object is \nullptr. This function is + suitable for use in \tt if-constructs, like: - \code - if (!weakref) { ... } - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 9 Note that, due to the nature of weak references, the pointer that QWeakPointer references can become null at any moment, so @@ -934,14 +875,12 @@ \b without ensuring that it cannot get deleted. To have that guarantee, use toStrongRef(), which returns a QSharedPointer object. If this function can determine that the pointer has already been deleted, it - returns 0. + returns \nullptr. It is ok to obtain the value of the pointer and using that value itself, like for example in debugging statements: - \code - qDebug("Tracking %p", weakref.data()); - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 10 However, dereferencing the pointer is only allowed if you can guarantee by external means that the pointer does not get deleted. For example, @@ -950,18 +889,7 @@ If that is the case, then the following code is valid: - \code - // this pointer cannot be used in another thread - // so other threads cannot delete it - QWeakPointer<int> weakref = obtainReference(); - - Object *obj = weakref.data(); - if (obj) { - // if the pointer wasn't deleted yet, we know it can't get - // deleted by our own code here nor the functions we call - otherFunction(obj); - } - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 11 Use this function with care. @@ -986,17 +914,7 @@ to a strong reference and, if it succeeded, it prints the value of the integer that was held: - \code - QWeakPointer<int> weakref; - - // ... - - QSharedPointer<int> strong = weakref.toStrongRef(); - if (strong) - qDebug() << "The value is:" << *strong; - else - qDebug() << "The value has already been deleted"; - \endcode + \snippet code/src_corelib_tools_qsharedpointer.cpp 12 \sa QSharedPointer::QSharedPointer() */ @@ -1465,12 +1383,18 @@ QtSharedPointer::ExternalRefCountData *QtSharedPointer::ExternalRefCountData::ge ExternalRefCountData *x = new ExternalRefCountData(Qt::Uninitialized); x->strongref.store(-1); x->weakref.store(2); // the QWeakPointer that called us plus the QObject itself - if (!d->sharedRefcount.testAndSetRelease(0, x)) { + + ExternalRefCountData *ret; + if (d->sharedRefcount.testAndSetOrdered(nullptr, x, ret)) { // ought to be release+acquire; this is acq_rel+acquire + ret = x; + } else { + // ~ExternalRefCountData has a Q_ASSERT, so we use this trick to + // only execute this if Q_ASSERTs are enabled + Q_ASSERT((x->weakref.store(0), true)); delete x; - x = d->sharedRefcount.loadAcquire(); - x->weakref.ref(); + ret->weakref.ref(); } - return x; + return ret; } /** |