Fix the remainingTime() result after the first activation of a QTimer

On Windows, t->timeout was updated only once, at creation time, so the
timer would always show as "overdue" after the first activation.

The timer is updated to indicate the full remaining time during the slot
activation, which is the behavior of the Unix and Glib dispatchers.

Task-number: QTBUG-46940
Change-Id: I255870833a024a36adf6ffff13ecadb021c4358c
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qeventdispatcher_win.cpp

@@ -561,6 +561,17 @@ static HWND qt_create_internal_window(const QEventDispatcherWin32 *eventDispatch
     return wnd;
 }
 
+static void calculateNextTimeout(WinTimerInfo *t, quint64 currentTime)
+{
+    uint interval = t->interval;
+    if ((interval >= 20000u && t->timerType != Qt::PreciseTimer) || t->timerType == Qt::VeryCoarseTimer) {
+        // round the interval, VeryCoarseTimers only have full second accuracy
+        interval = ((interval + 500)) / 1000 * 1000;
+    }
+    t->interval = interval;
+    t->timeout = currentTime + interval;
+}
+
 void QEventDispatcherWin32Private::registerTimer(WinTimerInfo *t)
 {
     Q_ASSERT(internalHwnd);
@@ -568,6 +579,7 @@ void QEventDispatcherWin32Private::registerTimer(WinTimerInfo *t)
     Q_Q(QEventDispatcherWin32);
 
     int ok = 0;
+    calculateNextTimeout(t, qt_msectime());
     uint interval = t->interval;
     if (interval == 0u) {
         // optimization for single-shot-zero-timer
@@ -576,17 +588,13 @@ void QEventDispatcherWin32Private::registerTimer(WinTimerInfo *t)
     } else if ((interval < 20u || t->timerType == Qt::PreciseTimer) && qtimeSetEvent) {
         ok = t->fastTimerId = qtimeSetEvent(interval, 1, qt_fast_timer_proc, (DWORD_PTR)t,
                                             TIME_CALLBACK_FUNCTION | TIME_PERIODIC | TIME_KILL_SYNCHRONOUS);
-    } else if (interval >= 20000u || t->timerType == Qt::VeryCoarseTimer) {
-        // round the interval, VeryCoarseTimers only have full second accuracy
-        interval = ((interval + 500)) / 1000 * 1000;
     }
+
     if (ok == 0) {
         // user normal timers for (Very)CoarseTimers, or if no more multimedia timers available
         ok = SetTimer(internalHwnd, t->timerId, interval, 0);
     }
 
-    t->timeout = qt_msectime() + interval;
-
     if (ok == 0)
         qErrnoWarning("QEventDispatcherWin32::registerTimer: Failed to create a timer");
 }
@@ -611,6 +619,9 @@ void QEventDispatcherWin32Private::sendTimerEvent(int timerId)
         // send event, but don't allow it to recurse
         t->inTimerEvent = true;
 
+        // recalculate next emission
+        calculateNextTimeout(t, qt_msectime());
+
         QTimerEvent e(t->timerId);
         QCoreApplication::sendEvent(t->obj, &e);
 

tests/auto/corelib/kernel/qtimer/tst_qtimer.cpp

@@ -54,6 +54,8 @@ private slots:
     void singleShotTimeout();
     void timeout();
     void remainingTime();
+    void remainingTimeDuringActivation_data();
+    void remainingTimeDuringActivation();
     void livelock_data();
     void livelock();
     void timerInfiniteRecursion_data();
@@ -79,14 +81,16 @@ class TimerHelper : public QObject
 {
     Q_OBJECT
 public:
-    TimerHelper() : QObject(), count(0)
+    TimerHelper() : QObject(), count(0), remainingTime(-1)
     {
     }
 
     int count;
+    int remainingTime;
 
 public slots:
     void timeout();
+    void fetchRemainingTime();
 };
 
 void TimerHelper::timeout()
@@ -94,6 +98,12 @@ void TimerHelper::timeout()
     ++count;
 }
 
+void TimerHelper::fetchRemainingTime()
+{
+    QTimer *timer = static_cast<QTimer *>(sender());
+    remainingTime = timer->remainingTime();
+}
+
 void tst_QTimer::zeroTimer()
 {
     TimerHelper helper;
@@ -158,6 +168,53 @@ void tst_QTimer::remainingTime()
 
     int remainingTime = timer.remainingTime();
     QVERIFY2(qAbs(remainingTime - 150) < 50, qPrintable(QString::number(remainingTime)));
+
+    // wait for the timer to actually fire now
+    connect(&timer, SIGNAL(timeout()), &QTestEventLoop::instance(), SLOT(exitLoop()));
+    QTestEventLoop::instance().enterLoop(5);
+    QVERIFY(!QTestEventLoop::instance().timeout());
+    QCOMPARE(helper.count, 1);
+
+    // the timer is still active, so it should have a non-zero remaining time
+    remainingTime = timer.remainingTime();
+    QVERIFY2(remainingTime > 150, qPrintable(QString::number(remainingTime)));
+}
+
+void tst_QTimer::remainingTimeDuringActivation_data()
+{
+    QTest::addColumn<bool>("singleShot");
+    QTest::newRow("repeating") << true;
+    QTest::newRow("single-shot") << true;
+}
+
+void tst_QTimer::remainingTimeDuringActivation()
+{
+    QFETCH(bool, singleShot);
+
+    TimerHelper helper;
+    QTimer timer;
+
+    const int timeout = 20;     // 20 ms is short enough and should not round down to 0 in any timer mode
+
+    connect(&timer, SIGNAL(timeout()), &helper, SLOT(fetchRemainingTime()));
+    connect(&timer, SIGNAL(timeout()), &QTestEventLoop::instance(), SLOT(exitLoop()));
+    timer.start(timeout);
+    timer.setSingleShot(singleShot);
+
+    QTestEventLoop::instance().enterLoop(5);
+    QVERIFY(!QTestEventLoop::instance().timeout());
+    if (singleShot)
+        QCOMPARE(helper.remainingTime, -1);     // timer not running
+    else
+        QCOMPARE(helper.remainingTime, timeout);
+
+    if (!singleShot) {
+        // do it again - see QTBUG-46940
+        helper.remainingTime = -1;
+        QTestEventLoop::instance().enterLoop(5);
+        QVERIFY(!QTestEventLoop::instance().timeout());
+        QCOMPARE(helper.remainingTime, timeout);
+    }
 }
 
 void tst_QTimer::livelock_data()