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authorMitch Curtis <mitch.curtis@qt.io>2019-09-23 13:42:03 +0200
committerMitch Curtis <mitch.curtis@qt.io>2019-09-30 09:22:23 +0000
commit83fbf44b980c4a072ede122f2f16921bfff8c08d (patch)
treee4dd33b52fbf24badad167981c64fa6cc5a23076 /examples
parent100550dd22dc8eaa47405cdb3e7e461edb01a7a3 (diff)
Fix a crash on exit when using ToolTip in a specific item hierarchy
QQuickPopup connects its parent item's (MouseArea, in this case) windowChanged() signal to QQuickPopupPrivate::setWindow(). It does this so that: 1) QQuickOverlay can keep track of all of the popups that it manages. 2) Fonts, palettes and locales can be resolved. 3) If the QQuickPopup component has completed loading and the popup is visible with a valid window, start the enter transition. The problem arises only when using a very specific item hierarchy: Window { width: 640 height: 480 visible: true Item { anchors.fill: parent Item { anchors.fill: parent ColorOverlay { source: parent anchors.fill: parent } MouseArea { anchors.fill: parent hoverEnabled: true ToolTip.visible: containsMouse ToolTip.text: "ToolTip text" } } } } When the window is closed and hence begins to be destroyed, the following events occur: - QQuickWindow's destructor is called. - The window's root item (QQuickRootItem) begins destruction. - QQuickOverlay is destroyed. - QQuickWindow's destructor is done, so the QWindow and then QObject destructors are called. - The QQuickItem destructor for the outer Item is called. - The child items of the outer Item have setParentItem(nullptr) called on them, one of which being the inner Item. - The inner Item's setParentItem() function calls derefWindow(), which in turn calls derefWindow() on its children. One of those children is MouseArea. - Since the MouseArea's window is deref'd, it emits the windowChanged() signal. MouseArea is the parentItem of the popup, so its windowChanged() signal causes QQuickPopupPrivate::setWindow() to be called. - setWindow() tries to remove the popup from the old overlay, which has already been destroyed. One approach I tried involved using QQuickOverlay::itemChange() to remove all of the popups (via setWindow(nullptr), to ensure that their window pointer is nullified), since that was called much earlier than the windowChanged() signal is emitted. However, this still resulted in a heap-use-after-free in the same place when running the newly added setOverlayParentToNull() test. I also tried removing the popups in QQuickOverlay's destructor, but this resulted in another heap-use-after-free (when accessing a popup in the destructor) in tst_QQuickPopup::Universal::visible(). The remaining options were: store the window in a QPointer or return early in overlay() if the wasDeleted member of the window was true. Using QPointer seems like it would catch more issues than a single check in overlay(), so I went with that. Fixes: QTBUG-73243 Change-Id: Ieb5ce26dd76d45771d28297031ec43e27d958b5b Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
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