diff options
Diffstat (limited to 'src/corelib/tools/qsharedpointer.cpp')
| -rw-r--r-- | src/corelib/tools/qsharedpointer.cpp | 260 |
1 files changed, 232 insertions, 28 deletions
diff --git a/src/corelib/tools/qsharedpointer.cpp b/src/corelib/tools/qsharedpointer.cpp index 85085c5..f18dee8 100644 --- a/src/corelib/tools/qsharedpointer.cpp +++ b/src/corelib/tools/qsharedpointer.cpp @@ -128,7 +128,7 @@ To access the pointer that QWeakPointer is tracking, you must first create a QSharedPointer object and verify if the pointer - is null or not. + is null or not. See QWeakPointer::toStrongRef() for more information. \sa QSharedPointer */ @@ -210,6 +210,8 @@ 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. + + \sa QWeakPointer::toStrongRef() */ /*! @@ -362,6 +364,8 @@ Returns a weak reference object that shares the pointer referenced by this object. + + \sa QWeakPointer::QWeakPointer() */ /*! @@ -478,10 +482,78 @@ */ /*! + \fn T *QWeakPointer::data() const + \since 4.6 + + Returns the value of the pointer being tracked by this QWeakPointer, + \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. + + 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 + + However, dereferencing the pointer is only allowed if you can guarantee + by external means that the pointer does not get deleted. For example, + if you can be certain that no other thread can delete it, nor the + functions that you may call. + + 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 + + Use this function with care. + + \sa isNull(), toStrongRef() +*/ + +/*! \fn QSharedPointer<T> QWeakPointer::toStrongRef() const Promotes this weak reference to a strong one and returns a - QSharedPointer object holding that reference. + QSharedPointer object holding that reference. When promoting to + QSharedPointer, this function verifies if the object has been deleted + already or not. If it hasn't, this function increases the reference + count to the shared object, thus ensuring that it will not get + deleted. + + Since this function can fail to obtain a valid strong reference to the + shared object, you should always verify if the conversion succeeded, + by calling QSharedPointer::isNull() on the returned object. + + For example, the following code promotes a QWeakPointer that was held + 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 + + \sa QSharedPointer::QSharedPointer() */ /*! @@ -792,6 +864,56 @@ #include <qset.h> #include <qmutex.h> +#if !defined(QT_NO_QOBJECT) +#include "../kernel/qobject_p.h" + +/*! + \internal + This function is called for a just-created QObject \a obj, to enable + the use of QSharedPointer and QWeakPointer. + + When QSharedPointer is active in a QObject, the object must not be deleted + directly: the lifetime is managed by the QSharedPointer object. In that case, + the deleteLater() and parent-child relationship in QObject only decrease + the strong reference count, instead of deleting the object. +*/ +void QtSharedPointer::ExternalRefCountData::setQObjectShared(const QObject *obj, bool) +{ + Q_ASSERT(obj); + QObjectPrivate *d = QObjectPrivate::get(const_cast<QObject *>(obj)); + + if (d->sharedRefcount) + qFatal("QSharedPointer: pointer %p already has reference counting", obj); + d->sharedRefcount = this; + + // QObject decreases the refcount too, so increase it up + weakref.ref(); +} + +QtSharedPointer::ExternalRefCountData *QtSharedPointer::ExternalRefCountData::getAndRef(const QObject *obj) +{ + Q_ASSERT(obj); + QObjectPrivate *d = QObjectPrivate::get(const_cast<QObject *>(obj)); + ExternalRefCountData *that = d->sharedRefcount; + if (that) { + that->weakref.ref(); + return that; + } + + // we can create the refcount data because it doesn't exist + ExternalRefCountData *x = new ExternalRefCountData(Qt::Uninitialized); + x->strongref = -1; + x->weakref = 2; // the QWeakPointer that called us plus the QObject itself + if (!d->sharedRefcount.testAndSetRelease(0, x)) { + delete x; + d->sharedRefcount->weakref.ref(); + } + return d->sharedRefcount; +} +#endif + + + #if !defined(QT_NO_MEMBER_TEMPLATES) //# define QT_SHARED_POINTER_BACKTRACE_SUPPORT @@ -803,29 +925,19 @@ # 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 +# if defined(BACKTRACE_SUPPORTED) # 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 inline QByteArray saveBacktrace() __attribute__((always_inline)); +static inline QByteArray saveBacktrace() { static const int maxFrames = 32; - Backtrace stacktrace; + QByteArray stacktrace; stacktrace.resize(sizeof(void*) * maxFrames); int stack_size = backtrace((void**)stacktrace.data(), maxFrames); stacktrace.resize(sizeof(void*) * stack_size); @@ -833,7 +945,7 @@ static inline Backtrace saveBacktrace() return stacktrace; } -static void printBacktrace(Backtrace stacktrace) +static void printBacktrace(QByteArray stacktrace) { void *const *stack = (void *const *)stacktrace.constData(); int stack_size = stacktrace.size() / sizeof(void*); @@ -884,11 +996,19 @@ static void printBacktrace(Backtrace stacktrace) namespace { QT_USE_NAMESPACE + struct Data { + const volatile void *pointer; +# ifdef BACKTRACE_SUPPORTED + QByteArray backtrace; +# endif + }; + class KnownPointers { public: QMutex mutex; - QHash<void *, Backtrace> values; + QHash<const void *, Data> dPointers; + QHash<const volatile void *, const void *> dataPointers; }; } @@ -896,38 +1016,122 @@ Q_GLOBAL_STATIC(KnownPointers, knownPointers) QT_BEGIN_NAMESPACE +namespace QtSharedPointer { + Q_CORE_EXPORT void internalSafetyCheckAdd(const volatile void *); + Q_CORE_EXPORT void internalSafetyCheckRemove(const volatile void *); + Q_AUTOTEST_EXPORT void internalSafetyCheckCleanCheck(); +} + +/*! + \internal +*/ +void QtSharedPointer::internalSafetyCheckAdd(const volatile void *) +{ + // Qt 4.5 compatibility + // this function is broken by design, so it was replaced with internalSafetyCheckAdd2 + // + // it's broken because we tracked the pointers added and + // removed from QSharedPointer, converted to void*. + // That is, this is supposed to track the "top-of-object" pointer in + // case of multiple inheritance. + // + // However, it doesn't work well in some compilers: + // if you create an object with a class of type A and the last reference + // is dropped of type B, then the value passed to internalSafetyCheckRemove could + // be different than was added. That would leave dangling addresses. + // + // So instead, we track the pointer by the d-pointer instead. +} + +/*! + \internal +*/ +void QtSharedPointer::internalSafetyCheckRemove(const volatile void *) +{ + // Qt 4.5 compatibility + // see comments above +} + /*! \internal */ -void QtSharedPointer::internalSafetyCheckAdd(const volatile void *ptr) +void QtSharedPointer::internalSafetyCheckAdd2(const void *d_ptr, const volatile void *ptr) { + // see comments above for the rationale for this function KnownPointers *const kp = knownPointers(); if (!kp) return; // end-game: the application is being destroyed already QMutexLocker lock(&kp->mutex); - void *actual = const_cast<void*>(ptr); - if (kp->values.contains(actual)) { - printBacktrace(knownPointers()->values.value(actual)); - qFatal("QSharedPointerData: internal self-check failed: pointer %p was already tracked " - "by another QSharedPointerData object", actual); + Q_ASSERT(!kp->dPointers.contains(d_ptr)); + + //qDebug("Adding d=%p value=%p", d_ptr, ptr); + + const void *other_d_ptr = kp->dataPointers.value(ptr, 0); + if (other_d_ptr) { +# ifdef BACKTRACE_SUPPORTED + printBacktrace(knownPointers()->dPointers.value(other_d_ptr).backtrace); +# endif + qFatal("QSharedPointer: internal self-check failed: pointer %p was already tracked " + "by another QSharedPointer object %p", ptr, other_d_ptr); } - kp->values.insert(actual, saveBacktrace()); + Data data; + data.pointer = ptr; +# ifdef BACKTRACE_SUPPORTED + data.backtrace = saveBacktrace(); +# endif + + kp->dPointers.insert(d_ptr, data); + kp->dataPointers.insert(ptr, d_ptr); + Q_ASSERT(kp->dPointers.size() == kp->dataPointers.size()); } /*! \internal */ -void QtSharedPointer::internalSafetyCheckRemove(const volatile void *ptr) +void QtSharedPointer::internalSafetyCheckRemove2(const void *d_ptr) { KnownPointers *const kp = knownPointers(); if (!kp) return; // end-game: the application is being destroyed already QMutexLocker lock(&kp->mutex); - void *actual = const_cast<void*>(ptr); - kp->values.remove(actual); + + QHash<const void *, Data>::iterator it = kp->dPointers.find(d_ptr); + if (it == kp->dPointers.end()) { + qFatal("QSharedPointer: internal self-check inconsistency: pointer %p was not tracked. " + "To use QT_SHAREDPOINTER_TRACK_POINTERS, you have to enable it throughout " + "in your code.", d_ptr); + } + + QHash<const volatile void *, const void *>::iterator it2 = kp->dataPointers.find(it->pointer); + Q_ASSERT(it2 != kp->dataPointers.end()); + + //qDebug("Removing d=%p value=%p", d_ptr, it->pointer); + + // remove entries + kp->dataPointers.erase(it2); + kp->dPointers.erase(it); + Q_ASSERT(kp->dPointers.size() == kp->dataPointers.size()); +} + +/*! + \internal + Called by the QSharedPointer autotest +*/ +void QtSharedPointer::internalSafetyCheckCleanCheck() +{ +# ifdef QT_BUILD_INTERNAL + KnownPointers *const kp = knownPointers(); + Q_ASSERT_X(kp, "internalSafetyCheckSelfCheck()", "Called after global statics deletion!"); + + if (kp->dPointers.size() != kp->dataPointers.size()) + qFatal("Internal consistency error: the number of pointers is not equal!"); + + if (!kp->dPointers.isEmpty()) + qFatal("Pointer cleaning failed: %d entries remaining", kp->dPointers.size()); +# endif } QT_END_NAMESPACE |