Use Qt::TimerType on Windows when starting timers

Make all Qt::PreciseTimers and timers with intervals < 20ms use
Multimedia timers for maximum accuracy. Qt::CoarseTimers and
Qt::VeryCoarseTimers use normal Windows timers, with
Qt::VeryCoarseTimers having their interval rounded to the nearest
full second.

Note that the Windows timer implementation does not attempt to align
timers and reduce CPU wakeups like the UNIX implementation does. This
might be done in the future, though. However, this change does the
best we can do now, keeping most timers working as-is, while allowing
explicit use of Multimedia timers via Qt::PreciseTimer.

Change-Id: I1898272b101c572a2a9b9454fef27a651eb178f5
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>

1 files changed, 13 insertions, 10 deletions

diff --git a/src/corelib/kernel/qeventdispatcher_win.cpp b/src/corelib/kernel/qeventdispatcher_win.cpp
index b52a4decac..41b1909bf1 100644
--- a/src/corelib/kernel/qeventdispatcher_win.cpp
+++ b/src/corelib/kernel/qeventdispatcher_win.cpp
@@ -530,18 +530,21 @@ void QEventDispatcherWin32Private::registerTimer(WinTimerInfo *t)
     Q_Q(QEventDispatcherWin32);
 
     int ok = 0;
-    if (t->interval > 20 || !t->interval || !qtimeSetEvent) {
+    uint interval = t->interval;
+    if (interval == 0u) {
+        // optimization for single-shot-zero-timer
+        QCoreApplication::postEvent(q, new QZeroTimerEvent(t->timerId));
         ok = 1;
-        if (!t->interval)  // optimization for single-shot-zero-timer
-            QCoreApplication::postEvent(q, new QZeroTimerEvent(t->timerId));
-        else
-            ok = SetTimer(internalHwnd, t->timerId, (uint) t->interval, 0);
-    } else {
-        ok = t->fastTimerId = qtimeSetEvent(t->interval, 1, qt_fast_timer_proc, (DWORD_PTR)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);
-        if (ok == 0) { // fall back to normal timer if no more multimedia timers available
-            ok = SetTimer(internalHwnd, t->timerId, (uint) t->interval, 0);
-        }
+    } 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);
     }
 
     if (ok == 0)