Javascript: When there is javascript running then it will spin the CPU at 100%

Zero timers on Windows would continue to fire even after being stopped
as long as a new timer was started that reused the pointer address of
the zero timer. Fix this by only re-firing zero timers if the zero
timer hadn't been stopped (we can check this by looking at the
inTimerEvent flag, which is set to false by registerTimer()).

Task-number: 247401
Reviewed-by: Denis Dzyubenko
Reviewed-by: Prasanth Ullattil

3 files changed, 81 insertions, 3 deletions

diff --git a/dist/changes-4.5.1 b/dist/changes-4.5.1
index de4eef7..eb8ec5f 100644
--- a/dist/changes-4.5.1
+++ b/dist/changes-4.5.1
@@ -68,6 +68,10 @@ Qt for Linux/X11
 Qt for Windows
 --------------
 
+- QCoreApplication
+   * [247401] Fixed a bug that would cause a restarted timer to fire
+     too early, causing Javascript in QtWebKit to consume 100% CPU on
+     Windows.
 
 Qt for Mac OS X
 ---------------
diff --git a/src/corelib/kernel/qeventdispatcher_win.cpp b/src/corelib/kernel/qeventdispatcher_win.cpp
index 880e95c..c4061f4 100644
--- a/src/corelib/kernel/qeventdispatcher_win.cpp
+++ b/src/corelib/kernel/qeventdispatcher_win.cpp
@@ -1059,11 +1059,20 @@ bool QEventDispatcherWin32::event(QEvent *e)
         QZeroTimerEvent *zte = static_cast<QZeroTimerEvent*>(e);
         WinTimerInfo *t = d->timerDict.value(zte->timerId());
         if (t) {
+            t->inTimerEvent = true;
+
             QTimerEvent te(zte->timerId());
             QCoreApplication::sendEvent(t->obj, &te);
-            WinTimerInfo *tn = d->timerDict.value(zte->timerId());
-            if (tn && t == tn)
-                QCoreApplication::postEvent(this, new QZeroTimerEvent(zte->timerId()));
+
+            t = d->timerDict.value(zte->timerId());
+            if (t) {
+                if (t->interval == 0 && t->inTimerEvent) {
+                    // post the next zero timer event as long as the timer was not restarted
+                    QCoreApplication::postEvent(this, new QZeroTimerEvent(zte->timerId()));
+                }
+
+                t->inTimerEvent = false;
+            }
         }
         return true;
     } else if (e->type() == QEvent::Timer) {
diff --git a/tests/auto/qtimer/tst_qtimer.cpp b/tests/auto/qtimer/tst_qtimer.cpp
index 527628c..bffb4f2 100644
--- a/tests/auto/qtimer/tst_qtimer.cpp
+++ b/tests/auto/qtimer/tst_qtimer.cpp
@@ -83,6 +83,7 @@ private slots:
     void recurringTimer();
     void deleteLaterOnQTimer(); // long name, don't want to shadow QObject::deleteLater()
     void moveToThread();
+    void restartedTimerFiresTooSoon();
 };
 
 class TimerHelper : public QObject
@@ -416,5 +417,69 @@ void tst_QTimer::moveToThread()
     QVERIFY((ti3.timerId() & 0xffffff) != (ti1.timerId() & 0xffffff));
 }
 
+class RestartedTimerFiresTooSoonObject : public QObject
+{
+    Q_OBJECT
+
+public:
+    QBasicTimer m_timer;
+
+    int m_interval;
+    QTime m_startedTime;
+    QEventLoop eventLoop;
+
+    inline RestartedTimerFiresTooSoonObject()
+        : QObject(), m_interval(0)
+    { }
+
+    void timerFired()
+    {
+        static int interval = 1000;
+
+        m_interval = interval;
+        m_startedTime.start();
+        m_timer.start(interval, this);
+
+        // alternate between single-shot and 1 sec
+        interval = interval ? 0 : 1000;
+    }
+
+    void timerEvent(QTimerEvent* ev)
+    {
+        if (ev->timerId() != m_timer.timerId())
+            return;
+
+        m_timer.stop();
+
+        QTime now = QTime::currentTime();
+        int elapsed = m_startedTime.elapsed();
+
+        if (elapsed < m_interval / 2) {
+            // severely too early!
+            m_timer.stop();
+            eventLoop.exit(-1);
+            return;
+        }
+
+        timerFired();
+
+        // don't do this forever
+        static int count = 0;
+        if (count++ > 20) {
+            m_timer.stop();
+            eventLoop.quit();
+            return;
+        }
+    }
+};
+
+void tst_QTimer::restartedTimerFiresTooSoon()
+{
+    RestartedTimerFiresTooSoonObject object;
+    object.timerFired();
+    QVERIFY(object.eventLoop.exec() == 0);
+}
+
 QTEST_MAIN(tst_QTimer)
 #include "tst_qtimer.moc"
+\