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, 4 insertions, 3 deletions

diff --git a/src/corelib/kernel/qwineventnotifier.cpp b/src/corelib/kernel/qwineventnotifier.cpp
index 24de491326..85d4ad4fa9 100644
--- a/src/corelib/kernel/qwineventnotifier.cpp
+++ b/src/corelib/kernel/qwineventnotifier.cpp
@@ -157,7 +157,6 @@ void QWinEventNotifier::setHandle(HANDLE hEvent)
     Q_D(QWinEventNotifier);
     setEnabled(false);
     d->handleToEvent = hEvent;
-    d->signaledCount = 0;
 }
 
 /*!
@@ -209,10 +208,12 @@ void QWinEventNotifier::setEnabled(bool enable)
         return;
     }
 
-    if (enable)
+    if (enable) {
+        d->signaledCount = 0;
         eventDispatcher->registerEventNotifier(this);
-    else
+    } else {
         eventDispatcher->unregisterEventNotifier(this);
+    }
 }
 
 /*!