"WARN: QCoreApplication::postEvent: Unexpected null receiver" since 5.10.1
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Dear Qt community,
Since I updated from 5.10.0 to 5.10.1, I have a few of those warnings appearing when running my application.
It usually happens when calling "deleteLater()" on a null pointer, but given the stack trace (see below) I don't think this is something in my code, is it a known Qt regression?
I see in the release notes the following item which could be related: * [QTBUG-65712] Improved performance of QObject::deleteLater.
Or is the new implementation bringing up old bugs in my code?Stack trace: https://imgur.com/9mYCi4f
Called from "QSoundEffect soundEffect.setSource(QUrl::fromLocalFile(fi.absoluteFilePath()));" -
1 QMessageLogger::warning qlogging.cpp 582 2 QCoreApplication::postEvent qcoreapplication.cpp 1440 3 QObject::deleteLater qobject.cpp 2168 4 QSampleCache::loadingRelease qsamplecache_p.cpp 144 5 QSample::loadIfNecessary qsamplecache_p.cpp 292 6 QSampleCache::requestSample qsamplecache_p.cpp 189 7 QSoundEffectPrivate::setSource qsoundeffect_qaudio_p.cpp 136 8 QSoundEffect::setSource qsoundeffect.cpp 176 9 Sound::Sound Sound.cpp 32Where Sound.cpp:32 is "soundEffect.setSource(QUrl::fromLocalFile(fi.absoluteFilePath()));"
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1 QMessageLogger::warning qlogging.cpp 582 0x6928f878 2 QCoreApplication::postEvent qcoreapplication.cpp 1440 0x6943236b 3 QObject::deleteLater qobject.cpp 2168 0x69452cd3 4 QSampleCache::loadingRelease qsamplecache_p.cpp 144 0x5a84254a 5 QSample::loadIfNecessary qsamplecache_p.cpp 292 0x5a8427c2 6 QSampleCache::requestSample qsamplecache_p.cpp 189 0x5a843492 7 QSoundEffectPrivate::setSource qsoundeffect_qaudio_p.cpp 136 0x5a847dc1 8 QSoundEffect::setSource qsoundeffect.cpp 176 0x5a840f1e 9 Sound::Sound Sound.cpp 32 0x10aaf5b 10 *** *** 19 0x12f4995 11 *** *** 45 0x12f7ba9 12 *** *** 1326 0x127c04f 13 *** *** 1145 0x127b7ea 14 QtPrivate::FunctorCall<QtPrivate::IndexesList<0>, QtPrivate::List<QString>, void, void (***:: *)(QString const&)>::call qobjectdefs_impl.h 136 0x16e0dd5 15 QtPrivate::FunctionPointer<void (***:: *)(QString const&)>::call<QtPrivate::List<QString>, void> qobjectdefs_impl.h 169 0x16fa3af 16 QtPrivate::QSlotObject<void (***:: *)(QString const&), QtPrivate::List<QString>, void>::impl qobjectdefs_impl.h 398 0x16e8712 17 QtPrivate::QSlotObjectBase::call qobjectdefs_impl.h 378 0x694556ad 18 QMetaObject::activate qobject.cpp 3750 0x694556ad 19 QMetaObject::activate qobject.cpp 3629 0x69455b70 20 *** moc_***.cpp 179 0x13d08fe 21 *** *** 260 0x10f1d78 22 ***:qt_static_metacall moc_***.cpp 114 0x13d064f 23 QMetaObject::activate qobject.cpp 3767 0x69455852 24 QMetaObject::activate qobject.cpp 3629 0x69455b70 25 QAbstractButton::clicked moc_qabstractbutton.cpp 308 0x235dc797 26 QAbstractButtonPrivate::emitClicked qabstractbutton.cpp 414 0x235dc9b2 27 QAbstractButtonPrivate::click qabstractbutton.cpp 407 0x235ddf50 28 QAbstractButton::mouseReleaseEvent qabstractbutton.cpp 1011 0x235de1f1 29 QWidget::event qwidget.cpp 8897 0x23529590 30 QAbstractButton::event qabstractbutton.cpp 968 0x235df3ac 31 QPushButton::event qpushbutton.cpp 682 0x2366cf9c 32 QApplicationPrivate::notify_helper qapplication.cpp 3732 0x234e8326 33 QApplication::notify qapplication.cpp 3208 0x234ef94d 34 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1050 0x6942c1c4 35 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 237 0x234eedeb 36 QApplicationPrivate::sendMouseEvent qapplication.cpp 2709 0x234eedeb 37 QWidgetWindow::handleMouseEvent qwidgetwindow.cpp 661 0x2353ed74 38 QWidgetWindow::event qwidgetwindow.cpp 280 0x23540ee7 39 QApplicationPrivate::notify_helper qapplication.cpp 3732 0x234e8326 40 QApplication::notify qapplication.cpp 3104 0x234ef66e 41 QCoreApplication::notifyInternal2 qcoreapplication.cpp 1050 0x6942c1c4 42 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 237 0x2f8ad0b8 43 QGuiApplicationPrivate::processMouseEvent qguiapplication.cpp 1960 0x2f8ad0b8 44 QGuiApplicationPrivate::processWindowSystemEvent qguiapplication.cpp 1741 0x2f8aeddd 45 QWindowSystemInterface::sendWindowSystemEvents qwindowsysteminterface.cpp 984 0x2f8910f3 46 QWindowsGuiEventDispatcher::sendPostedEvents qwindowsguieventdispatcher.cpp 82 0xe75d6e79 47 qt_internal_proc qeventdispatcher_win.cpp 237 0x6947f917 48 USER32!CallWindowProcW 0x7ffb08edbc50 49 USER32!DispatchMessageW 0x7ffb08edb5cf 50 QEventDispatcherWin32::processEvents qeventdispatcher_win.cpp 629 0x6947f07e 51 QWindowsGuiEventDispatcher::processEvents qwindowsguieventdispatcher.cpp 74 0xe75d6e57 52 QEventLoop::processEvents qeventloop.cpp 134 0x6942a83b 53 QEventLoop::exec qeventloop.cpp 212 0x6942ac59 54 QCoreApplication::exec qcoreapplication.cpp 1338 0x69433a9a 55 QGuiApplication::exec qguiapplication.cpp 1687 0x2f8a4df5 56 QApplication::exec qapplication.cpp 2917 0x234e8208 57 main ***.cpp 303 0x403288I've scrubbed the internal class names, company policy, sorry, but they should not be needed anyway.
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File a bug report. Here's the relevant code (dev branch):
void QSampleCache::loadingRelease() { QMutexLocker locker(&m_loadingMutex); m_loadingRefCount--; if (m_loadingRefCount == 0) { if (m_loadingThread.isRunning()) { m_networkAccessManager->deleteLater(); m_networkAccessManager = nullptr; m_loadingThread.exit(); } } }It probably is a bug in the multimedia module itself, I'd say
m_networkAccessManageris null - probably never initialized for a local file. But then, for whatever reason, them_networkAccessManageris deleted after loading has finished.
And to be frank it seems rather odd that someone would use a mutex to synchronize a simple counter ... not a semaphore, not an atomic int, but a mutex ...PS.
After some more thorough looking at it, I see why the mutex's there. Still I continue to think it's a bug in the multimedia module. You could see if any changes were made between the two mentioned Qt versions, as with theQSampleCache::networkAccessManager()creating the NAM on demand, it is possible that it was never created and then adeleteLaterwas invoked on it. -
Thanks, done.
https://bugreports.qt.io/browse/QTBUG-66910 -
Hello! Can you please explain how did you manage to get this call stack? Where did you put breakpoint? I had the same problem. I was trying to locate the exact place where the warning was issued, but with no success.
Do you have to install additional tools, or is it possible with Qt Creator and installed debugger only? -
@aha_1980 Thank you very much for the response. But what if the program doesn't crash? I only create QSoundEffect instance in main(), initialize it with correct path, play it and that's all. The program doesn't crash, but outputs to the console "QCoreApplication::postEvent: Unexpected null receiver" and exits with code 0. Is there any way to locate where this warning was issued?
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Hi @AlexZ,
I've searched for the string you gave me and found it in
qcoreapplication.cpparound line 1146:static bool doNotify(QObject *receiver, QEvent *event) { if (receiver == 0) { // serious error qWarning("QCoreApplication::notify: Unexpected null receiver"); return true; } #ifndef QT_NO_DEBUG QCoreApplicationPrivate::checkReceiverThread(receiver); #endif return receiver->isWidgetType() ? false : QCoreApplicationPrivate::notify_helper(receiver, event); }If you have the Qt sources installed or build Qt yourself from sources, you can try to set a breakpoint there to get the stack.
Regards
