QNetworkInformation: delete the instance as a post-routine

On Windows, on exit, the backend will deref (and then implicitly start
deletion of) a COM object. This object tries to communicate with an
object in another thread, though it seems this other thread quits before
the main thread in _most_ cases.

To get around this we move the deletion to earlier in the program. While
this is only reported as a Windows issue it makes for more consistent
behavior if all platforms behave the same.

Document and test that recreation of QNI works as expected after the
destruction (and recreation) of QCoreApplication.

Amends: 0875626e22ad4e709ddf505e701a8d699559f5b4

Fixes: QTBUG-92568
Pick-to: 6.1 6.1.0
Change-Id: Iffc07f38673019aa059efd4d64d2ad706a03f6fe
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

3 files changed, 74 insertions, 0 deletions

diff --git a/tests/auto/network/kernel/CMakeLists.txt b/tests/auto/network/kernel/CMakeLists.txt
index 89526fa14c..11b859011e 100644
--- a/tests/auto/network/kernel/CMakeLists.txt
+++ b/tests/auto/network/kernel/CMakeLists.txt
@@ -14,4 +14,5 @@ endif()
 if(QT_FEATURE_private_tests)
     add_subdirectory(qauthenticator)
     add_subdirectory(qnetworkinformation)
+    add_subdirectory(qnetworkinformation_appless)
 endif()
diff --git a/tests/auto/network/kernel/qnetworkinformation_appless/CMakeLists.txt b/tests/auto/network/kernel/qnetworkinformation_appless/CMakeLists.txt
new file mode 100644
index 0000000000..76cbf594c3
--- /dev/null
+++ b/tests/auto/network/kernel/qnetworkinformation_appless/CMakeLists.txt
@@ -0,0 +1,6 @@
+qt_internal_add_test(tst_qnetworkinformation_appless
+    SOURCES
+        tst_qnetworkinformation_appless.cpp
+    PUBLIC_LIBRARIES
+        Qt::Network
+)
diff --git a/tests/auto/network/kernel/qnetworkinformation_appless/tst_qnetworkinformation_appless.cpp b/tests/auto/network/kernel/qnetworkinformation_appless/tst_qnetworkinformation_appless.cpp
new file mode 100644
index 0000000000..ff058e8a9b
--- /dev/null
+++ b/tests/auto/network/kernel/qnetworkinformation_appless/tst_qnetworkinformation_appless.cpp
@@ -0,0 +1,67 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 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 <QtCore/qcoreapplication.h>
+#include <QtNetwork/qnetworkinformation.h>
+#include <QtTest/qtest.h>
+
+class tst_QNetworkInformation_appless : public QObject
+{
+    Q_OBJECT
+private slots:
+    void reinit();
+};
+
+void tst_QNetworkInformation_appless::reinit()
+{
+    int argc = 1;
+    char name[] = "./test";
+    char *argv[] = { name, nullptr };
+
+    {
+        QCoreApplication app(argc, argv);
+        if (QNetworkInformation::availableBackends().isEmpty())
+            QSKIP("No backends available!");
+
+        QVERIFY(QNetworkInformation::load(QNetworkInformation::Feature::Reachability));
+        auto info = QNetworkInformation::instance();
+        QVERIFY(info);
+    }
+
+    QVERIFY(!QNetworkInformation::instance());
+
+    {
+        QCoreApplication app(argc, argv);
+        QVERIFY(QNetworkInformation::load(QNetworkInformation::Feature::Reachability));
+        auto info = QNetworkInformation::instance();
+        QVERIFY(info);
+    }
+}
+
+QTEST_APPLESS_MAIN(tst_QNetworkInformation_appless);
+#include "tst_qnetworkinformation_appless.moc"