Call post routines from ~QGuiApplication

Currently depending if user uses QApplication
or QGuiApplication we end up in different behavior
when running post routines. For example QApplication
destructor calls post routines before stopping event dispatcher,
In case of QGuiApplication post routines are called
from QCoreApplication destructor, so no more event dispatcher.
This behavior is not consistent and creates troubles
when releasing resources of web engine.

Attached test will hang on windows with QGuiApplication,
however works fine with QApplication.

Task-number: QTBUG-79864
Change-Id: Ice05e66a467feaf3ad6addfbc14973649da8065e
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/gui/kernel/qguiapplication.cpp

@@ -134,6 +134,7 @@ QT_BEGIN_NAMESPACE
         return __VA_ARGS__; \
     }
 
+Q_CORE_EXPORT void qt_call_post_routines();
 Q_GUI_EXPORT bool qt_is_gui_used = true;
 
 Qt::MouseButtons QGuiApplicationPrivate::mouse_buttons = Qt::NoButton;
@@ -678,6 +679,8 @@ QGuiApplication::~QGuiApplication()
 {
     Q_D(QGuiApplication);
 
+    qt_call_post_routines();
+
     d->eventDispatcher->closingDown();
     d->eventDispatcher = nullptr;
 

tests/auto/gui/kernel/kernel.pro

@@ -25,7 +25,8 @@ SUBDIRS=\
    qguiapplication \
    qpixelformat \
    qopenglwindow \
-   qrasterwindow
+   qrasterwindow \
+   qaddpostroutine
 
 win32:!winrt:qtHaveModule(network): SUBDIRS += noqteventloop
 

tests/auto/gui/kernel/qaddpostroutine/qaddpostroutine.pro

@@ -0,0 +1,7 @@
+CONFIG += testcase
+TARGET = tst_qaddpostroutine
+
+QT += testlib
+
+SOURCES  += tst_qaddpostroutine.cpp
+

tests/auto/gui/kernel/qaddpostroutine/tst_qaddpostroutine.cpp

@@ -0,0 +1,66 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+
+#include <QtTest/QtTest>
+#include <QTimer>
+
+static bool done = false;
+
+static void cleanup()
+{
+     done = true;
+     QEventLoop loop;
+     QTimer::singleShot(100,&loop, &QEventLoop::quit);
+     loop.exec();
+}
+
+struct tst_qAddPostRoutine : public QObject
+{
+public:
+    tst_qAddPostRoutine();
+    ~tst_qAddPostRoutine();
+};
+
+tst_qAddPostRoutine::tst_qAddPostRoutine()
+{
+    qAddPostRoutine(cleanup);
+}
+
+tst_qAddPostRoutine::~tst_qAddPostRoutine()
+{
+    Q_ASSERT(done);
+}
+int main(int argc, char *argv[])
+{
+    tst_qAddPostRoutine tc;
+    QGuiApplication app(argc, argv);
+    app.setAttribute(Qt::AA_Use96Dpi, true);
+    QTEST_SET_MAIN_SOURCE_PATH
+    return QTest::qExec(&tc, argc, argv);
+}