This has me stumped. Problem:
I have an app with plugins. Each plugin has a form widget which is displayed in a dialog. If I bring up the dialog and click a QComboBox within the form, when I quit my app I get the following in the console: Warning: QBasicTimer::start: QBasicTimer can only be used with threads started with QThread (:0, (null)) and the app crashes. Here's the Mac stack trace: Thread 0 Crashed:: Dispatch queue: com.apple.main-thread 0 org.qt-project.QtCore 0x0000000101ef98eb QThreadStorageData::get() const + 43 1 org.qt-project.QtGui 0x0000000101904d36 QOpenGLContext::currentContext() + 22 2 org.qt-project.QtGui 0x0000000101b6b483 QPlatformBackingStorePrivate::~QPlatformBackingStorePrivate() + 19 3 org.qt-project.QtGui 0x0000000101b6b2c1 QPlatformBackingStore::~QPlatformBackingStore() + 33 4 libqcocoa.dylib 0x0000000105168d7e QCocoaBackingStore::~QCocoaBackingStore() + 14 5 org.qt-project.QtGui 0x0000000101a6b8cc QBackingStore::~QBackingStore() + 28 6 org.qt-project.QtWidgets 0x00000001011fa5fc deleteBackingStore(QWidgetPrivate*) + 204 7 org.qt-project.QtWidgets 0x00000001011fa408 QWidgetPrivate::deleteTLSysExtra() + 56 8 org.qt-project.QtWidgets 0x00000001011fa172 QWidget::destroy(bool, bool) + 834 9 org.qt-project.QtWidgets 0x00000001011f98d6 QWidget::~QWidget() + 1462 10 org.qt-project.QtWidgets 0x00000001012d753e QComboBoxPrivateContainer::~QComboBoxPrivateContainer() + 62 11 org.qt-project.QtCore 0x00000001020e0a83 QObjectPrivate::deleteChildren() + 227 12 org.qt-project.QtWidgets 0x00000001011f98ba QWidget::~QWidget() + 1434 13 org.qt-project.QtWidgets 0x00000001012d03f7 QComboBox::~QComboBox() + 71 14 org.qt-project.QtCore 0x00000001020e0a83 QObjectPrivate::deleteChildren() + 227 15 org.qt-project.QtWidgets 0x00000001011f98ba QWidget::~QWidget() + 1434 16 (my form destructor) and the Windows stack trace: 1 QThreadStorageData::get qthreadstorage.cpp 117 0x6b79923c 2 qThreadStorage_localData<QGuiGLThreadContext> qthreadstorage.h 65 0x3b878f0 3 QThreadStorage<QGuiGLThreadContext *>::localData qthreadstorage.h 139 0x3bb72dc 4 QOpenGLContext::currentContext qopenglcontext.cpp 415 0x388b59b 5 QPlatformBackingStorePrivate::~QPlatformBackingStorePrivate qplatformbackingstore.cpp 84 0x3be3f93 6 QPlatformBackingStore::~QPlatformBackingStore qplatformbackingstore.cpp 608 0x3a64b6a 7 QWindowsBackingStore::~QWindowsBackingStore qwindowsbackingstore.cpp 62 0x62891f4c 8 QWindowsBackingStore::~QWindowsBackingStore qwindowsbackingstore.cpp 65 0x62891f75 9 QBackingStore::~QBackingStore qbackingstore.cpp 142 0x3995f8f 10 deleteBackingStore qwidget.cpp 1858 0xef95352 11 QWidgetPrivate::deleteTLSysExtra qwidget.cpp 1875 0xef953e4 12 QWidget::destroy qwidget.cpp 12297 0xefad3b7 13 QWidget::~QWidget qwidget.cpp 1679 0xef94c46 14 QFrame::~QFrame qframe.cpp 256 0xf0b3d8a 15 QComboBoxPrivateContainer::~QComboBoxPrivateContainer qcombobox_p.h 208 0xf2fb8f2 16 QComboBoxPrivateContainer::~QComboBoxPrivateContainer qcombobox_p.h 208 0xf2fb8a3 17 QObjectPrivate::deleteChildren qobject.cpp 1963 0x6b8f6ed7 18 QWidget::~QWidget qwidget.cpp 1674 0xef94c18 19 QComboBox::~QComboBox qcombobox.cpp 1332 0xf088949 20 QComboBox::~QComboBox qcombobox.cpp 1343 0xf08897f 21 QObjectPrivate::deleteChildren qobject.cpp 1963 0x6b8f6ed7 22 QWidget::~QWidget qwidget.cpp 1674 0xef94c18 23 QGroupBox::~QGroupBox qgroupbox.cpp 206 0xf0b4dc8 24 (my form destructor) Possibly relevant info: 0) the form is being created & displayed in a plugin 1) the combo box is in a QGroupBox created with a designer form (.ui file) 2) the form widget itself is created once with "new Ui::FormName / setupUi()" when the plugin is loaded 3) the dialog takes temporary ownership of the widget and calls widget->setParent( nullptr ); in its destructor so the form does not get destructed 4) 4.x does not crash (been working for 10 years...) 5) 5.6.x and any 5.7 versions I have tried cause a crash 6) it crashes on both Mac OS X and Windows 7) I'm not doing anything funky with the combo box - just displaying it and taking action on selection 8) combo boxes in my main app don't seem to be an issue 9) if I don't touch the combo boxes (i.e. display the dialog, dismiss it, and quit my app) -> no crash Theories I haven't been able to prove/disprove: 1) there's a singleshot that is fired to display the popup selection and it's deleting or doing something it shouldn't 2) it's a thread problem because this is in a plugin 3) something isn't liking the dialog's temporary ownership of the form Anyone with some in-depth knowledge of the QComboBox have any ideas what might be going on here? Thank you for your time. --- Andy Maloney // https://asmaloney.com twitter ~ @asmaloney <https://twitter.com/asmaloney>
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