fix growth of event queue in QWinOverlappedIoNotifier::waitFor*

Do not emit _q_notified when we're in a wait function. Otherwise,
the queued signals could pile up in the event queue.

Task-number: QTBUG-48653
Change-Id: I071863e2356e17c7004e3b7ca359967cb115e343
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

src/corelib/io/qwinoverlappedionotifier.cpp

@@ -33,6 +33,7 @@
 
 #include "qwinoverlappedionotifier_p.h"
 #include <qdebug.h>
+#include <qatomic.h>
 #include <qelapsedtimer.h>
 #include <qmutex.h>
 #include <qpointer.h>
@@ -99,6 +100,7 @@ public:
     {
     }
 
+    OVERLAPPED *waitForAnyNotified(int msecs);
     void notify(DWORD numberOfBytes, DWORD errorCode, OVERLAPPED *overlapped);
     OVERLAPPED *_q_notified();
 
@@ -108,6 +110,7 @@ public:
     HANDLE hHandle;
     HANDLE hSemaphore;
     HANDLE hResultsMutex;
+    QAtomicInt waiting;
     QQueue<IOResult> results;
 };
 
@@ -286,6 +289,47 @@ void QWinOverlappedIoNotifier::setEnabled(bool enabled)
         d->iocp->unregisterNotifier(d);
 }
 
+OVERLAPPED *QWinOverlappedIoNotifierPrivate::waitForAnyNotified(int msecs)
+{
+    if (!iocp->isRunning()) {
+        qWarning("Called QWinOverlappedIoNotifier::waitForAnyNotified on inactive notifier.");
+        return 0;
+    }
+
+    if (msecs == 0)
+        iocp->drainQueue();
+
+    const DWORD wfso = WaitForSingleObject(hSemaphore, msecs == -1 ? INFINITE : DWORD(msecs));
+    switch (wfso) {
+    case WAIT_OBJECT_0:
+        ReleaseSemaphore(hSemaphore, 1, NULL);
+        return _q_notified();
+    case WAIT_TIMEOUT:
+        return 0;
+    default:
+        qErrnoWarning("QWinOverlappedIoNotifier::waitForAnyNotified: WaitForSingleObject failed.");
+        return 0;
+    }
+}
+
+class QScopedAtomicIntIncrementor
+{
+public:
+    QScopedAtomicIntIncrementor(QAtomicInt &i)
+        : m_int(i)
+    {
+        ++m_int;
+    }
+
+    ~QScopedAtomicIntIncrementor()
+    {
+        --m_int;
+    }
+
+private:
+    QAtomicInt &m_int;
+};
+
 /*!
  * Wait synchronously for any notified signal.
  *
@@ -296,24 +340,9 @@ void QWinOverlappedIoNotifier::setEnabled(bool enabled)
 OVERLAPPED *QWinOverlappedIoNotifier::waitForAnyNotified(int msecs)
 {
     Q_D(QWinOverlappedIoNotifier);
-    if (!d->iocp->isRunning()) {
-        qWarning("Called QWinOverlappedIoNotifier::waitForAnyNotified on inactive notifier.");
-        return 0;
-    }
-
-    if (msecs == 0)
-        d->iocp->drainQueue();
-
-    switch (WaitForSingleObject(d->hSemaphore, msecs == -1 ? INFINITE : DWORD(msecs))) {
-    case WAIT_OBJECT_0:
-        ReleaseSemaphore(d->hSemaphore, 1, NULL);
-        return d->_q_notified();
-    case WAIT_TIMEOUT:
-        return 0;
-    default:
-        qErrnoWarning("QWinOverlappedIoNotifier::waitForAnyNotified: WaitForSingleObject failed.");
-        return 0;
-    }
+    QScopedAtomicIntIncrementor saii(d->waiting);
+    OVERLAPPED *result = d->waitForAnyNotified(msecs);
+    return result;
 }
 
 /*!
@@ -324,6 +353,8 @@ OVERLAPPED *QWinOverlappedIoNotifier::waitForAnyNotified(int msecs)
  */
 bool QWinOverlappedIoNotifier::waitForNotified(int msecs, OVERLAPPED *overlapped)
 {
+    Q_D(QWinOverlappedIoNotifier);
+    QScopedAtomicIntIncrementor saii(d->waiting);
     int t = msecs;
     QElapsedTimer stopWatch;
     stopWatch.start();
@@ -350,7 +381,8 @@ void QWinOverlappedIoNotifierPrivate::notify(DWORD numberOfBytes, DWORD errorCod
     results.enqueue(IOResult(numberOfBytes, errorCode, overlapped));
     ReleaseMutex(hResultsMutex);
     ReleaseSemaphore(hSemaphore, 1, NULL);
-    emit q->_q_notify();
+    if (!waiting)
+        emit q->_q_notify();
 }
 
 OVERLAPPED *QWinOverlappedIoNotifierPrivate::_q_notified()