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Add a way to access QCoreApplication's instance atomically

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We use it from many places in Qt that may run before QCoreApplication
has been created (officially not supported but it happens) and after it
has been destroyed. In particular, we have code in QtDBus that runs in
another thread after QCoreApplication has been destroyed and uses the
event system. Accessing QCoreApplication::self anywhere but the main
thread was a race condition in those conditions.

Pick-to: 6.8
Change-Id: If4ad1af9301dca98ba69fffdf88c63b220db53ac
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
This commit is contained in:
Thiago Macieira 2024-11-06 09:21:28 -08:00
parent 5ecbba1648
commit 7d92ecd917
1 changed files with 11 additions and 5 deletions
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16
src/corelib/kernel/qcoreapplication.cpp
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@ -140,6 +140,11 @@ extern QString qAppFileName();
Q_CONSTINIT bool QCoreApplicationPrivate::setuidAllowed = false; Q_CONSTINIT bool QCoreApplicationPrivate::setuidAllowed = false;
Q_CONSTINIT QCoreApplication *QCoreApplication::self = nullptr;
Q_CONSTINIT static QBasicAtomicPointer<QCoreApplication> g_self = nullptr;
# undef qApp
# define qApp g_self.loadRelaxed()
#if !defined(Q_OS_WIN) #if !defined(Q_OS_WIN)
#ifdef Q_OS_DARWIN #ifdef Q_OS_DARWIN
QString QCoreApplicationPrivate::infoDictionaryStringProperty(const QString &propertyName) QString QCoreApplicationPrivate::infoDictionaryStringProperty(const QString &propertyName)
@ -199,7 +204,7 @@ Q_CONSTINIT QString *QCoreApplicationPrivate::cachedApplicationFilePath = nullpt
bool QCoreApplicationPrivate::checkInstance(const char *function) bool QCoreApplicationPrivate::checkInstance(const char *function)
{ {
bool b = (QCoreApplication::self != nullptr); bool b = (qApp != nullptr);
if (!b) if (!b)
qWarning("QApplication::%s: Please instantiate the QApplication object first", function); qWarning("QApplication::%s: Please instantiate the QApplication object first", function);
return b; return b;
@ -359,7 +364,6 @@ Q_CONSTINIT QAbstractEventDispatcher *QCoreApplicationPrivate::eventDispatcher =
#endif // QT_NO_QOBJECT #endif // QT_NO_QOBJECT
Q_CONSTINIT QCoreApplication *QCoreApplication::self = nullptr;
Q_CONSTINIT uint QCoreApplicationPrivate::attribs = Q_CONSTINIT uint QCoreApplicationPrivate::attribs =
(1 << Qt::AA_SynthesizeMouseForUnhandledTouchEvents) | (1 << Qt::AA_SynthesizeMouseForUnhandledTouchEvents) |
(1 << Qt::AA_SynthesizeMouseForUnhandledTabletEvents); (1 << Qt::AA_SynthesizeMouseForUnhandledTabletEvents);
@ -817,6 +821,7 @@ void Q_TRACE_INSTRUMENT(qtcore) QCoreApplicationPrivate::init()
Q_ASSERT_X(!QCoreApplication::self, "QCoreApplication", "there should be only one application object"); Q_ASSERT_X(!QCoreApplication::self, "QCoreApplication", "there should be only one application object");
QCoreApplication::self = q; QCoreApplication::self = q;
g_self.storeRelaxed(q);
#if QT_CONFIG(thread) #if QT_CONFIG(thread)
#ifdef Q_OS_WASM #ifdef Q_OS_WASM
@ -918,6 +923,7 @@ QCoreApplication::~QCoreApplication()
qt_call_post_routines(); qt_call_post_routines();
self = nullptr; self = nullptr;
g_self.storeRelaxed(nullptr);
#ifndef QT_NO_QOBJECT #ifndef QT_NO_QOBJECT
QCoreApplicationPrivate::is_app_closing = true; QCoreApplicationPrivate::is_app_closing = true;
QCoreApplicationPrivate::is_app_running = false; QCoreApplicationPrivate::is_app_running = false;
@ -1096,7 +1102,7 @@ void QCoreApplication::setQuitLockEnabled(bool enabled)
bool QCoreApplication::notifyInternal2(QObject *receiver, QEvent *event) bool QCoreApplication::notifyInternal2(QObject *receiver, QEvent *event)
{ {
bool selfRequired = QCoreApplicationPrivate::threadRequiresCoreApplication(); bool selfRequired = QCoreApplicationPrivate::threadRequiresCoreApplication();
if (selfRequired && !self) if (selfRequired && !qApp)
return false; return false;
// Make it possible for Qt Script to hook into events even // Make it possible for Qt Script to hook into events even
@ -1121,7 +1127,7 @@ bool QCoreApplication::notifyInternal2(QObject *receiver, QEvent *event)
if (threadData->thread.loadRelaxed() != QCoreApplicationPrivate::mainThread()) if (threadData->thread.loadRelaxed() != QCoreApplicationPrivate::mainThread())
return false; return false;
#endif #endif
return self->notify(receiver, event); return qApp->notify(receiver, event);
} }
/*! /*!
@ -1250,7 +1256,7 @@ bool QCoreApplicationPrivate::sendThroughApplicationEventFilters(QObject *receiv
bool QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject *receiver, QEvent *event) bool QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject *receiver, QEvent *event)
{ {
if ((receiver->d_func()->threadData.loadRelaxed()->thread.loadAcquire() != mainThread() if ((receiver->d_func()->threadData.loadRelaxed()->thread.loadAcquire() != mainThread()
|| receiver != QCoreApplication::instance()) || receiver != qApp)
&& receiver->d_func()->extraData) { && receiver->d_func()->extraData) {
for (qsizetype i = 0; i < receiver->d_func()->extraData->eventFilters.size(); ++i) { for (qsizetype i = 0; i < receiver->d_func()->extraData->eventFilters.size(); ++i) {
QObject *obj = receiver->d_func()->extraData->eventFilters.at(i); QObject *obj = receiver->d_func()->extraData->eventFilters.at(i);