Allow QWinEventNotifier to coexist with waiting functions

Many subclasses of QIODevice have a functionality to block execution
until some asynchronous I/O operation completes. In case we are using
QWinEventNotifier, a typical reimplemented waitFor{ReadyRead
|BytesWritten}() function could look like:

  if (WaitForSingleObject(notifier.handle(),...) == WAIT_OBJECT_0) {
      notifier.setEnabled(false);
      ResetEvent(notifier.handle());

      bool res = GetOverlappedResult(...);
      ...
      return true;
  }

Despite the fact that the operation ends synchronously, it leaves the
notifier in a state that indicates it has received the event, so its
next call to setEnabled(true) will produce a fake notification.

So, we should reset a notifier's history before enabling it again.

Change-Id: I62a9dd809ce6a7a40e9d8038f2a49299b36f8142
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/auto/corelib/kernel/qwineventnotifier/tst_qwineventnotifier.cpp b/tests/auto/corelib/kernel/qwineventnotifier/tst_qwineventnotifier.cpp
index 76efa008f7..74beab96a6 100644
--- a/tests/auto/corelib/kernel/qwineventnotifier/tst_qwineventnotifier.cpp
+++ b/tests/auto/corelib/kernel/qwineventnotifier/tst_qwineventnotifier.cpp
@@ -46,6 +46,7 @@ protected slots:
 private slots:
     void simple_data();
     void simple();
+    void blockedWaiting();
     void manyNotifiers();
     void disableNotifiersInActivatedSlot_data();
     void disableNotifiersInActivatedSlot();
@@ -104,6 +105,26 @@ void tst_QWinEventNotifier::simple()
     QVERIFY(simpleActivated);
 }
 
+void tst_QWinEventNotifier::blockedWaiting()
+{
+    simpleHEvent = CreateEvent(0, true, false, 0);
+    QWinEventNotifier n(simpleHEvent);
+    QObject::connect(&n, &QWinEventNotifier::activated,
+                     this, &tst_QWinEventNotifier::simple_activated);
+    simpleActivated = false;
+
+    SetEvent(simpleHEvent);
+    QCOMPARE(WaitForSingleObject(simpleHEvent, 1000), WAIT_OBJECT_0);
+
+    n.setEnabled(false);
+    ResetEvent(simpleHEvent);
+    n.setEnabled(true);
+
+    QTestEventLoop::instance().enterLoop(1);
+    QVERIFY(QTestEventLoop::instance().timeout());
+    QVERIFY(!simpleActivated);
+}
+
 class EventWithNotifier : public QObject
 {
     Q_OBJECT