QCocoaEventDispatcher: make 'interrupt' work

even if we are currently inside processEvents (apparently called manually
and not from QEventLoop::exec()). A carefully crafted application
(see, for example, the linked QTBUG or even updated auto-test)
can trigger itself into failing to exit the current (potentially nested)
event loop. We can harden our Cocoa event dispatcher to detect
such condition and properly propagate 'interrupt' to where it'll
do its job, indeed, interrupting the real event loop (aka [NSApp run]).
This mainly means we have to undo what bool blocker would erroneously do.
Also, long live (as people love to say these days) to another tricky
(somewhat) auto-test (surely, it's not flaky!).

Fixes: QTBUG-79477
Change-Id: I794f0cda23e24d36be67f2bb63d52b74be057c31
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 45 insertions, 0 deletions

diff --git a/tests/auto/corelib/kernel/qeventdispatcher/tst_qeventdispatcher.cpp b/tests/auto/corelib/kernel/qeventdispatcher/tst_qeventdispatcher.cpp
index 49c10c6a24..365508024b 100644
--- a/tests/auto/corelib/kernel/qeventdispatcher/tst_qeventdispatcher.cpp
+++ b/tests/auto/corelib/kernel/qeventdispatcher/tst_qeventdispatcher.cpp
@@ -67,6 +67,7 @@ private slots:
     void sendPostedEvents_data();
     void sendPostedEvents();
     void processEventsOnlySendsQueuedEvents();
+    void eventLoopExit();
 };
 
 bool tst_QEventDispatcher::event(QEvent *e)
@@ -314,5 +315,49 @@ void tst_QEventDispatcher::processEventsOnlySendsQueuedEvents()
     QCOMPARE(object.eventsReceived, 4);
 }
 
+void tst_QEventDispatcher::eventLoopExit()
+{
+    // This test was inspired by QTBUG-79477. A particular
+    // implementation detail in QCocoaEventDispatcher allowed
+    // QEventLoop::exit() to fail to really exit the event loop.
+    // Thus this test is a part of the dispatcher auto-test.
+
+    // Imitates QApplication::exec():
+    QEventLoop mainLoop;
+    // The test itself is a lambda:
+    QTimer::singleShot(0, [&mainLoop]() {
+        // Two more single shots, both will be posted as events
+        // (zero timeout) and supposed to be processes by the
+        // mainLoop:
+
+        QTimer::singleShot(0, [&mainLoop]() {
+            // wakeUp triggers QCocoaEventDispatcher into incrementing
+            // its 'serialNumber':
+            mainLoop.wakeUp();
+            // QCocoaEventDispatcher::processEvents() will process
+            // posted events and execute the second lambda defined below:
+            QCoreApplication::processEvents();
+        });
+
+        QTimer::singleShot(0, [&mainLoop]() {
+            // With QCocoaEventDispatcher this is executed while in the
+            // processEvents (see above) and would fail to actually
+            // interrupt the loop.
+            mainLoop.exit();
+        });
+    });
+
+    bool timeoutObserved = false;
+    QTimer::singleShot(500, [&timeoutObserved, &mainLoop]() {
+        // In case the QEventLoop::exit above failed, we have to bail out
+        // early, not wasting time:
+        mainLoop.exit();
+        timeoutObserved = true;
+    });
+
+    mainLoop.exec();
+    QVERIFY(!timeoutObserved);
+}
+
 QTEST_MAIN(tst_QEventDispatcher)
 #include "tst_qeventdispatcher.moc"